Nixie Tube Fluke 8100B DMM with Video - Page 1
Forum section: electronics / repair

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: October 01, 2015, 07:37:09 pm
content: Hi,I have acquired a Fluke 8100B DMM. This is a Burroughs based Nixie Tube meter. Sadly, this unit will not power up.FIXED: thanks to Tautech and Paul Moir for their incredible assistance.Here is a follow up video of it working... Lots of Nixie Tube Porn:https://youtu.be/bOKkrFakrysManual and schematic here:http://meanmutha.com/fluke_8100b_digital_multimeter.pdfI will post some pictures later. (Pics here now... see below)I followed the procedure for checking voltages on page 37 of the PDF. On mains power I get ~35V out of the transformer (on either terminal of F2). I have no battery pack, but the unit DOES have the battery option installed. This 35V does seem a little high since it is 24V nominal.On the -18V rail (case of Q1) I get around -1.7V. I followed the manual and disconnected the 15V side of R5 and hooked it up to a bench power supply. I still get the crazy low reading on the -18V rail.The power supply schematic is page 89 of the PDF. (and posted below)I disconnected from the mains and hooked up a bench supply to the battery terminals (as mentioned above this unit has the battery option, but I have no battery pack). I tried voltages from 24V (nominal) to 34V (what the transformer was putting out after rectification). I still get around -0.7 to -1.7V in this configuration.I swapped out Q2 and Q3, which had no effect.I measured R1, R2, R3, R4, R5, and R195. All are in spec.I replaced C58 with a MLCC at 0.1uF (original measure OK too).I replaced C3 and C5 (electrolytics, whose ESR was a tad higher than normal, but not terrible).I have a replacement for Q1 on order. I took it out, and it tests OK on the hFE and "GM328 Transistor Tester," but could still be bad I suppose.Note that testing with either the mains or the power supply attached to the battery terminals results in the meter (m1 on the schem) showing a "charge" up at the high level.Is there anyone out there with a working 8100 who might be able to take some readings for comparison?Thoughts?Thanks.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: October 01, 2015, 07:42:05 pm
content: See the attached image of the power supply.Would it be safe to remove F2 and connect up a (current limited) -18V supply such that the negative terminal goes to the highlighted wire and the positive terminal goes to ground? I would disconnect R5 as shown by the blue "Cut." I already have this disconnected anyway in order to isolate the -18v supply (per the manual).I would NOT have the power supply connected to the battery terminals, and obviously it would NOT be plugged in.Thoughts? I am trying to see if I can get this thing to work at all.Thanks.EDIT: That ground marking would actually go to TP1, which the manual describes as circuit ground. So the + side of the power supply would go to TP1, and the negative side would go to the wire highlighted in yellow.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: October 01, 2015, 07:48:13 pm
content: For those who do not want to dig through the PDF... Here is the power supply schematic.

author: tautech
author_rank: Super Contributor
timestamp: October 01, 2015, 08:01:47 pm
content: Just a thought.....IF the switching oscilator Q4 & Q5 was not working would the load of the primary of T102 drag the -18V to levels you are measuring? Check if Q4 & 5 are warm.You've drawn a Gnd symbol.... it doesn't match others on the schematic.Where are you referencing the -18V to?

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: October 01, 2015, 08:19:50 pm
content: Interesting. I will check Q4 and Q5.I was referencing ground to TP1 in the manual (marked as circuit ground). I guess I drew and earth ground symbol.I seems Q1 has an hFE of 33. I spoke with another owner and EEVBlog user Paul Moir in my other thread, and he said his Q1 had an hFE of 61.8 So possibly Q1 is bad after all.I have one on order, but what do you think of hooking up a power supply as shown (with the "ground," which in this case is the + side of the 18V power supply, going to TP1, and the negative side of the 18V power supply going to the highlighted connection).Thanks.

author: tautech
author_rank: Super Contributor
timestamp: October 01, 2015, 08:41:21 pm
content: Quote from: FlyingHacker on October 01, 2015, 08:19:50 pmTake note the -18V is referenced to +15V but the -18V rail has to power on first. Any excessive load on the -18V or faulty Q1 will prevent it firing up.Any external power supply should be current limited to prevent additional damage. Even a 24V bulb in series will limit current draw. If it glows real bright, you still have a problem.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: October 01, 2015, 09:01:03 pm
content: Quote from: tautech on October 01, 2015, 08:41:21 pmAll my supplies are current limited. Learned a long time ago the value of those!Does my wiring for the -18 supply look correct, though? Positive side to TP1 and negative side to the yellow highlighted wire (there is actually a jumper wire on the board). I would remove the fuse as well. Q1 is already out of the board (though R1 is still there, but I don't think this will matter as indicated). R5 is already disconnected as shown by the blue CUT line.Am I correct in thinking that feeding in -18V should make everything work, assuming there are no other problems?I would set the current limit around 1/4 amp or less and see if Q4 and Q5 get hot or what.Thanks.

author: tautech
author_rank: Super Contributor
timestamp: October 01, 2015, 09:55:23 pm
content: Quote from: FlyingHacker on October 01, 2015, 09:01:03 pmCheck Q4 & 5 for heating when mains powered.Check components associated with T102, FB windings, caps and flyback components for +200V.The snubber, C2 and R155 if failed might have damaged other components too, check all this simple stuff.Then it might be safe to proceed with an external supply, you don't want more damage.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: October 01, 2015, 10:04:58 pm
content: Quote from: tautech on October 01, 2015, 09:55:23 pmForgive my ignorance... What is a "FB winding?" You mean check the resistance of the coils in the transformer? Use small words. I am a hobbyist ;-)I will check the other components. I think I will hold off on checking the Q4 and Q5 until I get the new Q1, or try an external supply. I don't want to put Q1 back in again just to remove it. I already messed up some pads on Q2 and Q3. The initially came out easily, but then removing my replacements did not go well. Thanks.

author: tautech
author_rank: Super Contributor
timestamp: October 01, 2015, 10:22:08 pm
content: Quote from: FlyingHacker on October 01, 2015, 10:04:58 pmFeedback.T102 pins 6 & 7 is the feedback winding.C68 and C4 couple the feedback to Q4 & 5, and set the oscillator frequency.T102 is a switching transformer.Component removal requires practice and certain methodology to minimise the risk of damage to PCB's.Good sucker and a range of solders can help dilute the existing solder for easy removal of components, don't use too much heat and too cold will make things difficult too. Bigger tips can also be of assistance.Use old PCB's and practice, practice and practice.If you've got any of that lead free muck solder, biff it as far as you can.Quality low temp solders are invaluable for rework.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: October 01, 2015, 11:16:02 pm
content: Ok. Thanks. Pins 6 and 7 have 8.7 Ohms in circuit. Seems reasonable for the winding, no?C2 and R55 seem ok. The resistor measure correctly, but I did not desolder C2, though. I don't have a replacement and it has rather short legs.R6 and R7, and the diodes CR3,5,6, and CR45 look OK on the tester.Dare I apply the -18V via external supply?I only use lead solder. Specifically 60/40. I am open to suggestions on what works best for rework.What temperature would you recommend for both the desoldering station, and the iron for this type of repair? The desoldering iron sucked most of it out, but then I ended up chewing up the pads trying to get the legs of Q2 and Q3 free with the iron. You know that last bit of solder that keeps this pins stuf when they were bent upon installation? I have the desoldering set for 625F and the iron was at 750F. I think the iron was too hot and that damaged the board.Thanks for all the help.

author: tautech
author_rank: Super Contributor
timestamp: October 01, 2015, 11:34:29 pm
content: Your call on external power......Before you do, re-read this thread, study the manual, have a think, make a coffee, sleep on it. What's the hurry?For soldering temp, I only use adjustment settings as a guide, the rest is by feel.Fresh solder and then re-suck can do wonders, I often use this method if solder is hard/tricky to remove.Bent component pins can be a curse, if I have to bend any to retain components it is done very slightly, just enough to retain components.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: October 01, 2015, 11:41:19 pm
content: Some pictures...

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: October 01, 2015, 11:41:42 pm
content: Note in the second picture I am aiming a flashlight (torch) to light up the Nixies. They are not actually on... yet.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: October 01, 2015, 11:43:58 pm
content: The insides... Wires are where I am contemplating applying -18V. Q1 is removed, as is F2.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: October 01, 2015, 11:50:06 pm
content: Quote from: tautech on October 01, 2015, 11:34:29 pmI will check things over again. I do think it would be safer to apply power with a current limited supply then to turn the thing on again. I just want to make sure I am applying the power correctly. My diagram, assuming TP1 for the "ground" (positive side of the power supply) looks right, no?Do you think it is odd that I was getting 37V from the rectified mains? That seems awfully high. But I know line voltage used to be consistently closer to 115V here and my lab is 120V.Quote from: tautech on October 01, 2015, 11:34:29 pmYeah, perhaps... Suck, Resolder with new solder, and suck again? I have done this and it does help. But those bent pins can be a real pain. Makes you think twice about bending them when you put stuff together. It is just the lazy way to get the stuff to stay in place while you solder it

author: tautech
author_rank: Super Contributor
timestamp: October 02, 2015, 12:05:18 am
content: Quote from: FlyingHacker on October 01, 2015, 11:50:06 pmTP1 correct.Unloaded I wouldn't worry, it's likely to be very different when operating correctlyQuoteExactly, even repeat at times for difficult cases.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: October 02, 2015, 03:36:10 am
content: I applied the -18V as described... Q1 still removed.The current limiter kicked in, and I let it go up to a little over 200mA (do you think that is high enough? F2 is spec'd as 1/4 amp).Q5 was starting to warm up. Not hot, but warm to the touch. Note that I did not leave it on very long. Q4 did not seem to be warming.Whatever the cause of the load is it has pulled the voltage down to the -1.7V again. So I bet it is not Q1, but, as Tautech suggested, the load applied.Q4 and Q5 are listed as 2N4946 transistors. I found some on eBay, though in a slightly different package.I guess I will pull Q4 and Q5 and compare their hFE measurements.Any other thoughts? I am thinking going more current is probably not a good plan.Thanks.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: October 02, 2015, 04:45:22 am
content: The pictures say it all (as Dave might say, "Oh wait! Here we go... Bingo!")Q4 reads fine.... Q5 reads as a pair of diodes.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: October 02, 2015, 04:54:27 am
content: Just pulled Q5 now. Getting ~140 hFE.Ic on the hFE tester is about 0.75ma.So I guess the square window on the front is for the battery charge meter? I always wondered why that was there!

author: tautech
author_rank: Super Contributor
timestamp: October 02, 2015, 04:58:50 am
content: Quote from: Paul Moir on October 02, 2015, 04:54:27 amYou got one to fix too Paul?

author: Paul Moir
author_rank: Frequent Contributor
timestamp: October 02, 2015, 05:06:25 am
content: No I've got a junker and coincidentally the same multimeter with hFE meter as FlyingHacker. The power of the internet eh?Further coincident is that I just bought a 8120A to replace my old 8100B, which died about 25 years ago in the ADC end. I'm waiting for it to arrive.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: October 02, 2015, 05:09:37 am
content: Quote from: Paul Moir on October 02, 2015, 04:54:27 amOdd... My "good" Q4 reads an HFE on the Micronta of 11.98The bad transistor will not even read, which I guess is a good sign that it is bad.Yep, there is a little meter in that window. I kinda wish I had a battery pack for it. If I ever get it working I am tempted to make one, but at 21.6V that is 18 cells! Those NiCd batteries are kind of pricey at Mouser... $2.50USD each... So $45USD for a battery pack I would never use.. But it would be cool to carry around this "portable" like the guy in the picture in the manual. (Attached)

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: October 02, 2015, 05:15:54 am
content: Quote from: Paul Moir on October 02, 2015, 05:06:25 amJust shows you have good tasteAt least the 8120A measures current. I mainly use my 8600A for current measurements. It may not be Nixies, but red LEDs, and no batteries to change makes it nice. I use my 8810A for voltage and ohm, or one of my Digital Precision 245s, or the Simpson if I want to watch it. Something nice about numbers that glow!That Micronta was pretty slick when I bought it 25 years ago! It was the most expensive one at Radio Shack. Of course, even then Radio Shack was already going downhill mainly selling rechargeable NiCds for exorbitant prices.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: October 02, 2015, 05:21:46 am
content: So, given my bad transistor. Do you more experienced folks think that that the bad transistor is the disease, or a symptom of some other problem?

author: tautech
author_rank: Super Contributor
timestamp: October 02, 2015, 05:37:07 am
content: Quote from: FlyingHacker on October 02, 2015, 05:21:46 am2 bad transistors.hFE 100-300.http://download.njsemi.com/2N4946.pdfLet's hope a faulty T102 is not the cause.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: October 02, 2015, 05:45:25 am
content: (Currently hunting for a missing T102...)EDIT: Holey... Moley: found missing T102.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: October 02, 2015, 06:01:07 am
content: Quote from: tautech on October 02, 2015, 05:37:07 amGood point... I have ordered four.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: October 02, 2015, 06:01:54 am
content: Quote from: Paul Moir on October 02, 2015, 05:45:25 amYou found a T102? Where?

author: tautech
author_rank: Super Contributor
timestamp: October 02, 2015, 06:02:33 am
content: Quote from: FlyingHacker on October 02, 2015, 05:09:37 amA real man would wear it on his wrist.

author: tautech
author_rank: Super Contributor
timestamp: October 02, 2015, 06:04:31 am
content: Quote from: FlyingHacker on October 02, 2015, 06:01:54 amPaul's kindly measuring winding resistances for you.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: October 02, 2015, 06:16:26 am
content: Quote from: tautech on October 02, 2015, 06:04:31 amI love you guys!

author: Paul Moir
author_rank: Frequent Contributor
timestamp: October 02, 2015, 06:18:54 am
content: Making me work for it eh? Well I suppose it's penance for killing that poor thing all those years ago. I'm recalling putting in one of the chips backwards....OK from pin one, the one that goes to the electrolytic on the display side and powers up the nixies:1-2 - 276.4 ohms2-3 - 4.4 ohms3-4 - 5.3 ohms4-5 - infinity (No Connection)Looks like an IC pattern pinout. Pin 6 is across from pin 5:6-7 - 8.6 ohms8-9 - 4.1 ohms9-10 - 4.2 ohmsEDIT: Found T102 at the bottom of a box of mains transformers. Had to dig out a few microwave ones, a VIC-20 PSU, and a bunch of other similair junk. Box is a little mouldy but the transformer is OK.

author: tautech
author_rank: Super Contributor
timestamp: October 02, 2015, 06:25:16 am
content: And so we are all on the same page and for those finding this thread:

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: October 02, 2015, 06:41:13 am
content: Hmmm. Thanks for the measurements!I am thinking I would have to desolder that t102 to get meaningful readings... Really would like to avoid that to avoid damaging it.I am getting pretty similar readings in circuit:MY VALUES ARE AFTER PAUL'S VALUES1-2 - 276.4 ohms - 260.7 ohms2-3 - 4.4 ohms - 4.6 ohms3-4 - 5.3 ohms - 5.5 ohms4-5 - infinity (No Connection) - ditto6-7 - 8.6 ohms - 8.8 ohms8-9 - 4.1 ohms - 4.4 ohms9-10 - 4.2 ohms - 4.7 ohmsI think T102 looks good... Which is impressive since the last bloke that had this meter put a 1/2 amp fuse in F2 rather than the recommended 1/4 amp.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: October 02, 2015, 06:53:47 am
content: Yeah, I wouldn't take it out if I were you. That looks good enough.I *think* a 2n4401 would be a fine replacement for those 2n4946, but if want to stay original fire me a PM with an address and I'll send some pulls and whatever else you might want a spare of.

author: tautech
author_rank: Super Contributor
timestamp: October 02, 2015, 07:02:59 am
content: While waing for parts, it'd be a good idea to check E caps and devices that if failed across any of the rails might have overloaded Q4 & 5 and caused them to fail too.That should keep you busy till new bits arrive.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: October 02, 2015, 07:07:20 am
content: Quote from: Paul Moir on October 02, 2015, 06:53:47 amI appreciate all your help. I may take you up on that offer. Let me figure out what I need first. I think I can get the 2N4946 from eBay. But there would be a number of things it might be nice to have spares of.BTW, does your board have TWO small brown chicklet capacitors right next to Q4 and Q5 ? ( see my pic of the board, middle bottom). I only see one 22pf cap on the schematic, on the collector of Q4. I can't make out the values of either of them due to the angle. I don't know what serial number I have, as the little plaque on the front has come off (or was removed).Somebody marked this as less that .5% error in 2002, which is a good sign.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: October 02, 2015, 07:12:54 am
content: Quote from: tautech on October 02, 2015, 07:02:59 amYeah, good idea. I think I have checked most of the electrolytics, but I will check the, again. Small ones can be checked accurately in circuit with my little "Transistor Tester" which doubles as a cheap ESR meter, and usually finds any bad larger caps.

author: tautech
author_rank: Super Contributor
timestamp: October 02, 2015, 07:14:07 am
content: Quote from: FlyingHacker on October 02, 2015, 07:07:20 amSee "Changes" on the schematic.C68 (22pF) added SN 5050 and on.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: October 02, 2015, 07:26:17 am
content: Quote from: tautech on October 02, 2015, 07:14:07 amI saw that note, but nothing saying what those two caps are. I can barely read "100" on both of them, and "1%". I don't think either one is 22pF. So maybe this is prior to serial 5050. Really annoying that the serial is missing... Hopefully nothing nefarious... Likely it just popped off, ass it was a glued on sticker on the front. Sadly that is where the Fluke logo was.Thanks again for all your help (both of you).

author: Paul Moir
author_rank: Frequent Contributor
timestamp: October 02, 2015, 07:38:43 am
content: No, mine doesn't have those. I think mine is earlier: it never had a shield behind the nixie tubes and the top traces are gold plated. I don't have the serial number anymore (unless it also chooses to reveal itself again this fateful night.)Probably easiest just to circle what you want in a photo.(Lousy cell phone picture follows).https://picasaweb.google.com/lh/photo/AoBW6_-TLQ8tE3at4pQVuNMTjNZETYmyPJy0liipFm0?feat=directlink

author: tautech
author_rank: Super Contributor
timestamp: October 02, 2015, 09:09:27 am
content: Quote from: FlyingHacker on October 02, 2015, 07:26:17 amCorrect, they're as listed on the schematic.C2 3.3nF or 3300pF or 332C4 0.47uF or 470nF or 474Guessing both are MLC and 100V, fairly normal values for this old stuff.Even green caps should work.For a sanity check.....measure them.C68 (note 2) is only the revision after SN 5050 when this 22pF cap was added.No other changes are listed for the primary side of T102.As your unit has the C68 change and it seems you've found no other discrepencies, trust the schematic.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: October 02, 2015, 03:21:53 pm
content: Quote from: tautech on October 02, 2015, 09:09:27 amActually I don't think those two brown chicklets are C2 and C4. I believe C2 is the little round ceramic in the photo (came out reddish) between Q4 and the diode pair. Then C4 is the medium sized bright yellow-topped chicklet right above this (its left side next to the diode pair).So I am not sure what the dark brown chicklets are. I would have to pull them to measure them. I will see what I can figure out. I don't think they are in the schematic I have.The date codes on the two logic ICs seem to be 1972 (I think earlier in the year). Though they could have had stock on hand for a while.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: October 09, 2015, 05:07:22 am
content: Have some updates on the Fluke 8100B:Got a replacement Q1 (RCA 40250). The Beta was much higher and correct. - INSTALLEDGot some replacement 2N4946s for Q4 and Q5. Beta much higher and correct. - INSTALLEDAfter these were installed I still had some issues. When I applied +15V to the +15V side of R5 (per the manual) I ended up blowing the replacement F2 1/4 amp fuse when using the mains input. I didn't want to waste a bunch of fuses, and would always rather work with lower voltages, so I connected my power supply up to the battery input jacks and disconnected the mains. I set the PS for 250mA and jumped the fuse instead.At this stage I measured around -10V on the collector of Q1. Better, but not the -18V we should have. I noticed the power supply was current limiting. I also noticed that Q5 was getting warm again. I was doing short bursts so as not to kill another transistor. I noticed that I got only -2V on Q1 if I reconnected R5. So I began to think the issue was somewhere in the 15V supply.I decided to pull out the electrolytics C5 and C7, as I had not been able to get a good test result on them in circuit.C7 seemed OK. I replaced it anyway.C5 tested on my "Transistor Tester" as a .63ohm resistor! I replaced C5... and...

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: October 09, 2015, 05:16:53 am
content: BINGO! (as Dave would say).

author: Vgkid
author_rank: Super Contributor
timestamp: October 09, 2015, 05:20:02 am
content: Good job. The page jump killed me.I see you have a dtack of Lambda psu's in the background.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: October 09, 2015, 05:23:39 am
content: So I should have replaced those electrolytics right away. It looks like the failed C5 was causing too much current to flow through Q5 and Q4, damaging them. This was not helped by the fact that the last guy had installed a 1/2 amp fuse.I am still having an issue with the +15V supply, though. That photo was taken with me supplying +15V to R5 with an external power supply. When I reconnect R5 (with a jumper for now) I instead get ~+24V on the +15V side of R5. In other words, the +15V supply is pretty darned high.I am going to ask for some help from those more knowledgeable than myself as to where to look first for that. I will definitely replace any other electrolytics. I am not sure if I got C8 yet or not. Unfortunately, only the transistors are silkscreened on the board. You have to trace it out to find the other parts (though caps are not hard to find).I am pretty sure the -18V rail was close to -18V (will check). - CHECKED -18.4VI am excited by this progress, and hope to have this guy up and running and "calibrated" soon.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: October 09, 2015, 05:27:33 am
content: Quote from: Vgkid on October 09, 2015, 05:20:02 amYeah that page jump was really lucky in a suspenseful type of wayYes, I like the old Lambda supplies. Rock solid. I have two of the triple LPT-7202-FMs and one 130V DC LHC-130-FM supply as well. Both of the 7202s required replacement of a one key capacitor per sub-unit. I got them for great bargains (~$35 USD) as not working. Now they are fully functional. On the top unit I have two of the 20V supplies in tracking mode for OpAmps. That Wun Hung Lo PSU under the high voltage Lambda on the right isn't even plugged in. I just don't use it. The Lambdas are pretty much bomb-proof in their construction.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: October 09, 2015, 05:45:04 am
content: So, still trying to figure out why the +15V output is around +24V.The -18V "rail" is -18.4V when I am supplying R5 with a clean +15V. Should I be trying to get that closer to -18V? How? Maybe some tolerances have slipped. The specs call for up to -18.5VShould T102 be humming/buzzing? I am guessing that is OK. Sounds like an old fluorescent light (one working properly, not a failing one).Thanks!

author: Paul Moir
author_rank: Frequent Contributor
timestamp: October 09, 2015, 06:22:58 am
content: Congrats!My old one buzzed like that. I'm sure it's normal.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: October 09, 2015, 06:32:27 am
content: Quote from: Paul Moir on October 09, 2015, 06:22:58 amThanks for the reassurance on the humming.Any thoughts on how to get the +15V working within spec?Thanks!

author: Paul Moir
author_rank: Frequent Contributor
timestamp: October 09, 2015, 06:35:54 am
content: No. I guess it's time to power up Frankenstein?EDIT: Damn, I took my soldering iron to work. Will have to wait until tomorrow.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: October 09, 2015, 06:50:15 am
content: Quote from: Paul Moir on October 09, 2015, 06:35:54 amFrankenstein? Your 8100?

author: Paul Moir
author_rank: Frequent Contributor
timestamp: October 09, 2015, 06:52:31 am
content: What's left of it. It has been dead for some time now.But the PSU is intact, so I'll try powering it up so I can get some references for you. First though I'll have to reattach T102 and the transistors I've pulled.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: October 09, 2015, 06:56:52 am
content: Quote from: Paul Moir on October 09, 2015, 06:52:31 amAh. Thank you so much for all your help!Your power supply was putting out voltages within spec?

author: tautech
author_rank: Super Contributor
timestamp: October 09, 2015, 09:19:59 am
content: Quote from: FlyingHacker on October 09, 2015, 05:45:04 amYou still have some work to do.Reading the manual at section 3-53 and 4-39 and table 4-5 voltage at C5 pos should be +16.5- 17.5V.C7 pos after the +15V regulator shold be +15.There is a bit going on with this PSU and some study is needed.Problem is +15 regulator gets its reference from the zener portion of Q11, a bipolar/zener reference that does not have a device # in the BOM. I hope it's not unobtainium.Have you checked Q6?QuoteManual specs it's operating frequency at only ~250Hz.Yep, it's likely to hum.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: October 09, 2015, 03:25:34 pm
content: Quote from: tautech on October 09, 2015, 09:19:59 amChecking Q6 was next, after checking all the resistor values in that part of the circuit.That Q11 is a little metal can which may even include the Zener in it, though I have to check on that. It is supposedly factory matched to R15 and R22, presumably to set the voltage based on the particular Zener breakdown voltage. I am guessing Zeners of the day had far worse tolerances.If Paul can get some reading off his power supply then perhaps I could tune that by hand if I had to.As a LAST resort I could always add a 7815

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: October 09, 2015, 09:36:14 pm
content: So Q6 is bad... Measures as a 63 ohm resistor on the Transistor Tester, and the Micronta will not even read an hFE.Q6 is a 2N3906.I don't have any of those on hand, though I do have some on order (slow ship though). I do have a 2N2907 though. Do you think this would be a suitable replacement? Or should I really wait for the right part, which is coming from China?Boy, Tautech, you are 2 for 2 at guessing failed parts. I get the feeling you have done this a few times

author: tautech
author_rank: Super Contributor
timestamp: October 09, 2015, 10:35:56 pm
content: Quote from: FlyingHacker on October 09, 2015, 09:36:14 pmNo guess, Q6 is a linear regulator pass transistor and it was not doing it's job. It could be either conducting or open, in this case failed short. Remember the likes of pass transistors are doing some work, much like output stage transistors and they ocasionally fail, but why? Overcurrent?QuoteA 2N2907 should do to get her running although there's enough differences in datasheet specs to not leave it there. Watch the pinouts, they are very different.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: October 09, 2015, 11:39:34 pm
content: Quote from: tautech on October 09, 2015, 10:35:56 pmOk. I understand the basics of that. Not sure why the resulting voltage was more like +24V. I guess it was just taking the input voltage.I assume it was over current that caused the failure. I think C7 may have been bad. I should have taken notes. I had replaced it.QuoteI installed the 2N907 (which had a measured beta of ~234 even though AllTransistors said it was 35 minimum). And now everything is working!So Paul, keep that soldering iron cold for the moment.I am still powering it off my bench supply hooked to the battery terminals. Doing this just to watch current flow, and not waste fuses. It is drawing about 110 mA, if I recall.Voltage measurements to follow, but everything is within spec! None of the transistors are warm, either.Thank you guys for all your help. Paul, I may consider some of your parts as spares if you are game.Pics to follow too. I think I shall wait for the proper transistor to really calibrate this guy, but it is pretty close as is.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: October 10, 2015, 03:29:39 am
content: Here's where we are with the voltage test points:-18V = -18.29+15V = 14.81+17V = 16.82+7V. = 7.00+5V = 4.94+200V = 191.8The voltage remain rock solid if I vary the "battery" voltage up and down 8V or so.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: October 10, 2015, 04:23:18 am
content: Here is a video follow up with some Nixie tube porn, and an extremely cursory look at the problem and solution.https://youtu.be/bOKkrFakrysTo quote Dave, "If you like it please give it a big thumbs up."

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: October 10, 2015, 04:34:10 pm
content: Following that video I keep her running for a couple of hours. I did a little rough calibration of the kilo ohms, which was a tiny bit off.I periodically rechecked all the voltages, and kept an eye on the current. Everything was very steady!I think I shall wait for the actual 2N3906 to put back in for Q6, which I substituted with a 2N2907. After I get that in and stable then I will try it out on mains. I am not for seeing any issue running it off the mains, just don't want to risk more fuses until I know everything is stable.The DCV is surprising accurate. It was matching my Fluke 8810A, except when negative, in which case it was off in the last two digits. I believe there is a setting for that, but have not tried yet.Thanks again for all your help!

author: Paul Moir
author_rank: Frequent Contributor
timestamp: October 10, 2015, 07:33:04 pm
content: Hey, I had Q6 way back in the first post in the "Transistor Testing" thread! Must have been ESP because it certainly wasn't skill.Of course you're welcome to spare parts. Just let me know what you want.(I have to build up some good karma before the 8120A arrives.)

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: October 13, 2015, 06:14:45 pm
content: Quote from: Paul Moir on October 10, 2015, 07:33:04 pmI will PM you about the parts.Is the 8120A supposedly in working condition? Or do you need to troubleshoot it?

author: Paul Moir
author_rank: Frequent Contributor
timestamp: October 13, 2015, 07:08:08 pm
content: Sold "As is" due to inability to test. Shown powered up with some potentially correct and apparently changing digits on the AC range with the inputs floating. Seller sells a lot of old lab gear and it seems to be all "as is".Maybe good, maybe bad.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: October 13, 2015, 08:33:55 pm
content: Oh, it arrived!Mostly working OK from my brief checks. A little wonky at startup and displaying signs that it's range switches need to be cleaned. The only real fault I've found so far is that the DC autopolarity function does not seem to work - I can only read negative voltages. The +- circuit seems OK though. Will start a thread on it.Looks like about a '72 given the date codes and the "Inventoried 1972" sticker. Someone replaced the 74141 at some point. Oh, and the Sandia Laboratories sticker is staying.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: October 13, 2015, 09:18:01 pm
content: Quote from: Paul Moir on October 13, 2015, 08:33:55 pmAwesome! I would definitely leave the Sandia Labs sticker! Like some of my other items with McDonnell Douglas stickers.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: October 14, 2015, 06:36:20 am
content: Well, just cleaning the damn switches seems to have it working perfectly now. I'll post a teardown once I get some time since repair consisted of cleaning and replacing the current range fuse.Though I don't have any real standards, it matches my most trusted DMM and a few precision resistors I have around. I'm not even tempted to touch the calibration.The current shunt is neat. It's a board that goes on over the switch shafts, and picks up the range switches with little levers.

author: crispy_tofu
author_rank: Super Contributor
timestamp: October 14, 2015, 11:06:06 am
content: Quote from: FlyingHacker on October 09, 2015, 05:16:53 amWinner winner chicken dinner!Congratulations on the repair!

author: Chuy
author_rank: Newbie
timestamp: October 24, 2022, 01:32:52 am
content: Hello.What was wrong with the Lambda before you replaced the capacitor?I just bought one and have this problem, I just post a new post here at eevblog:Hello everyone.I just got this used Lambda LPT-7202 but it doesn't deliver enough current on all 3 outputs.I calibrated all 3 voltages and was able to bring the voltage to the maximum value but on the Current calibration, I was short 1 amp even though I rotated the R102. R202 and R302 to the maximum.The problem is when I connect a load even a small motor or light bulb, the voltage drops down to 3 volts and the motor bearly rotates or the lights barely light up, this happens on all 3 outputs.I also put a jumper to the V+ and V- to adjust the current to the maximum and it does the same thing.For example;I turn on the power supply without load and adjust the voltage to 10 volts with the maximum current then I connect a car light bulb (12 v) immediately the voltage drops to 3 volts and the light bulb bearly lights up.Photo attached.I can turn the voltage knob to a higher voltage but it doesn't go up, stays on at 3 volts.Happens on all 3 outputs.Any suggestions/advice on what to do?