Posted as I PMed it to a friend. This is most of the stuff you check if its NOT a passbank transistor and your overcurrent relay still trips when you press start: assumes you have the current turned down to below overcurrent trip when you press start:

control card or the two passbank driver transistors. In rare cases the line rectifer diodes on the heat sink. A few other possibles that rarely occur, including a bad emitter resistor in some emitter lead on the passbank or the filter cap is half dead. Assuming hes not in light mode: Since he already did the resistive passbank check per lexel:

Assuming its a straight 88D and not a zeiss swithcer

5 usual possibles on the control card

1 bad opamp

2. bad control zener string. ie the plus 30, +15, -15, 6.2 V thing.

3. bad transistor on the control card

4. bad voltage inverter circuit on the control card.

5. the motorola transistors they use on the cc are leaky to begin with, and they get real leaky over time.

control cards are best tested by applying 30V dc current limited to 100 mA to the cards +V input and checking for the voltages at the test points marked on the back of the card, voltages should be +- 5%

You then test all the card transistors with a LBT
or something else that rams a large current through the npns and pnps and shows reverse leakage as well as gain. I personally use a heathkit curve tracer at home and the LBT in the field. Ohm meter transistor testers are a joke as they dont source current.

you then just replace the opamp

next step, 2n3772 on the passbank, unsolder it and lbt it. resolder if it checks out
then the little guy next to it, unsolder, test and resolder.

check the diode in the driver circuit on the passbank next

check the 2 ohm emitter resistors and the sum buss resistors

look for case to passbank shorts

if that doesnt do it, look at the power rectifer diodes (must unsolder one at a time to truely test) The filter cap, the passbank protect zener (apply 90V current limited to 10 ma, check for zener action, if checking with a ohm meter should appear as a silicon diode when reversed.)

Then unsolder each ^%$# passbank transistor and check for reverse leakage with LBT or curve tracer.

If he mails me the control card and return postage, I usually charge XX$ to fix em and toss em back in the mail.

Does he have a schematic??????????