Fluke 332D repair..still sorting issues - Page 1
Forum section: electronics / repair

author: valley001
author_rank: Frequent Contributor
timestamp: March 04, 2019, 06:51:56 am
content: I was really hoping I would not have to repair this, but such is the risk of buying old used equipment like this untested. I am fairly green with repairing electronics and this would probably be my most challenging project yet.This 332D is non functional. It does not output voltage, I get -1.24v no matter the settings on the dials . Upon visual inspection I found the following:-Q4 and Q8 missing from the differential amplifier board (that cant be good).-Current limiter board shows evidence of heating in the vicinity of Q1 and Q2, especially at R3.-Some evidence of heating on the pre regulator board.On the plus side my example does have the extender card still in place.I have not done any voltage measurements yet, that will probably have to wait until next weekend unfortunately. I am hoping for some ideas on how to proceed. I am assuming at the very least I need to find Q4 and Q8 for the differential amp board.One other thing I notice is the decimal LEDs, only the 10v range decimal lights. When switching through the ranges 100v and 1000v the decimals do not light for those ranges.

author: wictor
author_rank: Regular Contributor
timestamp: March 04, 2019, 04:07:22 pm
content: Hi,Fluke voltage reference seems to be hot topic currently... You could start by reading following threads:https://www.eevblog.com/forum/repair/fluke-3330b-no-output-but-relays-clicks-some-life-in-it/https://www.eevblog.com/forum/repair/fluke-332d-initial-power-up-paper-caps-in-hv-motherboard/Wictor

author: wictor
author_rank: Regular Contributor
timestamp: March 04, 2019, 04:11:27 pm
content: QuoteI would say this is normal for these units.QuoteMost of the units have this problem, it's easy to replace broken bulbs with LEDs.Wictor

author: valley001
author_rank: Frequent Contributor
timestamp: March 04, 2019, 04:39:50 pm
content: I started taking readings on the semiconductors on the current limiter board, since this one seems to have taken a beating. Tests done in circuit.Q7- Reads in both directions B-EQ1 and Q2- Ive not tested these larger transistors before, but Q1 tests in both directions on one side. Q2 also tests suspiciously.C6 looks like its toast.Edit to add- CR6 is missing from the pre regulator board.Man what a bummer.Edit to add:OK, I think I will focus on the pre regulator board first. I managed to test all of the transistors and they seem fine I think. Some (Motorola SM4144) have hFE in the mid 30s-40s. Some diodes test strangely, many of them read both ways in circuit. Ill lift those and test again. In the mean time I will find a replacement for CR6, 1N4822 (could I use a 1n4005 here?)

author: valley001
author_rank: Frequent Contributor
timestamp: March 04, 2019, 11:57:05 pm
content: So CR6 on the pre regulator board is associated with the K1 power supply, which engages pin 7-8 to the "pre regulator bridge." I think the pre regulator bridge leads to the "pre regulator bridge attenuator."Am I correct in my assumption that the entire device would fail to operate if K1 does not engage?

author: kawal
author_rank: Frequent Contributor
timestamp: March 05, 2019, 03:13:37 am
content: I just revived my completely dead 3330B.Here is what method I used to trace the source of failure:Remove all boards to inspect the boards for visual inspection and bad electrolytic capacitor via ESR. I found only 2 bad ones but will replace all of them when my part arrive. These things are now over 45 years old.Check all diods and transistors for conductivity. Please check the Power boards as first priority - I found 1 broken transistor and later zener diod.Pull any socketed transistors and check for Beta loss. Another member ( Frank ) mentioned this and I was not aware that its a thing to worry about. But found 1 transistor with good diod test but with no gain.Look at the schematic for your unit . It is possible to test most cards outside the unit by providing the right voltages to the cards. - Most cards its 1 or 2 voltages for power.My unit was completely dead too but now its working with only a few days effort. It might take less or more time but its worth restoring these awesome units.In my unit the pre driver was suspect as it had burnt wires. At the end it turned out the current sense resistor at the emiter of the driver transistor had bad contact with the board due to thermal cycling. After re soldering that resistor (and earlier replacing a transistor with 0 HFE ) the board worked.Good luck and be careful. The units can output deadly voltages.Maciej

author: kawal
author_rank: Frequent Contributor
timestamp: March 05, 2019, 03:18:45 am
content: Yes the device will not output voltages if K1 is off.But lights should turn on the front panel even if K1 is off.The decimalpoints are bulbsare LEDs in the 332D but the older diods could be dead due to the high current of 16mA used for such early diods. My unit had bulbs with only only had 1 working bulb. Now all replaced with White LEDs. In the 3330B the bulbs get power from -25V so a 2K resistor and a white LEDs I used 0.5W leds running at 11mA. They are super bright at the 30mW power. Use in min 0.5W resistors for the diods.Make sure all the power rails are there - the low voltage ones (+25, -15, +35, -35 , +12, -12 )On my unit the contacts on K1 where not in best shape so i took them off the relay for a good cleaning and polishing before putting back in the unit.Quote from: valley001 on March 04, 2019, 11:57:05 pm

author: kawal
author_rank: Frequent Contributor
timestamp: March 05, 2019, 03:51:28 am
content: These are general purpose diods and the ones you mentioned will be fine - I would change all 4 to the same type in the bridge.If the transistor conducts in both ways its bad, assuming its out of circuit. Q7 should not conduct both ways even in circuit.Quote from: valley001 on March 04, 2019, 04:39:50 pm

author: valley001
author_rank: Frequent Contributor
timestamp: March 05, 2019, 04:11:35 am
content: kawal- I appreciate your responses, thank you. Sometimes I get ahead of myself...I need to study the circuit more carefully so I understand how the boards interact with each other.I will check voltages this weekend, along with the other suggested tests in the troubleshooting portion of the manual.In the mean time, the differential amp board is missing Q4 and Q8...any idea on a modern replacement for these? The originals seem to be unobtanium.

author: texaspyro
author_rank: Super Contributor
timestamp: March 05, 2019, 05:32:25 am
content: These units are famous for bad electrolytics on the main board. It is one of the few devices where I would recommend replacing all of them.

author: beanflying
author_rank: Super Contributor
timestamp: March 05, 2019, 05:50:42 am
content: Quote from: texaspyro on March 05, 2019, 05:32:25 am332D only or the 335D as well? My recent acquisition touch wood looks good but I haven't cracked the case yet.

author: texaspyro
author_rank: Super Contributor
timestamp: March 05, 2019, 06:14:57 am
content: Quote from: beanflying on March 05, 2019, 05:50:42 amAssume all of them are guilty... I pulled around 10 bad caps off of my 332D.

author: kawal
author_rank: Frequent Contributor
timestamp: March 05, 2019, 03:30:12 pm
content: ValleyI would replace Q4 and Q6 together as a pair. Something like KSC1008YBU will work just fine are a cheap (34cents each). NPN 60V moderate gain and moderate bandwidth.You could also use KSD1616AYTA for both Q4, Q6 or just for Q8, one type would make it easier. Thats what I would use ( original 60V, 1A, 0.8W device) .MaciejQuote from: valley001 on March 05, 2019, 04:11:35 am

author: valley001
author_rank: Frequent Contributor
timestamp: March 05, 2019, 06:29:04 pm
content: I made the same assumption on Q8, the unmarked one makes the most sense.OK so:Q4 and 6 use: KSC1008YBUQ8 use: KSD1616AYTAIll order 1n4005G for the rectifier diodes.I am hoping Q1 and Q2 are good on the current limiter, I have not tested them out of circuit yet.Do you have a suggestion for Q7 on the current limiter board?

author: kawal
author_rank: Frequent Contributor
timestamp: March 05, 2019, 08:58:54 pm
content: ValleyLooking at the schematic (and confirmed in section 3-41 in the manual) the Q7 on the current limit board seems to be an LED controller .It blinks the the LED when current limit happens.Based on that I would let you pick any NPN with Vce>=60V and Ic >= 200maMaciej

author: valley001
author_rank: Frequent Contributor
timestamp: March 06, 2019, 05:41:21 pm
content: Had some time to test transistors this morning, here are the results all out of circuit:Pre Regulator:Q1- BJT-NPN, hFE 178, Vf 542mVQ2- BJT-NPN, hFE 96, Vf 651mVThere two look good no?Current Limiter:Q1- BJT-NPN, hFE 149, Vf 618mVQ2- BJT-NPN, hFE 5, Vf 36mVLooks like Q2 is toast. I see NOS available so thats a plus.I think I am going to replace the electrolytic on the pre regulator and the diodes CR6-9 and then call it good. Ill try to power up again after doing the voltage checks and installing the replacements for diff amp Q4 and Q8.I did do the resistance checks on each readout step, these all seem good.

author: kawal
author_rank: Frequent Contributor
timestamp: March 06, 2019, 05:50:12 pm
content: Q2 is definitely toast. New old stock makes it easier but some of the current transistors should be more reliable.

author: valley001
author_rank: Frequent Contributor
timestamp: March 06, 2019, 06:05:49 pm
content: Quote from: kawal on March 06, 2019, 05:50:12 pmWhich model would be a good equivalent?I did the resistance checks on the pre reg board and aux power. Current limiter pin 1 and 3 to sense read over 1 meg. Q2 is out of circuit so perhaps that is the cause.

author: valley001
author_rank: Frequent Contributor
timestamp: March 07, 2019, 03:53:19 pm
content: Man someone was really into this thing before I. Inspecting the boards it looks like the chopper FET was removed at some point for some reason. . It tests fine. Many resistors and caps also show evidence of having been removed. I tested a bunch of electrolytic caps and all the ones I tested seem fine on my little component tester.I tested every other socketed transistor in this thing, they all seem good.List of needed repairs so far:Bridge in the relay PSU on the pre regulator boardQ2 on the current limiterInstall missing Q4 and Q8 on the amp boardReplace two dead decimal LEDsHopefully I will have voltage after these repairs. I am still concerned with the resistance readings I am getting between sense and pins 1 and 3 of the current limiter board.

author: kawal
author_rank: Frequent Contributor
timestamp: March 07, 2019, 11:24:17 pm
content: Dont worry about current limiter The schematic has 2 pages and 1 and 3 are the +35V and -35V lines that go to may devices. Check out all the items connected to the board internally

author: Fred_47
author_rank: Contributor
timestamp: March 08, 2019, 05:56:54 am
content: Quote from: valley001 on March 04, 2019, 06:51:56 amThe 332 shares a lot (almost all) circuitry with the 335. However there seems to be several versions over the years so compare any schematics to your circuit before taking any action.The K1 relay is a safety switch that allows the high voltage to be energized only when all the cards are installed and the covers are in place. It is slightly delayed to allow K2 to pick up first. (A diode & capacitor circuit.)The decimal point LEDs on my 335D all failed about 6 months after I got it working and when I checked the circuit I found that the 2.4K resistor (R3) on the current limiter board was burnt black. This is the ±35V supply. The lamp supply is tapped before the regulating transistor. My notes indicate that this voltage is about 60 V and I'm driving the LEDs to about 20mA.The original circuit with filament lamps had 3 resistors in series and the circuit card had traces in place for all 3. I replaced the LEDs (had to file down the diameter to fit) and used 2- 1500, 2 Watt resistors to spread out the heat & compensate for the higher ambient temp. BTW, the LEDs are held in place by single pin 'sockets' on the wiring. No need to unsolder anything except the failed resistor and jumper on the card. (At least that was the case on mine.)Also note that all of the circuitry can be energized up to 1100V WRT the chassis so double/tripple check your replacement LED installation. The grommets and heat shrink are important.I've also checked all of the capacitors and replaced most that were questionable. So far I've replaced about 15% of the caps. Someone before me had replaced many of the larger electrolitics. I suspect that Fluke gave it an updating the last time it was calibrated in 1992 as there seems to be a mix of old & new cards and components. (The oldest date code I've found is 1980 IIRC)Here's a picture of the card before the failure. (I can't see the full part number but I think it's 354266, it's A5A6 in the parts list) You can see the traces and holes for the other resistors. I eventually replaced the blue cap (and most 'blue' caps on the other boards) and a one of the silver (Sprague) ones. Also, for what it's worth, a spreadsheet that I made as I checked the caps, the 1971 version of the power supply & the 1978 version with my modification. It may not match your unit.

author: valley001
author_rank: Frequent Contributor
timestamp: March 08, 2019, 04:53:36 pm
content: I did lift all of those 2 watt resistors and test them, since some obviously got hot. On mine, R3 is a 2.7K 2 watt resistor and tests pretty close. I guess this resistor is dissipating a lot of heat?Q2 was toast (see above) so I wonder what sort of mayhem that may have caused.I lifted the big electrolytic caps and they all test fine on my component tester, however I know the small tester is not really capable of testing these up to their operating conditions. I have had a cap (obviously bad) test fine on the component tester in the past.Ill recap the whole thing once I can get some life out of it.

author: valley001
author_rank: Frequent Contributor
timestamp: March 10, 2019, 01:12:52 am
content: Its been a somewhat disappointing day.-Installed new bridge for the relay PSU on pre regulator board-Installed Q4, Q6, and Q8 on the amp board-Installed new LEDs for the decimalsI was hoping with the relay PSU now functional and the missing transistors installed in the amp board I would get some sign of life from this thing, but no. Completely the same behavior when the unit is turned to "operate." I get 1.22v ish no matter the range or readout setting. The new LEDs work great so at least thats somethingOne thing I know is bad and has not been replaced is Q2 on the current limiter board. It has low hFE so figured it may not have a large effect on the function of the overall unit (correct, incorrect?).Before cleaning the bench for the day I took voltage readings per 4.16 in the manual. Hoping someone may see something I dont/cant. I do see collector Q8 on the reference supply board is very high. Hoping that is not too ominous. I appreciate all the responses so far, hoping someone has some idea where I should go next.Oh. On thing I have noticed is a intermittent buzzing sound (60hz maybe) from the HV mother board area. It comes and goes, but I have not isolated it to a specific component or to see if a specific relay energizes when it happens (dont want to stick my ears too close!) . Does not appear to be coming from the transformer.I am absolutely determined to get this thing going.Aux Power BoardPin 10 24.9vPin 9 -14.86vCurrent LimiterPin 1 -35vPin 3 37.4vRange Calsense to red test point 15.06vReference SupplyCollector Q145v(Should be 26-35v) Maybe l need to look at R19 or further up?Rear Bulkhead ResistorYellow lead 748vSeries PassCollector Q8 137.5v

author: kawal
author_rank: Frequent Contributor
timestamp: March 10, 2019, 05:10:57 am
content: Well that is some progress. Aux power and power on current limit board look good. Remember to check the pre regulator supply as well.That board cause some issues for me . The Mica/metal foil current sense resistor had bad solder joints. Basically causing so weird over current condition. Check the board out of the chassis.Are the decimals also working now ?Maciej

author: valley001
author_rank: Frequent Contributor
timestamp: March 10, 2019, 05:20:15 am
content: Decimals are working now. I am not sure how to check the pre regulator board out of chassis. Which resistor is the current sense?Unrelated: Checking resistance per 4-57 on the current limiter I still get some odd results, like 500K between pins 1 and sense and 3 and sense.I guess I am shooting in the dark now.Quote from: kawal on March 10, 2019, 05:10:57 am

author: wictor
author_rank: Regular Contributor
timestamp: March 10, 2019, 11:12:17 am
content: Valley, have you verified that those K1 and K2 relay are good and operating when safety switch is closed?Wictor

author: kawal
author_rank: Frequent Contributor
timestamp: March 10, 2019, 03:13:31 pm
content: I confused the versions of the Prereg. Mine has that weird resistor and your will not. In your case its R2 on top of the board (power sense resistor). I would also check R6 which is part of the same circuit.All this circuit is is a variable resistor (Q1) that reduces the voltage going to the HV transformer. This makes the voltage only as high as it needs to be versus always 1200V.With it out there is no dangerous voltages and should draw very little current and produce no heat.There are at least 2 ways to check the preregulator.1) Take out the card and supply it +12/-12V - thi sis better as you will get the current draw - should be pretty small less than 50ma2) Solder wires to the card and measure externally but have car in the unit. - cant get current draw.

author: valley001
author_rank: Frequent Contributor
timestamp: March 10, 2019, 03:59:37 pm
content: Forgive my ignorance but I am not certain exactly where I should apply 12v (is it terminations "a" and "p?") and then where I should be measuring (where on the schematic). The board layout on my pre regulator is different from the picture in the manual. I have been working up the courage to operate this thing with the panel removed but im not there yet..so a way to test out of the chassis would be welcome.wictor- I did verify visually (peering through the holes in the outer case) that K1 is actuating. Whether it is making good contact or not, I am not sure. I am also not sure if K2 is operating. It is open without power, I would apply 35v to it and it should close no?I do not have a proper low voltage power supply, so that leaves me using batteries to test.

author: kawal
author_rank: Frequent Contributor
timestamp: March 10, 2019, 04:26:29 pm
content: Power supply makes it so easy to troubleshoot. Think about getting one. Maybe you have a transformer with 2x10V winding that will also work.The place to connect would be at the capacitor after the bridge rectifier. Or directly at the rectifier. If its better with dedicated S but yo could do it with some 12 V power bricks we all have laying around.In case you have the same as me here is that version. The schematic is on 3330B manual .The power resistor is the big flat thing also on top of the board (R2). Mine had bad solder joints from thermal cycling. This board gets toasty so might be good to resolder the bigger power devices. Clean up the flux after soldering.The picture is before the repairs i did. Notice the burnt cables. These are signs of over current and something being wrong. In my case one of the transistors was low on HFe and R2 had a bad connection.

author: kawal
author_rank: Frequent Contributor
timestamp: March 10, 2019, 04:41:18 pm
content: here is the repaired pre reg with comments

author: valley001
author_rank: Frequent Contributor
timestamp: March 10, 2019, 04:58:18 pm
content: I think K2 may be faulty, is it safe to jumper it and then test the unit?I did operate it with the interlock engaged and confirmed that K1 closes when I switch to operate. I dont know if this matters but I would expect to see a small spark from the contacts when the relay closes, I do not see a spark.

author: kawal
author_rank: Frequent Contributor
timestamp: March 10, 2019, 05:01:16 pm
content: Did you test it? I think the K2 coil needs about 20V to turn on - apply 20V to the coil and check with ohm meter. Do not jumper the contacts . Its part of the safety feature of the unit.K2 just controls the turining on of K1. So there must be a fault in the current limit board if K2 is not turing on. I would not jumper anything in this beast.

author: valley001
author_rank: Frequent Contributor
timestamp: March 10, 2019, 05:09:15 pm
content: Understood..will not jumper.I tested K2 and it is functional and reads closed with +18 volts applied (2x 9v batts).

author: kawal
author_rank: Frequent Contributor
timestamp: March 10, 2019, 05:24:40 pm
content: could be not enough voltage or contacts are welded.

author: valley001
author_rank: Frequent Contributor
timestamp: March 10, 2019, 05:26:38 pm
content: I do have a 12v AC output wall wart, I suppose I could test the board with that?

author: wictor
author_rank: Regular Contributor
timestamp: March 10, 2019, 07:02:55 pm
content: I don't recommend that 12V AC for testing.

author: valley001
author_rank: Frequent Contributor
timestamp: March 10, 2019, 07:38:54 pm
content: The voltages at pin 7,8 and 9,10..will those give me an idea of the problem is in the pre regulator board?

author: wictor
author_rank: Regular Contributor
timestamp: March 10, 2019, 08:33:03 pm
content: Quote from: valley001 on March 10, 2019, 07:38:54 pmYou should have some AC voltage between 7 & 6 on preregulator. And when safety switches are closed, you should have voltage between 9 & 6.

author: valley001
author_rank: Frequent Contributor
timestamp: March 10, 2019, 08:43:47 pm
content: Between 7 and 6 I get 106v AC in standby and operate.Between 9 and 6 I get .226v AC only in operate mode.I also checked the wave form of Q1 on my scope (scope not grounded per instructions), it does not change between standby and operate. The standby wave form is about .5v pp, but does look to be the correct pattern. Ill see if I can load a screenshot of it.

author: wictor
author_rank: Regular Contributor
timestamp: March 10, 2019, 08:50:14 pm
content: Then there is something wrong in preregulator. Check the voltage path between 7 and 9.

author: valley001
author_rank: Frequent Contributor
timestamp: March 10, 2019, 08:52:52 pm
content: WTF the unit is working now. Outputting voltage to the terminals.

author: wictor
author_rank: Regular Contributor
timestamp: March 10, 2019, 08:54:06 pm
content: Great

author: wictor
author_rank: Regular Contributor
timestamp: March 10, 2019, 08:55:40 pm
content: There are many possibilities for contact problems in those units.

author: wictor
author_rank: Regular Contributor
timestamp: March 10, 2019, 09:02:00 pm
content: And of course preregulator voltage between pins 9 &6 is depending of wanted output voltage.

author: valley001
author_rank: Frequent Contributor
timestamp: March 10, 2019, 09:10:09 pm
content: The only difference between today and other days messing with this thing is that I have cycled many more times. It takes a few times of switching to operate before it comes to life.I notice on the meter, it will flicker a bit before rising to voltage. In the past I had a problem with electrolytic caps causing problems like this. I guess I may recap the power supplies and clean all of the contacts I can reach.

author: Fred_47
author_rank: Contributor
timestamp: March 11, 2019, 12:37:46 am
content: Quote from: valley001 on March 10, 2019, 01:12:52 amWhat is the part number of the bulkhead resistor on the schematic?Have you noticed that there are 2 K1 relays? There is one in the preregulator ckts shown at the lower left on sh 1 of 332B-1001 and 1 in the interlock ckt shown on the right hand side of sh 2 of 332B-1001.If the preregulator K1 doesn't pick up, there will be no high voltage from T2. There is still high voltage from T1 thru the bridge on the lower right on sh 1 of 332B-1001. This may be the source of the voltages you're measuring. Its purpose is to provide a minimum forward current thru the series pass ckt.If interlock K1 doesn't pick up the negative leg from the HV ckts is disconnected from the output and you will read 0 or very low voltage at the output.There are also 2 K2 relays. One is the 'crowbar' which throws a load across the HV capacitors to quickly lower the voltage. It is located a little below and right of center on dwg 332B-1001 sh 1. There is a N.C. K1 contact in parallel with the K2 crowbar contact. (I don't know which K1 relay but I suspect it's the interlock K1)The interlock K2 is shown in 2 places. One is at the lower left of sh 1 dwg 332B-1001 (to energize the preregulator K1) and also in the interlock on the right side of 332B-1001 sh 2. This one allows energizing the HV supply if all the cards & covers are in place.I haven't figured out how the interlock K1 & K2 get energized. The circuit description says that they are energized by Q3 on the series pass driver board when relay K2001 is energized in STDBY. The drawings that I have show the connections but interlock K1 has diodes connected in opposition and the 332 dwg (sh 2 of 332B-1001) has a single diode connected in reverse of what I would expect. A drawing error to check out the next time I open the beast.My 335D 'buzzes' when it is in current limit. The protection circuit trips on high voltage (as it should) and limits current on a short circuit (as it should).Do you get any current reading on the meter?Here are the 332 drawings I'm working from. They are from the April 1972 Rev 1 3/75 332D manual. (P/N353292) Do they match your unit?I have 2 sets (1971 & 1978) for the 335 and a 4th set made up of a mix from 332/335 drawings that seem to match my 335D.Also attached is a block diagram from the 335A/D 1/69 manual rev 1 8/71. The 332 is the same but without the null detector. The 335 HV assemblies are A8... and the 332 HV assemblies are A7.... The block diagram doesn't show the 500V supply feed from T1.According to a note above the editor, there have been 8 new messages added to the tread since I started composing this. I see that today the 332 has decided to work.

author: valley001
author_rank: Frequent Contributor
timestamp: March 11, 2019, 01:17:02 am
content: Hi Fred,Thanks for chiming in. The K1 and K2 I was referring to are both on the Pre Regulator board.I still have the bad Q2 on the current limiter to change, maybe that is the cause of my buzzing.

author: Fred_47
author_rank: Contributor
timestamp: March 11, 2019, 07:00:45 am
content: Quote from: valley001 on March 11, 2019, 01:17:02 amI don't think your Q2 is bad.On Dwg 332B-1004, Q2 is a PNP that regulates the -35V supply. You reported upthread that the -35V supply is outputing -35V. The BOM lists a 2n2869 PNP Ge and the card in my 335D has a 2n5883 PNP Si with a 1991 date code. (Maybe the newest part that I didn't put in.)Double check because there are a few different versions but all seem to have the same ±35V supply on the current limiter board.Also, I found yet another relay labeled K1.There is a relay 'K1' that is switched directly by the OFF-STDBY-ON switch that has contacts K1A and K1B. The relay is energized thru a time delay ckt between pin 8 & 12 on the Auxiliary Power Supply when the switch is turned to ON. The ckt is 40V from pin 15 to K1 to the ON switch to Pin 8. It has a contact K1A that parallels the crowbar in the HV supply and a contact K1B that shorts the output terminals thru a 5.1ohm resistor at the far right side of Dwg 332B-1001 sh 3.I notice that the power distribution dwg in the 3/75 rev of the 332A/D manual doesn't show the capacitor that creates the time delay. It is shown on the Dwg 335A-1004 in the 1978 rev of the 335A/D manual which I attached in my 1st post to this thread. It's in the BOM for the 332 Aux Power Supply board (C1 68uF, 15V Ta on the Aux Power Supply, A5A5) .The relay K1 that is in the interlock string has a contact that disconnects the neg output between the HV supply and output terminal.The 3rd K1 is on the preregulator board and is energized by the K2 interlock relay using the AC power input. It drops out immediately if AC power is lost while the other relays hang on as the DC power decays.I suspect that the reason for the convoluted circuitry is to make sure that the HV supply can't be connected unless the control voltages are energized and that the HV gets disconnected first in the event of any failure. Any one of the K1s failing to energize would have given symptoms similar to what you had. All of them are energized via various contacts which could have been dirty or oxidized or ....There is a 4th K1 on the capacitor switch that controls the voltage on C5 when the range is down switched too fast. It apparently doesn't have any function beyond that.

author: kawal
author_rank: Frequent Contributor
timestamp: March 11, 2019, 04:31:36 pm
content: The K1 you mention on the preregulator board was the same K1 that I had to clean via taking the relay apart. There was heavy oxidation on my unit and the cleaning removed all the oxidation. I reconnect you do that as you probably also have a lot of oxidation and carbon buildup on that K1.I circled the contacts to clean but best way is to take the contacts out. Remove the spring on the back and then you can remove the contact points for a good cleaning. This contractor has not protections from dust or other elements.I found this in an application note from TE connectivity"Contact MaterialsFine SilverFine silver has the highest electrical and thermal properties of all metals.It is the best general purpose material available. However, it is affectedby sulfidation. The rate of sulfidation indoors in a metropolitan area isapproximately 70 micrograms per square centimeter per day. Thissulfidation forms a film on the surface of the silver which increases contactinterface resistance.Because silver and silver alloys sulfidate, contact pressures must be greatenough to break through this film. (Controlled arcing will also be helpfulin that it burns off the sulfidation, and contact overtravel wipes away theresidue.) While such pressures have no appreciable effect on silvercadmium contacts, they do result in increased material wear of fine silvercontacts. Also, an interface voltage of several tenths of a volt can resultwith fine silver contacts because of the sulfide film. This film has beenknown to capture and imbed airborne dirt. Breaking through this filmgenerates electrical noise. Because of this, fine silver contacts are notused for low-level switching, such as audio circuits. Rather, fine silverand silver alloy contacts are for use in circuits of 12 volts, 0.4 ampere, ormore."I agree with Fred about Q2. That transistor is Germanium and measures strange on modern testers. We are so used to Silicon that no one remembers that there was a Germanium transistor before Si. Either way these will have low forwward voltage. Mine measures about 0.1V and i thought its broken too. But its old school and will show low Froward voltages.

author: valley001
author_rank: Frequent Contributor
timestamp: March 11, 2019, 05:28:27 pm
content: Hi all,I allowed the unit to operate for about 4 hours, and is supplying a voltage in the "correct" range more or less to 3-4 places after the decimal. Ive found myself in the position of not having a volt meter with sufficient resolution to view the output voltage accurately. I think a voltmeter upgrade is in my future.This morning I discovered a cap on the current limiter has leaked electrolyte during the 4 hours it was operating. This is disturbing to me because it tested fine on my component tester. I think I may replace more electrolytic caps to avoid future issues. For starters I plan to replace C1-5 on the HV mother board, C1, C4, C6, and C10 on the current limiter, C2 on the series pass, and C2 on the Aux Power board.Any thoughts on this plan? I would not want to disturb the accuracy or linearity potential, I dont think any of these caps would effect this correct?

author: Fred_47
author_rank: Contributor
timestamp: March 11, 2019, 06:56:25 pm
content: Quote from: valley001 on March 11, 2019, 05:28:27 pmGood luck finding a high resolution VM at a reasonable price.Replacing caps on any of the removable boards is pretty straightforward once you get the cap. I found that axial caps are a dying breed.Replacing caps on the HV MB is very difficult. Fortunately I only had one (C7 which parallels the interlock K1) which measure bad. Getting to the big 3, C1,2,3 is very difficult. I found that the 'paper' tube was not the actual capacitor but a cover. I my unit the actual caps filled about 2/3rds the height of the tube.My first round of replacements allowed setting 0 volts output on all ranges and dropped the power input from 40 to about 30 watts. Prior to replacement I couldn't get below a few mV at 0 setting.As near as I can tell, linearization doesn't depend on any caps.My 335D has been on or in standby continuously for almost a year with no problems except the decimal LEDs and null meter 0 setting on the 1mV and under ranges. (Optical chopper aging I think)I originally set the 335D reference with a new DM3068 that was still in cal. The three meters on the top (2 HP3478As and an HP3456A) are as received from eBay sellers with far out of date cal stickers from well known labs associated with either the gov't or big manufacturers. I fiddled with the HP3456A on the bottom.I've had the 335D up to 1100V a couple times to check a couple VTVM meters with 1500V ranges. Most of the 335D use is at 10V or less. I did use the 100V range a couple times to match neon bulbs for the optical chopper in the null meter and to check a couple zeners.PS: I have modified the bench for better thermal management, i.e., I added some space above the 335D for better cooling.

author: valley001
author_rank: Frequent Contributor
timestamp: March 20, 2019, 11:45:25 pm
content: Hello all,Today I tried using the 1000v range on the 332D. No dice. When switched to 1000v range it could not make it to 900v. Where should I look on this problem?

author: Fred_47
author_rank: Contributor
timestamp: March 21, 2019, 01:37:13 am
content: Quote from: valley001 on March 20, 2019, 11:45:25 pmHow did it not make it?Voltage trip? Voltage fell to 0 when you dialed above a certain value.Current limit? Voltage rose to a value and no higher as you dialed in more voltage.1000V range calibration? The 3 ranges have separate calibration pots.Was it approximately correct at voltages below 900?

author: valley001
author_rank: Frequent Contributor
timestamp: March 21, 2019, 01:46:03 am
content: Hello Fred,Yes, it seems reasonably close at voltages lower that 900v. When I switch for say, 100v to 1000v, it rises slowly and peaks out around 850-900v.

author: Fred_47
author_rank: Contributor
timestamp: March 21, 2019, 04:57:06 pm
content: Quote from: valley001 on March 21, 2019, 01:46:03 amI'm not sure if the 'slow' rise is normal. I've never switched my 335D from range to range at full scale setting of a range. Too much potential for excess excitment ;-)What happens when you make 10V steps on the 100V range? (This checks the sample string. You should get ≈10V/step)On the 1000V range start at 100V and raise in 100V steps. How close is the output to the dialed in value. Assuming problem with range calibration setting (A4 Range Calibration Assy), you would get something like 90V per step.Could also be preregulator or series pass element. (I have no experience with problems there.)Have you replaced any caps yet?What manual are you using? Do the schematics match your unit?Edit:The first diagram was supposed to be the original 'simplified' diagram from the 1978 rev of the 335D manual. What is posted here is a combination of the 2 pages from the manual. It is slightly modified based on my observations of the interlock circuit and isn't exactly the same as the diagram in the manual.

author: Fred_47
author_rank: Contributor
timestamp: March 21, 2019, 05:12:20 pm
content: Quote from: Fred_47 on March 21, 2019, 04:57:06 pmHere is the diagram that I intended to post. It differs in the A8 interlock connections.

author: valley001
author_rank: Frequent Contributor
timestamp: March 21, 2019, 09:13:48 pm
content: Hello Fred,Perhaps it is not a good idea to switch full range to range, ill refrain from that. I will test 10v increments in the 100v range and see how it behaves. I know on the 10v range it tracks fairly well one volt at a time however I only have 5.5 digit meters that I have repaired, nothing that has been properly calibrated.On the 100v range, stepping in 100 volt increments it tops out 850ish volts and will not go higher.I have not replaced caps outside the one that looked bad. I am learning but do not yet know enough to read the schematic and know which circuit/s could be causing this problem.

author: Fred_47
author_rank: Contributor
timestamp: March 21, 2019, 10:17:22 pm
content: Quote from: valley001 on March 21, 2019, 09:13:48 pmThis is a dangerous piece of equipment to learn on. Plus, I have found some mistakes and confusing (maybe mistaken) circuitry on the schematics. Exercise care when probing this beast. Even with the unit in STDBY there are very high (>500V) voltages present. The only way to have no voltage is to unplug it and let the caps discharge.The reason for checking the 100V range in 10 volt steps is that it uses exactly the same resistors in the sample string as the 1000V range in 100V steps. (As does 1V step on the 10 volt range so maybe the sample string is OK.) Actually, you're looking for all the steps to be the same size on any given range.Am I right that on the 1000V range you are getting close to 100V steps until you get to above 800V?EditI always seem to think of one more thing after I hit post.Does the voltmeter on the unit work?Does it agree (approximately) with your bench meter?Does the meter on the unit show any current when you try the 332 on high voltage?

author: valley001
author_rank: Frequent Contributor
timestamp: March 21, 2019, 10:25:47 pm
content: I take heed of the high voltage warnings, and have done all tests with the extender installed and diagnostic connections made without power applied. I am particularly nervous with powering it on case open but I take precautions for safety.Yes, when stepping 100v steps in the 1000v range it will make 800 but then when switched to 900 it labors (seemingly) and stalls.

author: Fred_47
author_rank: Contributor
timestamp: March 22, 2019, 01:37:44 am
content: See the edit to my post above your last post.We're trying to eliminate all the stuff on the right hand side of the simplified schematic.Operation of the meter should be confirmed as it will give you an easier way to monitor the output. Also, operation of the current limit should be checked. If it is somehow becoming active at around 850V, it will hold the voltage down to keep a constant current. It's been a while since I operated my 335D in current limit, but IIRC it hums rather noticeably.The meter and protective ckt procedure begins at Para 4-32 in the 332D manual Rev 1 3/75. For now I would skip doing the current tests at full voltage on the 1000V range. Maybe try them at a lower voltage like 4-500V after you get a feel for how it works.

author: valley001
author_rank: Frequent Contributor
timestamp: March 23, 2019, 03:07:54 am
content: I had some time to experiment with the 332D this evening.-I verified 100v range steps. I see 10v change per step: 10v, 20v, 30v, etc to..100v. The analog meter tracks with each range along with the digital meter hooked up to the output.-Going through the current limit setting procedure per 2-18. When switching to operate and attempting to set the current limit via the current limit knob the meter will rise to 10ma and then stall, sometimes simply failing to rise higher or will fall to 0.I am guessing the root of my issues lie in this discovery.

author: valley001
author_rank: Frequent Contributor
timestamp: March 23, 2019, 03:31:29 pm
content: Investigating this morning, so far:C7 on the HV mother board reads 3500pf, so I guess that one is toast. Will test more caps I guess.Uh oh... I tested three more of the small sprague electrolytics on the current limiter board, C2, C3, and C5, all test in the 1000pf range out of circuit. Unless I am missing something these are all toast right?

author: Fred_47
author_rank: Contributor
timestamp: March 23, 2019, 04:17:08 pm
content: Quote from: valley001 on March 23, 2019, 03:07:54 amCould be. It's certainly not the expected behavior.The meter circuit is on DWG 332B-1001-2 Series Pass Driver. R22 is the shunt. It's the only resistor on the schematic that doesn't have a value listed. The BOM says it's 101%, 1/2W.That same shunt drives the current limiter but I've never figured out exactly how. The end result is to reduce the drive to Q8 on the series pass element.What does the current do when you repeat your original test that stalls at 850V? (Not shorted)Does the current limit LED come on? (Do you know that it works? I think it comes on with the unit in STDBY.)I've added PS voltages to the ~ where they were missing. (Hasn't been double checked). Note that the ±35V supply common is connected at flag '10' which is the center tap of the T1 winding that feeds the ±35V supply.Your 'Still sorting issues' post came thru while I was drafting this. I'll post this then look into the cap issues.

author: Fred_47
author_rank: Contributor
timestamp: March 23, 2019, 05:03:23 pm
content: Quote from: valley001 on March 23, 2019, 03:31:29 pmSomewhere up thread, I posted a PDF of the caps I measured (mostly in ckt) with an Extech LCR200 using the 120Hz setting. I confirmed the choice to replace by measuring them when I made the replacement.Of your list I replaced C7 on the HV MB & C3 on the Current Limiter/±35V supply along with 11 others scattered across the other boards about a month after I got my 335D. That dropped the STDBY power draw from 40 to 30W and allowed setting the zero outputs on all 3 ranges. Except for the null meter (probably the neons in the optical chopper) my 335D seems to function properly.I replaced 5 more Ta caps last Nov along with one of the neon lamps in the chopper trying to improve the null detector. It worked for a while.C7 on the HV MB had an insainly high ESR along with low capacitance. It parallels one of the K1 relays (shown on the drawing I attached to my post about 2 up in this thread). This circuit is confusing because the diode seems backwards on some drawings. I actually have a 335D dwg that shows 2 diodes in opposition. Originally I thought the cap was to slow the pickup of K1 but it could also slow the dropout. Figuring out the diode is one of the projects when I open the beast to work on the null detector. Right now a Wavetek 114 is in the way.I also replaced C3 in the ±35V supply which had about 20X the esr of either C2 or C5. All 3 had acceptable capacitance.I think you're on the right track.

author: valley001
author_rank: Frequent Contributor
timestamp: March 23, 2019, 05:11:37 pm
content: OK great. At frist so many were testing bad I thought it might be my methods but my component tester and my DMM both show very low capacitance on the ones I have taken out of circuit. The component tester would not give an ESR reading. My DMM says something crazy like 10 megs resistance.There are a ton on of these small sprague electrolytics on the chopper amp and aux power board, guess ill be busy.

author: valley001
author_rank: Frequent Contributor
timestamp: March 23, 2019, 06:25:50 pm
content: I investigated a number of small electrolytics on the chopper amp and aux power board, none that I removed from circuit tested particularly bad.I am letting it warm up and will see if replacing C7 on the HV motherboard and C2, C3, and C5 on the current regulator have an impact.

author: valley001
author_rank: Frequent Contributor
timestamp: March 23, 2019, 06:58:50 pm
content: With these 4 caps replaced the unit seems more stable, but there are still problems with reaching higher voltage and setting the current limit.There does, however, seem to be improvement with the current limit setting. Now when switching to operate per 2-18 the current needle will rise slowly to 60ma. If I operate the current limit knob the current limit light will flash once and the needle will go to zero. I have to cycle the operate knob to get it to show current on the meter.

author: valley001
author_rank: Frequent Contributor
timestamp: March 23, 2019, 09:32:18 pm
content: I went back in and replaced C5 on the series pass (high ESR and low capacitance) as well as C1 on the current limiter, just because it looked bad (tested fine, but seemed to be bulging a bit and possibly leaking electrolyte).Results are more stable operation and now it is reaching up to near 1000v, so I am seeing improvement.I think im going to order the other caps for the current limiter, C4 and C6.I have some 680uf 100v on hand, the originals are specd at 350uf +75% would I be pushing it installing the 680uf caps?I did test the three big caps on the HV board and they are all showing about 160uf. I may order those and replace them as well.It is frustrating that a cap will test good on the component tester but it is obviously bad in practice.

author: valley001
author_rank: Frequent Contributor
timestamp: March 24, 2019, 03:09:43 pm
content: I all,Sorry for all the posts but I encountered yet another issue. What I thought may be problems with the output voltage turned out to be a problem in the range selector switch itself. With the output set to 0.000000 I will see a reading of approximately 0.000040 (around 36-44uv flickering). If I apply clockwise pressure to the range knob it will jump to approx 0.000140. I can get it to go back anf forth between the two (0.000040 and 0.000140). I assume this is a problem.The switch is several layers of sealed contact assemblies (see pic). I know from experience these do not readily disassemble.Would it be a good idea to apply a small amount of deoxit D5 (the only type I have) to the contact through the hole in the plastic for each layer? Applied with a toothpick or something like that. I have also read to clean with Isopropyl alcohol but I dont know how I could accomplish this short of soaking each contact assembly.

author: Fred_47
author_rank: Contributor
timestamp: March 24, 2019, 08:26:32 pm
content: Quote from: valley001 on March 24, 2019, 03:09:43 pmDon't know about contact cleaner but my 0 problem went away after I replaced some caps. I was then able to adjust the 0 setting for each range and they have been good for about a year with small adjustment for drift after about 6 months.

author: valley001
author_rank: Frequent Contributor
timestamp: March 24, 2019, 11:59:47 pm
content: Quote from: Fred_47 on March 24, 2019, 08:26:32 pmI discovered yet another bad cap, this time on the aux power board (C7). I also replaced C2 on the series pass board just because I had a 10uf 450v cap on hand.I also checked all of the electrolytic caps on the chopper board, many have ESR in the 3-6 ohm range. I think ill replace all of those eventually.With C7 replaced on the aux power board the drift on 0 setting has settled, flickering only 6-7uv so far but its only been operating for 30min or so. Maybe what I was seeing was not related to the range switch at all.Another thing, when the unit is first turned on I can get some life out of the current limit function, but when its been on for a while and trying to set current limit it will fail to operate. When switched to operate the needle (on current setting) will flicker and peg past 0. I plan to assess the transistors listed in the current limit description section 3-41, is this sound?. I discovered this now that I have been allowing the unit to operate for longer periods.

author: Fred_47
author_rank: Contributor
timestamp: March 25, 2019, 02:02:12 am
content: Quote from: valley001 on March 23, 2019, 05:11:37 pmA number of the aux power supply filter caps had been replaced before I got the 335D in Mar 2018. As I mentioned up-thread, the HV filters C1, 2, 3 only fill about 2/3rds of the paper tube so they may have been replaced. The (1978) 335 manual lists Fluke as the mfg for them but both the(1971) 335 and (1975) 332 manuals lists Sprague. I think the ones in my 335D are Mallory.This is what I replaced in April 2018 (The silver Sprague were mostly original circa 1980 the blue ? were circa 1990)Edit... I'll have to look at the current limit but checking the transistors is a good idea. It sounds like there is some intermittent or thermal problem. The current limit and voltage trip have been dependable on my 335.

author: valley001
author_rank: Frequent Contributor
timestamp: March 25, 2019, 02:40:23 am
content: Quote from: Fred_47 on March 25, 2019, 02:02:12 amHello Fred,Are there date codes on the blue caps? Mine has a mix of the Sprague and the blue ones and I think they are all original based on the intact coating on the rear of the PCB. So far only one of the blue caps on mine has tested bad with high ESR. The majority of the bad Sprague caps were testing in the pf range, some with high ESR. Pic of my dead caps attached.I think I have largely solved the stability problem, the 332D has been operating for a few hours now and it is flickering around 4uv. It has settled at -104uv +/- 4uv on my Dana 5004 which was last calibrated in 1998, with the readout set to 0.000000

author: Fred_47
author_rank: Contributor
timestamp: March 25, 2019, 07:21:09 pm
content: Quote from: valley001 on March 25, 2019, 02:40:23 amPack rat that I am, I still have all the caps that I removed. They now include a few that I replaced in Nov 2018. The count is up to 16 + a couple Ta that I couldn't find (but they're here ...somewhere). Most of the first batch were from various boards and most of the second batch were from the Null Detector boards.The "blue" caps were either MEXICO or PHILLIPS, none of the caps were leaking or obviously failed by visual inspection.I've included a txt file with the data but in summary:All of the MEXICO caps were either low capacitance, high ESR or both. (one turned out to be in spec)The closest approximation to a date code is in the line with the name (MEXICO) and is either 030, 031 or 032. Based on the cal sticker from Fluke (Apr-14-92 by #39) and date codes on some other parts, my assumption is that this is 1990, 30 thru 32nd week. I don't think this instrument was worked on after that.(3 were marked 47uT not 47uF)The remaining blue caps are PHILLIPS and have a similar codes 031 & 032. One of these appears to be close to spec but the others wouldn't give a steady reading on my LCR meter. One actually read out as an inductor.Of the 4 Sprague cap, 3 have date codes from 1980, '81 and one is 1990. All are type 30D and have very low capacitance wrt their marked rating. So, I didn't bother to calculate the ESR.

author: valley001
author_rank: Frequent Contributor
timestamp: April 02, 2019, 07:58:07 pm
content: I went through Q3-Q7 on the current limiter. None of them test broken but some are showing hfe in the 50-100 range, these are silicon transistors.I did replace C1-5 on the HV board, along with C1, C4, and C6 on the current limiter. This did not have any effect on the current limit setting, though the output is closer to 0 with the readout set to O. It still does not set current per the manual. When I switch to operate the needle pegs to the floor. I am not sure where to look next.

author: Fred_47
author_rank: Contributor
timestamp: April 02, 2019, 09:49:35 pm
content: Quote from: valley001 on April 02, 2019, 07:58:07 pmYou're braver than me. I couldn't get the HV MB far enough out of the chassis to work on it. The wiring harness didn't have any slack & I was afraid of nicking a wire on the chassis.On my 335D current limiter, the PNPs (Q3,5 & 6) measured 62, 60 & 82 and the NPNs (Q4 & 7) measured 140 & 170. The PNPs are 'selected' SS7504 & NPNs are f203489. I didn't find data sheets for either one.Pegging negative current or voltage?What does a meter at the output show?

author: dacman
author_rank: Frequent Contributor
timestamp: April 02, 2019, 10:22:46 pm
content: Are the safety switches working (consistently)?

author: valley001
author_rank: Frequent Contributor
timestamp: April 03, 2019, 01:24:34 am
content: Quote from: dacman on April 02, 2019, 10:22:46 pmThe voltage trip seems to work. I am not sure about the current switch, since I have not been able to set the current trip. I have also not attempted to use this as a power supply.

author: Fred_47
author_rank: Contributor
timestamp: April 04, 2019, 10:04:52 pm
content: Quote from: valley001 on April 03, 2019, 01:24:34 amThe current setting isn't a trip, it's a limiter. It turns the 332 into a constant current source. There is a trip (not adjustable) for gross overcurrent. It's on the series pass driver board along wth the voltage trip, voltmeter dropping resistors and the current shunt.

author: dacman
author_rank: Frequent Contributor
timestamp: April 04, 2019, 10:32:09 pm
content: The safety switches I was referring to are the interlock switches that are intended to sense whether or not the top and bottom shield covers are installed.

author: valley001
author_rank: Frequent Contributor
timestamp: April 05, 2019, 03:36:27 pm
content: Thank you Fred,I experimented with the current setting again this morning. After a 10-15 min warm up I attempted to set the current limit. To my surprise it would allow adjustment of current setting but tripped when needle passed the 10ma position. I reset and it let me adjust down to 40ma before again tripping. I tried once more and it would not allow any adjustment at all, tripping immediately after moving the current knob. Subsequent attempts mimic the condition I described earlier where it trips immediately after moving to "operate."My thought is the problem is either in the non adjustable current trip circuit you described or the unit is somehow producing a gross over current causing the trip. Does this reasoning sound correct? If so, any ideas on where to check?I did measure all transistors with removable sockets on the unit, all test "correct" but some with lowish hfe but without spec sheets I have no basis for comparison. I think you pointed that out earlier.Quote from: Fred_47 on April 04, 2019, 10:04:52 pm

author: wictor
author_rank: Regular Contributor
timestamp: April 05, 2019, 03:40:28 pm
content: How about the current setting pot itself? I would check that first.

author: valley001
author_rank: Frequent Contributor
timestamp: April 05, 2019, 03:47:14 pm
content: Quote from: dacman on April 04, 2019, 10:32:09 pmI have not tested those directly yet. I did operate the unit with the top cover removed for reading voltages but only assumed those switches were functioning.

author: valley001
author_rank: Frequent Contributor
timestamp: April 05, 2019, 09:46:46 pm
content: This is embarrassing...My unit was missing the shorting bar between + sense and + output. I have been using a cable with banana plugs to connect sense to output. When attempting to set current limit I used the cable to short the output, but that left the sense unconnected.With sense connected and output shorted it seems to behave correctly when setting the current limit.I now need to get a better meter to see how stable this thing is.

author: texaspyro
author_rank: Super Contributor
timestamp: April 05, 2019, 10:39:31 pm
content: Quote from: valley001 on April 05, 2019, 09:46:46 pmI have a nice paper bag with eye holes cut out... fits all head sizes.

author: RandallMcRee
author_rank: Frequent Contributor
timestamp: April 05, 2019, 10:44:34 pm
content: Quote from: valley001 on April 05, 2019, 09:46:46 pmPM me your address so I can send you my unit--it *does* have the behaviour you describe *with* the shorting bar in place. It must be your karma to fix my unit. Glad I found you.

author: Fred_47
author_rank: Contributor
timestamp: April 06, 2019, 03:21:38 am
content: Quote from: valley001 on April 05, 2019, 09:46:46 pmIt shouldn't 'trip' <from simple current limiter action> , i.e., require going from OPR to STDBY/RESET in order to restore output. The non-adjustable overcurrent is set by Q4, R24 and R22 (the current shunt) on the Series Pass Driver board. According to my 335D manual, the trip point is about 120mA. On the Series Driver Board, Q1 is the voltage trip. Q1 or Q4 turn on Q2 which shorts the output of Q3 and drops out K1 & K2.I would check the diode between +output and +sense. If it is open the driver will run the output voltage up to the voltage trip point which does require a RESET. There is a similar diode between the -output and -sense. Their purpose is to keep the sense leads from becoming 'too disconnected' from the output leads.The interlock string that Dacman is referring to allows relays K1 & K2 (shown on sh2 of dwg 1001) to pick up from current source Q3, when you switch from STDBY/RESET to OPR. K1 connects the negative HV output & K2 enables the input to T2. You should not be able to energize the output if any card is in the wrong slot or either top or bottom inner chassis cover is removed or if any of the control power supplies isn't working. (I use a wood clothespin and popsicle stick to hold the top switch down when I'm troubleshooting.)I think the diode, CR22, in series with K1on the Series Pass Driver, is drawn backwards. I have a 335D drawing in the 1978 revision of the manual, that has 2 diodes labeled CR22, one on each end of the K1 relay coil, facing each other such that NO current will pass. One of the things for me to check the next time I open the beast is which way that real diode is installed.Edit to add <from simple current limiter action>.

author: valley001
author_rank: Frequent Contributor
timestamp: April 06, 2019, 06:43:11 pm
content: Fred, it no longer trips now that I have the sense connected to output. Are you saying it should not trip when setting current limit with the sense disconnected?I will check out those diodes though.I alluded to needing to find a better meter to see how well this is really working. The Dana 5004 works fairly well but sometimes I see spikes of a hundred uv or so, and a drift range of roughly 100uv. I am not sure if these are the result of the meter or the 332D. I let the Dana sit for a few hours with the input shorted and it did not drift at all, but not sure if that rules the meter out. I am looking for a better meter.

author: dacman
author_rank: Frequent Contributor
timestamp: April 07, 2019, 02:15:43 am
content: The 332D does have noise specifications (40 uV rms on the 1000 Vdc range). Make sure the chopper is properly adjusted.

author: valley001
author_rank: Frequent Contributor
timestamp: April 07, 2019, 04:35:09 am
content: dacman, thank you for your input. Do you have an idea why the 332 would appear stable for a period of time and then suddenly begin to jump around 50-100uv? I can observe the unit output stability dither around 3uv in the 10v range suddenly jump 50-100uv for 5-10 counts and then settle back to a 3uv dither.Quote from: dacman on April 07, 2019, 02:15:43 am

author: valley001
author_rank: Frequent Contributor
timestamp: April 07, 2019, 04:48:10 am
content: Quote from: RandallMcRee on April 05, 2019, 10:44:34 pmI just noticed this. There are surely better people than I to troubleshoot your unit. I am really a noob at this.On mine I made a lot of progress testing capacitors and replacing the ones I found to be defective.

author: Fred_47
author_rank: Contributor
timestamp: April 07, 2019, 03:51:29 pm
content: Quote from: valley001 on April 06, 2019, 06:43:11 pmI haven't tried it on my 335D but, the diodes should prevent output voltages higher than 2 diode drops above the setting (about 1.4V) when the sense straps are removed.Thinking about this, if the current limit can drive the output voltage to zero (or low enough to get to the current limit), the unit will (should) not trip with a short at the output terminals. If, for whatever reason, the output can't be reduced to zero the unit will trip if the current is above the gross trip value set by the Series Driver Board (not adjustable). If the current limit does completely shut off the Series Pass Element, the minimum current supply (rectifier bridge CR13 thru CR20)* will drive current backward thru the short and the current shunt (meter) limited only by R9 & 10 (on the HV MB). I'd guess this current to be about -5mA or less. Without the short, the reverse output voltage will be limited to the drop across the reverse voltage limiter (CR2, 3 & R8, 5.1Ω). In the standby mode, this current is blocked by open contact K1 and snubber ckt R7, C8. This thing is just full of surprises.The current limit isn't designed to trip the unit. I've used mine to test LEDs and Zeners. Set the current to say 10mA and run the voltage up until the current limit light comes on. Read the voltage from the dials.Note that a suddenly applied load can have a high initial current as the output caps discharge. The current limit can't prevent that. The current limit will prevent the voltage from RISING above the point where V/R= (current limit) but if the output voltage is already above that point, the load has to deal with the stored coulombs. You can't set a voltage of say 100V and plug in an LED and then dial the voltage down to find the 10mA point.My 335D seems rock steady. The highest resolution meters I have are 6 1/2 digit HP3456As. It's been a while since I've tried it but I can usually walk the meters up or down 1 count at a time with the 335D. However, I don't know if that would be true with a higher resolution meter.*Found another drawing error, there are 2 CR11's and no CR14 shown on the HV MB on the 335D drawing 335A-1001 sht 1 of 3, Fig 8-4 Fluke manual P/N 353300 rev 1 6/78, fig 5-17 shows CR14. The 332B drawing has a CR14 on 332B-1001 sht 1 of 3, Fig 8-1 Fluke manual P/N 353292 rev 1 3/75.

author: valley001
author_rank: Frequent Contributor
timestamp: April 20, 2019, 11:11:18 pm
content: This can be a frustrating unit to work on.I am still chasing issues with stability in the microvolt level. It will not settle on a stable reading, it jumps around 10-100uv at times.I cleaned and lubricated the contacts, this did not help.In an attempt to rule out the switch contacts as a part of the problem I did the sample string test per the manual, with my HP 3456A in 4 wire mode. I did not observe the resistance readings jumping around much. Not sure if this would rule out the switch contacts.I decided to go back and check voltages and resistance readings per the checks in the manual. Below are my findings so far.4.57 (resistance between points and + sense)C: Aux pin 9- 7.17KAux Pin 10- 2.45KCurrent limit pin 1- 5.3KCurrent limit pin 3- 3.0K4.61Aux pin 10: 25.6vAux pin 9: -15.17vCurrent limit pin 1: -35.7vCurrent limit pin 3: -36.99vRange cal test points: 14.9998Ref supply Q1 collector: 47vI probed additional voltages on the ref supply board, it appears the voltage reference is 8.1v rather than the 6.5xxxx indicated in hand writing on the tag. I am wondering if this could be related to the Q1 collector voltage being too high? There is a note in the manual that mentions this voltage should start at 1v and then rise to 26-35 after 10 min, it does not exhibit this behavior. It goes immediatelt to 40v and rises to 47ish.The ref supply Q1 voltage is obviously too high, where should I look on this problem?

author: dacman
author_rank: Frequent Contributor
timestamp: April 21, 2019, 04:57:30 am
content: Reference Supply Q1 Collector is tied to the (unregulated) 40 Vdc power supply through a 33 Ohm collector resistor. I do not see how it could be 1 V even if Q1 shorted. If left off overnight, what is the startup voltage when first powered on?

author: Fred_47
author_rank: Contributor
timestamp: April 21, 2019, 05:06:31 am
content: Quote from: valley001 on April 20, 2019, 11:11:18 pmOne thing that makes it hard to work on is that many of the circuits are spread over a couple drawings. Sometimes it helps to draw a circuit out from one end to the other to trace the signal thru all the various parts that may affect it.Also, there is an amazing number of errors on the drawings. Did anybody at Fluke check these drawings?One thing I'd look at is whether the 'jumping around' is the 332 or the meter you're using to measure it.... test leads?... is the reference output steady?Does the output jump or is it drifting? (temperature change caused by a draft for example if the top is open)Current limit pin 3 should be +35V. (I will assume you hit [-] by mistake.)None of the voltages seem super bad. IIRC the 25V is supposed to be within 10mV tho.What voltage starts at 1V and increases? I would expect the ref output to be close to 15V from the start.Thoughts as I browse thru the drawings.Looking at the Master Voltage Ref dwg, I'm confused. It shows the same node labeled 6.6V & 8.6V. I would expect practically 0 voltage between the op-amp inputs. With 15V at the op-amp output, 8.6V (as marked) is about right at the inputs for the resistor values shown. 6.6V is probably the (approximate) voltage at the cathode of the reference diode and the arrow points to the wrong node. The master ref output is 15V (per Dwg 332B-1001 sh3). 14.9998 is pretty close so the ref is probably working.Q1 in the heater ckt is a current controller using R20 for feedback. I suspect that the heater voltage (approximately the emitter of Q1) should start at a low voltage and rise slowly. It won't do that unless the heater is 'cold' at the start. The collector voltage of Q1 will be high from the start.What are the other heater ckt voltages? If only the collector of Q1 is off I wouldn't be super concerned if the other voltages in the heater ckt are near the proper values. (provided Q1 isn't super hot) What are the currents thru (voltage across) R19 & R20? Resistance of R19?The 40V supply is an unregulated tap from the bridge serving the 25V supply. One of the (many) K1 relays is connected between it and the timer SCR, Q1 on the Aux Power Supply. (Note: if my 335D dwg is correct there is a capacitor, C1, missing between the node R1 to R3 and pin 12 on the 332B Aux Power Supply drawing.) What is the transformer secondary voltage? Is the primary voltage high?I see that dacman replied while I was composing this. If Q1 shorted it wouldprobablymight destroy the heater. The ref would work but it wouldbe unstabledrift (but I don't think the output would 'jump').

author: Fred_47
author_rank: Contributor
timestamp: April 21, 2019, 02:49:21 pm
content: Quote from: Fred_47 on April 21, 2019, 05:06:31 amThis thing wouldn't let me sleep.A1 is an MC1723CG (volttage regulator) which has a max input voltage of 40V. So, at 47V, it may have gotten toasted. Q1 extends it's capacity.Based on the values on the dwg, the heater voltage should be about 23.2V. If A1 is toast, and assuming that A3 is OK, I would try to design a ckt using modern regulator components. I would provide a pre-regulator (zener) for A1 to guard against high voltages.According to the data sheet, Isc= Vsense/Rsc. At Tj = 25C with Rsc =1.5Ω, Isc works out to 440mA. As Tj increases Vsense decreases. There is a curve in the datasheet. If the whole heater control draws more than 212mA, the chip may be OK.

author: valley001
author_rank: Frequent Contributor
timestamp: April 21, 2019, 03:27:25 pm
content: Thank you Fred and Dacman for your continued input.I will check voltages across R19 and R20, and voltage at the junction of Q1 base and pin 6 of A1. These readings will give an indication on the status of Q1 and A1 correct?I have been using a new to me HP 3456A for measuring. It was last calibrated in 2006 or so, with intact anti tampering stickers. I am fairly confident it at least will provide a stable reading, for instance when measuring a battery it is steady as a rock.Quote from: Fred_47 on April 21, 2019, 02:49:21 pm

author: valley001
author_rank: Frequent Contributor
timestamp: April 21, 2019, 04:17:18 pm
content: OK so Q1:Base: 24.8vCollector: 47vEmitter: 24.2vR19:Collecor Q1: 47vOther side: 48vR20-Emitter Q1: 24.2vOther side: 24.08v

author: Dr. Frank
author_rank: Super Contributor
timestamp: April 21, 2019, 05:09:41 pm
content: Quote from: valley001 on April 20, 2019, 11:11:18 pmHello,I made some stability characterization, also on the reference circuit a few years back, on a similar unit:https://www.eevblog.com/forum/testgear/fluke-332baf-in-the-slaughterhouse/msg399283/#msg399283These old calibrators are not that stable, and quite noisy.Therefore, you first have to make clear for yourself, on what scale you see these variations of 10..100µV, i.e. in which range, and at which output voltage.If you see 10µV variation on 10V output, that's 1ppm, and that might be ok, 100µV would be too much, but on 100V, it would be ok.Your DMM might also create this noise.Please compare that to my measurements.The contacts usually do not create such noise.Please measure the 15V master reference voltage, accessible on top of the shield.What is the relative noise / stability?Seems to me, that it is rock stable. Therefore, the whole reference is ok, including the oven circuit, which is fully separate from the reference circuit.The oven consists of a precise and stable 24V supply by the 723, which to me seems fully functional as intended, also these 47V raw supply.I can't find the hint of a slow rise of the 47V, these should also be available instantly.Oven set point of about 72°C is achieved by this KLIXXON heater element itself, which has a resistance extremum at the oven set point.Very crude technique, but working.The reference amplifier itself, that is the zener diode combined with the transistor, 'outputs' the printed reference voltage at the base of the transistor, which you can measure at the wiper of the trimmer.The arrow labeld 6.6V should indicate there, instead of the collector of this transistor, which indeed has these 8.6V.That's the fault in the schematic.Everything seems to be fine there, also.If you see excessive noise, the root cause seems to be elsewhere, maybe in the chopper amplifier.. please indicate, which version you have in your instrument, the mechanical chopper, or the MOSFET chopper.But again, please analyse therelativestability first.Frank

author: Fred_47
author_rank: Contributor
timestamp: April 22, 2019, 02:03:18 am
content: Quote from: valley001 on April 21, 2019, 04:17:18 pmIt seems backward to have 30mA thru R19 and 80mA thru R20. I would expect to have nearly the same current on both sides of Q1.In any event the heater voltage seems close enough. The voltage agrees with the value that Dr Frank gave. He has much more experience with these than I who has only worked on one unit that was mostly working to begin with.I've finished working on my Wavetek 114 so the bench is clear and I plan to work on the null meter chopper in my 335D. Hopefully I can eliminate the neon bulbs.

author: valley001
author_rank: Frequent Contributor
timestamp: April 22, 2019, 03:22:30 am
content: Dr. Frank, thank you for your input.I have observed noise with the dials set to 0.000000 in the 10v range. The device will behave for a time moving 3-4uV and then spike 100uV or more. It also settles to different readings at times, sometimes displaying around -88uV and sometimes -104uV or so. It is not consistent. I have not observed the other ranges as much, but I have switched through them with the dials at 0000000 and see similar behavior. If I set the dials to 1.000000 on the 10v range I will see similar behavior as above.This unit has the solid state chopper board installed.This unit was missing Q4 and Q8 on the differential amp board, I replaced them with the following modern components (Q6 replaced along with Q4):Q4 and 6: KSC1008YBUQ8: KSD1616AYTAI have also replaced many caps, some were obviously bad (externally swollen) and some tested bad.I plan to probe voltages outlined on the schmatic of the chopper board next and possibly the differential amp board.Quote from: Dr. Frank on April 21, 2019, 05:09:41 pm

author: wictor
author_rank: Regular Contributor
timestamp: April 22, 2019, 04:08:15 am
content: One reason for unstable behaviour can be bad connections between boards.Wictor

author: Dr. Frank
author_rank: Super Contributor
timestamp: April 22, 2019, 10:18:46 am
content: If you observe instability at 000000 setting, this is very probably not caused by the reference.Static offsets might be caused by bad connections/contact between the PCBs, but these are gold plated, or in the several intermediate switches.Sporadic spikes probably have different root cause, like oscillation or bad components.Maybe you take an oscillogram of these spikes at the output jacks, how they look like.Another source of joy might be the pre regulator board, which might be mis-firing, and then disturb the feedback regulation. Check the waveform inside that circuit, if you see frequent, regular pulses, or erratic/ sporadic bursts.The filter electrolytic caps after the rectifier bridge should also be under observation.The preregulator should provide an estimate of 35V overhead supply compared to the chosen output voltage at these camps. Also check the waveform at the unijunction transistor circuit.Always pay attention with ground of circuits and oscilloscope ground.. 'how not to blow up your scope'Pay attention there, high voltages may be present.Frank

author: valley001
author_rank: Frequent Contributor
timestamp: April 22, 2019, 05:54:16 pm
content: Here are waveforms from Q1 on the pre regulator board. The scope is un grounded per the manual. Scope "common" on emitter and "input" on base.The first is with the device on stanby, the seconf on operate.These do not look the same as the manual, what may this indicate?

author: Dr. Frank
author_rank: Super Contributor
timestamp: April 22, 2019, 06:21:24 pm
content: Doesn't look bad.. I don't know what output voltage you have selected, but the Duty Cycle depends on that. small voltage => very small D.C. .D.C. should go from about 100% at 1kV down to maybe 1..2% at near zero out.Maybe you get a picture of the output spikes, if you output 10V and chose AC coupling in a small mV range. Osci ground should be tied to + output jack, as this is the 'real' internal ground of the 335D.Frank

author: valley001
author_rank: Frequent Contributor
timestamp: April 23, 2019, 02:41:38 pm
content: On the above wave forms the output was set to 50.00000. The manual is contradictory, it says to put range to 1000 but output to 50.0000 (1000 range and 5000000 dials would net 500v, 500.0000 no?). I tried boith and did not see a noticable difference in the waveforms.I am not sure how to hook up the oscilloscope with the ground on + sense. Would I then hook up the input to - sense? Would I disconnect the shorting bars?I did hook the scope with the ground on - and input on + with shorting bars present between sense and output. I am not sure I see anything meaningful. I do see a 30-50Khz ish (fluctuating) spike with the scope sweep speed set high, (don’t recall how fast exactly).On the HP 3456A I do note that as I increase the output the noise seems to travel with the increase in output. That is, if I set the output of the 332D to 1.000000 I see noise in the uV range, if I set the output to 100.0000 I see noise in the mV range. (noise is amplified?)There is also a noticeable buzzing coming from the rear of the unit (HV mother board, pre reg, or series pass) that sometimes becomes louder for a brief period. I do not notice any correlation to the increase in this buzzing and noise on the output. I am wondering if other units exhibit this buzzing sound.

author: Dr. Frank
author_rank: Super Contributor
timestamp: April 23, 2019, 04:30:49 pm
content: Quote from: valley001 on April 23, 2019, 02:41:38 pmThey have to be identical, independant from range chosen.Quote from: valley001 on April 23, 2019, 02:41:38 pmSimply have a look on the principle schematic. The 33x are simply big inverting opAmps, and + jack is the (virtual ) zero. Input can be tied to -. leave the shorting bars where they are.Quote from: valley001 on April 23, 2019, 02:41:38 pmThat buzzing sound is probably the pre-regulator,which changes its duty cycle proportional to the output voltage.noise is amplified, as the amplification factor is determined by the range switch (input resistor of opamp), and by the sample string (output/feedback resistor of the opamp)

author: Fred_47
author_rank: Contributor
timestamp: April 23, 2019, 05:14:24 pm
content: Quote from: valley001 on April 23, 2019, 02:41:38 pmMy 335D hums/buzzes when feeding high(ish) currents especially when in current limit. I very rarely have it above 100V but it probably makes noise when outputting high voltages.Don't disconnect the sense terminals from the output terminals except to regulate voltages at the input terminals of a load.Be very aware of the scope grounding; the ground prong on the plug at the wall socket is connected to the test lead 'ground/common'. You can get into very serious trouble if you isolate the scope case/chassis (assumed to be metal). Touching it or any other exposed metal (USB socket, BNC sockets, common of any other channel, etc.) while the scope common is connected to a voltage source can be fatal. If the scope is connected to anything (computer, scope cart, terminal whatever) the scope chassis common voltage is coupled thru to that device. There are many opportunities to let the magic smoke escape or worse.The ground prong on the 332 is connected to the outer case*/front panel BUT NOT TO THE INNER CHASSIS WHICH IS CONNECTED TO THE + OUTPUT/SENSE! The + output is the common terminal for the various control power supplies. You need to think of 'ground' and 'common' (and 'Guard') as different nodes that can sometimes have very high voltages between them. It is possible to ground (to earth) either the + output terminal or the neg output terminal or neither of them.To do what Dr Frank asks you need to make sure that both of the 332 outputs are isolated from ground or that the + terminal is grounded. That way you don't have to float the scope.**If you examine the mechanical attachment of the front panel to the inner chassis, you will see that the guard terminal is connected to a metal strip between them and there is a rather complex stack of metal and insulation. It's all arranged so that the front panel (and the screws attaching it) is grounded and the guard intercepts any leakage current between the inner chassis to the front panel. I think the guard is also connected to shield terminals on the transformers. For most usage, you can put a shorting bar between the guard and ground terminals on the front panel. I think the guard may be connected to the shield inside of the case but haven't checked to see if that is true.My 335D had a shorting bar between the ground terminal and - output/sense terminals.*The outer case is only grounded when the inner chassis is fully inserted. Otherwise it is floating. Same is true for the inner shield which may be connected to the guard terminal )or ground, I don't know which) when the chassis is fully inserted.**Edit: You DO have to float the scope to examine anything in the pre-regulator circuit. It has direct ohmic connections to the power plug and is not isolated from the power outlet <by a transformer>. In that case power distribution wires labeled 'line (hot)', 'neutral' and 'ground' must be considered wrt the scope connections.Edit again to add <by a transformer>

author: valley001
author_rank: Frequent Contributor
timestamp: April 23, 2019, 09:58:09 pm
content: Hello Fred,I need to study this more deeply (the + side used as common) before I hook up the scope again. I am not fully grasping this concept. I am very careful around this instrument. The manual actually states that you must isolate the scope from ground when testing the pre regulator.Mine make a harsher buzzing sound all the time, even with in standby. I gather this is not normal.

author: Fred_47
author_rank: Contributor
timestamp: April 23, 2019, 10:32:48 pm
content: Quote from: valley001 on April 23, 2019, 09:58:09 pmAbsolutely correct about the preregulator. It is on the line side of T2 with direct connections to the power plug. I will edit my post.

author: Fred_47
author_rank: Contributor
timestamp: April 23, 2019, 11:14:57 pm
content: Quote from: valley001 on April 23, 2019, 09:58:09 pmThere is a circuit that drives a small current thru the series pass element even in standby. It is the source of the 700 odd volts that you measured early in this thread. The source is the big T1 transformer that supplies all of the control power (I found that there are 2 T1 transformers in this thing). The rectifiers and filter caps are on the HV MB. That could be the sound you hear.As to the concept of + side being common; string the 3 sheets of the 1001 dwg together and follow the plus and minus leads back from the front panel. All of the controlling devices are within +/- 35V around the plus lead (except for the series pass element bias ckts @ 150V). The minus lead simply goes thru a relay contact to the neg side of the main rectifier (and positive side of the minimum current rectifier).It's like any positive regulator except on a much larger scale.

author: Fred_47
author_rank: Contributor
timestamp: April 23, 2019, 11:56:19 pm
content: Quote from: valley001 on April 23, 2019, 09:58:09 pmThinking about your noise.Maybe examine the HV MB in a dark room with the lights out.I remember doing that with a noisy 230KV switchyard on the roof of a certain pumped storage hydro plant one night about 50 years ago. Quiet the light show with arcs jumping 2-3 sheds (about 6 inches) on 6 foot insulator stacks. The other startup engineers and I agreed that it was pretty spectacular, then we called the dispatcher and him shut down the switchyard before it had a chance to do an ultimate light show

author: valley001
author_rank: Frequent Contributor
timestamp: April 28, 2019, 03:38:57 am
content: Hello Everyone,I thought I would update this. I would like to thank member RandallMcRee, who very generously offered to send off a set of boards from his non working 332D. Installing his chopper board has resulted in my 332D becoming stable. It is still "warming up" but only dithers between a uV or so, no more radical spikes.I suppose I should look at waveforms on the chopper board and see what might be going on.

author: RandallMcRee
author_rank: Frequent Contributor
timestamp: April 29, 2019, 01:19:03 am
content: I extricated the hermetic resistors out of my 332D parts mule to send to another member. The first deck of the KVD divider is completely isolated using teflon grommets and teflon wires. I have never seen this before. Thought it would be of interest to this group.