Effects Loop Troubleshooting

[surlybastard]

Hi,

New here in the forums and I was hoping someone might be able to help me with an issue I'm having. I bought a 2266 head off a guy I know, like the amp so far but for whatever reason I cannot get the effects loop to operate. When I plug in my effects loop chain into the send/return and enable the loop the amp goes dead. I've tried a number of different ways right down to plugging in a single six inch cable between the send/return and any time you enable the loop the amp goes silent. I tried cleaning out the inputs, I even took the amp out of the chassis and took a look at the board to see if there was any obvious damage or loose solder connections, but I'm not an amp tech or electrical engineer so unless it's something obvious I'm not going to see it (I didn't see anything).

The guy I purchased the amp from never used the loop (doesn't use lots of effects and runs them all in front of the amp).

My question is: Is the VM's effects loop tube driven, and if so which tube operates it? If not then I guess I'm off to the dealer or tech to see what this will cost to fix.

Thanks!

[C0ldFart]

test the loop with a guitar cable from send->return and it should be almost the same level when you push the loop enable/disable button

[Mr. Mother Head]

It's not tube driven. I think it's usually one of the FETs that fail. Steve D will be able to help you for sure.

[surlybastard]

test the loop with a guitar cable from send->return and it should be almost the same level when you push the loop enable/disable button

I tried that with a six inch pigtail and no matter what level you set the loop at the second you enable it the amp goes silent.

-- Thu May 19, 2011 6:40 am --

It's not tube driven. I think it's usually one of the FETs that fail. Steve D will be able to help you for sure.

Out of curiosity what do the four tubes do then? One is input, one is overdrive, one is the phase inverter. I'm wondering what the other tube does

[Bailz]

V2 is the extra gain stage only used when HDR is engaged.

[SteveD]

Welcome to the forum surlybastard.

It's almost certainly a failed fet on the FX PCB, usually 'fet 3' but all three of them should be checked.

It is a TN2404KL high voltage mosfet as is 'fet 2'. 'fet 1' is a j202 jfet.

I recommend taking it to a qualified tech for repair as these components are static sensitive and should be replaced with the correct precautions observed.

[surlybastard]

Welcome to the forum surlybastard.

It's almost certainly a failed fet on the FX PCB, usually 'fet 3' but all three of them should be checked.

It is a TN2404KL high voltage mosfet as is 'fet 2'. 'fet 1' is a j202 jfet.

I recommend taking it to a qualified tech for repair as these components are static sensitive and should be replaced with the correct precautions observed.

Great thanks so much for the help SteveD. Would you be able to ballpark what this repair would cost?

[SteveD]

Couldn't say really but it shouldn't be too much to change out 1, 2 or 3 transistors. They are not expensive components.