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2245 in protection

Good morning guys: Thanks for all your help yesterday. Cold as hell here, so a good day to take the rt.ch. board out again, for testing. Not really looking forward to that, but maybe I'll learn something. I'll get to that in a little while, unless anyone has thought of anything else before I disable it.
 
Theres a new development. I don't know what the implications are, will await your comments.
Sometime/somewhere I must have lost the mica insulator between the leads and heat sink shown in the attached pic. I am sure that this was lost last year when I removed the heat sink to inspect the board because when I removed the lead this time the heatsink was clean and dry (no thermal compound). This means that all test numbers in this thread were taken with the lead against the metal heatsink. The left ch. mica is still in place.
 

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Thanks Pete!
BTW I noticed your location your location UK (in the middle). I was stationed in the Midlands (between Huntingtonshire and Peterborough) back in 65 thru67. Have a lot of great memories of my time in your country, would love to come back sometime!!
 
The HFE on H755 measures 087. When first inserting the legs into the meter it read 088 and remained there for 10 nsec. or so then dropped to 087 and stayed there. Good or Bad or inconclusive??
 
Testing transistors involves diode tests, not HFE. Check this thread for understanding:

http://www.audiokarma.org/forums/showthread.php?t=43186

As for that other transistor, I do not believe the back case is live- the only reason to use a mica would be to insulate the case, I think you are good. I'm wondering if a bad cap is causing this issue. It's too bad the schematic doesn't show voltages.
 
Thanks Brad: I'll read your link and see if I can figure it out. Is there anything else I can use to insulate (other than mica) I'll look online to see if I can source mica. I guess now is a good time to recap "?". I was of the understanding that it was best to get it operating before recapping. Guess that doesn't hold true if a cap is keeping it from working.
 
Did a dide test on H755: I got .676v on initial test, no reading on the reverse and other 2 readings involving the collector (can't remember what it's called)
My opinion is that H755 is ok. Correct me if you think I didn't test it right.
 
i still think the problem is a resistor such as r760 10k r764 5.1k . r766 270 ohm r755 22k . etc
r762 trimmer 2.2k
zener diodes h762 h763


cant see any marked as fuse resistors though so i could be wrong .
 
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