pearl, q4 no voltage

[noelectrix]

unfortunately one channel of my pearl phono stage stopped working and needs some help. First aid indication:

No voltage on Q4 (the ztx 450) next to the 2sk 389. There is a "control point" were I should measure 13,8 V or so. Any hint what that points to?

help is highly appreciated
stefan

 

[noelectrix]

It´s not exatly zero, Imeasured 750 mV.
stefan

 

[cviller]

What is the voltage on either pin of R8 in reference to gnd?

You can measure the 13.6V on the emitter of Q4. The emitter is the one which is not the middle pin and not connected to R14...

 

[noelectrix]

hi cvi,
late answer.
on R8 i measured 28,1 and 28,6 to gnd.
the same points at the working channel give 28,4 and 28,7. So seems to be the same.
stefan

 

[cviller]

My best guess is that you have burned the 2sk389 (not your fault, but a lot of people have had this problem).

If you don't think that is the problem. Please take the schematics and put all your measurements on the schematics (you can do this is in paint), then I might be able to point you to the problem.

 

[noelectrix]

hey cviller, that is veery kind of you. When Leela finished, I´ll also have a look at the schematics and report

 

[noelectrix]

I heard that it is wise to split the source resistors. If i can find another 2sk 389 i´d try it this way.
stefan

 

[cviller]

You can easily use two 2sk170, but you'll have to match them (idss).

Here's to us poor schmoes, working for the man. Although she is a hot, sexy female man.

 

[noelectrix]

yes, of course, i read that somewhere with the sk 170 substitution. and i got some here
but how to do that will be my tomorrow´s research. huhu, i dip my feet n electronics
tnx,
stefan

 

[noelectrix]

cviller, thanx again for offering your help.
After a friend of mine also supposed that the double fet is gone, i was offensive and changed it with two 2sk 170. I matched them with a 9V battery and a 10Ohm resistor.
Than i split the source resistors (two 20 Ohms) and everything is fine now. soundstage still in the middle.

When i plugged it in there still was no sound on the left channel, but it turned out that the cable was broken. (but the channel was also )

tnx
stefan