Scored a broken Fluke 8800A - Repair attempt

[halexa]

Got a Fluke 8800A for 50$ on an local auction site. The unit was sold as broken for parts, but maybe its something easy to fix.

At first inspection i notice the sense input jacks a broken off and that something is loose inside the unit. So before i power it on I do as Dave does and take it apart. Because of the risk that the loose thing maybe will damage the unit.

It turns out that the loose think was a 0.05uF 1kV disk cap (see picture). I have not checked the schematics yet but guessing it's for the input protection.

Everything else seems to be on place inside the unit at a quick inspection  so I tried to power it up - and it powers on but as expected the reading is off.

***To be continued

[halexa]

Checked the manual for the 8800A and found the location of the loose cap. Its C1 on the AC converter PCB. Did not have anything good at home as replacement for this cap. But placed an order on Ebay for a substitute and hopefully this will fix the bad reading issue.

If any one have a suggestion for a good substitute for the broken sense input jacks please let me know.

***To be continued.

[wiss]

The instrument will (should) work without the AC-converter.

[MCCSolutions]

Just needs calibration? 

[halexa]

Just needs calibration? 

Nope, somethings wrong with the unit.
I have gone through the error checking guide in the manual and I think a found a problem. Diode CR10 on the main board measure 0.5V in both directions.
This diode is an MDR300 forward reference diode. However I have not been able to find an replacement diode on the web yet.
If anyone out there know an available replacement diode please let me know. 

[MCCSolutions]

I mite, do you have a pic?

[wiss]

Be careful! The controller (the huge DIP) and the input pair are not replaceable (practically)! 

[MCCSolutions]

Checked the manual for the 8800A and found the location of the loose cap. Its C1 on the AC converter PCB. Did not have anything good at home as replacement for this cap. But placed an order on Ebay for a substitute and hopefully this will fix the bad reading issue.

If any one have a suggestion for a good substitute for the broken sense input jacks please let me know.

***To be continued.

Hey one of the fuses look blown!

[wiss]

Nope, somethings wrong with the unit.
I have gone through the error checking guide in the manual and I think a found a problem. Diode CR10 on the main board measure 0.5V in both directions.
This diode is an MDR300 forward reference diode. However I have not been able to find an replacement diode on the web yet.
If anyone out there know an available replacement diode please let me know.

It is there to set ~1.2 V over the emiter-resistor?
3 1n4148 should work?

[halexa]

Thx, I Will check that out. Found some more issues with the power rails that I need to sort out also.

[particleman]

I have that same meter my filter caps were bad now after a cal it works like a dream.

[halexa]

Yep, I suspect the filter caps to be bad since the -35V rail measuers -22V. I'm waiting for replacements caps, should be in the mail next week.
I also got a donor unit for a couple of bucks on E-bay today so I can replace the broken binding posts. And also replace the broken display segments have on my Fluke 1900A.

[particleman]

Thats funny in a few hours im picking another up too. I found one locally on a sale site.  Ill post some pics after I get it.

[halexa]

Sweet, we can stay in touch if we need to swap parts then.

[particleman]

Picked it up it seems right on (or really close) Has a small issue with the ohms. Last digit never settles but after I do the filter caps im betting it will. Also it has not been calibrated since 1985.

[halexa]

Success!

Got my donor unit today from the US. And new caps from Farnell.
Switched the broken binding post, the input cap and replaced the electrolyte caps and Bobs your uncle.

Compared the 8800A to my Fluke 8600A and they shows the same result in both DC and Ohms mode.

Picture 1: ~+10VDC
Picture 2: Donor unit