Fluke 8600A Problems, teardown and analysis

[xchg.ca]

Hi guys,

I got this cheap of ebay, in somewhat working order.
But it has weird behavior illustrated in my video - http://youtu.be/ZHNbfLao69Q
After all I decided to open it, at look what might be a problem. Inside I discovered a bonus - DOU board ! Some kind of ancient data interface, grandpa of GPIB probably
I took it all apart, There few bodges as well, but I see nothing obviously wrong with it inside. I can only guess that some caps are getting old and bad.

OHM metering drift a lot by the way, either up - continually increasing resistance or down (very rare). If you measure the same resistor in 2 minutes it will have different resistance, in another 2 minutes - different again ! and so on, sometime if you leave it like that, it eventually hits the range limit!!! (200OHm range for example)

Illustrations are in this public Picasa album - https://plus.google.com/photos/103976720797990893155/albums/6066763873477207585

If you guys already observed similar problems with multimeter of this kind, please give me advise, I will be in the mean time checking all caps

[ModemHead]

First off, don't worry about the display wandering around in the lowest two ranges.  The 200mV and 2V ranges have an input impedance over 1Gig, so the input will pick up a random charge when the leads are open.  20V and above ranges are the standard 10Meg input impedance, and should zero out with no input.

It's old, so do the easy stuff first, you might get lucky.  Disassemble and clean the circuit boards with IPA and a brush.  Re-seat the socketed chips.  Pull the daughter boards up and off, clean them too and re-seat.

I have a couple of these units. Fortunately they only needed simple repairs to get going, so I never studied the circuit that closely.  But I do know the ranging is done with relays, one big one over to the left side, and some reed relays on the daughter boards.  Perhaps one has sticky contacts?

[xchg.ca]

Thank you for reply, I stared doing what you suggested and when I pulled relay I noticed something, pictures attached, first of all - take a look at broken connection from the terminal to the PCB, so Amp measurements were just impossible! Have to check where it suppose to go, also this is teeny-tiny wire, this DMM is only works up to 2A, but still it is too this for my liming!
One more thing it distance between V+ and V- Terminal... 5-6mm.... it is a bit too close for my liking as well, will definitely add insulation.

[xchg.ca]

Fixed it, apparently black terminal wire for mA was completely yanked from the board and another black terminal was holding on a thread, so that is why such intermittent measurement, also tap for front panel was broken. I re-solder everything properly, and then manufactured new tap, glued it on top of broken one. Now it looks good and measures better ! Still have to test current settings.

BTW. My revision of my Fluke 8600A use single chip solution for +/-15V instead of separate regulators....

[ModemHead]

Good work!  Yes those front-panel connections are a pain, later portable models like the 8010A and 8050A had a better design in that respect.

[Gertjan]

Hello,

I also recently found and restored a Fluke 8600A
When compared to my 8000A I noticed that the 8000A has a screening plate on the underside of the PCB, but my 8600A does not. (see Photo)
The 8000A screening plate fits perfectly under the 8600A

So now I am wondering: does the 8600A not have this screening plate, or has my sample lost his somewhere during the last forty years?

Thanks, Gertjan

[ModemHead]

None of my 8600As have the shield plate.

[Gertjan]

Thanks ModemHead!

Of course, in the 8000A all the signal switching is done with the front-panel switches.
On the 8600A the signal switching is done with reed-relays in situ.
I figured that could be the reason that on the 8600A the shielding is not necessary.

Regards, Gertjan