FET replacement

[Vintagecasey]

Base Qd17 and Qd18 looked like one maybe turned on in the other not?

I don't think I have the equipment or knowledge to do the testing that you're asking, I wish I did...

 

[Vintagecasey]

I know I probably keep saying the same thing in different ways to someone who understands but I'm trying to make some sense out of it in my own head. Not being able to do the signal tracing I just keep poking around. Something else I noticed, When I test pin 12 and pin 11 on the preamp board and listen to FM I get anything from 33 mv to -40 mv on both depending on the music. If I switch to phono #1 and play an album I get basically - 2 mv on pin 11 and, and pin 12 is between 18 mv and -23 mv. If I hit my reverse switch then pin 11 jumps to between 18 mv and - 20 mv and 12 is at 2mv. if I go to mono pins 11 & 12 both vary +25 to 20mv.

If I test on FM, pins 5 and 6 on the preamp board I basically get both channels very similar -40 to +35 but phono #1 is pin #5 is -.9 to -1.1mv and pin #6 -40 to 40 mv.

On bord x11- 1360-10 B/2 (volume switch) pin #2 is variable between - 30 and +30 pin #1 -2 to .9mv.

Seems to me that the problem is in the first section of the phono stage specifically, Not the section that both phono 01 and phono 2 end up going through? Does that tell anybody anything or am I just spinning my wheels?

 

[Vintagecasey]

Would snipping the wire at any of those points help prove if the problem was before or after the snip point?

 

[Nashou66]

Would snipping the wire at any of those points help prove if the problem was before or after the snip point?

Don't snip any wires, couldn't you de solder them?

 

[Vintagecasey]

They're wound, I would try to unwind them enough to remove them.. but would it show me anything?

 

[Nashou66]

They're wound, I would try to unwind them enough to remove them.. but would it show me anything?

Unsolder the entire pin they are wound on. Easy to remove and replace that way.
Not sure it would help but it helps when needing to remove and entire board to work on it.

Athanasios

 

[Vintagecasey]

Thinking maybe if there is a grounding problem down stream it might show up at one of these 3 locations....

 

[Vintagecasey]

Thanks everyone for the input, I think I found the problem! Doing my best to trace the signal path I came to capacitor c11. Took out c11 and got
505 pf. Replaced it with a 2.2 UF 50 volt audio grade bipolar and both sides are equal!!! That should be fine there right or should I replace it with an upgrade?

 

[Vintagecasey]

Okay continuing on with my phono sections again phono 1 and phono 2 are completely different sections not the typical one section with a switch. I replaced all of the electrolytic capacitors I've replaced all of the transistors phono 1, works correctly now. After setting up a second turntable phono 2 has a problem and again all of these transistors and capacitors on phon02 were all original. I have a situation where for a second or two where the volume will all of a sudden increase two or three times so it's not a pop it's a increase in volume and then it will go back to normal. I have since replaced all of the electrolytics and all of the transistors on phono 2 and the problem remains. Looking for some assistance what could be an obvious problem or what suggestions are to check next. My next step is to check all other solder joints to make sure there isn't a cold solder joint. I've poked and prodded around on each of the resistors transistors capacitors just to see if maybe I can get it to make the noise by pushing on each component to see about a cold joint. No change.

 

[Vintagecasey]

Sorry forgot to mention I did flip flop the two turntables and it does only remain on phono 2.