Crate GT1200H need help troubleshooting reverb issue

[Jimijames31]

Hi Everyone,

I have a Crate GT1200H that I have been using as a beater amp in my rock band. The guy I bought it from told me right before I bought it (in person). That the reverb didn't work and that he had tried a different tank in it but with no success. Being the curious S.O.B. that I am I plugged the tank in to see what the issue was. Surprisingly you can hear reverb, unfortunatley there is also a loud buzz. Additionally the LED on the footwsitch associated with the reverb lights up and turns off when you hit the switch however this does not actually turn the reverb off if level of the reverb is turned up.

Let me try to sum this up in a way that may allow someone to get the picture and help.

I turn the reverb knob from 0 to 10 and reverb is audible as well as crackling and a buzzing sound. I can press the footswitch and the LED will light up to indicate the reverb is on but the reverb stays on weather the LED is lit or not. I have tried reversing the RCA jacks on the tank just for fun and no change. The footswitch functions normally on other amps so I am ruling it out for now.

I am not sure where to start with testing and I am a complete novice with my multimeter. I have pulled out the chassis and all connections look good and clean. Any advice would be greatly appreciated. I would love to be able to sell this amp with a working reverb.

[Jimijames31]

I decided to test the RCA connections with another RCA wire and this easily pulled out. I soldered it back in but unfortnately the problem remains. I have also obtained a schematic from another post involving this amp. I am looking it over but still not exactly sure what all I'm looking at. I am assuming the problem is some how ground related. The potentiometer for the reverb is functioning it is just the footswitch that, even though it lights up, does not turn the reverb off. will keep posting as I go.

[Jimijames31]

PWA Guitar Amplifier PCB Schematics (199SCH_B).zip

schematic

[Chuck H]

With the reverb turned up and the footswitch indicating "on" is there a crash sound when the amp is shaken? Do you have a meter?

[Jimijames31]

I will check for the crashing sound under the conditions you stated. I do have a cheapy multimeter someone gave me. I have been watching videos on how to operate it and test compnents.

[Jimijames31]

So there is a craashing sound when the reverb is up and the led on the reverb button is illuminated. There's also a crashing sound if the reverb is up and the footswitch is not illuminated.

I have to shake the amp pretty hard to get the classic reverb crashing sound from the springs but it's there.

[Chuck H]

Ok, so the recovery end of the circuit is working. It's the send and switching, or just the switching and how it affects the sending, that is the likely problem. The switching is all on the recovery end of the reverb though.?. It's also the same opamp used for the send and return, though that doesn't mean the whole opamp is working I suppose. I'd go ahead and check the E low voltage supply. Is there voltage? And scrutinize any board plugs associated with the reverb or it's switching to make sure it's correct. You'll need to be able to do this by tracking the schem. It's hard to believe that the switching weirdness and the failure to operate aren't related, but that would seem to be the case if you get a good, loud reverb crash. Sort of a corker. Any chance it's the wrong footswitch? I'm still thinking something isn't plugged in right.

[Jimijames31]

I wish it was the wrong footswitch or that something isn't plugged in correctly but I have gone over it all several times. Plus the person who owned it before me had the same issue he couldn't solve. I am going to post a video to give more clearly of an idea of whats happening.

https://youtu.be/_TZvQP9ZlUA

I promise I have gone through all the easy things like something not being plugged in right, I have tested the footswitch on different amps to make sure it's not the footswitch. I have pulled the reverb can out and checked over it to make sure everything is normal.

[g1]

Q26 at the reverb return is what kills the reverb when switched off. It is shown below rev. return in the 4B area of pg.1 schematic.
It gets it's control signal 'E' from Q27, 4C area of pg.2. Q27 is switched on and off by the footswitch.
Measure DC voltage at collector of Q27 (at R102/C74 junction).
What is the DC voltage when switch on? And when switch off?

[Enzo]

I have no idea what yopu know, so...

Are we SURE the footswitch cords and jacks are in the right holes? There is a TRS cord and a TS cord. Are the jacks labelled on the rear panel?

Ditch the footpedal, plug a plain guitar cord into the reverb switch jack. Ground the tip of the free end. Does THAT turn the reverb on and off?

But to eliminate any doubt, don't plug anything into the reverb FS jack, that way it SHOULD default to ON.

Your guy tried another reverb pan, but we don't know if it was the proper type or even if it was a good one. Unplug the two cables from the reverb pan. Use your meter to measure resistance across each little jack on the pan. Neither end should measure open.

Your two cables puch onto those posts, and could easily be wrong. One cable plugs into the OUTPUT jack on the pan. It should be shielded. The center conductor plugs onto J7. The shield plugs onto J16. Now with the amp running and the reverb turned up, touch the plug end (the end that would go into the reverb pan), You should get a loud hum.

The INPUT jack on the reverb pan has two wires as well. The center wire plugs onto J6, wwhich you soldered. The remaining wire plugs onto J9.

If we get any of those wires on the wrong posts, your reverb will not work right.

[Jimijames31]

Thanks I'll look into these and see what I come up with. I appreciate the detailed breakdown that is a huge help for a novice like myself.

[Jimijames31]

I would like to believe that I have all these things correct. I was very maticulous about making sure everything is pluged into the correct places. Traced everything around to make sure all the right wires were in the right places. I will however go over all of it again just to be double sure. I like the idea of using a standard instrument cable and grounding it to see if it can turn the reverb off.

Sadly I get freakin obssesed over problems like this because I feel like it could be fixed easily if I could identify the problem. My greatest education has almost always been experience and I am not affraid of hurting this amp like I would be with my Mesa.

I appreciate all the ideas and the time you have taken to ask these good questions. I am going figure out whats up with this!!

[Enzo]

Maybe you do have it right, buit we need to be sure. For example if we made sure the wires all went back in the way we found them, we don't know if they were wrong from the last guy who worked on it. That is why I said it the way I did, to be functionally sure. Same with testing the pan, even a good reverb pan won;t work if it is the type Fender used, say. So we check it for resistance. What type pan are you using? 4EB2C1B? DO not want 4ABxxxx.

[Jimijames31]

Enzo you were right on so many levels. I had made to many assumptions. First I assumed the reverb pan in the amp was the one that had originally came with it. Based on the conversation I had with the previous owner I thought he said he tried a different pan but put the old one back in. It turns out that it is a type used in fender or mesa style tube amps. TAD RV-8AB2A1B. Secondly I had lined up the colors of the rca jacks to the colors on the pan the result was I had the send pluged into the output and vice versa. At the moment I think the initial problem the old owner was trying to fix was the connector on the board that wasn't soldered correctly or had come loose some otherway. At that point everything else just made the problem worse. I will see about getting the right reverb tank and see what problems if any remain.

Thanks again for suffering my inexperience.

[Enzo]

Reverb pans come in lengths. The long ones have a number starting with 4 or 9. The shorter ones start with 8. Electrically, the length doesn't matter. You can use a short one in place of a long, and if you have the room, a long one will replace a short one.

Your circuit wants a higher impedance drive coil. 8EBxxxx Or even 8FBxxxx.

It is also very important that your 5th character be a C, not an A. That means an insulated INPUT jack, but a grounded OUTPUT jack.

https://www.amplifiedparts.com/tech-...specifications