JCM 2000 DSL no output

[Jazz P Bass]

Yeah but......

By lifting R41 & R43 you removed the Jfets from the circuit.

A jfet is a in a normally closed condition from D to S.
You still have not proved that the jfets are at fault.

Have you looked at the Gate voltage at all?
The Gate voltage will 'Open' the D to S junction.
I cannot follow that schematic without having the amp in front of me.
Where does the voltage come from to turn the jfets Off (Open)

[sweatyk]

Have you looked at the Gate voltage at all?
The Gate voltage will 'Open' the D to S junction.
I cannot follow that schematic without having the amp in front of me.
Where does the voltage come from to turn the jfets Off (Open)

No I have not checked the voltage at the gate. Do I need to put R41 and R43 back in the circuit before checking that? Would a picture of the PCB be helpful being it's not in front of you?

[Jazz P Bass]

The gate can be read without those resistors.

It's a p channel jfet, so you will need a negative voltage to open the junction.

[sweatyk]

Readings for TR1 at the gate = +21.9 VDC and TR3 = +11.6VDC

[g1]

It's a p channel jfet, so you will need a negative voltage to open the junction.

I think you need positive to turn off?
Both of them are receiving positive voltage at the gate. Tr3 gate can only go up to 12V due to ZD1 12V zener.
One of the Fets or both must be leaky. You can try to determine which one by re-connecting those resistors one at a time, or just replace both fets.

[sweatyk]

Yeah but......

By lifting R41 & R43 you removed the Jfets from the circuit.

A jfet is a in a normally closed condition from D to S.
You still have not proved that the jfets are at fault.

Have you looked at the Gate voltage at all?
The Gate voltage will 'Open' the D to S junction.
I cannot follow that schematic without having the amp in front of me.
Where does the voltage come from to turn the jfets Off (Open)

Gate Voltage

TR1 = +22.2VDC
TR3 = +11.6VDC

[Jazz P Bass]

Well then the jfets should be off.
And they are not.
So they are bad.

[sweatyk]

Well then the jfets should be off.
And they are not.
So they are bad.

That's after I put the new jfets in..................

[The Dude]

So you put in new jfets and the amp still doesn't work?

[Jazz P Bass]

Are they installed in the correct orientation?

[sweatyk]

Put the power tubes back in to see what I get and I'll be a son of a.........now V6 is not glowing. Swapped it with one that is and it still wont. I know compared to you guys I'm just an amateur however I didn't just start playing around with electronics and I'm very meticulous about things being right. I'm not sloppy and I double and triple check things but I'm beginning to wonder if there are gremlins in this SOB! Last night I install the new jfets and with the power tubes out I injected a signal and just like before I changed them I was not getting the signal at V3. So this morning I decide to put the power tubes back in and now this...........banging my head against the wall

[sweatyk]

How shall I proceed?

[Enzo]

I am not going to read back through 147 posts to get up to speed, but if only V6 refuses to light, then check the heater fuse for V6. Each power tube has its own heater fuse. The fuse could have blown for whatever reason, or the fuse holder could be partly sprung. Just takes a second to find out.

[sweatyk]

I agree Enzo, this thread has become too long to reflect back on. This will be my last post on this. As to your suggestion with the fuses. I checked them out of the holder and they are good, but what I discovered is that they seem to not be making a very good connection. I hit the ends lightly with some sandpaper and it completed the circuit. So here is what I plan to do. I’m going to work on all of the fuse ends and the holders, back track this thread and go over everything again. The last real progress was when I lifted R41 and R43 out of the circuit and the signal made it to V3. I’m going to revisit that but lift them one at a time to identify which area is at fault. Once I have completed all of this and I still need some assistance then I will start a new thread with the current symptoms only. Everyone has really helped in a major way and I have learned a few things that will help in my troubleshooting skills and I thank you all for that. This is the best forum out there by far!