FLUKE 3330B no output but relays clicks - some life in it - Now FIXED - Page 1
Forum section: electronics / repair

author: kawal
author_rank: Frequent Contributor
timestamp: February 26, 2019, 03:06:02 pm
content: Got a nice piece of gear in great overall physical condition. This is the FLUKE 3330B from 1974. I looked over all the boards and replaced a few dried out caps - so far found 2 that measured high ESR and complete lack of capacitance when removed. Both blue colored electrolytics but there could be more that i missed. Also had to replace burnt insulators and cables on two power resisters in the pre-regulator board.I checked fuses and made sure links are installed in the outputs. So far the unit starts up and i hear relays clicking but there is zero output. No matter what the output setting , crowbar option, current limit option I get zero reading from the output.I did measure most of the large power transistors and found a strange thing on the pre regulator board . The regulator transistor Q1 (round case on the heatsink) measures like an PNP but is supposed to be NPN. I double checked it but will check again. I did that in circuit so maybe that is the issue.Next plan of attack is to remove the power supply boards one by one and test outside the circuit. Also most bulbs need replacing. probably will install some Leds in place of the bulbs. The bulbs are on the -25V supply so might need to move them to the -5V. Two if the bulbs light up so most likely -25V is there. When changing setting there seems to be clicking of relays on the ladder boards but not 100% sure.I am open to suggestions on the right way to proceed with troubleshooting this kit.I also need advice on the lacquer used on the board. When done repairing what should i use for protecting the board ?Here are some pictures of the beauty:https://photos.app.goo.gl/1eqCgKT6KxZD8Hzh9Help appreciated

author: Dr. Frank
author_rank: Super Contributor
timestamp: February 26, 2019, 05:02:53 pm
content: The 3330 shares several compatible PCBs with the 332/335 calibrators, like the reference, pre-regulator board, crowbar, chopper, and so on.My 332B/AF was wrecked, because on this pre-regulator board all semi conductors had died, especially the fat zener and end transistor, all other had no beta any more.See here:https://www.eevblog.com/forum/testgear/fluke-332baf-in-the-slaughterhouse/msg393609/#msg393609I think, I had exactly the same pre-regulator PCB as yours.Check that you get the correct schematics, because there were many basic changes.Get the latest 332D manual with schematics also.You may check the other voltage supplies, apart from the HV pre regulated one, which you may pull outside upfront to avoid dangerous voltages.Check whether the reference module delivers its ref voltage of about 6.71838V.You may temporarily provide 15V from an external PSU to the +/- supply points of the pre-regulator, simply to check if the instrument is working besides that.I also replaced all the light bulbs by LEDs, simply by putting a resistor of a few kOhm (2.2k ??) in series to the 25V supply.Good luck, that 3330 is a fine instrument, and yours is just looking crisp.Frank

author: kawal
author_rank: Frequent Contributor
timestamp: February 26, 2019, 05:34:19 pm
content: FrankGood advice. I was planning to take out the low voltage supplies and bench test them for proper voltages. I will also test the reference on the bench.Looks like no one has messed with this unit so there is hope in fixing it.I will get the 332D schematic to compare it to the 3330B. I found 2 versions of the 3330B manual online but both are the same vintage. I do not see any differences apart from one part hand corrected in the part list.I will do the Leds tonight to see if the correct functions are turning on.Maciej

author: kawal
author_rank: Frequent Contributor
timestamp: February 26, 2019, 06:10:25 pm
content: FrankThe boards might be compatible but they are different. The 3330B has a sub par voltage reference when compared to t the 332D. The newer (1981) 332D has a oven stabilized reference and the 3330B (1974) uses the same reference but without the oven.The pre regulator is a little different but not a lot - the idea is the same. I am still going over the schematics. Again thanks for the tip.Maciej

author: kawal
author_rank: Frequent Contributor
timestamp: February 27, 2019, 12:50:56 am
content: Checked the voltages on Aux power and main power +25V, -25V -5V -15V all there . Should have load tested but forgot to do it.Reference had a blown output transistor (I might have caused that...ooops). The schematic for that board shows wrong type off output transistor as NPN when old part was PNP. I replaced it with one NPN an struggled for a while with a 13.5V output . Finally replaced that transistor with a general purpose PNP and the board started working. Reference shows 10.000014V on my Keithly 192 at room temperature (19C) and goes to 9.99983 when heating the zener with my finger for a few min (lets assume 30C-19C=>11c difference 31ppm/11C or ~3ppm/C) . I guess ok for reference without oven.At that point i tried my luck with inserting all boards but still no output.I did notice the pre regulator is getting really hot - specifically the 2 power 10 Ohm power resistors. The power transistor measures ok for conductivity but did not check Hfe.

author: Dr. Frank
author_rank: Super Contributor
timestamp: February 27, 2019, 07:40:36 am
content: Correct, Q2, the output transistor, is on the wrong side of Q1, to make an NPN Darlington pair, so it must be a PNP. That's also in the BOM of A4A1.Although this version of reference has no oven, the Reference Amplifier IC2 is usually trimmed to <1ppm/°C. See also 731A/B reference. This zero T.C. occurs at a certain environmental temperature, in this case, that should be the inner working temperature of the 3330B.The currents through R4 and R15 determine the T.C. of the zener diode and of the transistor diode inside IC2, which have different sign.The zener current through R4 is fixed to about 3mA, and R15 is determined at the factory to give about 38µA for a combined zero T.C. , as written on the label, a bit misleading: 'Icz ... 38'Calculation: 1.23 Volt across R15 (given by R4 over R3), R15 is 32.4k, and that gives 1.23V/32.4k = 38.0µASo you may desolder R15 on one side and check, whether its value has changed (I assume, it drifted upwards). If that's not the case, you may later trim R15 for zero T.C.My pre regulator board had sockets for the small transistors, and most of them had hfe < 10, or so.Q1 and CR14 both were blown.And pay attention.. if you open the case, there are some switches to disengage dangerous HV, which is present on the inner cage.Frank

author: kawal
author_rank: Frequent Contributor
timestamp: February 27, 2019, 04:15:36 pm
content: Went back to the Pre regulator and checked all the Socketed transistors . one of the SS7504 shows hfe =0 rest show 30...50 range , seems to conduct fine in diod test. Only if i knew what the specs are for SS7504.

author: wictor
author_rank: Regular Contributor
timestamp: February 27, 2019, 06:25:22 pm
content: I have a question: why is beta decreasing with those transistors?

author: Dr. Frank
author_rank: Super Contributor
timestamp: February 27, 2019, 06:44:31 pm
content: The SS7504 is obviously a PNP transistor, I have 4EA here, hfe between 40 ..100.The case size looks like a 500mA Si-pnp type, but I assume any general purpose pnp @ 100mA will do the job.Driving currents of all pnp seems to be < 30mA @ 10V, so maybe you better use a 500mW type, hfe >= 100.I also found that most of the smaller transistors on this board showed a decay of beta, all hfe being lower than 10.Reason for that may be the regular, high inductive pulses on this board, which probably killed the power zener and the driving transistor.Another might be heat and age, and the bad quality of the silicon crystals / wafer in the 1970ties.

author: wictor
author_rank: Regular Contributor
timestamp: February 27, 2019, 09:27:11 pm
content: Thanks for explanation!

author: kawal
author_rank: Frequent Contributor
timestamp: February 28, 2019, 04:01:14 pm
content: FrankFound some specs for SS7504 onwww.csgparts.comPNP modest gain 40...100 per Frank - modest CE voltage (85V) per specI used 2SA1220 as replacement. (Vce =120V...160V), gain 100....300, current 1.2A.Still no go after replacement and still a lot of heat from the 5ohm resistor. That worries me as this means the transistor Q2 is fully conducting from the 10V supply to ground. There should be no reason for that. I will have to setup some kind of external test for the board. Q2 must be conducting to ground but dont know whyGot the LEDs installed and wired for the decimal points and working on the other control lights. Decimal points are easy - just cut the trace forthe -25V common added a 0.625W 2kohm resistor (made from 5x 10k 0.125W) in the cut. I drilled the PCB near the cut trace to locate the resistor on the parts side. I snipped off 3 of the 4 commons. All decimals connected as common Cathode to the 2kOhm. The anodes are individually connected to the signal wires- switched ground. That circuit is at ~20ma supply to white diod with 2.6V drop and is plenty bright. The diod's are epoxied to the aluminum light pipes.I plan to get the rest of the control indicators wired this week. Maybe that will give me more information on the fault - maybe over current or over voltage fault ?I think most parts can be replaced with more modern parts but perhaps in different packages.I hoped for an easy fix (with some measuring and shotgun replacement of parts) but it looks like this one will take a while to troubleshoot due to the dangerous nature of the High Voltage.

author: wictor
author_rank: Regular Contributor
timestamp: February 28, 2019, 04:17:49 pm
content: I also have that 3330B. It had quite many problems also. Some of the white reed switches were bad, contact problems in board connectors, some wire was broken near big trafo and if I recall right the overcurrent protection was tripping.. I got it working, but still need to fix the front panel indicator lights.

author: Dr. Frank
author_rank: Super Contributor
timestamp: February 28, 2019, 07:28:31 pm
content: 1.5A transistors might be a bit too beefy.Have you checked all the diodes, especially CR15 between base of Q1 and GND?Maybe Q1 is also damaged, that's no darlington, and what about CR14?

author: kawal
author_rank: Frequent Contributor
timestamp: February 28, 2019, 07:35:24 pm
content: WictorSounds like you got it working without the lights and I will have the lights working first.I am jealous that you where able to fix. A good catch on the reed switches - I started measuring the resistance of the coils but maybe it is better to try to energize them with an external power supply to confirm they work. I will add that to my to do list.If you have any more notes or any more details it would be great to post here. Some people in the future will have it much easier when they try repairs on this 45 year old tech.Maciej

author: kawal
author_rank: Frequent Contributor
timestamp: February 28, 2019, 07:38:03 pm
content: FrankFirst thing is - thank you so much that you are replying to this thread. Its good to know there is someone out there that has experience with the 3330B. I am looking forward to your posts.Q1 measured OK on a diod test but gain is really high when doing HFE for some reason. - maybe that is the indication that its not OK ?Maciej

author: wictor
author_rank: Regular Contributor
timestamp: February 28, 2019, 07:40:45 pm
content: Quote from: kawal on February 28, 2019, 07:35:24 pmThread is here:https://www.eevblog.com/forum/repair/fluke-3330b-questions/msg1377140/?topicseen#msg1377140But it does not have a lot info what was wrong with the unit... I'll try to collect some info about what parts I had to fix/change.

author: wictor
author_rank: Regular Contributor
timestamp: February 28, 2019, 07:53:07 pm
content: Relay K2 was broken on relay driver board also with my unit:There was also one broken relay under preregulator board, replaced it with Meder relay:Ladder board relay K3 broken solder joints:I think that also orange wire(5th from top right) pin was broken:Some mods done by someone:

author: kawal
author_rank: Frequent Contributor
timestamp: February 28, 2019, 08:10:44 pm
content: WictorWhile looking at the K2 board I noticed a +35V line but when i was testing the power supply boards I did not see that voltage. It seems that the +/- 35V supply is on the Current limiter board so i did not think to look at it.I will be checking that next....

author: kawal
author_rank: Frequent Contributor
timestamp: February 28, 2019, 11:14:08 pm
content: Ok Finally making progress.The Circuit limiter board that contains the +35V and -35V power supply was checked today. I first checked the transistor in the sockets -Q3, Q5, Q6 all SS7504 measured HFE 53, 56, 34 respectively. So all goodQ7, Q4 are 203489 NPN 60V 0.8W measured Hfe of 105 and 140power transistor Q1 did diod check = OKPower transistor Q2 - 2N297A was a little puzzling - a 35W Germanium 5A Collector max. Was measuring .1V on junctionsTried to power the board -the 35V positive was fineThe 35V negative was less then 1V . Turns out 36V zener is dead measures 0.05V in either direction on multimeter and about 0.8V with 5...20ma current using bench power supply.I didn't have a zener to replace the broken one but installed a 3.3K resistor in its place. The supply is outputting 23V or so.I installed all the cards and the system now works. Will need to get the zener diod and finish the diods on the front.First least significant digit decade has a problem with the 4th digit. The relay for the 4 position is stuck or driver is broken - I measured the coils show the same resistance. of 2kOhm . I am happy for today.So I would call that progressI updated the pictureshttps://photos.app.goo.gl/1eqCgKT6KxZD8Hzh9BTW - how to load more than 1 picture at a time to the post ?Maciej

author: wictor
author_rank: Regular Contributor
timestamp: March 01, 2019, 04:01:19 pm
content: Hi,I had similar digit problems caused by bad connection between the A4A10 ladder driver board and main board. It's the board nearest to lowest digit.Wictor

author: Dr. Frank
author_rank: Super Contributor
timestamp: March 01, 2019, 06:57:16 pm
content: Wow, that's great.Reed contacts may easily be available, if stuck.

author: kawal
author_rank: Frequent Contributor
timestamp: March 01, 2019, 07:40:53 pm
content: FrankFor the reed contacts I removed each card that has reed switches and removed all the drive transistors.I then setup my power supply for 20V and cycled each reed switch a few times. I verified the Resistance in open and closed positions and moved to the next switch.After that I replaced all the transistors and reinserted all the cards. All reed switches worked via power supply but each one was making a different "ping" sound when turning on. Some louder some less loud.This took about 20 min and seems to have fixed the issue with the first decade. I dont know what actually helped : either cycling the reed switches or by re seating the drive transistors. Either way the switches now function in each decade which i verified.I do get a big drift (300uV) and some inaccurate readings (scaling) but I will not worry about it till I replace the zener diod. The -35V supply is definitely not stable and definitely not at -35V.I ordered a lot of capacitors to do a total recap with the exclusion of the 1200V caps (these are expensive and most likely OK ). After that i will recheck the source and calibrate if its needed. So far i did not adjust anything hoping its within specs .I am so happy to get this working so fast and without getting shocked.Maciej

author: Dr. Frank
author_rank: Super Contributor
timestamp: March 01, 2019, 08:18:20 pm
content: These reed contacts really have a very long lifetime.Anyhow, I've repaired a lot of analogue instruments (e.g. P.A.R. Lock-In -amplifiers) from the 80/70ties, which had a lot of bad reed contacts. Cycling alone would help only temporarily.Can't tell anymore, whether these made bad contact, or no contact at all, but anyhow, the clicking sound alone, which I also observed/listened to, was not the only criterion. In the end, it's a quick fix to simply replace these reed contacts (apart from the coil).Maybe you can make some electrical measurements, like on-resistance on these..should be in the mOhm range.I think, over time these loose their spring force, and show higher than usual resistance.

author: kawal
author_rank: Frequent Contributor
timestamp: March 02, 2019, 05:19:09 pm
content: FrankI went back in and measured the reed contacts on all the ladders. The resistance of the contacts with 4 wire Ohm measurement on the Keithley 192 andthe readings are between 35mOhms and 50mOhms on all of the contacts. Based on the results I think that they are still in very good condition.I made some measurements and the calibrator is fairly spot on - The reference was off by off by a lot when put back in as the replacement transistor i put in the reference has Emitter and Collector reversed. Switching the terminals of the transistor made the reference pop back in to 10.0000X volt.Now waiting on caps and zener diods which should arrived Tuesday.P.S. The more I use the Keithley 192 the more I like it and the less I use the HP 3478. I think its time to sell the HP meter.The Keithley needs a slight adjustment as it shows different results on the different ranges.Maciej

author: wictor
author_rank: Regular Contributor
timestamp: March 03, 2019, 07:00:47 am
content: Hi,I mentioned that I had to replace two reed relays, one smaller NO relay and one bigger three pole relay. Now the smaller one seems to be fine, when measured in test bench. The on resistance is 20 mOhms, coil resistance is about 4.2k and I think it was about 2k with others same size relays.The bigger one had problem with both NO and NC contacts. NC is showing resistance of 20-60 ohms when coil is not energized and is opening properly when coil is energized. The NO does not close when coil is energized and when coil is not energized, it shows resistance of few mega ohms. Coil resistance is 2.4k.Wictor

author: kawal
author_rank: Frequent Contributor
timestamp: March 05, 2019, 03:02:48 am
content: WictorThat is a good Watch. I did measure all contacts with no power and with Power.I am pretty happy with the 30..50mOhm of measured contact resistance. And open they all measured more than the meter can show.This time I am attaching the corrected schematic for the reference :

author: Dr. Frank
author_rank: Super Contributor
timestamp: March 05, 2019, 10:27:28 am
content: Quote from: kawal on March 05, 2019, 03:02:48 amHello,I think you have drawn Q2 incorrectly, emitter and collector have to change position.Frank

author: kawal
author_rank: Frequent Contributor
timestamp: March 05, 2019, 02:59:06 pm
content: I made that mistake already - this one is right but will recheck.I did place it like you say but only worked with no load. Without load i was getting 10.000X volts but with load I was getting 13.5V so i flipped the transistor and got 10.000X with load. I can verify again when I start recapping - it is possible that I got it wrong the first time but I don't think so.Maciej

author: Dr. Frank
author_rank: Super Contributor
timestamp: March 06, 2019, 08:04:26 am
content: Quote from: kawal on March 05, 2019, 02:59:06 pmSorry, but the circuit as you have drawn and assembled Q2, can't operate properly.Its base will always be more positive than the emitter, so the transistor will never conduct and amplify in its normal way.The CB diode anyhow will deliver excess current to Q1, so Q1 alone will deliver the necessary current, which would be otherwise limited to about 1.5mA by R23.If you have the emitter of Q2 at the other side, connected to CR2/C4, this transistor is intended to take over at currents > 1.5mA.Please also check the damaged transistor, its pinning and original placement in the circuit!.If that circuit does not operate properly in the way I described, probably IC1 is defective, maybe causing the damage of Q2, and also being the reason, why the circuit has a too high T.C.You also might first check the proper operation by checking the voltages at pin 6 vs. 9, both must read identically 8.77V. I bet, that's not the case.Then I would desolder IC1 and check its correct operation.You might simply replace that IC (and maybe Q1/Q2 also) by a universal bipolar operational amplifier, like in the 731A/B.Frank

author: kawal
author_rank: Frequent Contributor
timestamp: March 06, 2019, 01:09:10 pm
content: Ok you are right about the schematic - I miss identified the legs of the transistor (So i got it right in the board but wrong in the schematic) . I updated the old post to include the correct schematic. Here is a pic of the board after recap.Question is - how stable should the reference be ? Not sure if my meter is causing the readings to fluctuate or the actual reference but I get about 5 micro volts over 10V and the adjustment is very touchy. If i tap the adjustment it will change a few microvolts . Current reading is 10.000005 if itry going lower it undershoots to 9.999985. That is 0.5ppm over or 1.5ppm under.

author: Dr. Frank
author_rank: Super Contributor
timestamp: March 06, 2019, 07:49:00 pm
content: Quote from: kawal on March 06, 2019, 01:09:10 pmThank you for the confirmation, I was already doubting my own mind.The answer to your other question is quite easy, in several aspects.First, your KEI 192 is an old 6 1/2 digit DMM, but you're obviously measuring to 7 1/2 digits resolution. I assume, that you're using data coming over GPIB?Anyhow, I assume that the stability / noise of these old DMMs are not good for < 1ppm resolution.Although, it already has an LM299/399 reference, and a discretely built A/D, which might be quite ok... well, I really don't have any practical experience on that peculiar model (190 and 199 only).2nd, the whole 3330B instrument is also of the 6 digit class in terms of resolution and stability/noise, see its specs. Its specified stability is 5ppm/day and an accuracy of 30ppm, so you can't expect a better physical trimming of its reference than maybe 1ppm. The linearity calibration is also at about that resolution.The reference itself is quite noisy, compared to modern references like LTZ1000, or even LM399, but really not bad for 1970ties vintage. I have measured and evaluated that using a 3458A, i.e. 0.25ppm 1h short term stability:https://www.eevblog.com/forum/testgear/fluke-332baf-in-the-slaughterhouse/msg399283/#msg399283If you look at that graph, the peak-peak variations of the Reference Amplifier are on the order of +/- 1ppm.3rd: apart from 1) and 2) aspects, you obviously are referring to the trimming resolution of trimmer R10.That can be estimated quite easily.That R10 is a 50 Ohm Cermet trimmer, suppose it has 20 turns. I always calculate, that 1/50 of one turn can be resolved safely and stably.That means, that 50 Ohm / 20 / 50 = 0.05 Ohm is the physical resolution.This R10 fine tunes the lower of the gain resistors, i.e. R12 = 11.425k.So the resolution of the 10V trimming is in the ballpark of 0.05 Ohm / 11425 Ohm = 4.4 ppm. Maybe a little bit better, due to the gain factor of R12 and R13 ~ 1.5 (an error calculus of the total differential is required), and maybe the angular resolution of the CERMET trimmer is a bit better than 1/50.In the end, it's definitely > 1ppm, exactly what you observe in practice.Frank

author: kawal
author_rank: Frequent Contributor
timestamp: March 08, 2019, 06:12:22 pm
content: FrankYou are keeping me honest. The meter is 6.5d and I am suing the display directly to read the voltage. I am also using a secondary meter , HP 3478A to calibrate the readings to. I did the zero adjustment on the uV and with all the zeros I got confused about my readings. While int he 20V rage I get only 10's of uv resolution not single digit uV. So the the reading was not 10.000005 but 10.00005 or 50uV over or 9.99985V -150uV under. Otherwise 5ppm over and 15 ppm under. The biggest variation seems to be coming from the offset voltage on the system. It seams to vary each time i turn the unit on and off. Would that be a function of the chopper amplifier or the deferential amplifier ? I recapped almost all the boards now and the performance otherwise seems acceptable. I am even ok with the ~10ppm or so reference variation - I can work on that later but would like a stable offset voltage. I am open to suggestions on hunting down the potential reason for the variance in the offset or improvements that could be done.BTW after the recap I did the voltage adjustment on all power rails that are adjustable. +25, -25 -5V if i recall correctly. So i do not think its power rail related but it could be.Maciej

author: kawal
author_rank: Frequent Contributor
timestamp: March 18, 2019, 02:04:29 am
content: Now the source is fully functional and all lights working (White LEDs versus bulbs). I followed the calibration steps in the manual but not sure if i have good enough gear to do it precise enough.I have been using the voltage source to transfer calibration from 1 Keithley 192 to another. The Source seems very stable (3 days on now ) with zero movement based on Hp 3478A. I am also measureing with 2 Keithley's 192 and the 1.9V help get most of the resolution from the Keithley's.The HP reports 1.90001 V and when i have zero set on the calibrator there is a 10uv offset and also a lot of noise.The old Keithley has been reporting 1.900007 to 1.900010 The 2nd one i got had a bad heater in the reference so I replaced it with a new LM399 a few days ago. That one has been changing with time which is expected for a new reference.Anyway I do not like the offset or the noise - any suggestions to reduce both. The 10V range has the lowest offset 10uv is within spec (20uV max) but the other ranges are much higher (Spec is 200uV and 2mV max )My question is : Is this due to the chopper amp or to the differential amp or both ?I was planning on messing with the reference but that seams stable - most likely will not be changing it.Open to suggestions on possible improvements.

author: dacman
author_rank: Frequent Contributor
timestamp: March 18, 2019, 03:02:25 am
content: The chopper can cause noise. There is an adjustment procedure for the chopper, but it also has lots of aluminum electrolytic capacitors. I'd suggest checking them with an LCR meter. The dry tantalum capacitors (which look similar to an aluminum electrolytic) generally do not go bad in the chopper. There will be noise, but it should be within specifications.There are range zero adjustments in the front left. Do they not work? I've replaced lots of trimmers on earlier models (332A/B/D), including for the zero adjustments.

author: kawal
author_rank: Frequent Contributor
timestamp: March 18, 2019, 03:21:47 pm
content: Thanks for the advice about trimmers . The trimmers on all 3 ranges seem to work but a little hard to get dialed in precisely. The 10v range will stay pretty constant at 10uV but I can't adjust any lower as it will move through 0 and then get much worse on the other side. 100V range is impossible to keep at a stable 2000uV . It will drift over time to higher levels. 1000V range is even worse. Maybe trimmer related? Should I replace with multiturn?

author: Ordinaryman1971
author_rank: Frequent Contributor
timestamp: March 18, 2019, 09:25:21 pm
content: how did you fix the overcurrent tripping, that's the problem I have with mine, it's tripping at 945V, can't get it to 1kV

author: dacman
author_rank: Frequent Contributor
timestamp: March 19, 2019, 02:35:05 am
content: I didn't realize the zero adjustments were not multiturn trimmers, which the 332 series have. The way I would try to fix the zero trimmers in the 3330B is to work lubricant into them (initially). If that didn't work, then I would use contact cleaner (or IPA) and then follow that with a lubricant, such as LPS-1.For the overvoltage or overcurrent trip, have you tried the internal adjustments? (There are internal adjustments for both.)

author: Ordinaryman1971
author_rank: Frequent Contributor
timestamp: March 19, 2019, 01:42:01 pm
content: No, didn't try to adjust anything. It's very accurate. All the way to 945V it's right on the spot so I've decided to not to mess with it... but it's tempting

author: dacman
author_rank: Frequent Contributor
timestamp: March 19, 2019, 10:27:14 pm
content: The internal voltage and current limit adjustments do not affect the accuracy of the dial settings. They do affect the point at which it trips.

author: kawal
author_rank: Frequent Contributor
timestamp: March 20, 2019, 12:28:06 am
content: Quote from: Ordinaryman1971 on March 18, 2019, 09:25:21 pmI was able to adjust to over 1KV without even cleaning the pots

author: wictor
author_rank: Regular Contributor
timestamp: March 20, 2019, 04:44:43 am
content: I had problems with voltage tripping too early. But I don't remember right now, what was causing the issue. I need to check the schematics and device to refresh my memory.At least Q2 was broken on series pass driver board.Wictor