JCM2000 DSL 100W - No power amp output - Preamp seems fine!

[bw1985]

Hi all,

Hoping somebody can shed some light on this weird issue I am seeing on a JCM2000 DSL 100W head. I am not getting any output from the amp at all. I have checked all voltages on the sockets and everything looks healthy. I have checked the effects loop connections and I can successfully take preamp output into another amp and it sounds fine. If I plug into the power amp input, I still get no output.

I am also hearing what appears to be "amp sound" from the OT itself...very strange. I checked all the multipin connectors and they seem secure. I've also tried the different speaker outputs on the amp.

Any advice on where to start with this would be greatly appreciated, as always.

Thanks and all the best!
-Brian

[g1]

Make sure there is no bad connection between OT secondary and speaker jacks (or short across them).
Be careful running signal as if there is a bad connection there will be no load on the OT and it could get damaged.

[Jon Snell]

If the transformer is 'ringing' with the sound you are producing, it must be a secondary wiring issue to the speaker jacks.
The transformer noise shows there is energy trying to flow.
This is the same on both 8R and 16R out?
What are the DC resistances of the speaker output sockets, (winding resistances)?

[Valvehead]

There was an issue with the grounding of the speaker jacks on those. Pull the output pcb (super easy) and check the grounding of the 3 speaker jacks , also all solder joints on that board . Ive had several Jcm 2000 come in with bad OT's also .

[Greg_L]

There was an issue with the grounding of the speaker jacks on those. Pull the output pcb (super easy) and check the grounding of the 3 speaker jacks , also all solder joints on that board . Ive had several Jcm 2000 come in with bad OT's also .

This ^^^^^

The speaker jacks and their related board is a problem on these amps. Start poking around in that area.

[Helmholtz]

If there's no ground return for the speakers, the OT runs open and is at risk.

The test recommended by Jon Snell should reveal that condition.

[g1]

This is the one where the 4 & 8 ohm jacks get their ground through the switch on the 16 ohm jack. If the contacts don't close the 4 & 8 jacks don't work. Some people just hardwire across the switch contacts of the 16 ohm jack for better reliability.

[bw1985]

Thank you all so much for your input! Sure enough, I removed the jack board, re-soldered everything on the jacks and 4/8ohm switch and everything works great!
I also sprayed out the switch with contact cleaner and cleaned out the jacks as well. Weird because nothing "looked" suspicious, but of course everyone here knows the tricks.

You guys rock! Thank you again! Cheers!

[bw1985]

This is the one where the 4 & 8 ohm jacks get their ground through the switch on the 16 ohm jack. If the contacts don't close the 4 & 8 jacks don't work. Some people just hardwire across the switch contacts of the 16 ohm jack for better reliability.

Thanks for your reply! I'm still having some issues with this amp. I hard-wired the ground across the bottom of the board, but is there something else I'm missing?
Still having issues with the 4/8ohm jacks not working - it was fine then failed again. The 16ohm output works great and sounds amazing!

[g1]

I hard-wired the ground across the bottom of the board, but is there something else I'm missing?

Hard to describe without the board layout. There are 2 contacts on the 16ohm jack itself that need to be joined together. Can you post a picture of the solder side of the speaker jack board?

[bw1985]

Hard to describe without the board layout. There are 2 contacts on the 16ohm jack itself that need to be joined together. Can you post a picture of the solder side of the speaker jack board?

Here it is! Do I need to extend that ground wire over?

[The Dude]

You jumpered the wrong (positive) connections instead of the ground. I've edited your picture. Remove the wire you added (red x) and add the jumper (blue line).