Bugera 333XL effects loop switching on/off by itself.

[Danglin' Fury]

Soooo... as the title says, the effects loop likes to switch on and off on its own. Sometimes rapidly, sometimes slowly. It doesn't matter if I have the foot switch plugged in or not. It seems to do it after the amp has been on for a while, say, 15-20 minutes. I thought it might be some cracked caps on the little digital board it has and I found a couple and changed them. No joy. Then I changed out the 7805 voltage regulator and put it on an actual heat sink thinking it was getting too warm. Once again, no joy. The channels do not switch on their own, just the loop. I can't just turn it off either. It switches on and off no matter what. Any suggestions? Thanks all.

[Jazz P Bass]

Have you checked the actual loop switching circuit?

T3 base going high will turn the A06 transistor On, giving Relay 4 coil a ground reference.

Bugera 333 xl FX Loop.pdf

[Danglin' Fury]

Soooo.... I changed T3 and no joy. Still switching. Then I ohmed the ribbon cable, x60 I believe and I thought I found a problem there. So I built a new 20 pin ribbon cable and took the digital board off to check for cracked caps. Found a couple in the loop switching path so Hooray! Fixed it. For about a week. Now, it is back to switching on and off very rapidly. Even when I have the loop off it will "flicker" on and off rapidly. I'm at a loss. I tried changing the relay as the shop I work in has a boat load of parts. But that didn't work as I don't have the correct relays. I have 24 volt relays here but on the Data sheet for the Bugera relays, says they are solid state relays and not just plain ol' normal ones. I don't think that is the problem though. I REALLY hope it's not one of the programmable chips on the digital board. I'm gonna reflow everything and change all the surface mount stuff on that board to an 0603 or 0805 package as most of the caps and resistors are sub 0603. Crossing my fingers.

[Danglin' Fury]

So far, so good. Reflowed everything on BDM1 board and no loop flickering yet. If this doesn't work, does anybody know where I might be able to purchase a replacement BDM1 board for this amp? Thanks again everybody.

[Danglin' Fury]

Sooo. The amps effects loop is still flickering on and off. I have replaced the transistors, reflowed the solder, and it seemed to fix it for a while but it is back doing the same thing. Anybody have anything? Does anybody know where I can grab up a new BDM1 board? Thanks for lookin'.

[Danglin' Fury]

The effects loop on/off self-switching seems to happen around 15-30 minutes of playing and about the same when the amp is in standby mode. Once again, heat thing??? Sounds like it to me. Found several cracked caps (smt) and that "fixed " it for a while but the problem persists. I changed the transistor (T3 on the schematic) in the switching circuit but the length of time that it takes for it to start turning on and off really leads me to believe it is heat related i.e. bad capacitor. I've also checked the resistors and no luck there. Really has me buggered. Could the programmable I.C. that is on the BDM1 board be causing this problem? If so, anybody know where I can pick up a new BDM1 board for this thing? Thanks for looking.

[Enzo]

That is why they sell freeze spray. If this needs to warm uop 20 minutes to start, then once it starts, spray the FX card with circuit chiller spray. If that stops the symptom, then it is heat related. Let it warm up and start doing it again, now when we spray, we just spray a small area of the card. Holding a 3x5 card or some other flexible thing against the board acts as a shield to keep spray off other areas. That lets you narrow down what is sensitive.