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Carver TFM-15 assistance needed

Half Life

Half Life

New Member
I recently came across a Carver TFM-15 in the local Goodwill store for $10. Got the unit home and opened it up. Did not see any evidence of any burnt components. Plugged the unit in and no meter lights, no relay click, nothing. Did some reading on the Interwebs and decided to recap the unit to start. Also cleaned up the solder connections on the outputs.

Plugged the unit back in and now have lights and relay click. Unfortunately now have +50VDC on the outputs. The schematic I have is a copy of a copy of a copy and is difficult to read. I would welcome any assistance to point me in the right direction.
 
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UPDATE

Further troubleshooting led me to D701, 22V Zener. Had 50V on the cathode side and 48V on the anode side. The anode is supposed to be tied to ground. Jumpered the anode to ground and the 50VDC on the outputs all but disappeared. Traced the ground path out and found that it comes through J001, then to the chassis. Turns out the trace on J001 where the left and right input grounds are tied together was lifted and broken. I drilled and set two eyelets into the trace (with a little epoxy underneath the trace to adhere it to the pcb) for the two ground wires.

Now the L side DC Offset is reading 13mV and the R side DC Offset is reading 146mV. Have not checked or set the Idling current until I can solve the R side DC Offset error.
 
Check or swap the differential pair transistors. Search a recent thread where I suggested the same with picts attached
 
Thanks for the pointer! I was going to look into those transistors and had placed an order for replacements from Mouser. If that doesn't get me where I want to be then I'll add some resistance to bring the off set down.

By the way, I see you're in BA. Spent about 7 months in Resistencia working for CTI, building cell sites in and around Chaco and Formosa. This was during the mid-90's.
 
You've been in the jungle !! I never been there, but I know it's a very hot whether and a lot of wild forest and nature up there. Chaco is known because some o the larger meteorites fallen on the planet were found there. (out of topic : https://en.wikipedia.org/wiki/Campo_del_Cielo )

Matching the transistors, and swapping some pairs should correct the offset.
 
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