Fluke 8400A; No display. - Page 1
Forum section: electronics / repair

author: neo
author_rank: Super Contributor
timestamp: November 25, 2017, 08:29:52 pm
content: I just got my 8400A after a fed ex screw up or two, no worries it arrived intact just delayed slightly.Only problem is i get it and the display doesn't light up, i know HV is present because the + lights up on DCV and it appears to work as part of the display changes as i change inputs.The only thing that does not work it seems are the actually numeric part of the display, i know one or two tubes could be bad but all of the except for the +- seems unlikely to me.It appears some of the transistors got very hot at some point, see pictures,This thing appears to have been sitting on a shelf since the 80s judging by the amount of dust, mild rust and or corrosion but nothing that should be an immediate issue.Also it was made sometime in early '73 judging by the date codes.I know it is not a factory dud due to the 5 calibration stickers on it, 4 local and 1 from fluke.Also of note it has from the factory, Ac converter, OHMs converter, Data output unit (DOU), Remote control unit (RCU) and Rear input. someone later added the card for DC external reference (DC-ER)There is only one unfilled card slot and two missing options, does this mean someone also added the RMS converter? Crazy as it may sound i would prefer it if it measured peak to peak AC.I can't find the 8400A manual for free though I can find the 8300A one, can it be used or should i just buy the 8400A manual?I would greatly appreciate help, hints or even a general clue what to look for.P.S. It is only 6 digit nixie tube meter, not 6.5 digit.EDIT: For typos.

author: Specmaster
author_rank: Super Contributor
timestamp: November 25, 2017, 08:43:31 pm
content: Oh dear thats bad news. It might help everyone if you could resize your photos to something like 800 x 600 pixels at least, it gives everyone chance to study them and see if they can spot anything to assist you.

author: neo
author_rank: Super Contributor
timestamp: November 25, 2017, 08:44:11 pm
content: Will do, was just worried they wouldn't all fit was all. Its very apt that your the first poster, with that signature i mean, my name may not be Murphy but it may as well be with my luck.

author: neo
author_rank: Super Contributor
timestamp: November 25, 2017, 08:58:44 pm
content: A thought occurs to me, one just went onto ebay for 80 (less than i paid for mine) with a shown working display, if i can get the wallet to agree with me would it be wrong to choose the easier path and buy that one?

author: neo
author_rank: Super Contributor
timestamp: November 25, 2017, 09:22:56 pm
content: Also of note with the DOU out, if it is set to ac and turned on it will display either a 0 or 1 on the furthest left digit.Also the sample rate light does not flash, i presume it is meant to.While messing with the cards to see if anything changes the AC converter and another set of wries popped off the little block they were on, does it matter where they go? I assume it does but due to accident i didn't have chance to take note.

author: Specmaster
author_rank: Super Contributor
timestamp: November 25, 2017, 09:56:34 pm
content: Quote from: neo on November 25, 2017, 08:44:11 pmYeh, well you know what Dave says, "Murphy will get you every time" and hence my signature reflects how my lucks goes at times too.To keep the size of the post down if you have loads of photos to post, you could use a site like Flickr or Imgur, post your photos there and then insert the links to them in your message and they appear as if they are part of your message rather than attachments and also there is no restrictions on file size either as they are not stored on this server and thus using bandwidth, if you notice posts by bd139, he uses this method as well. I do as well if I need to show details.

author: Specmaster
author_rank: Super Contributor
timestamp: November 25, 2017, 10:00:02 pm
content: Quote from: neo on November 25, 2017, 09:22:56 pmI assume you meant wires popped off, and I would say yes it does matter and without a service manual, I would not attempt to reconnect them incase Murphy really does get you.

author: neo
author_rank: Super Contributor
timestamp: November 25, 2017, 10:08:30 pm
content: Quote from: Specmaster on November 25, 2017, 10:00:02 pmi believe i said that they popped off.

author: Specmaster
author_rank: Super Contributor
timestamp: November 25, 2017, 10:13:28 pm
content: You did indeed but you said "While messing with the cards to see if anything changes the AC converter and another set of wries popped off the little block they were on, does it matter where they go? I assume it does but due to accident i didn't have chance to take note." I have no idea what block you are referring to hence I said I wouldn't reconnect them without the service manual.

author: neo
author_rank: Super Contributor
timestamp: November 25, 2017, 10:21:56 pm
content: Quote from: Specmaster on November 25, 2017, 10:13:28 pmFair point in my excitement/ annoyance i was little non specific.To see if anything changed drastically i started take cards out, with the AC converter and another board i can't remember the name of right now their wires popped off this little grey block which seems to distribute the signal input from the front panel.Now in hindsight i know i should have taken notes to, but i didn't think too. I asked just to query if it was common knowledge in any way.

author: Specmaster
author_rank: Super Contributor
timestamp: November 25, 2017, 10:29:37 pm
content: No, its not, I have the Fluke 8505A (just discovered that above 4M it is miles out of calibration) have you searched for a manual?

author: neo
author_rank: Super Contributor
timestamp: November 25, 2017, 10:34:05 pm
content: Only one i have found is 12 for digital of 15 for paper, truth be told i prefer paper. Though i'm considering getting another 8400A with a known working display

author: Specmaster
author_rank: Super Contributor
timestamp: November 25, 2017, 10:49:03 pm
content: I'd get a digital (pdf) then you can print it out hundreds of times and also make multiple copies of the files and store it various drives, USB sticks, NAS drives and of course CD's in case you accidentally erase it. Get the paper one and anything happens to you're screwed.

author: neo
author_rank: Super Contributor
timestamp: November 25, 2017, 11:08:23 pm
content: Only problem is the digital is Artek, from what i know they use heavy copy righting.

author: Specmaster
author_rank: Super Contributor
timestamp: November 25, 2017, 11:52:20 pm
content: They do copyright the pages is true, but why would that worry you? You can still make as many copies and prints as you like, you could also give away the odd copy if you can trust the person who you give it to not to pass it onto anyone who is likely to post it on a forum so that that it can be traced back to you. In reality I doubt if they would mind if you did give the odd copy away, as its advertising their services for the manuals that the recipient can't cadge from anyone else isn't it?If you paid for an original manual in paper format, the same is true, you could photocopy and give it away if you so wished.

author: Specmaster
author_rank: Super Contributor
timestamp: November 26, 2017, 12:15:12 am
content: I attach a couple of pages from a manual I purchased from them, they are very fair as well, as you see from page 2, should your copy become corrupted or lost in a disc crash etc, they will replace it for you.The copyright is not intrusive either.

author: neo
author_rank: Super Contributor
timestamp: November 26, 2017, 12:50:31 am
content: Quote from: Specmaster on November 26, 2017, 12:15:12 amBetween your recommendation and the fact that i get it immediately, you have convinced me.

author: Specmaster
author_rank: Super Contributor
timestamp: November 26, 2017, 12:52:15 am
content: Glad I could help

author: neo
author_rank: Super Contributor
timestamp: November 26, 2017, 01:29:33 am
content: Quote from: Specmaster on November 26, 2017, 12:52:15 amJust talking me through the problem helps, just the way my brain works.

author: NeedsMoreFlux
author_rank: Newbie
timestamp: November 26, 2017, 02:56:25 am
content: I might have another transistor/thermistor. I have alot from old ham radios. If that one isn't functioning properly let me know. I might have one.

author: neo
author_rank: Super Contributor
timestamp: November 26, 2017, 03:58:09 am
content: Quote from: NeedsMoreFlux on November 26, 2017, 02:56:25 ami'll let you know, thanks for the offer.

author: Cubdriver
author_rank: Unknown
timestamp: November 26, 2017, 05:01:37 am
content: Quote from: neo on November 25, 2017, 08:58:44 pmOh, crap - I think I just bought that one.(Though in my defense, I'd been watching it for over a week after initially learning of the model when you bought yours.)-Pat

author: neo
author_rank: Super Contributor
timestamp: November 26, 2017, 05:43:19 am
content: Quote from: Cubdriver on November 26, 2017, 05:01:37 amI don't mind Pat, if you wanted one and got it then good on you. I would of just used it to take the easier path.So instead of sniping something from under me you simply removed temptation from my path

author: Cubdriver
author_rank: Unknown
timestamp: November 26, 2017, 05:54:57 am
content: Quote from: neo on November 26, 2017, 05:43:19 amSo I helped to save you from yourself?Ok, I can live with that.-Pat

author: neo
author_rank: Super Contributor
timestamp: November 26, 2017, 06:04:01 am
content: As far as i can tell the problem with mine is just that it doesn't display, i think something has gone screwy in the analog to digital converter.The furtherest left digit with flash between 0 and 1 occasionally while playing with the range buttons and from that and the + i know HV is present.

author: Specmaster
author_rank: Super Contributor
timestamp: November 26, 2017, 10:10:16 am
content: Quote from: neo on November 26, 2017, 06:04:01 amI think that I'd be inclined to strip it to the motherboard and check for foreign objects on or under the board and cold or dry joints. I found a stray screw under Flukes MB but it didn't rattle so it was caught somewhere. I was glad I took apart before switching it on.Sent from my SM-J510FN using Tapatalk

author: neo
author_rank: Super Contributor
timestamp: November 26, 2017, 05:23:37 pm
content: Good idea, only problem is the chassis, i'm pretty sure i would need to strip the thing completely because of a metal plate riveted on the bottom.

author: neo
author_rank: Super Contributor
timestamp: November 27, 2017, 01:31:35 am
content: After looking at the manual i now know that it is a 5.5 digit meter though they used a proper nixie for the half digit, thats what threw me.An understandably mistake i think, due to the lack of any information on it and the fact it did not work when i got itEDIT: I'm, still at a loss for the difference between this and the 8300A but there has to be something because there appears to be a high demand for 8300As.

author: neo
author_rank: Super Contributor
timestamp: November 28, 2017, 07:27:37 pm
content: OK i've narrowed it down yet again, there is rectification of the dc and the ripple is acceptable, 1V peak to peak under normal conditions slightly more on HV line for the nixies.No screws lodged in it, though one of the 8 holding on the front is stripped.I'm not sure how to test the transistor that was hot, but there at one point were some repairs using fluke issued parts in 77 so it is possible it was a soldering accident.I know it worked after they put the new parts in because it was later calibrated.I've narrowed it down slightly i think.

author: Specmaster
author_rank: Super Contributor
timestamp: November 28, 2017, 07:33:14 pm
content: Good work, did you get that manual in the end?

author: neo
author_rank: Super Contributor
timestamp: November 28, 2017, 08:16:37 pm
content: Quote from: Specmaster on November 28, 2017, 07:33:14 pmYes i got the manual, I've yet to test the voltages other than to check that there isn't obviously wrong.Its good I've narrowed it down, except i don't know what to do next. I think i'll go through and check every voltage and then maybe check what is actually going to the A to D converter.Regardless of what i do next i think i've run out of ideas.

author: Specmaster
author_rank: Super Contributor
timestamp: November 28, 2017, 08:36:21 pm
content: With something like this its essential to check not just the supply rails but at every point that the manual shows a voltage reading, ie every IC for instance because it might just be confined to just one small section and if thats the case checking the voltage on pin as designated in the manual will be an invaluable tool in pinpointing the area of concern. I'd do that in preference to anything else at this stage, you might get lucky and it could show you precisely where the problem is.

author: neo
author_rank: Super Contributor
timestamp: November 28, 2017, 08:42:17 pm
content: Only small problem is i do not have a extender card, so it may or may not be possible to do that.

author: neo
author_rank: Super Contributor
timestamp: November 28, 2017, 08:55:55 pm
content: Now that i think about it i could start by testing voltage to the cards, then using the knowledge of which pins are which voltage could test continuity between them and their respective locations. Aided by the manual of course, not just stumbling around.

author: Specmaster
author_rank: Super Contributor
timestamp: November 28, 2017, 08:56:57 pm
content: Oh, of course I expect your cards are like these in my 8505A are they?

author: Specmaster
author_rank: Super Contributor
timestamp: November 28, 2017, 08:59:09 pm
content: Quote from: neo on November 28, 2017, 08:55:55 pmYes, that is the only way to ensure that the IC's are being fed without having access to an expansion lead.

author: neo
author_rank: Super Contributor
timestamp: November 28, 2017, 09:08:06 pm
content: Quote from: Specmaster on November 28, 2017, 08:56:57 pmThey are similar though mine is slightly more basic.

author: Specmaster
author_rank: Super Contributor
timestamp: November 28, 2017, 09:13:06 pm
content: Hmm, well I don't think there's much chance of getting that lead or a card so that is your only option at this stage I believe. I'm not the only having problems with these old meters so thats a relief. I have not yet tested mine on the current ranges, but voltages so far seem to OK but the resistance is causing problems with the odd erratic reading and anything over 3 to 4M is totally unreliable as 10M reads about 11.25M

author: petepdx
author_rank: Newbie
timestamp: November 28, 2017, 11:06:43 pm
content: Artek is is two person show (wife & husband). They ask a very fair price and do an amazing job at cleaning up, indexing, etc etc.Why not just buy one from the ?-pete a very happy customer of theirs

author: neo
author_rank: Super Contributor
timestamp: November 28, 2017, 11:13:13 pm
content: Well this is something, with a meter's leads on the HV test point the display gets brighter and the half digit's 0 and 1 aways come on. Only with RCU out.Spec Val Actual+- 5V 200V - 190V-200V it varies.+- 10mv 18V - 17.986V+- 375mv -18V - -18.038V+- .15V 5V - 5.017VVoltage testing done with RCU in.(removed and reposted for correction)

author: neo
author_rank: Super Contributor
timestamp: November 28, 2017, 11:16:18 pm
content: Quote from: Specmaster on November 28, 2017, 11:05:13 pmThis meter is from '73 but to be entirely clear yes it is in fact linear.Digital, keithley 177 if you want me to be specific and eevblog seems to be glitching.Quote from: petepdx on November 28, 2017, 11:06:43 pmActually i have bought the manual from them, i will admit the copyright isn't invasive and they did a good job of digitizing it.

author: Specmaster
author_rank: Super Contributor
timestamp: November 28, 2017, 11:20:59 pm
content: Quote from: neo on November 28, 2017, 11:16:18 pmYes it is glitching, it took my post about 5 times I think, and yet it was still showing as trying to connect on my screen.What is the RCU that you speak of?I think I would check all the caps on the power rails as my next thing to check, you may some with a high ESR or miles out of spec on the capacitance values.

author: neo
author_rank: Super Contributor
timestamp: November 28, 2017, 11:23:31 pm
content: The Remote Control Unit.Also i don't have an ESR meter, nor do i have a capacitance meter yet, As for the capactiors i'm going to get some new ones soon.What, if anything, should i do about a couple of the transistors getting hotter than the others?

author: Specmaster
author_rank: Super Contributor
timestamp: November 28, 2017, 11:32:59 pm
content: Quote from: neo on November 28, 2017, 11:23:31 pmYou do really need some sort of ESR meter, just poking about in the dark otherwise. Caps can look perfectly OK visually but have low capacity or have very high ESR values and neither and desirable and can cause all kinds of problems. I have 2, one is battery operated and is a cheap chinese product but does a reasonable job and can test transistors as well and identify the pinouts for you. The other is again Chinese and mains powered via wall wart and is very accurate indeed, comes with kelvin leads and will measure resistance, capacitance and inductance, both were via Ebay and I'll post some photos soon to help you. Some DMM's will have a capacitor test range on them but most will only measure the capacity and not the ESR which is the real killer.

author: neo
author_rank: Super Contributor
timestamp: November 28, 2017, 11:37:30 pm
content: Looking closer, and thinking, there is no way this heat damage is due to soldering there are marks on the surrounding metal for it.For lack of an esr meter i'll order a Chinese one soon if they actually work.https://www.ebay.com/itm/121593935597the one i was looking at.

author: Specmaster
author_rank: Super Contributor
timestamp: November 29, 2017, 12:09:55 am
content: Looking at your photos again since you made them larger, it is very clear that the heat damage is not the result of the soldering but is what looks like a sustained overloading of the power supply and I bet that is the HT side that your having the issues with. Those caps also look like the originals and so I'd tend to treat those as suspects as well but I'd also look for excessive current draw on the plug in cards as well and that could be shorted tants and other caps on the power rails.That tester looks to be OK, heres mine, the XJW01 is the one that is most most accurate and displays plenty of information as you can see and you can select the test frequency of 100Hz, 1KHz or 7.8KHz and it will automatically detect what it is your testing and go to that range, ie., L, C or R and their is also a calibration setting where you can further refine the accuracy. People have tested these against much more expensive HP LCR meters costing many times the price and the results have been very close indeed.As you can see from the photos, there is a only a small difference in the readings between the mains and the battery unit, both were testing the same cap, a 1000uF 50VDC and some of the difference may be down to the testing frequency the battery one, I have no idea what frequency it tests at and the XJW01 should really have set at 100Hz for that test as it was cap typically used for power smoothing so would be seeing most likely a 100Hz rectified frequency.

author: neo
author_rank: Super Contributor
timestamp: November 29, 2017, 12:15:15 am
content: OK i put a new cap in for now, when cold it is 198.21V, upon warming up, that is being turned on for a bit, it drops. To the schematics for me to see if the 3 suspect transistors have anything to do with it.

author: Specmaster
author_rank: Super Contributor
timestamp: November 29, 2017, 12:23:59 am
content: As matter of interest, the 1000uF cap tested @ 100Hz reads 1004.9uF with an ESR of 0.076 Ohms and at 1KHz it reads 995.3uF and ESR is 052.9 m Ohms but @ 7.8KHz it ceases to be a capacitor and turns into a resistor of 43.6m Ohms which shows the importance of selecting the right type of capacitor for the right job and electrolytics are no good at high frequencies as shown above so are best suited to smoothing duties and tested at 100Hz.

author: Specmaster
author_rank: Super Contributor
timestamp: November 29, 2017, 12:25:46 am
content: Quote from: neo on November 29, 2017, 12:15:15 amThe fact that it drops after a bit does look like either an overload which gets worse when it warms up or leaky caps.

author: neo
author_rank: Super Contributor
timestamp: November 29, 2017, 12:34:23 am
content: What do you propose i do?My idea is buy at least 2 spares of the offending transistors and swap them out, but that isn't going to be until Dec 2 that i have them so i could use ideas of what to look for while i wait.Its going to be a fight to get the the heat sinked one off, i think i have to take the heat sink with it, but at least i don't risk cooking a pcb thats already cooked.EDIT: Replacement transistors is off the table unless absolutely necessary.

author: Specmaster
author_rank: Super Contributor
timestamp: November 29, 2017, 01:16:31 am
content: Well with that LCR tester you have found, when that arrives you can test the transistor as already mentioned, you only have to remove it from the circuit and clip one of those leads to cach connection and the tester will tell which is the base, collector and emitter if the transistor is good or not. If it isn't then it will show up as a short circuit (resistor) or a diode and then you need to replace them, once you know what their state is . The same with caps, although with caps after a few years of service many people will replace them anyway as an insurance because after a few years it almost certain that they will fail at some point. That point will vary according to how often the equipment is switched and used and how hot the caps get. I always replace with 105C ones rather the lower 85C rated ones which will last for less time, especially in power supplies where the ambient temps are going to higher and will cause them to dry out quicker.

author: Specmaster
author_rank: Super Contributor
timestamp: November 29, 2017, 01:27:39 am
content: This is how the display will depict a transistor and as you can see it will show what each pin is and tell you if the transistor is npn or pnp and also the hfe as well as the forward voltage.

author: neo
author_rank: Super Contributor
timestamp: November 29, 2017, 07:35:53 am
content: Ok I've reached another impasse, that is to say I've stumped myself.The 200v line seems to be my chief concern with its odd behavior, of course the reason why the transistors getting hot is also pressing.Q3 is part of the +18V regulator, Q6 is part of the +5 and both are getting hot.If there was a problem with either than i would expect to see it reflected as ripple or the like but instead it looks copacetic, their not even being dragged down.The 200V railed seems to be fine at start up only to be dragged down lower and lower the hotter the transistors get.Either ways i included schematics for those among us that actually understand transistor only power supplies, they make me go

author: Specmaster
author_rank: Super Contributor
timestamp: November 29, 2017, 09:26:11 am
content: Alright, I fear that you're leaping ahead here before you've been able to confirm the very basics of the psu. Firstly you have the psu out of the unit and those caps must be checked and replaced if they are leaky, have a high ESR or of course a lower capacitance value than what they should be, these will have a direct bearing on the rest of the circuit and could be one of the reasons for the apparent overheating of Q3 and Q8.The 5v supply is referenced from the +18v supply rail, so the 5v will be affected by any problem with +18v supply. Do you have a infra red thermometer or camera at all? If so I'd be inclined to pull the data sheets for those transistors and check their normal running temps against what your device tells you they are currently running at.While I was waiting for the ESR tester to arrive, I'd also be dropping one leg on the resistors in the PSU and double checking the values are broadly in line with the schematic.

author: Specmaster
author_rank: Super Contributor
timestamp: November 29, 2017, 11:42:13 am
content: To show you how the LCR and transistor tester functions and is a great tester, it has helped me a lot with resolving problems with my various oscilloscopes I show you a couple of photos testing a suspect transistor from a vertical amplifier in a scope. I only just noticed that while I was using red, black and blue cables, with matching clips, somehow, the clips got soldered to the the wrong colour cable in the case of the blue and black ones as you will notice in the 2nd photo.The first photo shows the suspect transistor which was supposed to be providing a +ve 5V in the middle of a PCB (not on the power supply as you would suspect, it was I think because it was only required for a couple of IC's) and it was actually chucking out 0.8V. After testing it and then replacing the transistor, it gave out the +ve 5V and it started to function correctly. I know that there are those that will not touch these chinese testers but I can honestly say so far I have nothing but praise for both of my testers they have been well worth their cost.I also show a couple of photos of the battery one testing a resistor @ 15R +/- 10% and also my newly made resistor decade box maxed out which measures on my DMM's as being 9.998M, so the little lcr tester is again pretty close.

author: neo
author_rank: Super Contributor
timestamp: November 29, 2017, 05:16:44 pm
content: The replacement caps are on their way, I've said that already i think.I don't have a digital thermometer but i do have a fairly accurate analog one, and checking the resistors i can do.

author: Specmaster
author_rank: Super Contributor
timestamp: November 29, 2017, 05:26:29 pm
content: Quote from: neo on November 29, 2017, 05:16:44 pmOk check the resistors,but you cannot use an analogue thermometer to check the transistors etc, you need a Infra red on or a infrared thermal camera.https://www.ebay.co.uk/itm/142456227542is like the one I use and will measure upto 250C

author: neo
author_rank: Super Contributor
timestamp: November 29, 2017, 05:28:35 pm
content: It has a proper thermocouple, just an analog scale.

author: Specmaster
author_rank: Super Contributor
timestamp: November 29, 2017, 05:36:05 pm
content: Quote from: neo on November 29, 2017, 05:28:35 pmYou can try it but I never find them any good, you need to be able to make contact with the item you want to measure and that means that if it is really hot you will get burned or if the item is alive, you will get a shock and also of course you just cannot get easy access to make contact but with this 9one as long as you can point the laser beam at the item / part you need to check then you're good to go, it just takes a seconds to find out an items temperature,

author: neo
author_rank: Super Contributor
timestamp: November 29, 2017, 08:06:34 pm
content: I forgot to do a thermal probe before i de-soldered an end to each resistor.One looks measures like a diode, except has resistor bands. White blue orange red. By my logical conclusion this is CR9.The last resistor is a bit odd the code is green brown brown gold yellow which, besides being the only 5 band resistor, indicates 51.1 ohms except that it measures 538.9 and there is meant to be a 510 ohm resistor in circuit. By logical conclusion this resistor is meant to be that one.SPEC VAL ACTUAL1% 7.20K 7.202K1% 4.02K 4.022K5% 5.60K 6.022K1% 9.53K 9.496K5% 220K 244.6K1% 40.2K 40.27K5% 5.60K 6.115K5% 68.0K 69.17K1% 383K 382K1% 40.2K 40.41K1% 10.0K 10.054K5% 51 57.121% 10.0K 10.023K5% 51 54.86

author: Specmaster
author_rank: Super Contributor
timestamp: November 29, 2017, 08:57:07 pm
content: None of those resistors are suspects, the CR9 is I think a Zener diode so the culprits on the PSU are going to be one or more of the following, transistors, capacitors (still my firm favorite) or it is just possible a bridge rectifier / bad solder joint/s.Both the capacitors and the transistors will of course be tested by the chinese tester when you order it and it arrives.The transistors that are getting hot, do they have heat sinks?

author: neo
author_rank: Super Contributor
timestamp: November 29, 2017, 08:58:43 pm
content: Quote from: Specmaster on November 29, 2017, 08:57:07 pmThe reason their (almost) irreplaceable is that they are custom packages with integrated heatsink.Should i replace the ones out of spec since i am in it anyways?

author: Specmaster
author_rank: Super Contributor
timestamp: November 29, 2017, 09:00:39 pm
content: When they get hot, does the heatsink feel as hot or is it cooler?

author: neo
author_rank: Super Contributor
timestamp: November 29, 2017, 09:09:25 pm
content: Quote from: Specmaster on November 29, 2017, 09:00:39 pmAlmost as hot but not quite.

author: Specmaster
author_rank: Super Contributor
timestamp: November 29, 2017, 09:15:34 pm
content: Quote from: neo on November 29, 2017, 08:58:43 pmNo, they are not that far out that would cause any problems, the biggest one out of spec is the 220K R17 if you read the notes, may or may not be fitted as it is essentially in parallel with others to help trim out the +5v which is OK so I'd leave it.The large transistor on the heatsink appears to have no screws to hold it on the heatsink, is that so?

author: neo
author_rank: Super Contributor
timestamp: November 29, 2017, 09:18:37 pm
content: Quote from: Specmaster on November 29, 2017, 09:15:34 pmCorrect, though i think it may be held together somehow, not sure how.

author: Specmaster
author_rank: Super Contributor
timestamp: November 29, 2017, 09:19:05 pm
content: Where are the other transistors, I can only see 3 in the photo?

author: Specmaster
author_rank: Super Contributor
timestamp: November 29, 2017, 09:20:33 pm
content: Quote from: neo on November 29, 2017, 09:18:37 pmAre there any holes in the heat sink?

author: neo
author_rank: Super Contributor
timestamp: November 29, 2017, 09:23:37 pm
content: http://www.electronicsurplus.com/rca-40372-transistors-npn-cross-2n3054That is Q6The round brown things are transistors, the brown is their heatsink.EDIT: to add that the only transistors on this board are either heat sinked or not in metal cans.

author: Specmaster
author_rank: Super Contributor
timestamp: November 29, 2017, 09:33:41 pm
content: Quote from: neo on November 29, 2017, 09:23:37 pmOh, I see, I that they might be sockets, they look as if they have been getting very hot and got discoloured then, do they get hot?If you put a ohm meter across the heat sink and the 40372 body, are they connected electrically at all?

author: neo
author_rank: Super Contributor
timestamp: November 29, 2017, 09:40:56 pm
content: Only one gets hot, that heatsink is lighter than the others, though they are meant to be that color i think.Between the 40372 case and its heatsink is 0 ohms.Also i stand corrected there is one transistor in a metal can that does not have a heatsink

author: Specmaster
author_rank: Super Contributor
timestamp: November 29, 2017, 09:57:45 pm
content: Quote from: neo on November 29, 2017, 09:40:56 pmOK, I'd be inclined to put some screws and nuts through the holes on the 40372 and heatsink then as you will see from the RCA manual, the hotter that gets, the greater derating factor has to be applied and as can be seen from the browning all around that area it has been really hot.

author: Specmaster
author_rank: Super Contributor
timestamp: November 29, 2017, 10:01:35 pm
content: Once the new caps arrive and are fitted, and if the transistors can be proved to be OK, then we are looking somewhere else for the problem.

author: neo
author_rank: Super Contributor
timestamp: November 29, 2017, 10:02:16 pm
content: Quote from: Specmaster on November 29, 2017, 09:57:45 pmI would have to drill through the pcb to add screws.

author: Specmaster
author_rank: Super Contributor
timestamp: November 29, 2017, 10:07:28 pm
content: In that case leave it, it was obviously designed to be like that.We can't do anymore now until we can check / replace the caps and the transistors.

author: neo
author_rank: Super Contributor
timestamp: November 29, 2017, 10:37:32 pm
content: Quote from: Specmaster on November 29, 2017, 10:07:28 pmThanks for your help so far, i will get the caps relatively soon, either December 1st or 2nd.

author: Specmaster
author_rank: Super Contributor
timestamp: November 29, 2017, 11:22:55 pm
content: I don't know but you mind find this useful if you require spares for it as well?http://www.dontscrapit.com/Ohio-/Construction-/Fluke-8400A-s-range-benchtop-dmm-digital-multimeter-rm.php5I've sent you a personal message as well.

author: neo
author_rank: Super Contributor
timestamp: November 29, 2017, 11:29:48 pm
content: PROGRESS!!!!I re-soldered the joints on the power supply and checked my work twice for flaws. Now instead of being immediately unstable it has a bit of delay and then a much more gradual fall.So not fixed but i at least made some progress.

author: Specmaster
author_rank: Super Contributor
timestamp: November 29, 2017, 11:31:49 pm
content: Quote from: neo on November 29, 2017, 11:29:48 pmMaybe when the caps arrive it might be fixed then

author: neo
author_rank: Super Contributor
timestamp: November 29, 2017, 11:32:55 pm
content: With that link you sent me, will they ship it and how much is the item itself?

author: Specmaster
author_rank: Super Contributor
timestamp: November 29, 2017, 11:34:56 pm
content: Quote from: neo on November 29, 2017, 11:32:55 pmI have no idea, you have the same info as I have there. I was searching for a manual and found that link.

author: neo
author_rank: Super Contributor
timestamp: November 29, 2017, 11:42:42 pm
content: I kinda want it, if for nothing else the rack ears alone. The ears are rare it seems, my fluke has none and my HP5340A has 1.

author: Specmaster
author_rank: Super Contributor
timestamp: November 29, 2017, 11:44:04 pm
content: send em a message then and see what they say.

author: neo
author_rank: Super Contributor
timestamp: November 29, 2017, 11:57:01 pm
content: Quote from: Specmaster on November 29, 2017, 11:44:04 pmI have, speaking of messages check yours.

author: neo
author_rank: Super Contributor
timestamp: November 30, 2017, 12:12:20 am
content: Well this is interesting, may even give us something to work with.This is being caused by the regulator, at the capacitor this is not there.

author: Specmaster
author_rank: Super Contributor
timestamp: November 30, 2017, 12:22:37 am
content: Where on the circuit are you taking this from?

author: neo
author_rank: Super Contributor
timestamp: November 30, 2017, 12:24:39 am
content: The test point, specifically test point 1 for 200V line

author: Specmaster
author_rank: Super Contributor
timestamp: November 30, 2017, 12:30:00 am
content: What do you at C1? is Q1 the large TO66 transistor on the heatsink?

author: Specmaster
author_rank: Super Contributor
timestamp: November 30, 2017, 12:31:31 am
content: You say to check my messages, which ones, emails or a PM, because I have checked the PM's and there is no message there?

author: neo
author_rank: Super Contributor
timestamp: November 30, 2017, 12:33:27 am
content: No the large transistor is Q6, when i measure the 200V line at the capacitor i get what i expect, a little ripple but not much.I sent what you asked for to your email.

author: neo
author_rank: Super Contributor
timestamp: November 30, 2017, 12:52:40 am
content: Q6 hits temps as high as 70C perhaps higher.

author: Specmaster
author_rank: Super Contributor
timestamp: November 30, 2017, 01:48:19 am
content: you measured Q6 with your thermocouple then yes, or is that 70C a guess? If it then I'd say that was way to high and you need to measure the current being drawn on that 5V line, maybe the ADC is faulty? I got the manual now, thanks

author: neo
author_rank: Super Contributor
timestamp: November 30, 2017, 01:55:53 am
content: With my thermocouple.I found a smoking gun.no cards, 80v stable copacetic ripple with no noise. Nothing on the display.All cards except A8 and A9 the same.Add A8 and A9 it goes up to 200v but adds noise and parts of the display turns on.

author: Specmaster
author_rank: Super Contributor
timestamp: November 30, 2017, 02:01:07 am
content: Quote from: neo on November 30, 2017, 01:55:53 amNow we're getting somewhere, what about if you just A8 or A9, what happens then?

author: Specmaster
author_rank: Super Contributor
timestamp: November 30, 2017, 02:06:16 am
content: I take it for granted that you've checked to make sure that the correct boards or cards are plugged into their correct slots, if their like the 8505A, they have to be in the correct sequence or else nothing works properly.

author: neo
author_rank: Super Contributor
timestamp: November 30, 2017, 02:12:52 am
content: Quote from: Specmaster on November 30, 2017, 02:06:16 amYes i have checked that, at least twice.If only A8 and A9 the same result as having none except that that 80V is not stable, it drifts down.EDIT: Amendment, the no card state is 102V relatively stable, more testing is required then i will post a list.

author: Specmaster
author_rank: Super Contributor
timestamp: November 30, 2017, 02:25:33 am
content: Some good points, Logic Card has 3 test points and they are all accessible from the top of the card when in situ, and the ADC card has 7 test points and likewise all accessible in situ from the top of the card.I'm off to bed now, catch you tomorrow.

author: neo
author_rank: Super Contributor
timestamp: November 30, 2017, 03:51:33 am
content: No card= No display, 106V initially dropping to 102 though relatively stable at floor. No heat on Q6, mild heat on Q3. Copacetic ripple.A2= sameA3= 86V erratic behavior, no settling but swing between 85 and 90. Copacetic ripple, same heat patterns, no display.A5= same as with A2A6 and A7=same as with A2A8 and A9= 200V relatively stable, noise on the line 1V peak to peak square wave + previous ripple on top of each other Q3 hot, Q6 unaffected, Q2 warm.A10=80v initially drifting down to 75, copacetic ripple, no display, same heat patterns as A2A11 same as A2A12, same as A2A13 same as A2 except it starts at 76V and settles to 74A13 and A2 = same as just A13A13 and A3 = same as just A13A13 and A5 = same as just A13A13, A6 and A7 = same as just A13A13, A8 and A9 = same as just A8 and A9A13 and A10 = same as just A13A13 and A11 = same as just A10A13 and A12 = same as just A13A12 and A2 = 110V settling to 103VA12 and A3 = 85V settling to 78VA12 and A5 = 107V settling to 103VA12, A6 and A7 =107V settling to 103VA12, A8 and A9 = Same as A8 and A9A12 and A10 = 80V settling to 77VA12 and A11 = 80V settling to 75VEach test given a minute.If i wasn't so invested in this thing i might be tempted to take it out back and shoot it.

author: neo
author_rank: Super Contributor
timestamp: November 30, 2017, 04:24:46 am
content: i bought thishttps://www.ebay.com/itm/128-64-LCD-NPN-Transistor-Tester-Capacitance-ESR-LCR-Meter-Diode-Thyristor-BL/121684741402?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

author: Specmaster
author_rank: Super Contributor
timestamp: November 30, 2017, 07:59:22 am
content: Quote from: neo on November 30, 2017, 04:24:46 amThat is good let's hope it arrives in a couple of days, it will be one of the most used items in your toolkit. It does PNP & NPN transistors, diodes, zeners, mosfets, caps, inductors, and resistors. I was a bit dubious about buying it myself when I started in electronics. I had heard so much from others about the Chinese stuff being crap. Fact is however that it isn't, when see that bigger global and well known and respected brands are putting their names on Chinese produced products, so that you can buy the same thing from different companies with their names on, makes you think, don't it?Sent from my SM-J510FN using Tapatalk

author: Specmaster
author_rank: Super Contributor
timestamp: November 30, 2017, 08:09:59 am
content: Quote from: neo on November 30, 2017, 03:51:33 amWow, you have been busy, it seems that the regulation requires a certain load before it will allow the full HT through. When it does the regulation goes to pot, so it is looking like Q1 and Q2 need to be replaced but it also seems that 5v rail is struggling hence Q6 getting so hot. Let's get the HT up first and see if the display comes up, it might be Q6 is dependent on the display to settle down to normal levels of heat.Sent from my SM-J510FN using Tapatalk

author: Specmaster
author_rank: Super Contributor
timestamp: November 30, 2017, 10:43:12 am
content: Ok, I've had a quick look through the manual and all the voltage rails are interlinked with each other and the main one that everything references is the 18v so that has to be 100% healthy before the others can function correctly so if the regulators and the transistors are readily available I think I'd be inclined to replace them all without exception and also the caps on A1 card, the PSU. The diodes all checked out as OK and the resistors so then you will have effectively, a refurbished PSU card.Next I'd run the meter with the bare minimum card set up, which as going to be the following cards installed, A1, A2, A8, A9, A10, A11, A12 and A13 and see what happens both to the voltage rails, ripple and display, then I'd follow the chart on pages 4.16 and 4.17.Section 6 deals with the option cards and suggests items to check if checks run on them fail so it looks to be a good manual, just need to be patient and read it through and follow logical steps before moving on to new things.

author: neo
author_rank: Super Contributor
timestamp: November 30, 2017, 10:53:23 am
content: What leads you to believe Q1 and Q2 needs replaced? Their not getting hot in themselves, maybe warm.Also i apologize if i seem to drag my feet on spending money, but the transistors, while available, are relatively expensive.EDIT: A full transistor rework would only cost about 20 bucks so if it is necessary it's necessaryIn that plan of just replace everything do i also replace the non heat sinked 2n3053?Q7 is 2 cents so i might as well, the 2n3053s are cheapest in a 4 pack.http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=360901874911http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=263311413215http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=172991048457

author: neo
author_rank: Super Contributor
timestamp: November 30, 2017, 11:19:54 am
content: I found one thing odd, Q5 is listed as 2n4037, but is marked as 2n4890 and is the only motorola part i have seen.

author: Specmaster
author_rank: Super Contributor
timestamp: November 30, 2017, 01:09:34 pm
content: Quote from: neo on November 30, 2017, 10:53:23 amThe reason why I said that is the fact that many since you have had it, have been getting rather hot to say the least, transistors are not meant to get hot, warm yes if they are power ones like the big TO66 one with its heatsink, the others with their heatsinks warm only and the plastic one not at all. What we do not know is just long they have been getting hot before you acquired the meter or what that has done to their characteristics. You do know that Q1 and Q2 are producing some odd artifacts and a square wave on the noise floor.If you read the manual, in the power supply section it describes how it all works together and the 18v section is linked to both the 200v and the 5v, both of which seem to be having issues, 200v changes and even drops to 75v but the information in the manual states that at TP1 you should be getting 200v +/- 5v, so anywhere between 192-205v is acceptable, 80v etc is not.Q6 is on the 5v rail and getting extremely hot at 70C and this is once again linked and referenced to the 18v section and this section is common to both of the sections that you currently know for certain have issues, the 18v itself might also have issues but not exhibiting it at the moment.We know that the resistors and diodes, are OK so if the other suspect parts are replaced then you will know for sure that your starting off with a rock solid platform that you can then outwards from card by card until you have it up and running again.If you don't want to spend money at the moment thats up to you, but you currently have a whole box full of unknown cards and a motherboard, all of which all rely on a good healthy source of power to work so that why I feel that you need be certain in your mind that that it is good and fit for purpose.

author: Specmaster
author_rank: Super Contributor
timestamp: November 30, 2017, 01:26:31 pm
content: Quote from: neo on November 30, 2017, 11:19:54 amThats not unusual as most major manufacturers will have their own part numbers and references printed on the parts to make sure that the parts for it were purchased from them should they ever become required. It probably means that someone has trouble with the PSU before you and they discovered the original part was in fact a 2N4890 or that was an equivalent transistor transistor to the 2N4037.In fact that is what appears to be the case, I just googled the 2N4890 and here is the resulthttp://www.datasheets360.com/part/detail/2n4890/6089189740660391419/?alternatePartManufacturerId=0and you will see that it is a functional equivelent to the original 2N4037 and so are 2N3503, 2N3576 and also 2N4028, and that 2N4037 is now obsolute and discontinued.Remember, Google is your friend and solve many mysteries for you.

author: neo
author_rank: Super Contributor
timestamp: November 30, 2017, 07:17:15 pm
content: I will admit google can be useful, i just sometimes miss something.The non heat sinked parts are not getting warm, Q1 and Q5 are not getting particularly warm either, Q2 gets warm and Q3 gets hot. But you do have a point about giving myself one reliable card so i'll definitely consider it.

author: Specmaster
author_rank: Super Contributor
timestamp: November 30, 2017, 07:45:32 pm
content: At the end of the day its your money, you spend it how you want to, but if I was attempting to do what you're doing, thats what I'd do and then I have a known position of strength to work from. I don't know how much you paid for the 8400A but whatever it was it could become an expensive boat anchor and the first basic rule is to work from the power supply outwards and you do know that its not anywhere near 100%.But for now, I'd read the part of the manual through where it describes the way the whole system works to gain an idea of what to do next.

author: neo
author_rank: Super Contributor
timestamp: November 30, 2017, 07:56:33 pm
content: My collection of vintage parts finally paid off i found i had a set of 4 2n3053s from '72.You said 2n3053 can be used for the 2n4037?

author: Specmaster
author_rank: Super Contributor
timestamp: November 30, 2017, 08:06:01 pm
content: Quote from: neo on November 30, 2017, 07:56:33 pmNo No, 2N3503 I said, check on the link I sent you.

author: neo
author_rank: Super Contributor
timestamp: November 30, 2017, 08:09:00 pm
content: Thank you for correcting me, i get numbers confused sometimes.

author: Specmaster
author_rank: Super Contributor
timestamp: November 30, 2017, 08:26:09 pm
content: Quote from: neo on November 30, 2017, 08:09:00 pmBest be very careful with that then, 1 digit out can get you a totally different animal altogether in this game.

author: neo
author_rank: Super Contributor
timestamp: November 30, 2017, 08:47:03 pm
content: Quote from: Specmaster on November 30, 2017, 08:26:09 pmI tend to double check myself, though thank you for your warning.

author: neo
author_rank: Super Contributor
timestamp: November 30, 2017, 09:22:37 pm
content: The original 2n4037 is available new for 2 bucks.I got a big box of capacitors coming for this and for several things in my repair que, and i probably will have the transistors coming soon.Quote from: Specmaster on November 30, 2017, 07:45:32 pmDon't say that to the wallet (as i jokingly refer to her), she might disagree.

author: Specmaster
author_rank: Super Contributor
timestamp: November 30, 2017, 09:31:33 pm
content: Quote from: neo on November 30, 2017, 09:22:37 pmGreat news, another term for the wallet could be "Her indoors"

author: neo
author_rank: Super Contributor
timestamp: December 01, 2017, 02:51:11 am
content: Quote from: Specmaster on November 30, 2017, 09:31:33 pmI may be a bit dim but i don't get it.Regardless i have all the replacement transistors coming, as well as diodes just to be extra sure.Diodes are all going to be vishay 1n4005, 1 2n4037 transistor, 2 RCA 40372 and a complete set of electrolytics for the unit.I may not get them all at once, i ordered all of it today because of it being the end of the month. Most of the capacitors are coming from arrow, some from digikey with the diodes and lone transistor. The 40372s are coming off ebay as is the transistor tester so it may be some time.When i'm done the only originals on this board will be the resistors and two op-amps.

author: neo
author_rank: Super Contributor
timestamp: December 01, 2017, 02:54:51 am
content: In case your wondering why i bought two 40372s there is one on the power supply and then there is one in the A8 and A9 set that, if all these are going and or are suspect, is the next likely suspect.

author: Specmaster
author_rank: Super Contributor
timestamp: December 01, 2017, 09:39:02 am
content: Quote from: neo on December 01, 2017, 02:51:11 amHer indoors, is term that is often used as a name, reference to the other half, partner, wife etc. Another one is SWMBO is She Who Must Be ObeyedSent from my SM-J510FN using Tapatalk

author: neo
author_rank: Super Contributor
timestamp: December 02, 2017, 04:45:27 am
content: Well i've made some progress, the guy who replaced the transistors in '77 couldn't solder for shit. Q1 and Q2 did not have a good solder joint, the last guy damaged the pads/traces.

author: Specmaster
author_rank: Super Contributor
timestamp: December 02, 2017, 11:09:32 am
content: Quote from: neo on December 02, 2017, 04:45:27 amGood, what's the noise floor like now? I suspect that the voltage regulation is the same if you juggle the cards like before.Sent from my SM-J510FN using Tapatalk

author: neo
author_rank: Super Contributor
timestamp: December 02, 2017, 07:59:45 pm
content: Quote from: Specmaster on December 02, 2017, 11:09:32 amI've yet to test, i figured i would wait for the last 2 capacitors from digikey before i attempted anything. I forgot them on the arrow order.

author: neo
author_rank: Super Contributor
timestamp: December 04, 2017, 09:19:14 pm
content: Well i got good news and really really bad news and then more bad news.the display worked!I think i killed part of the display.The power supply, almost completely new parts, somehow put out -400 volts!!!Edit: IT PEAKED AT 2KV WHERE IS THIS VOLTAGE COMING FROM?!

author: Specmaster
author_rank: Super Contributor
timestamp: December 04, 2017, 09:26:12 pm
content: Quote from: neo on December 04, 2017, 09:19:14 pmThis is why I was suggesting that all the parts in the power supply be replaced apart from the resistors as we know that they are correct. For all we know, this 400V symptom might have been there before temporarily and that could have resulted in the burning of of the PCB etc.

author: neo
author_rank: Super Contributor
timestamp: December 04, 2017, 09:28:17 pm
content: Quote from: Specmaster on December 04, 2017, 09:26:12 pmAll but 2 transistors, replaced, all but 2 capacitors, replaced. Now i think the display is doomed.

author: Specmaster
author_rank: Super Contributor
timestamp: December 04, 2017, 09:28:56 pm
content: There was just so many unexplained and unknown variables / symptoms with the power supply to start with and its best to start with a something that is known to be working 100% and work outwards from there.

author: neo
author_rank: Super Contributor
timestamp: December 04, 2017, 09:30:03 pm
content: Well what do i do know? i think the 5s in the display are now mostly burned out.

author: Specmaster
author_rank: Super Contributor
timestamp: December 04, 2017, 09:38:20 pm
content: Quote from: neo on December 04, 2017, 09:30:03 pmDid you replace Q1 and Q2? these 2 in the main are responsible for regulating the 200V, but also bear in mind that I did point out that both the 200V and the 5V are both referenced to the 18V supply so if there was any transistor in the 18V supply that you didn't replace could also have contributed to the excessive output.You can always pull the nixies out (and all the other cards) and see if the power supply can be pulled back into alignment with only itself in circuit. You may be able to source replacements for the nixie tubes and hope that 400v does not go anywhere elses on the circuits.

author: neo
author_rank: Super Contributor
timestamp: December 04, 2017, 09:45:49 pm
content: Quote from: Specmaster on December 04, 2017, 09:38:20 pmI think this one is a write off without a parts unit, i got my eye on one with limited time left.If i get a parts unit then this power supply is going into the junk bin,

author: Specmaster
author_rank: Super Contributor
timestamp: December 04, 2017, 09:49:27 pm
content: Quote from: neo on December 04, 2017, 09:45:49 pmIs this the one?https://www.ebay.co.uk/itm/FLUKE-8400A-DIGITAL-VOLTMETER/232439511136

author: neo
author_rank: Super Contributor
timestamp: December 04, 2017, 09:49:56 pm
content: Yes, why?

author: Specmaster
author_rank: Super Contributor
timestamp: December 04, 2017, 09:51:19 pm
content: Quote from: neo on December 04, 2017, 09:49:56 pmIts the only one I can see that why I thought it was, wack a offer on it now and that way you should prevent anyone else grabbing it.

author: neo
author_rank: Super Contributor
timestamp: December 04, 2017, 10:06:44 pm
content: Quote from: Specmaster on December 04, 2017, 09:51:19 pmThats me when she gets home, i called it.I am so dead if this blows up, i technically bought it with money i don't technically have yet. Piecing together earlier conversations to give myself a "yes".

author: Specmaster
author_rank: Super Contributor
timestamp: December 04, 2017, 10:12:08 pm
content: Asking price or an offer accepted? When you get it, pull out the boards and run the power supply alone and see what you get and also check for any signs of burning on the PCB, you now know where to look for that don't you?

author: neo
author_rank: Super Contributor
timestamp: December 04, 2017, 10:13:39 pm
content: The $28 was acceptable, and yes i now know what to look for. At least mostly. I still have no clue why it lost regulation, or even where the insane voltage came from.

author: Specmaster
author_rank: Super Contributor
timestamp: December 04, 2017, 10:15:06 pm
content: Quote from: neo on December 04, 2017, 10:13:39 pmI think that that could well be put down to the 2 transistors that you took a chance on don't you?

author: neo
author_rank: Super Contributor
timestamp: December 04, 2017, 10:19:57 pm
content: Quote from: Specmaster on December 04, 2017, 10:15:06 pmThe only one i didn't replace is Q8, turned out i was smart and replaced all 2n3053's.I fail to see how the voltage could become 10X what it was.

author: neo
author_rank: Super Contributor
timestamp: December 05, 2017, 04:04:10 am
content: Well the thought occurs to me in hindsight, after properly kicking myself for my mistake, is that i at least found the root of all problems, the power supply is completely FUBARepair

author: neo
author_rank: Super Contributor
timestamp: December 05, 2017, 04:31:39 am
content: The furthest right digits on this meter are the two i tested and they both look fine so the rest of the display probably works.One, not so small, problem, the board pretty much disintegrated when i touched it. So unless i get creative or have a new board made i am more or less screwed.I'm probably just awful at de-soldering but it seems as it the circuit boards in this thing are particularly weak and prone to being destroyed

author: Specmaster
author_rank: Super Contributor
timestamp: December 05, 2017, 09:18:56 am
content: Quote from: neo on December 05, 2017, 04:31:39 amOr of course have they been fried?

author: neo
author_rank: Super Contributor
timestamp: December 05, 2017, 04:21:17 pm
content: The two nixies i got out say the others will be fine, though the problem is they won't go back in unless i get creative because of damage to the board.

author: neo
author_rank: Super Contributor
timestamp: December 05, 2017, 10:59:45 pm
content: All transistors and capacitors replaced, its back into somewhat normal operation but now it's even more screwed up, just a different kind of screwed.+200V = + 104V stable+18V = + 5.42V stable-18V = -31.42V stable+5V = + 4.35V stableSo, it's completely lost it's mind but hey at least it's stable!It's down 2 digits that i took out to check how bad the damage was, turns out no damage but i cannot easily add them back. Due to damage, my fault.EDIT: I also measured ripple,+ 5V, less than a quarter mV RMS- 18V, 100mV RMS+ 18V, less than a quarter mV RMS+200V, 200mV RMS.

author: Specmaster
author_rank: Super Contributor
timestamp: December 05, 2017, 11:23:20 pm
content: Quote from: neo on December 05, 2017, 10:59:45 pmHmm, so its getting a bit better, so the only other thing its now pointing directly at is UI and U2, the 2 voltage regulators on the 18Vrails, 1 on the +ve rail and the other on the -ve rail. If you add up the +5.42v and the -31.42v you actually get 36.84v and it states in the manual if you remember that the +200v and the +5v rails are referenced to the 18v rails.Is this with the other cards in or out of circuit?

author: Specmaster
author_rank: Super Contributor
timestamp: December 05, 2017, 11:24:59 pm
content: Oh, I forgot, what's the temperatures like on the transistors now?

author: neo
author_rank: Super Contributor
timestamp: December 05, 2017, 11:25:42 pm
content: With the power supply card completely removed from everything except the transformer.

author: neo
author_rank: Super Contributor
timestamp: December 05, 2017, 11:27:19 pm
content: Transistors are cool, and at this point shouldn't the resistors that are way out of spec be of the slightest concern?

author: Specmaster
author_rank: Super Contributor
timestamp: December 05, 2017, 11:27:55 pm
content: Can you track the data on the regulators U1 and U2 if you can find their part number?

author: neo
author_rank: Super Contributor
timestamp: December 05, 2017, 11:32:56 pm
content: LM301A, in this format they are rare and expensive. I'd have to buy 13 at once for $25.

author: Specmaster
author_rank: Super Contributor
timestamp: December 06, 2017, 12:15:54 am
content: Quote from: neo on December 05, 2017, 11:32:56 pmIts because the form factor has changed to DIP8 which are much cheaper but you'd have to come up with an interface to make it fit.https://www.digikey.co.uk/products/en/integrated-circuits-ics/linear-amplifiers-instrumentation-op-amps-buffer-amps/687?k=lm301Ahttps://www.mouser.co.uk/Search/Refine.aspx?Keyword=LM301ABoth of these have the round ones in stock but are costly as you said.With regard to the resistors I can't really see these making that much difference but if you have some there you could swap them out and just see if they do alter anything, even if you use a couple pots for the temporary trial.Checking your list against the stated tolerances in your list the ones that fall outside of the tolerances arespec Val Actual Max value + tol5% 5.6k 6.022k 5.88k5% 220k 244.6k 231k5% 5.6k 6.115k 5.88k5% 51 57.12 53.555% 51 54.86 53.55Can you find a spec sheet for the LM301A and see what the typical voltage on pin 3 is? On the +18v rail there is a connection from pin 3 to Power Supply Ref.

author: neo
author_rank: Super Contributor
timestamp: December 06, 2017, 12:22:04 am
content: I have to admit when it comes to OP-amps i don't have the slightest idea what i am doing.

author: Specmaster
author_rank: Super Contributor
timestamp: December 06, 2017, 12:26:24 am
content: Found you another supplier for the LM301A, much much cheaper and in lots of 4 matched units here is the link.https://www.ebay.co.uk/itm/4-Pcs-matched-National-Semiconductor-LM101AH-LM201AH-LM301AH-MIL-SPEC/322330297685andhttps://www.ebay.co.uk/itm/Integrated-Circuit-HP-1820-0223-LM301AH-GOLD-PIN-M1-HP-3/253216886787Plus also looking at the pins on these, they would appear to arranged in 2 rows of 4, so it could be that a DIP8 package might be interchangeable with them and thus a fraction of the price as these seem to really cheap.

author: neo
author_rank: Super Contributor
timestamp: December 06, 2017, 12:29:57 am
content: Mine use a circular foot print. DIP might could be mangled to fit if the pin arrangement is right

author: Specmaster
author_rank: Super Contributor
timestamp: December 06, 2017, 12:33:35 am
content: Still be able use them I think, just reform the leads into a circular pattern?

author: neo
author_rank: Super Contributor
timestamp: December 06, 2017, 12:41:29 am
content: Quote from: Specmaster on December 06, 2017, 12:33:35 amOnly if the pin arrangement is right, definitely worth checking

author: Specmaster
author_rank: Super Contributor
timestamp: December 06, 2017, 12:53:17 am
content: Of course, but an alternative could to get some DIP8 sockets and solder these in using resistor or capacitor tails to form extensions to the legs of the socket in such a fashion that they can be neatly formed into a circle and soldered in and then the new chips carely inserted into the sockets. Thats way even if the pins are in a different arrangement, the leads can be made long enough and if need be, insulated with heat shrink to get them in the correct order to match your pcb?Like you I don't really understand much about OP Amps, but in this situation we don't need to because we are not designing this from scratch, simply trying to effect a repair and that is done, just as we are here in many cases by replacing bits until the smoking gun is found. This is also only necessary as there is no obvious culprit here, nothing has been fried to a crisp, nothing has spilled its guts out etc.

author: neo
author_rank: Super Contributor
timestamp: December 06, 2017, 12:57:43 am
content: I could do that, but only if the leads wouldn't overlap.For good measure i replaced the diodes and the new voltage values are100V settling to 99, adverse reaction5.4V in place of 18V-31.75V in place of -18V4.42 in place of 5V

author: neo
author_rank: Super Contributor
timestamp: December 06, 2017, 01:01:08 am
content: Good news, arrow has the op-amp for only 5 bucks in metal can, i assume LM301AH is acceptable to replace LM301A.

author: Specmaster
author_rank: Super Contributor
timestamp: December 06, 2017, 01:03:28 am
content: The pins are in the same order and so will not cross over, I down loaded a datasheet from Digikey but the file size is too big to post here. but the dip8 pins etc are the same as the round package and so will be less expensive by far even with mounting sockets on stilts.

author: neo
author_rank: Super Contributor
timestamp: December 06, 2017, 01:09:07 am
content: Here are the contenders,DIP, 2 parts with sockets 5 bucks and a fair bit of a work.TO , 2 parts 10 bucks, no excess work and qualifies my order for free overnight shipping.

author: Specmaster
author_rank: Super Contributor
timestamp: December 06, 2017, 01:13:54 am
content: Quote from: neo on December 06, 2017, 01:09:07 amThats a call for you to make is that, now heres another, it seems that you have another 2 choices here, you could also use either LM101A or LM201A as there are effectively the same as the LM301A but have higher tolerances, pull down a datasheet from Digikey (its Texas Instruments one) its 24 pages long. Suddenly the world looks a bit brighter eh?

author: neo
author_rank: Super Contributor
timestamp: December 06, 2017, 02:06:26 am
content: So if were going down the replace everything path then what do i do when the only thing left to replace is the board itself?

author: Specmaster
author_rank: Super Contributor
timestamp: December 06, 2017, 02:12:11 am
content: The board is not the problem here, it cannot regulate the voltages can it? It could have a short though but that would not give you 400v. The other option you have is to wait till your other 8400A arrives and swap the power supply over from that one, assuming it's ok that is.

author: neo
author_rank: Super Contributor
timestamp: December 06, 2017, 02:22:51 am
content: Quote from: Specmaster on December 06, 2017, 02:12:11 amLet me rephrase this to be entirely clear.What do we do when there is nothing left to replace?EDIT, To add: I think i found a removed the cause of the major problem when i replaced the last transistor.

author: Specmaster
author_rank: Super Contributor
timestamp: December 06, 2017, 03:15:07 am
content: So you have replaced yet another transistor then, since the ones you did yesterday when you got 400V, yes?Well lets hope so then if you think that was the cause, still be inclined to replace the OP amps incase they have been damaged by the strange and abnormal events that the PSU has been having.To answer your question about what if, if everything is replaced and there is no improvement then, we shall need other peoples involvement on the remaining circuitry as that is way out of my comfort zone then. What I would do if it was mine is to carefully and methodically lift a leg of each discrete component on each board and check it for value and ESR etc and if found to be OK resolder the leg and move on to the next part until I had covered every discrete part on the boards and then evaluate again.Unless of course the service manual says otherwise, if it shows TP and voltages and trace patterns that should be present, then I'd check for them as stated in the manual. Its a long slow process of test and replace anything that is miles out of spec. I know of no other way unless I had a parts mule, in which case swapping out suspect cards one at a time is an option, but problem, is of course, you have no idea if the other cards are in working order til you try them.

author: Specmaster
author_rank: Super Contributor
timestamp: December 06, 2017, 03:59:15 pm
content: Here is a link to the other LCR meter I was referring to earlier, so I have one of these and also one of the ones that your ordered as well which I tend to use for a quick and dirty test although it is reasonably accurate especially when it's low cost taken into consideration. This one in the video however just blows it away and has results more in line with a professional piece of kit.https://youtu.be/rMFpWbLVTHo

author: neo
author_rank: Super Contributor
timestamp: December 10, 2017, 10:05:48 pm
content: I got one working, pot is a bit scratchy so i'll contact clean it, now to the buttons, a keycap is missing, i can borrow that from the other one. Some are sticky feeling and don't actuate well. As for the sticky ones, contact cleaner and perhaps a bit of sewing machine oil if their stubborn?Regardless, it is almost dead on it, reads 1.216 as 1.213, thats as far as i tested it.

author: Specmaster
author_rank: Super Contributor
timestamp: December 10, 2017, 10:07:21 pm
content: Great news

author: Cubdriver
author_rank: Unknown
timestamp: December 10, 2017, 10:49:42 pm
content: Excellent news!!!! Congrats, neo!-Pat

author: neo
author_rank: Super Contributor
timestamp: December 11, 2017, 12:36:03 am
content: I was able to install the DOU, RCU, and ohms converter, i'm still figuring out the wiring from the ohm's converter however. I have not tried the external dc reference board, the reason is that i don't have a external reference and it is a lot of work to install. Not a drop in part unless it came with an external reference card from the factory.Also going over this thing again i notice alot of tantalums, after what they did to my 8800A i'm going to replace them all.If tants from the 80's are scary, then what are tants from the 70's? Terrifying?

author: neo
author_rank: Super Contributor
timestamp: December 11, 2017, 12:38:28 am
content: Also i'm wondering if the lack of an AC RMS converter means it will measure true peak to peak voltage? it would be quite useful if it does.

author: Specmaster
author_rank: Super Contributor
timestamp: December 11, 2017, 12:44:31 am
content: Quote from: neo on December 11, 2017, 12:38:28 amNot sure, it might just default to a pseudo RMS or average value?

author: Cubdriver
author_rank: Unknown
timestamp: December 11, 2017, 12:50:05 am
content: Quote from: neo on December 11, 2017, 12:38:28 amMy understanding is that RMS converters allow the meter to measure the RMS value of non-sinusoidal waveforms, and that AC meters that do not have them basically rectify the AC and measure the resultant DC average and apply a correction factor to get the AC RMS value. The caveat with this method is that it 'assumes' that the AC being measured is sinusoidal - if it is not, the displayed voltage will not be the actual RMS value of the input wave.If you only measure sine waves, then true RMS is not needed. If you want to measure AC that's not a straight sine wave (such as the output of a triac type controller that gates the AC on at mid cycle), then the results will be inaccurate.https://en.wikipedia.org/wiki/True_RMS_converter-Pat