Electronics > Repair

Keithley DM6500 repair - error 1153

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BeamDump:
Was going over DCV measurements on a LED driver board, powered from AC source supply. Everything was what you'd expect, then DMM caused short on DUT and AC PSU went to OCP. Highest voltage on board is DC bus, 320V. Nothing the meter hasn't seen before. Both supply and DUT recovered no problem but DMM suffered error 1153. Looking inside, some analog power rails are down. Only 6VA = 10V.7V , 18VA = 22.8V and -18VA = -22.8V left, nothing on +5VA, -5VA, +15VA.

If i try switching measurement types, it gives communication error...

Anyone experienced this before?

gamerpaddy:
very unusual fault.

you still got warranty ?
if not, try to check the basics first
the regulators in and outputs.  if outputs are down, you might have a short somewhere. if inputs are down, rectifier or transformer issues.
when checking, look up the regulator part numbers if they require a enable pin.

the missing +-5V and +15v are required for it to work obviously.
the +-18v sitting at +-23v is a problem, its too much for most opamps.

BeamDump:
I found these notes from another user (attached), apparently he measured his +18/-18VA rails and it's the same reading as mine, so i assume no problem there...
Unit bough in 2020, so no warranty i think.
Transformer gives out all the voltages, rectification is present, caps are charged.
Only 3 linear regulator: LM317D2, LM337BD2T, MC7805CD2T
Will check them, so far haven't seen any Vout ot Vin from any of them.

Kleinstein:
The +-18 V and 6 V are likely unregulated, raw voltage to be regulated to 5 V and +-15 V.

The main suspect is a short somethere on the +15 V and some possibly odd problem on the +-5 V. The -5 V may need another voltage to work and may be rather low power. In the pictures there are only 3 somewhat power capable regulators and also not that many large filter capacitors. The -5 V may have a rather power max current.

With a short the regulator for the +15 V should get rather hot. If not this would more point to an issue with the regulator.

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