Tremolo not working anymore on SR...

[SleepLess]

Hi!
I posted quite some time ago here on this forum (in March I think) about my 1973 Super Reverb that I blackfaced. It rocks! 8 days ago everything was working as it should and on Saturday night, just before starting my gig, NO Tremolo!  It's not an effect that I use a lot, but still...

Today I have tried a few things: pulling V1 and putting it at V5. I tried two different tubes at V5 and I still have the same symptoms: The speed control works because I can hear an oscillating signal through the speakers that goes faster or slower according to the dialing of the speed knob, and the amp works, but I don't have the tremolo sound!

Could you guys help me quick because I have another gig in ten days and I'd like to use it. If I do have to order a few items I need to do it tonight or tomorrow at the latest since I'm in Europe and the shipping will take some time... Would you guys say to order the optocoupler straight away? Could it be something else? A resistor, something?

Thanks a lot guys... 

[jojokeo]

You don't say if you've taken the chassis out and inspected for any bad/loose connections? I'd do this and also look at your sockets, solder joints, or anything else that you may find on visual inspection. Then carefully turn it on w/ a signal (an iPod or radio can work here if you don't have a signal generator) and speaker hooked up and chop stick away before blindly ordering parts.
I don't know your troubleshooting experience but don't forget to ground the tremolo rca jack which is what (completes) turns the circuit on.

[SleepLess]

Thanks. No I haven't taken the chassis out yet. I don't think I have bad connections since it worked pretty well 8 days ago... I'll check the grounding stuff but since the tremolo worked as it was supposed to 8 days ago I don't think that's the cause... But again, I'm taking the chassis out tonight and I'll check the solder joints and stuff... So far the only thing I've done is seeing if it worked again with other tubes on V5.

What are the symptoms for a non working optocoupler (no tremolo sound aside obviously): no light? Other signs?

Thanks again!

[sluckey]

The fact that you can hear the trem heartbeat in the speaker means the oscillator is working and that the neon half of the roach is probably working. Look closely at the ends of the roach and you should see the flash of a neon light.

Since the trem has no effect on the guitar signal, a very likely cause is the LDR half of the roach has failed. You can check the LDR by connecting an analog ohmeter to the wiper of the intensity pot and chassis. Turn intensity to 10 and speed to 0. (Amp must be on) Engage the tremolo. The needle on the analog meter should wobble around 50K if the LDR is good. If the needle just sits at 50K, the LDR side of the roach is bad. You may be able to use a digital meter, but the display update may cause the reading to just appear goofy if the LDR is good, but it will be steady if the LDR is bad. Hard to say exactly how your DMM will behave.

[SleepLess]

So guys I've opened her up... And the light on the optocoupler works, shines, and varies according to the speed knob... Does it ean that it's something else or can it still be the culprit?
Thanks for helping me out on this one!

[SleepLess]

You can check the LDR by connecting an analog ohmeter to the wiper of the intensity pot and chassis.

Apparently you diagnosed things right... But I don't understand your procedure here... What is the "wiper of the intensity pot and chassis"? How do I connect to that thing? Ground on what and red wire on what? Just a random ohm setting on my MM?

Thanks!

[sluckey]

The intensity pot is the potiometer with knob that you turn to adjust the tremolo intensity. The wiper is the center lug on that pot. The chassis is the metal box that the amplifier is assembled in. Connect the red lead to the center lug on the intensity pot. Connect the black lead to the chassis. Set your meter to measure 50K ohms. Be advised that using a digital meter for this check may not give you conclusive results.

I'd say the roach is a very likely suspect at this point. If you are really pushed for time, you may want to get one soon.

[SleepLess]

So after doing some research it seems that what is called the "wiper" is the centre lug of a pot... So could someone tell me what I should do there?

Looks I'm on my way to order a new optocoupler... 

[SleepLess]

LOL double posts again!!!! Thanks a lot Sluckey... I'm gonna test that and order one if it's responsible!

A million thanks!

[SleepLess]

Crap... The readings vary betwenn 50K and 54K... Does it mean that my optocoupler is good? Crap... I almost wished that would be the reason cuz now I don't know what to check...

sluckey... still around? 

[sluckey]

I don't think 50K to 54K is nearly enough variation.

[SleepLess]

Thanks a lot sluckey! I ordered a new optocoupler from Antique Electronics this morning. Hopefully I'll get it in time and I hope it was the thing to change! The DMM didn't stay on 50K so I figured that there might be another cause... I opened the footswitch and the connections are all good. I'll see and keep you posted!
Thanks again! 

[SleepLess]

Hi again!
If you guys think that there might be another reason than the optocoupler just shoot and I'll check what you advise. So far I've ruled out the V5 tube and the footswitch, and the 25v/25uF cap in the tremolo section is a brand new Sprague I installed when I blackfaced the amp in March... If you don't come up with new ideas I'll wait until I receive the optocoupler and tell you the results!

Thanks! 

[SleepLess]

Hi!
I'm back with some news. I received the optocoupler yesterday and I put the new one in. The tests are good and values vary between 34K and 67K now... Much better than 50-54! It works! So the optocoupler was the culprit! It's ready for 30 more years now...
Thanks again guys!