Author Topic: #51 Fluke 8520A How far does this rabbit hole go? Part 1  (Read 1796 times)

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Offline The Radio Shop

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#51 Fluke 8520A How far does this rabbit hole go? Part 1
« on: May 15, 2016, 08:26:52 PM »
#51 Fluke 8520A How far does this rabbit hole go? Part 1

In part 1of this video we tackle a few tantalum capacitors that has gone dead short. We also have to replace a faulty LM340T-12 regulator after checking the voltage rails. Just how many problems does this "Working EBay Find" have?
 I am at a stand still till I do more research...




https://www.youtube.com/watch?v=ULQroWJUZdw
Fluke 8520A service manual:
http://assets.fluke.com/manuals/8520A___smeng0100.pdf


In the first picture we have to replave C238 due it is shorted. We also had to replace R256 and 257





Here we finf C450 is also shorted. This was dragging the +15 volt rail down.




We find that U704 has a dead short from input to output. This is a LM340T-12





When you boot the 8520A on it is showing a voltage on the display. This should show"000"



If you hit 2-wire or 4-wire to test the Ohm setting you will get Error 1. This means high voltage when selecting ohms scale




After repairing the voltage rails we still have the error 1. But if you pull J19 we get no errors. But ofcourse the meter does not function.



And again with J19 removed we can go into ohms mode.



So with J19 removed the error goes away. The unit does not function but it looks like we are closer to the problem.
We still have to trouble shoot error code 01.
Err01 HV - High voltage present with ohms function selected.
Buddy kc4umo

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Re: #51 Fluke 8520A How far does this rabbit hole go? Part 1
« Reply #1 on: May 15, 2016, 09:04:34 PM »
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Re: #51 Fluke 8520A How far does this rabbit hole go? Part 1
« Reply #2 on: January 27, 2020, 09:26:50 PM »
Your first video is reassuring for my new project to debug an 8520A - eBay description, "works great" is not what arrived. Passes self-tests, but does not measure DC/AC/resistance. I do get a small non-zero voltage read-out with nothing connects, and note your comment to suspect something shorting that allows an internal voltage to be read.  I now have all the (three) manuals, just need to patiently work through the detail tests for specific circuits and see what comes up. 

I do see on my example that resistors R256 and R257, although no sign of distress/replacement, are mounted off the board like in your unit.

2/1/2020 update - received 20 pin EDAC 516 series receptacle and wiring pins to allow rear signal inputs.  Unit reads correct DC, AC volts, resistance from rear panel but not front panel.  Wiggling switch got a little erratic front panel action, but never correct values. Tracked down the cross-over switch as Schadow TA8UEE / F8UEE 8 Pole 8PDT Standard Size Latching Switch, findable on the eBay and now on order...