Multiple issues on Bugera 333xl 212

[dougie tamson]

I got the amp low cost because the mini 5 pin plug from the foot switch had been tripped over with enough force to leave the pins in the socket. I've replaced it with a full size 5 pin DIN socket and wired up a 5 pin plug to the foot switch cable, foot switch all working ok

pic



So next issue, the reverb only works on the clean channel but still with an issue, I can't switch it off, the button stays lit. If I switch to the crunch/lead channel the button goes un-lit and pushing the button does nothing.

The next issue is a common one, after 15 mins of use, the channel randomly switches to crunch, a known issue, overheating?

Doug.

[Enzo]

Unplug your foot switch. DO all the panel buttons work or not?

All of this runs through the DSP board. A stuck switch could be confusing it. Also make sure the voltage regulators on the DSP board are doing their jobs.

[dougie tamson]

Unplug your foot switch. DO all the panel buttons work or not?

All of this runs through the DSP board. A stuck switch could be confusing it. Also make sure the voltage regulators on the DSP board are doing their jobs.

1st, thank you for your help

Here's the test sequence:
I powered up the amp with the foot switch disconnected.

The CLEAN channel is selected by default, clean channel LED state is ON. The reverb LED state is ON and reverb effect is heard depending on how much reverb knob is set. All other LEDs states are OFF.

I pressed the reverb button to try switching it off, no effect, reverb is heard, LED state remained ON no matter how many times I hit the button. Not normal behaviour.

I pressed the effect/boost switch, the boost effect was heard and the LED state changed to ON. I pressed the button again, the boost effect was unselected and LED state changed to OFF.

I pressed the CRUNCH channel button, the channel switched ok, LED for clean channel changed state to OFF, crunch LED changed state to ON. The reverb LED state changed to OFF, reverb effect not heard.

I pressed the CLEAN channel button, the channel switched ok, LED for clean channel changed state to ON, the CRUNCH LED changed state to OFF. The reverb LED state changed to ON, reverb effect heard.

I pressed the LEAD channel button, the channel switched ok, LED for clean channel changed state to OFF, the LEAD channel LED changed state to ON. The reverb LED state changed to OFF, reverb effect not heard.

I pressed the CLEAN channel button, the channel switched ok, LED for clean channel changed state to ON, the LEAD channel LED changed state to OFF. The reverb LED state changed to ON, reverb effect heard.

So far everything seems normal except for the reverb effect switch not responding.

I played for 30 mins to warm up the amp, repeated the tests.

This time in addition to the reverb button issue I noticed that the CRUNCH channel button didn't always respond, had to press it a few times to get it to switch, I tried a long/short press, made no difference, was random whether it worked or not.

Looks like I'm going to have to take the chassis out...

Doug.

[Jon Snell]

As Enzo suggested, check the regulators on the DSP board. Low voltage = poor response/random response.

[g1]

schematics

[dougie tamson]

Been a while since I had the chassis on the bench, just ben using it without reverb but thought I'd give it another try...
I removed the front panel PCB for a closer look and to test the components around the reverb switch, all ok.
I tested all the relays and found an issue with D7 - 1N4148 at RL4 - it had failed short circuit, replaced it. The transistor TR3 beside it (KSP06-G12) tested ok.
I traced the PCB tracks from the reverb switch terminals to X3 and onto the correct pin on the atmega8, tested ok when pushed/released so the signal is getting through.
Also noticed the gold plated pads around the screws holding (and earthing) it to the chassis were corroded so gave them a good clean.

Put it back together and the reverb functions as normal, can switch it on/off for all 3 channels.

Doug

[TomCarlos]

I had a similar channel switching problem with a Bugera 1990. It was a bad positive regulator. Here is my post -

Bugera 1990 Channel Switching Problem

You can see how I retrofit a regulator with a heatsink.

[The Dude]

D7 is across the relay coil and would measure low resistance both ways in circuit. Did you check it out of circuit? Though not impossible, I rarely find shorted diodes across relay coils as any excessive current in the circuit would likely pass through the coil instead of the diode.

[dougie tamson]

D7 is across the relay coil and would measure low resistance both ways in circuit. Did you check it out of circuit? Though not impossible, I rarely find shorted diodes across relay coils as any excessive current in the circuit would likely pass through the coil instead of the diode.

Yeah, measured out of circuit on my mini tester.
I'm thinking the cleaning of the pads where the screws attach to the chassis helped, also noticed some previous work done by the previous owner/s reflowing solder to the jumper pins and on the pads.

Only gave it a 30 min test yesterday at low vol, will hit it harder/longer today and with my power soak/attenuator.

I also run it with 2 tubes pulled and 6L6GC's. The impedance switch set to half the actual speaker load, switch is set to 8Ω and speakers are 2 x 8Ω in series for 16Ω. Just need to check the bias is set where you like it.