While playing through this amp I stepped on the channel changing footswitch and lost all sound from amp. all tubes and pilot light remained on but amp went silent. Disconnecting footswitch and cable f

You could buy a Lehle switch, or simply use one on each separately. If you are using a multieffect unit you could make a Y cable to take the output to both amps but that will not allow you to select the drive channel - you still need the Fender footswitch for that, one for each amp. Lehle is a German company and they make a lot of different footswitch combinations but you will pay for the convenience.


I recommend the Fender single button footswitch for this use - Type: Footswitch

Number of Footswitch Buttons: 1

Manufacturer Part Number: 0994052000

It's about $35.00 each, compared to the Lehle which starts at $200. Just put the two side by side and make a metal bar to attach to the two switches - then you have a single bar to activate both drive channels at the same time. I recommend using aluminum bar stock with holes drilled into it for the switches, or find a C channel aluminum bar that will put the footswitch buttons in the channel. You can also make it one inch overhang past both switch bodies and then use bolts to keep the bar in place. If I was doing this I would mount the footswitches on a board and secure the bar to be on top of the footswitches, using coil springs to maintain the bar's alignment vertically at the end bolts.

I once used uART & some latches to decode & hold the difference between "odd & even" midi program changes. Then used the output to switch a relay in a twin necked guitar to change between necks as it were in response to a midi pedal. Perhaps you could do something similar? Else get a Studiomaster MA-36 midi analyser & hack into it to use one piece of midi data (from across an LED?) to switch channels on your amp? Good Luck!

Sounds like either your "front-panel" switches are not set for channel switching or the footswitch's mechanical "Channel" switch is defective. According to the OM the "Channel Select Switch" on the front becomes inactive with the footswitch plugged in.

If disconnecting the footswitch causes this front-panel switch to operate properly then it has to be your mechanical switch in the footswitch. Repair of these footswitches are pretty simple provided you find a replacement and have soldering abilities.

Is this happening only with the foot switch plugged in? A bad cable on the footswitch is the most likely cause but there could also be a problem within the footswitch jack on the amp.

If it is within warranty take it back to the shop. If not then its going to need an engineer to look at it. Its not worth fooling around inside a tube amp as the capacitors can retain lethal voltages even when unplugged.

The P803 is designed to work with the "Valvestate" and Tube amps. I don't think it is compatible with the Haze40 since they have an optional 4 button footswitch so the optional one would necessitate different interface than the P803.

Test if it does it with the guitar cable unplugged from the amp. If it does, then it is time for servicing... If not, then you have a system grounding problem and the guitar cable is "leaking" signal into the amp. This can happen even if guitar is NOT connected.

Surge protector would NOT have protected it so don't kick yourself. If you had your footswitch plugged into the amp, the surge may have ruptured components in the circuit. Most likely are components on page 2 of the schematic in the upper left corner associated with the channel selection, C77 and TR1 would be first suspects. Deeper into the circuit is the channel switch chip IC9.

A voltmeter test of the FS_B input from the footswitch to verify that with the footswitch disconnected that this approaches 5 volts is first step. If it doesn't then the three components mentioned should be tested in the order I mentioned them. If it does go to nearly 5 volts, then IC9 is likely the culprit... it is a DG212 analog switch chip. It is readily available from DigiKey.com and others... in several different type packages. If yours is surface mount, you need to find someone with the proper tools to change the chip.

Here is link to schematic: http://elektrotanya.com/marshall_mg50dfx_sch.pdf/download.html

Wayne, There's a time to take the amp to a pro shop andf get it done right. It' saves time and headaches, and also keeps you from inadvertantly smoking other parts or yourself. Now is that time.

have you tried the footswitch to change channels. also. my amp has to be in channel 2 position (with the button on the head) before i can use the footswitch. sometimes the input/footswitch jack wears out and you need to bend the internal tip/ring tabs of the jack to make better contact. also like on my fender amp, i had just a standard mono instrument cable going to my footswitch and it was acting wierd cause it needed a stereo instrument cable. one last thing on the grounding resistors on the pcb, they get hot and break the solder welds which messes with all sorts of stuff in amps. usually look like sugar cubes , cement resistor. 5watt usually under 1k ohm. check for bad solder welds on the pcb where the big resistors are and the switches/buttons and at the footswitch. there may be a bad ic or transistor for the channel swithing