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I am troubleshooting a buddy's Mark V 25 which is working, but with no reverb.
I've tried swapping reverb tanks to another Mesa amp, and the tank in the Mark V is fine (and the other tank works, but not in the Mark V either).

I am looking at this schematic (https://el34world.com/charts/Schematics/files/Mesa_boogie/Mesaboogiemark_v.pdf), especially page 5.
The tube sockets are easy to probe, and I see the input signal go through the preamp sections fine, but the signal doesn't make it into V4A pin 1.
I am aware of the JFETs on the reverb circuit going bad, and am thinking the issue is likely J175M2.
But I'm having a hard time finding it on the actual PCB.
I see various J174 JFETs on the PCB (not J175), but none that say M2, D, or E.

Does anyone have a parts placement diagram (or blank PCB) with the reference designators on it?
Or can you circle where the J174/J175 JFETs in the reverb circuit are on this picture?

TIA!

https://drive.google.com/file/d/1e8nBE_KU67n9ZLiBAmjfWEkJWfvnvox1/view?usp=sharing
https://drive.google.com/file/d/1e3P2O4gytW-F1rtDW_SIdDxe_xVuS_tm/view?usp=sharing

<blockquote data-quote="funkmasterron" data-source="post: 530213" data-attributes="member: 84255">I am troubleshooting a buddy&#039;s Mark V 25 which is working, but with no reverb.I&#039;ve tried swapping reverb tanks to another Mesa amp, and the tank in the Mark V is fine (and the other tank works, but not in the Mark V either).I am looking at this schematic (https://el34world.com/charts/Schematics/files/Mesa_boogie/Mesaboogiemark_v.pdf), especially page 5.The tube sockets are easy to probe, and I see the input signal go through the preamp sections fine, but the signal doesn&#039;t make it into V4A pin 1.I am aware of the JFETs on the reverb circuit going bad, and am thinking the issue is likely J175M2.But I&#039;m having a hard time finding it on the actual PCB.I see various J174 JFETs on the PCB (not J175), but none that say M2, D, or E.Does anyone have a parts placement diagram (or blank PCB) with the reference designators on it?Or can you circle where the J174/J175 JFETs in the reverb circuit are on this picture?TIA!<a href="https://drive.google.com/file/d/1e8nBE_KU67n9ZLiBAmjfWEkJWfvnvox1/view?usp=sharing" target="_blank">https://drive.google.com/file/d/1e8nBE_KU67n9ZLiBAmjfWEkJWfvnvox1/view?usp=sharing</a><a href="https://drive.google.com/file/d/1e3P2O4gytW-F1rtDW_SIdDxe_xVuS_tm/view?usp=sharing" target="_blank">https://drive.google.com/file/d/1e3P2O4gytW-F1rtDW_SIdDxe_xVuS_tm/view?usp=sharing</a></blockquote>

[QUOTE="funkmasterron, post: 530213, member: 84255"] I am troubleshooting a buddy's Mark V 25 which is working, but with no reverb. I've tried swapping reverb tanks to another Mesa amp, and the tank in the Mark V is fine (and the other tank works, but not in the Mark V either). I am looking at this schematic (https://el34world.com/charts/Schematics/files/Mesa_boogie/Mesaboogiemark_v.pdf), especially page 5. The tube sockets are easy to probe, and I see the input signal go through the preamp sections fine, but the signal doesn't make it into V4A pin 1. I am aware of the JFETs on the reverb circuit going bad, and am thinking the issue is likely J175M2. But I'm having a hard time finding it on the actual PCB. I see various J174 JFETs on the PCB (not J175), but none that say M2, D, or E. Does anyone have a parts placement diagram (or blank PCB) with the reference designators on it? Or can you circle where the J174/J175 JFETs in the reverb circuit are on this picture? TIA! [url]https://drive.google.com/file/d/1e8nBE_KU67n9ZLiBAmjfWEkJWfvnvox1/view?usp=sharing[/url] [url]https://drive.google.com/file/d/1e3P2O4gytW-F1rtDW_SIdDxe_xVuS_tm/view?usp=sharing[/url] [/QUOTE]

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