Problem with Mark IV footswitch.

My Mark IV footswitch is totally unreliable these days. Last week I was doing a gig and Al of the sudden it just stopped switching, no matter what button I pressed. After a few minutes into the song it started working again but 30 minutes later it the same thing happened again. I unplugged it after that and finished the gig with one channel.
Now what happens exactly?

I was playing in lead mode (button 3 on the pedal). I finish my solo and press the rhy 2 button when all of the sudden it jumps into the lead + EQ mode (button 4). No matter what I pressed, it didn't do anything.
Second time this happened again, it jumped into lead + EQ while I pressed a totally different button.

What could be the problem? Is it the footswitch or could it be that there's something wrong with the connection of the footwitch to the amp?

Good luck with that one, hope somebody knows, I had a problem too, with my footswitch, I brought it to a good repairman in my area but nothing did the trick, sometimes if I press the lead+eq button, the eq light doesn't shine and instead of a distorted sound I have a poor clean sound.....the only good thing is that it didn't happen when I tried another footswitch......so now I just cross my fingers when I hit the susmentioned button

anyways as I said, good luck :wink:

I have a question about what you describe. Does the footswitch show that it is in lead+eq mode or just the amp. If the footswitch is showing this something is going wrong with the circuit. One thing that can cause erratic behavior with switching circuits is low voltage to the logic devices. This could be something happening at the connection or internal to the footswitch. The voltage coming in to the footswitch is +15v and there is a voltage regulator inside that bumps it down to +5v. Do all the led's seem to light up properly. If they are dim it could be voltage reltated. Another thing that can cause the problem is a poor ground connection which is really a power problem just at the other end of things. Check that the connector is clean and properly inserted. Try wiggling it to see if you can affect the switching behavior. Better yet try swapping in a working footswitch or try your footswitch on another mark iv. If this fails time to go inside the footswitch or off to a tech. If you do go inside look for flakey solder connections. Also check continuity in the cable. Lots of things to try on this.

When it switches to Lead + EQ, the amp switches along to the same channel. All the leds burn like they supposed to do and match the settings of my amp. The problem is that when I press the footswitch, it doesn't do anything for a while.

Maybe I should start off with some contact spray? Or is this something that won't help?

Ednolb said:

Maybe I should start off with some contact spray? Or is this something that won't help?

Click to expand...

No that is a good idea, spray the connector on the cable and the switches. Are the switches r1, r2, r3 nice and free? You might have to press down a switch and clean with a toothbrush.

And what about the connection of the footswitch cable to the amp? Can I use contact spray there?

Ednolb said:

When it switches to Lead + EQ, the amp switches along to the same channel. All the leds burn like they supposed to do and match the settings of my amp. The problem is that when I press the footswitch, it doesn't do anything for a while.

Maybe I should start off with some contact spray? Or is this something that won't help?

Click to expand...

Ok everthing you are describing suggests that the cable is connected fine. Hitting it with contact spray won't hurt but I doubt that it will solve your problem. I also don't think it is the switches. Again hitting them with contact spray won't hurt but the odds of all the switches going out at the same time and tnen all of them working again at some point doesn't really make sense.

The major componet in the switching is a 74C922 device. Here is a link to the spec sheet on it.

http://www.datasheetcatalog.com/datasheets_pdf/7/4/C/9/74C922.shtml

There is a signal called the Output Enable on pin 13 of the dip package. I am assuming this is the package Mesa uses since I have not been inside the footswitch. If this pin is not making good contact the outputs of the 74C922 will go into what is called a high impedance state and allow the logic input of the next stage to float high. In this state no matter which of the switches you push nothing will change and it is also the output code for lead+eq. This is exactly the behavior that you are seeing. Is this the problem? I don't know for sure but it is something to go check. The device is probably soldered in. Make sure that there is a good solder joint particularly at pin 13. If the device is in a socket you can pull it. Sometimes when these devices are inserted into a socket a pin will miss and then curl up to the inside. It will make partial contact with the socket but it will be flackey. Also pay attention to pins 9 and 18 as they are the power pins for the device. Flakey connections here will lead to erratic behavior from the device.

A disclaimer. This is a guess on my part. It would be oh so much easier if I had the footswitch in front of me with some good test equipment. From everything you describe this could be it but very often there are surprises with this stuff. If you have experince with electronics this is something you can do. If not I would suggest a good tech. The solder joints for these devices are pretty close together and it does to some skill to touch them up without bridging the pins with solder. Good luck and keep posting your results.

EDIT : I made a mistake and thought the Output Enable was pin 12. It is pin 13. I have corrected this mistake in the text above.

I agree with Blueracer you probably have a faulty 74C922. Especially if it has been working for some time until now. Check also the 7805 voltage regulator for +5 volts output. I must also note these are static sensitive devices and you can damage them simply by handling them. I recently had a Nomad with a similar problem and it turned out to be a faulty 15 volt zenor inside the amp which was intermittently surging the + side of the low voltage supply and damaging the chips in the ft. sw. Probably should see a tech.

A year later...

I still haven't looked into this matter as I rarely gig and so I never use the footswitch. I'm thinking about getting it fixed though, because one never knows when he might need it and at that moment you want your gear to be reliable.

Is this component (74C922) located inside the amp or inside the footswitch?

This chip is inside the ft sw. Unfortunatly the switching matrix is for sure the most NON user freindly part of the entire amp system. If you are not equiped and experienced to trouble shoot a logic based switch save yourself some time and error and seek out a Boogie tech. If you have access to a known good MkIV and ft switch try to A/B them and narrow it down to the ft sw or the rotary switch in the amp. If it turns out to be confined to the actual foot switch then you could simply send that in to Boogie for repair.

I am currently helping someone with a footswitch problem. Check out this thread.

http://forum.grailtone.com/viewtopic.php?f=3&t=30607

If you think you can follow the same sort of directions as given in this thread and have some soldering skills and equipement I can probably help you. Otherwise sending the footswitch in for repair is probably the best you can do.

Very old thread, but NOS issue 8)

Im having troubles with my mk IV FS . . . after a gig saturday, put it in the bag, went home and voilá . . .stopped working the leds doesnt lit, the more "mechanical" switching, EQ and loop functions, still work, but the channel switching does not . . .what gives???

any help will be much appreciated! 8)