Fluke 5200A repair (?)

[bdunham7]

I've read - and still do - that page spec differently - I assumed there's a built-in attenuation doing that linear decrease in output to the 8.33 at 1MHz. The OL actually kicks in most of the time in that part of the range, though not all of the time.

I assume you mean this figure?  I'd think it's clear they don't specify it for over 10⁷ V-Hz.  Your seems to produce 10X that on demand, but that can't be good.  I didn't catch that before, but you have to watch the meter input rating as well as 100V_RMS @ 1MHz is beyond the limits of most meters.

[Rax]

I assume you mean this figure?  I'd think it's clear they don't specify it for over 10⁷ V-Hz. 

You're probably right, but that's not how I read it during the RTFM process. I think the protection circuit provisions for this, but not sufficiently. I think Bill is right, they should have provided something on the controls side of things. On his observation 200kHz is stable on his unit - note p. 4-11 (table 4-7) sets the voltage for 60V @ 200kHz for a verification step - so they factored in stability mid way through that slope by design. But admittedly, my unit is stable much above that (I am leaning on assuming my protection circuit in a bit out of whack, actually), though I will not rely on it at those levels. Nor do I need do.

Your seems to produce 10X that on demand, but that can't be good.  I didn't catch that before, but you have to watch the meter input rating as well as 100V_RMS @ 1MHz is beyond the limits of most meters.

I guess I was too absorbed by testing the unit in all ranges (and couldn't believe it can output 100V at 1MHz!... so I really had to test its limits and determine the causes of instability - I thought - to trigger the OL actuation; other than design!) to really be mindful of the meters I expose to this stimulus...
At any rate, no meter has been damaged in the making of this hectic story.

[TheDefpom]

I did a 19 part repair series on one of these, every single board had faults.

[tridac]

Still going through that saga on mine, though most functions and levels now work. What faults did you find on the boards, and did you document it as it progressed ?...

[Rax]

I did a 19 part repair series on one of these, every single board had faults.

Interestingly, the first thing showing up in your video is loose parts inside. When mine arrived, there was at least a screw bouncing around inside. Upon opening the case and shields, I noticed there were more screws missing than present. For this unit, I think that's a major structural issue. Luckily, the packing job was fantastic so it traveled safely and there was no damage.

This far, I've found no real issue with the unit as far as I could tell.  I still have to really dive inside, but basic functionality is OK. May need to do more detailed checks to determine all that may be going on.

Well, I put that there too fast. As soon as I did it, I walked to the unit and turned it on. Which reminded me that, as opposed to what should happen (I think), the OVERLOAD LED doesn't come on (mind you, it does in an actual OL condition) for a bunch of seconds. What does happen is the STDBY/OPER LEDs both stay off for about a matching length of time (meaning, what I'd expect the OVERLOAD light to be on during startup), then STDBY comes on and I need to switch it over to OPER to get signal out. Really, more of a nuisance than anything (it seems to have no impact on any relevant functions of the unit), and the OVERLOAD light does come on when actually needed.

Also, the actuation of OVERLOAD during regular operation has not occurred for many days now. I'll assume it was more of a case where the unit needed be run for a while after sitting mostly in storage, and/or some learning curve of its controls and regime by yours truly.

A couple of questions on the issue still outstanding:

• Can anyone confirm this is not expected behavior? The non-lit OVERLOAD at startup, that is.
• Any initial assumptions what could be causing it? If this is not expected behavior, what's puzzling me to is why it's working correctly in an actual overload condition but not at startup. I likely have to investigate how those two different conditions are designed to actuate the LED

Thanks!

[TheDefpom]

Here is the playlist:

Fluke 5200A AC Calibrator Repair
https://www.youtube.com/playlist?list=PL2z3V9RkHQE0pdgzjmzo3Oa11TdnvxtE5

[Rax]

Here is the playlist:

Fluke 5200A AC Calibrator Repair
https://www.youtube.com/playlist?list=PL2z3V9RkHQE0pdgzjmzo3Oa11TdnvxtE5

I've had the opportunity to scratch about .1% of the whole thing (awesome stuff, btw), and I wasn't able to identify a specific video where the sequence is being confirmed. I could use a confirmation if anyone has a chance.

[Bill158]

A couple of questions on the issue still outstanding:

• Can anyone confirm this is not expected behavior? The non-lit OVERLOAD at startup, that is.
• Any initial assumptions what could be causing it? If this is not expected behavior, what's puzzling me to is why it's working correctly in an actual overload condition but not at startup. I likely have to investigate how those two different conditions are designed to actuate the LED

Thanks!

First read page 2-9 of the manual right hand side of page if you haven't already done so.
Mine flashes the "overload" light on during "power on" for about 1 second, goes out briefly and then very briefly flashes again for maybe 0.1 second.  I see that the manual does say that this can occur, however in my case it is not the 5 - 10 seconds in the manual.  I would assume that this is mainly dependent upon how the various power supplies come up during power on.  Mine does take the required 30 seconds or so for the "Standby" light to come on as stated in the manual.
Bill

[tridac]

I had a look at some of videos, much later model, 1986,  than mine, which  has 1979 date codes internally. Thing is that the psu assembly can be first level verified with no other cards in the box. Verify the voltages are correct and even dummy load the rails to make sure. In particular, if the power amp is faulty, that can kill the psu board, so taking it an assembly at a time can save a lot of time and effort. Take all the mainbox boards out and check for shorted tants (yes, a lot of them :-). Get the psu right first, then put boards back one at a time, far left reference board first and verify the voltage looks ok. Then the rest, power cycle between each. Leave the power amp until last and set the slide switch to debug, as it can be checked for stability in that state. Also, the other parts of the system can be checked out by removing the power amp and fitting a jumper.  Buying a bad one can be a really bad idea, if you don't have at least one spares donor for card swaps and robbing for spare parts. Far more complex beast than it looks and there are loads of dependencies and gotchas for the unwary. Lot of volts as well...

[Rax]

First read page 2-9 of the manual right hand side of page if you haven't already done so.

Of course! That's how I had an inkling I should expect the "OVERLOAD LED on at startup" behavior in the first place. Not a case of "RTFM," quite the contrary. It's the first time I have one of these at my bench.

Mine flashes the "overload" light on during "power on" for about 1 second, goes out briefly and then very briefly flashes again for maybe 0.1 second.  I see that the manual does say that this can occur, however in my case it is not the 5 - 10 seconds in the manual.  I would assume that this is mainly dependent upon how the various power supplies come up during power on.  Mine does take the required 30 seconds or so for the "Standby" light to come on as stated in the manual.
Bill

Thank you, this is perfect. It confirms I don't need to expect the solid light on solidly for seconds at a time. I think my unit essentially behaves expectedly, at least it's definitely doing the 30s delay to STDBY.

[Martian Tech]

Mine flashes the "overload" light on during "power on" for about 1 second, goes out briefly and then very briefly flashes again for maybe 0.1 second.  I see that the manual does say that this can occur, however in my case it is not the 5 - 10 seconds in the manual.  I would assume that this is mainly dependent upon how the various power supplies come up during power on.  Mine does take the required 30 seconds or so for the "Standby" light to come on as stated in the manual.
Bill

Thank you, this is perfect. It confirms I don't need to expect the solid light on solidly for seconds at a time. I think my unit essentially behaves expectedly, at least it's definitely doing the 30s delay to STDBY.

FYI: Mine operates similarly, but the initial overload light is less than 1 second - probably about 1/10 second, and then I get 2 additional flashes (one at about the 1 second mark and the second around the 4 second mark).  But 30 seconds(-ish) to STDBY.

[Rax]

FYI: Mine operates similarly, but the initial overload light is less than 1 second - probably about 1/10 second, and then I get 2 additional flashes (one at about the 1 second mark and the second around the 4 second mark).  But 30 seconds(-ish) to STDBY.

Knowing what to watch for now, I'm noticing some very quick flickers (not occurring at every turn on), something similar to what you're describing (which I may have missed before). Like Bill, I am assuming this accounts for some transitory conditions triggered by the power supply rails while coming to stable operation.

I think all is well. Both issues that concerned me are clarified and not a concern... Thank you very much for your assistance with this.

My plan from this juncture is to continue observing its hopefully continued stable and - as far as I can tell, at least "loosely" - within calibration operation. If things stay fine, I am planning to check all boards for signs of stress such as leakages (caps), burned areas on the PCBs, etc. - maybe as soon as this weekend - likely recap what needs to be recapped, replace some/most power resistors that are carbon comp, then adjust the power supply rails. Then seek to adjust the bias/zero of some stages that seem to need it. It's very possible the unit may arrive closer to cal after that.

If still needed, I'll examine options for calibration at that juncture.

[Rax]

After a s#!%load of measurements with four meters - two of which having cal data attached - (I may try to attach that data here later) there's some indication the calibrator is pretty consistently high by about 400-600ppm or so.

I feel that it's entirely possible the PS adjustments and - more importantly - the zero and bias adjustments have a great chance to throw this back into specified tolerance.

[Rax]

Getting that second look inside underway, I looked again at this handle inside the PS cage that I am not sure what the purpose for is. Can anyone shed some light?

The only position I can have it in is diagonally as the picture shows it, but that's a little unsettling to me, as it's so close to the can of some caps in the PS. It doesn't seem to rotate enough to touch, but it doesn't seem to be particularly locked in place by anything (other than the U-shaped extrusion affixed to the top shield.

[Rax]

A couple of further work items:

• The loose parts sliding around inside the case were a couple of pieces of shattered plastic cable tie, and apparently a small screw... Still trying to figure where the latter belongs. Re-affixing the cable under the shield with new cable ties required detaching the bottom shield for access to the holes.
• The VOLTAGE RANGE switch's contact actuation was a bit "wobbly" and was triggering some flickering of the OVERLOAD light, and would sometimes jump ranges. Pretty perilous thing as far as the health of this thing goes (and instruments hooked up to it...). Some careful cleaning and application of Deoxit with a foam swab later, it's now sliding smoothly like a well oiled machine

[TheDefpom]

The handle in the PS cage holds the cards in, it presses against the end to push them into the slots, I had to cable tie mine in place so the cards didn't fall out, as mine is missing the internal cover.

[Rax]

The handle in the PS cage holds the cards in, it presses against the end to push them into the slots, I had to cable tie mine in place so the cards didn't fall out, as mine is missing the internal cover.

That makes perfect sense, thank you. Had I taken those cards out, this would have been apparent to me, but I had not done that this far (only the cards in the main compartment). A little clunky a system, isn't it?...

[Rax]

BTW, once I started populating all screws around the case, shields, and everything, it became kind of clear either why the screws were taken out, or that the screws not being in caused some pretty serious flexing and abuse to the unit (maybe during ground transit to me). The whole chassis is a bit wonky (not quite square everywhere), and some of the screws don't quite find their holes seamlessly, but after some whining and complaining and once in, it snaps.

It will feel good to have all this buttoned up and squared as it was meant to be.

[bdunham7]

BTW, once I started populating all screws around the case, shields, and everything, it became kind of clear either why the screws were taken out, or that the screws not being in caused some pretty serious flexing and abuse to the unit (maybe during ground transit to me). The whole chassis is a bit wonky (not quite square everywhere), and some of the screws don't quite find their holes seamlessly, but after some whining and complaining and once in, it snaps.

It will feel good to have all this buttoned up and squared as it was meant to be.

After working on a dozen or so of these various older Fluke monsters (and having a few to go) I feel that about half of the repair job is similar to doing auto body work.  Maybe someone could set up a mini frame and paint repair shop for electronic equipment.

[tridac]

That lever is to hold the psu boards in when the top lid is in place, stop them falling out with vibration. Also, use it to press the boards into their socket, which can be difficult otherwise. Might seem crude, but works..

Chris

[Rax]

After working on a dozen or so of these various older Fluke monsters (and having a few to go) I feel that about half of the repair job is similar to doing auto body work.  Maybe someone could set up a mini frame and paint repair shop for electronic equipment.

Seriously. In the case of this one here, after a handful of (different kinds of) screws (not kidding!) from a eclectic and unrestrained McMaster Carr order, it finally feels solid and chunky, like it could stand a... diagonal trip over the entire territory of the US! There were screws missing from more parts of it than I ever thought (before diving in and looking closer at some hidden parts...).

All in all, I'm am extremely happy and grateful camper (none of the above is a complaint to any stretch, quite the contrary). The unit works much better than I imagined, and the only thing I can fault it for is a slight out of cal output (about those 600ppm high). 

[tridac]

I know it's a heavy lump. but Fluke are good at lightweight aluminium consruction, with each chassis section a stressed member. They are actually quite rigid when all the panels are on and all the screws in and tight. Check by resting the unit on the back corners of the case, then lift one front corner and see how much it twists. As an engineer, quite respect that and the isolated internal chassis work...

[Rax]

I know it's a heavy lump. but Fluke are good at lightweight aluminium consruction, with each chassis section a stressed member. They are actually quite rigid when all the panels are on and all the screws in and tight. Check by resting the unit on the back corners of the case, then lift one front corner and see how much it twists. As an engineer, quite respect that and the isolated internal chassis work...

I agree. I think, if you compare it with the later units, it's a very eclectic mix of structural, functional, and esthetic solutions. But very solid once all together. And essentially all parts converge to the whole - meaning the shields fully screwed in will serve structural duty also.

As a matter of perspective, it's also quite interesting how rationalization occurred over time with the Fluke units - they became simpler, having fewer types of screws, etc. At least in my experience.

[Rax]

R40 and R46 replaced with Vishay Dale RS05 (5W WW) - solid as a granite slab. One of them was drifted by about 5%. Maybe not worrisome, except the other one was dead on and assuming same production batch, that's a bit off.

I also attempted to replace the electrolytic caps on A7, but hit the "desoldering brick wall of the massive ground plane" and decided to back off... I'll reassess later if they show serious signs of aging.

I also had a bit of a false flag (I think - after a good chunk of checking and double checking) where the third VOLTAGE switch would give me a persistent "4" on a "0" setting. Due to its intermittence, I assumed the switch may be faulty (not the logic circuitry), cleaned it up with Deoxit, and it seems to be behaving now. I'll keep an eye on it. I think all these will benefit from a serious switch reconditioning.

Third picture shows the resistors adjusted a bit to clear the "HV cage" - for heat and whatnot. Good sleep factor.

For now, I think this is possibly ready for adjustment...

[Rax]

I thought I'll be able to start adjustments tonight, but I am not sure I understand the Power Amplifier DC Zero Calibration (4-75, p.4-17). It mentions using an 887A etc., all sounding unnecessarily complicated - I assume the adjustment just makes sure there's zero DC on the output between OUTPUT HI and LO - is that right?

The instructions involve removing INT SENSE and whatnot and I'm not sure any of that is necessary.