from Tim P (UK)
Having another go at fixing my 5116 - the one that burns the 5.1 ohm
'sacrificial' resistor on the HV board. Naive question - am I right to
assume the LVPS needs loading before it will regulate ? Like having the
boards connected and plug-ins installed? All voltages except the +5V are
off spec:
+200V is +225V, +30V is +37, -30V is -34V and won't adjust.
I still suspect the HV board but, as is oft repeated here, first check LVPS
Its the version with the row of fuses, as in the 5111A.
many thanks
Tim

Hi Tim,

The 200V is unregulated so 225V should be ok if unloaded.
As for the +30V, -30V, and +5V they should regulate even without load.
Can you basically disconnect everything from the LVPS and check?
Start the debugging with the -30V as it is independent with the other low voltages.

Best regards,

The + and - 30 Supply have current-sharing resistors across the pass transistors, so the supplies will not regulate without a load. R841 and R861

--
Bob Haas

Ok, my bad. I thought it was the usual voltage divider feedback, and these resistors were for current limiting purpose.