Help! No +48v!

[jdurango]

I have a console with a 48v phantom supply (linear Power One HB48). I'm getting 76v between the pos and neg outputs. I have schems, but they aren't marked with any voltages or values of circuit components, which makes troubleshooting a PITA. I'm not even sure what to use as a "0 volt" reference to make measurements by.

Tried:
- New LM723 @ U1
- New 3771 voltage reg @ Q1 (original was 3773, I believe 3771 is a higher power version of the 3773 but honestly I might be missing something on the data sheets)
- New 2222 transistor @ Q2
- Checked all diodes (all good)
- Checked a handful of possible resistor culprits.
- Adjusting output voltage with trim pot, no effect at all, voltage stays pretty steady @ 76v even though trim pot varies resistance between in/out as pot is turned.
- Transformer SEEMS good, (no shorts between primary and secondary) and secondary output voltages seem intuitive, but again, schems aren't marked, so I'm not sure what they're supposed to be.
- All caps are new. All values for capacitance and voltage ratings were roughly doubled from stock.

I'm running out of ideas. Please help! Only schem I have is attached hereto. Thanks fellas!

 

[gridcurrent]

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[Walrus]

Although the 2N3771 is higher current, it is *much* lower voltage. You should definitely use the 2N3773 or correct equivalent!

 

[jdurango]

Thanks fellas! And thanks for the more detailed schems! I've got 3773's on order. I have a feeling that's the culprit. Honestly not sure what else it could possibly be, and I've already shotgunned more parts than I would've liked. Thanks again!

 

[jdurango]

3773 didn't do it. I give up....maybe the xformer is fried? Not sure what voltages are supposed to be on secondaries, but voltage to VR seems high (76v) for a 48v supply, so I have a feeling that's the issue. Ordered a NOS HB48 on the bay for $50. Much better than "investing" more time in this old thing! Plus I'll have some spare parts now! Thanks fellas!