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Old 17th Sep 2021, 5:30 am   #25
Diabolical Artificer
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Join Date: Jul 2009
Location: Sleaford, Lincs. UK.
Posts: 6,223
Default Re: Carlsboro Cobra 1100 repair.

Progress though I reckon you'e not quite out of the woods yet. So, the 7915 is dead. The pinout on these is different to the 7815. The 7815 goes IP, GND, OP, the 7915 goes GND, IP, OP. They often fail but what damage has it caused downstream. As we have no schematic to guide us I'd start buzzing the PCB out. That means one probe on the -15v 7915 OP or output pin then the other probe to all PNP type small signal Q's. When you get a beep or a reading check the tranny, might be toast.

What is the voltage going into the 7915? It should be only a few volts, which you wouldn't think would cause much trouble but the designers/makers might have been silly and it could be a lot more. There might be a dropping resistor somewhere that's failed dropping 35v say (or 50v! I've seen 80v rails and a dropping R and a poor LM78/79 at the end) down prior to the 7915, worth a look and check.

Andy.
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