Bugera 333XL switching problem

[nanodocl]

Hello..
I am trying to fix a switching channel problem in a bugera 333xl. Clean channel stays always on, when i push crunch or lead, the channel actually changes, but quickly returns to clean, I can hear the relays and see the leds changing, but go back to clean in less tan a second.
I did ask to Jazz P Bass to repost the schematics for this amp and the result is here Bugera 333 Blowing Fuse - F2 Thanks JPB . After a look of the schematic I see that ATMEGA microcontroller is doing all the switching so I resolder all joints and solder points on every component, but problem still remain. Looks like the microcontroller is working properly but no idea why always come back to clean. Any information will be appreciated.

Nano

[Enzo]

First thought - bad clean switch stuck on.

The schematic shows relays driven by transistors. You may have a shorted transistor leaving the relay always on. Or check the base of each transistor to see if it is being held on. On the little card, there is a custom IC that does most of the work.

[nanodocl]

Thanks Enzo, helping as always!
I did check the switch and its ok. Transistor T2 (mps06) was shorted, I change it but problem persist.
Microcontroller seem to be working ok. Do not know where to look anymore.

[nanodocl]

Hi..I did remove and check all transistors, diodes and relays. All fine. Problem seems to be in the digital board. Pin 27 (CL_SW) of the Mega8 microcontroller is low, so I am guessing problem is the microcontroller because output pin 11 (CL_LED) is always high. Thing is that other microcontroller functions as reverb and FX loop are working, looks like the transistor of that output pin is shorted. Any ideas? Should I buy a new board or that microcontrollers can be reprogramed?

[nanodocl]

FIXED

Finally fixed!!
Due to Pin 27 (CL_SW) of the microcontroller was always LOW (faulty input), I installed a pullup resistor between 5V (output pin of the regulator) and pin 27 to force pin to HIGH. The value of the resistor installed was 150 ohms, I did tried many values starting from 10K to 10 ohms. The best results in stability was between 100 ohms and 470 ohms.

[peppoz72]

Hi, most likely the problem is in the firmware of the ATmega8, I'm reprogramming
check my video
https://www.facebook.com/photo.php?v...type=3&theater

[nanodocl]

Hi, most likely the problem is in the firmware of the ATmega8, I'm reprogramming
check my video
https://www.facebook.com/photo.php?v...type=3&theater

Nice done, will you share the code?

[AleixFerrero]

Hi, most likely the problem is in the firmware of the ATmega8, I'm reprogramming
check my video
https://www.facebook.com/photo.php?v...type=3&theater

Hello!
I am trying to solve the same issue, a 333XL stuck in clean chanel. All voltages seems good around, then I am begining to think it's a frimware problem because every time the amp powers up, in seconds it switch 5 or 10 times the lead channel with the crunch then switch to clean channel definetely where it gets stuck. FX Loop switch gets stucked at ON too. If you push clean or lead channel system tries to switch, but roll back instantanely to clean channel.
Pushbuttons are not stuck and operate as it needs, relays seems to work fine too.
Could be possibe to get that firmware to try to burn it on the Amega8? peppoz72