Re: 50W Amp problem


Evan, et als.,
I have tested until I am cross-eyed.  From the schematic, pin 1 of the 78L05Z connects to one end of the 4.7 trim pot.  The other end is at ground.  The middle pin (the wiper pin) goes from dead short to ground at full anticlockwise to 2.02 k ohms at highest and back to short at full.  I think the pot is squirrelly and shot.  I also think the two IRF510s are also probably shot, because the gates are not working at all and pin 3 (source) shorts to ground, and I don't see that path on the schematic, except through C6 and C7 (which do not test as shorted.).
So, I will get my hands on a collection of 78L05Zs, IRF510s, proper winding wire, and 4.7k trim pots and rebuild the whole network from regulator through the power transistors.  Unless you have a better suggestion.

Thank you for your patience and great help.  I have learned a lot tracing all this down.

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