Mezmerize DCB1 Building Thread

[42001]

Leg Trick????

 

[Salas]

Do this first (leg trick). Only the K170 thing in the pic.

http://www.diyaudio.com/forums/power-supplies/153484-using-hypnotize-general-shunt-reg-pcb.html

And remeasure.

 

[Salas]

Ow, something is not ok I think:

Left signal out 1.8MV
Right signal out 35.8MV

That's not good is it??

Its not good. Lets hope its only due to the rail differences for now.

 

[42001]

Just so I get it.... Just "unsolder" the middle leg of that K170?

 

[Salas]

Yes, and stick it to S pin above board with little solder. Talking for only the one K170 pictured that belongs to the IRP9240s side.

 

[42001]

One side is now 0.2MV

The other is 33.02MV

What could be the problem???

 

[42001]

VDROP over resistor 10 Ohm is 44.7MV

 

[42001]

And over the other one 54MV

 

[Salas]

One side is now 0.2MV

The other is 33.02MV

What could be the problem???

So in the good offset channel its even better but in the bad offset channel its still high. What are the DCV measurements on the power rails now?

 

[42001]

10.02 and 10.12

 

[Salas]

OK, much better, keep that mod. But..the main problem was not coming from the rails difference it proves. Now the audio signal JFET pair in the right high offset channel is under suspicion. Maybe one of the two damaged or grossly mismatched. Pull them out and remeasure their IDSS.

 

[42001]

I hope not! I got them from the DIYAUDIO store.... Paid good money for them

 

[42001]

Question is...witch two are the right channel ones

 

[Salas]

The thing is that when the rails are good then only those two are powered by them in the audio path. So they are the ones to check now. Did you measure their IDSS before stuffing them? Because if they were matched, then only soldering too hot could damage one and the offset. One pair in left channel is champ and they use the same power rails...

 

[42001]

I can only measure GDS here... Never did measure LDSS and don't know how to they were all the same, 132GDS

I have 4 of the A types left from the same batch... so if you can tell me the ones that I need to take out, I'll replace them...

 

[Salas]

Question is...witch two are the right channel ones

The output socket print on the pcb has also R and L printed to its sides. Facing those letters there are the two corresponding JFETS pairs down lower in the PCB.

 

[Salas]

I can only measure GDS here... Never did measure LDSS and don't know how to they were all the same, 132GDS

I have 4 of the A types left from the same batch... so if you can tell me the ones that I need to take out, I'll replace them...

http://www.diyaudio.com/forums/solid-state/23546-matching-jfets.html#post274893

 

[Salas]

See if you had populated one in reverse by mistake also.

 

[42001]

Ok, changed them... no luck... even worse now :-(

 

[42001]

Right channel now 40.6MV