- Joined
- May 14, 2014
- Messages
- 2,287
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- Southwest Kootenays BC
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- No such things as bad days, just bad moments
If I may pick a brain or three,
This might be a basic "Electronics 101" question and the component make/modle may be irrelevant.
I've spent some time dabbling inside a free NAD 7225PE receiver. The power amp section has a problem. Both channels work and the volume it produces is equal on both sides. But the audio is quite distorted, again equally on both sides.
After following the service manual proceedure for adjusting bias - removing solder bridge and using designated test points, I saw that rotating the adjustment pots have no effect. The reading continued to show 0.0mv.
I've pulled some of the non-TO92 transistors to test out of circuit and so far all seem to be OK including the TO3 outputs. Which in this case are one pair per side of an MJ2955 and a 2N3055.
There has been previous work done. One channel's pair of output transistors have been replaced.
As I cleaned off the old thermal paste, I noticed that two of the insulating sleeves used to attach the TO3's have pieces broken off. Also that 2 of 4 mica insulators had cracks.
If the collector/case was shorted to ground, how would that manifest? Destruction of the transistor or distortion of audio?
The schematic is one channel of the receiver and the TO3's are Q415 and Q417.
This might be a basic "Electronics 101" question and the component make/modle may be irrelevant.
I've spent some time dabbling inside a free NAD 7225PE receiver. The power amp section has a problem. Both channels work and the volume it produces is equal on both sides. But the audio is quite distorted, again equally on both sides.
After following the service manual proceedure for adjusting bias - removing solder bridge and using designated test points, I saw that rotating the adjustment pots have no effect. The reading continued to show 0.0mv.
I've pulled some of the non-TO92 transistors to test out of circuit and so far all seem to be OK including the TO3 outputs. Which in this case are one pair per side of an MJ2955 and a 2N3055.
There has been previous work done. One channel's pair of output transistors have been replaced.
As I cleaned off the old thermal paste, I noticed that two of the insulating sleeves used to attach the TO3's have pieces broken off. Also that 2 of 4 mica insulators had cracks.
If the collector/case was shorted to ground, how would that manifest? Destruction of the transistor or distortion of audio?
The schematic is one channel of the receiver and the TO3's are Q415 and Q417.
