Fluke 8400A; No display.

[Specmaster]

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.

I 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

[neo]

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.

[neo]

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 it

EDIT: 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.

[neo]

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.

[Specmaster]

Good work, did you get that manual in the end?

[neo]

Good work, did you get that manual in the end?

Yes 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.

[Specmaster]

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. 

[neo]

Only small problem is i do not have a extender card, so it may or may not be possible to do that.

[neo]

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.

[Specmaster]

Oh, of course I expect your cards are like these in my 8505A are they?

[Specmaster]

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.

Yes, that is the only way to ensure that the IC's are being fed without having access to an expansion lead.

[neo]

Oh, of course I expect your cards are like these in my 8505A are they?

They are similar though mine is slightly more basic.

[Specmaster]

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 

[petepdx]

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

[neo]

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 -    5.017V


Voltage testing done with RCU in.

(removed and reposted for correction)

[neo]

Well there's part of your problem and may even be all of your problem right there, the HV is out of spec and is fluctuating and the fact that putting test meter on it makes it work a bit, suggests that you do infact have a problem with the HT side of your power supply. Is it a SMPS or a linear one and are you using a DMM or an analogue meter?

This 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.

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

Actually i have bought the manual from them, i will admit the copyright isn't invasive and they did a good job of digitizing it.

[Specmaster]

Well there's part of your problem and may even be all of your problem right there, the HV is out of spec and is fluctuating and the fact that putting test meter on it makes it work a bit, suggests that you do infact have a problem with the HT side of your power supply. Is it a SMPS or a linear one and are you using a DMM or an analogue meter?

This 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.

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

Actually i have bought the manual from them, i will admit the copyright isn't invasive and they did a good job of digitizing it.

Yes 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.

[neo]

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?

[Specmaster]

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.

You 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.

[neo]

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/121593935597 the one i was looking at.

[Specmaster]

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.

[neo]

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.

[Specmaster]

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. 

[Specmaster]

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.

The fact that it drops after a bit does look like either an overload which gets worse when it warms up or leaky caps.

[neo]

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.