Crate VC50 FX loop trouble.

[rockon1]

Recently fixed up an old VC50. Cleaned the pots, jacks and fixed it with a set of tubes that ran in good range. Cleaned it up, replaced the grill etc. Sitting pretty ,looking good, sounding good...until I tried the FX loop. Plug into it and the sound dies. Checked the cable Im using in my other VC50 and its fine. Its a TRS single jack loop.

Looked over the solder joints -nothing. Contacts look ok -wiggling does nothing. Power is coming from the power amp section cause I get loud hum if I touch the return end of the insert cable. Hopefully someone can give me a heads up on where to look. Thanks Bob

http://www.chasingtone.com/schematic...ge_club_50.pdf


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[Enzo]

Don't LOOK contacts into health. Check with an ohm meter. Those contacts that open when you plug in have to carry the signal otherwise. Measure their closed resistance. it needs to measure under half an ohm.

Wire a TRS plug shorting tip to ring and plug it into the jack. Does the amp still pass signal now?

And make sure you are not getting send and return reversed in the plug.

[rockon1]

I took the pedal and cable and plugged it into my other VC50 and it works fine- cable is plugged in correctly. The contacts close fine too since the amp works OK when I unplug it. Just no signal gets thru if I plug into the the loop. If I turn the amp way up I here a faint bit of guitar getting thru. With the chassis out and everything plugged in I can see the contacts connecting with all 3 parts of the plug too. I'll try and find a TRS and try your suggestion. Bob

[g1]

So you are connecting the loop up to a pedal? And the setup works with another VC50?
You said you get a hum from the power amp if you touch the return of the insert, so there must be a problem with the send circuit (Q7 area of loop), which is bypassed when the loop is not in use.

[rockon1]

So you are connecting the loop up to a pedal? And the setup works with another VC50?
You said you get a hum from the power amp if you touch the return of the insert, so there must be a problem with the send circuit (Q7 area of loop), which is bypassed when the loop is not in use.

Yes , my other VC50 is a few feet away. I just unplug it from the one I'm having trouble with into the other one and the cable/pedal works fine. Yes -if I touch the return when its plugged into the loop I get a loud power amp hum. I tried what Enzo suggested -plugging in a TRS jack with the tip and ring shorted together and nothing.

Any prime suspects in Q7 area of the loop? Bad transistor? Thanks Bob

[Enzo]

It is a one transistor circuit, so check the voltages in it, check the resistors in it, a bad cap. etc.

[rockon1]

Ordered a few transistors, caps and resistors. I'll report back when I know more. Thanks, Bob

[rockon1]

Thanks guys! Went right for the throat and soldered in a new transistor. Bingo! loop works fine now! Just have to pull it apart and solder it in properly now. Thanks again! Bob