nashou
Unmoderated Off Topic
Tech in Training.....
Posts: 1,239 
|
Post by nashou on Dec 3, 2016 20:03:57 GMT -5
I wouldn't think it were those either but something is going on. Maybe put those other tr's back in so both channels are the same and compare some voltages. So everything in except R137 and R138 and test voltage on: B+ 24.83 B- -24.92 R153 both sides -24.45, -24.48 R154 both sides -24.49, -24.53 |
|
|
|
Post by mastertech on Dec 3, 2016 20:09:30 GMT -5
How about both sides of R139 and R140?
|
|
nashou
Unmoderated Off Topic
Tech in Training.....
Posts: 1,239
|
Post by nashou on Dec 3, 2016 20:19:17 GMT -5
How about both sides of R139 and R140? -25.35 for both as it warmed up. At first the left channel was a volt lower then they equalized after a few checks. Nashou |
|
|
|
Post by mastertech on Dec 3, 2016 20:20:47 GMT -5
Just curious. Where are you attaching your neg probe for testing?
|
|
nashou
Unmoderated Off Topic
Tech in Training.....
Posts: 1,239
|
Post by nashou on Dec 3, 2016 20:24:46 GMT -5
Ok just noticed something weird as it warmed up . I wanted to see what the voltage was again on R137 the side closest to the edge of the board.
At first it was + 24.xx volts!!!! then it started to move lower and then go to the negative side and stoped at the readings I gave you earlier !!!
|
|
nashou
Unmoderated Off Topic
Tech in Training.....
Posts: 1,239
|
Post by nashou on Dec 3, 2016 20:27:16 GMT -5
Just curious. Where are you attaching your neg probe for testing? Umm, the chassis.... is that not good?  aslo read my above post |
|
|
|
Post by mastertech on Dec 3, 2016 20:29:55 GMT -5
Saw your post. Set your meter to ohm and test between chassis where you are connected and the outer part of the phono jacks and see if close to zero or short. Unplugged of course.  |
|
nashou
Unmoderated Off Topic
Tech in Training.....
Posts: 1,239
|
Post by nashou on Dec 3, 2016 20:32:36 GMT -5
Saw your post. Set your meter to ohm and test between chassis where you are connected and the outer part of the phono jacks and see if close to zero or short. Unplugged of course. its 0.000 |
|
|
|
Post by mastertech on Dec 3, 2016 20:43:51 GMT -5
Did you try your experiment on R138 to see if it did the same?
|
|
nashou
Unmoderated Off Topic
Tech in Training.....
Posts: 1,239
|
Post by nashou on Dec 3, 2016 20:52:12 GMT -5
Just did and R138 starts off Neg and stays there.
R137 build slowly up to +24.36 then begins to back off and collapse then rise to -24.5 pretty fast after the collapse .
I have to let the amp sit for about 5 minutes to be able to repeat it otherwise it it starts out Neg.
I wonder if the 1N5253B 25 volt zeners I used are the issue?
Just checked they seem fine.
Nashou
|
|
|
|
Post by mastertech on Dec 3, 2016 21:05:15 GMT -5
Ok, one more test and then have to make a decision.
I want to see the voltages on TR107 and TR108. I know some are tied together but give me each pin anyways but just identify the gates. Don't need to know which side. I will ask later if need be so you may want to remember. I can figure out otherwise. This should be quick and easy.
TR107:
G ____ S ____ D____
G ____ S ____ D ____
TR108:
G ____ S ____ D ____
G ____ S ____ D ____
|
|
nashou
Unmoderated Off Topic
Tech in Training.....
Posts: 1,239
|
Post by nashou on Dec 3, 2016 21:11:18 GMT -5
Ok, one more test and then have to make a decision. I want to see the voltages on TR107 and TR108. I know some are tied together but give me each pin anyways but just identify the gates. Don't need to know which side. I will ask later if need be so you may want to remember. I can figure out otherwise. This should be quick and easy. TR107: G 56mV S 118.8mV D 3.71 G 0 S 118.8mV D 3.71 TR108: G 15.2mV S 91.4mV D 3.66 G 0 S 92.1mV D 3.68 First numbers on each are the outer halfs. |
|
|
|
Post by mastertech on Dec 3, 2016 21:36:47 GMT -5
Well aside from your slight anomaly of R137, both channels appear to be acting the same. So I have to look at something that can affect both channels equally. Now 1 thing could be the current components of TR107 and TR108. But it doesn't seem likely.
The other thing is how the base of TR115 and Tr116 are triggered off the same source. And this is the same source that you had found a bad diode in and replaced. And before you replaced it the good channel was working properly even though we cannot confirm that had anything to do with it.
So with that said, I would go over each of those components on that line and check them very carefully: D103,D104,D105 and R159.
Lift at least 1 leg on each and test for value an also check to make sure diode direction is installed correctly.
If all this checks ok then I would have to suggest you put the original TR108 in and see if it fixes that channel. At least it should be safe with R138 removed.
I really cannot see anything in that servo section causing a problem like this but if all else fails you may have to test each component in that circuit too.
|
|
nashou
Unmoderated Off Topic
Tech in Training.....
Posts: 1,239
|
Post by nashou on Dec 3, 2016 21:45:17 GMT -5
ok, off to bed. ugh this is a tough one !
I have a lot of those diodes so I could change them. And I now have the 1N1555 original diodes in stock and
can use those instead of the the 1N4148's in there now.
|
|
nashou
Unmoderated Off Topic
Tech in Training.....
Posts: 1,239
|
Post by nashou on Dec 4, 2016 20:52:54 GMT -5
I first changed D103 and then tested the voltage and the voltage on R137 where it started positive then went neg.
Now it starts up Neg right on turn on.
I also changed D104 and 105 again to the 1S1555's and no change. still getting -24.xx on R137 and R138.
What should they be there Mac?
I'm taking a break to watch Westworld on HBO.
See you in an hour if your around.
|
|
