LA-3A No Output

[craigmorris74]

I've got a vintage LA-3A with no output.  The meter shows gain reduction, but shows no output when I switch it over and the unit is barely passing signal (less than -70dB is registering on the input of my audio interface).

Looked inside and couldn't see anything oviously wrong, and did a few tests, although I couldn't find a test procedure online..  At test point 1, I measured 14VDC.  I don't know anything else to measure.  Any help would be appreciated.

Thanks,
Craig

 

[PRR]

C5, T2, all the wiring to the output screws. Also simple external mis-connection (how often are fuzz-pedal plugs got wrong in/out?).

 

[craigmorris74]

Checked and rechecked the external wiring, and that's not it.

C5 is a possible problem.  Is there a way I could check it without replacing it?

 

[PRR]

> Is there a way I could check it without replacing it?

I don't know what tools you have. "Specially if replacing a cap is daunting.

You really want a 'scope or a listening probe.

If these's signal on one side of a coupling cap, not the other, suspect the cap and its joints.

This is based on some wild-a$$ assumptions. You have signal in the sidechain but not after the program amp (two separate units). Your 11V is not wrong so I ass-ume the transistors and such work. The input caps on the program path are low-value and less likely to fail. The output cap is a large electrolytic which WILL fail, and maybe about now. And wiring (internal and external) is always suspect.

 

[craigmorris74]

Thanks for the tips.  I've got a scope, and have been waiting for the time to check it.  I'll have to order the parts that need replacing, so I wanted to figure out what was wrong before I did.  I really hope its the output cap.

 

[craigmorris74]

I checked this out with a scope, and everything seemed to be fine.  I guessed something had to wrong right at the output.  I remembered that I had put new screws into the barrier strip, and sure enough, they were too long and just touching the chassis.  Robbed some screws out of a strip I wasn't using, and the problem was solved.  Thanks for the guidance, PRR.

 

[mjrippe]

Congrats for solving it!  And I'll file that under the "things to remember" category.  On some gear the panel is cut out behind the terminal strips, on others there is chassis!

 

[PRR]

..., all the wiring to the output screws.

I guess I only implied "screws", wasn't explicit.

Anyway I wudda thought they worked for 40 years, are unlikely to quit now. Didn't know they were changed.