Grandmeister effects stopped working

During soundcheck last weekend my Grandmeister 36 amp was working normally. The sound guy happened to own the same amp, and at some point he connected his amp and cab to mine. I have no idea what exactly he did or what all cables he used, but all of a sudden my amp completely changed. The amp is now making popping noises every five or six seconds. Also, all my presets are still there, but the amp can no longer access the onboard effects. I have tried to access the effects using both the amp itself and an iPad without success. I have done a hard reset by pressing the store and fx access buttons while powering on, but this did not fix the problem, the amp is still popping and I still cannot access effects. Does anyone know what might be causing this and how I could fix it?

Sorry to hear about your problem Ismith. You say "The sound guy happened to own the same amp, and at some point he connected his amp and cab to mine." That could mean a number of things, not all of them good. What was he trying to achieve by doing that? Nothing can be passed between two amps and they certainly can't be used to drive the same speakers together.

If it was just MIDI connections he played with then there should be no damage. MIDI hardware is set up to be virtually bombproof when connecting among itself. It is possible that, as a sound guy, he was just using the Red Box out into his own FOH desk. He may have been trying to connect the extra amp via the other amp's Line Out so they could both work under the control of one preamp. None of that should have caused any problems unless he has plugged something into the wrong socket.

I'm afraid it's impossible to say what could actually be wrong without knowing something about what has been connected to what. Can you get any more info from him which might help?

One thing we should know is, is the amp working in the meantime? I mean, is the problem just the effects so you can play through it as normal without them and it just doesn't add the effects into the signal when told to? Or has it given up the ghost completely and is now just not playing any music? (It must be working on some level to hear the popping.) Do you see the lights on the switches change when you try to access the effects and select different settings?

That popping noise can sometimes be caused by a valve going down on you but it doesn't explain why the effects should drop out as well.

The amp is working normally and I can play through it, except for the popping and the lack of effects. I can switch through all the different midi presets I've got saved and everything is the same, except the effects are gone. Trying to add effects using the amp itself as well as an ipad does not work. I do not know what was connected to what, but I do know that the sound guy had a cable connected to the midi out of my amp as well as the line out and the redbox out of my amp. Thank you for your reply.

Ok, that sounds good.  We know the amp is actually working and the problem is isolated to the effects section.  It would be a sensible guess to suggest that the MIDI control lines are working as you can use them to change channels and basic settings from the iPad.  Have you been able to test the Line Out and Redbox Out connections?  If you haven't it would be good to check them as they are the ones the sound guy actually says he interfaced to.

The connections to MIDI Out, Line Out and Redbox Out should have had no direct effect on the effects circuitry other than to tell it to change via the MIDI and even that is done from elsewhere in the control section.  Your MIDI socket only transfers the request signals to and from the control processor, it doesn't access the effects unit directly.  Each of those connection lines is isolated from the inner circuitry by its own buffers.  There could be damage to the buffers but not to anything further into the circuit.  That's one of the important reasons we use buffers in electronics, they are sacrificial and save more complex or sensitive or expensive circuitry elsewhere!

If the amp is responding to changes to channel and the other parameters and it is only the effects which are not responding it really sounds as though the problem is either with the Effects PCB itself or with the digital control circuitry specific to the effects area I'm afraid.  The effects unit is a standalone PCB which mounts onto the controller board and is not serviceable in any way being based around surface mount microprocessor and other custom chips.  If it turns out to be that it would mean a replacement board unit.  The official H&K designation for that is "Effectboard H&K 8xDSP" Part Number: 9590161.

It is possible that the control circuitry on the microcontroller board has been damaged in some way.

In the meantime, the popping could be down to other things and may be fixable yourself.  The simplest cause would be a valve going down and that should be ruled out first.  What is your TSC telling you when you access the "pickup switch slot" on the back?  Are the output valve bias readings on the LEDs as they should be?

If you can get your hands on a spare couple of working valves, one 12AX7 and one or a pair of EL84s, you could change each one out, one at a time, for the known good one and see if the popping stops.  The output valves should ideally be swapped out as a pair, either both of the outer two or both of the inner two, but if you only have a single EL84 handy you could get by exchanging one at a time just to test this.  If you can't get a spare 12AX7 try swapping first V1 and V2 and see if the popping changes character.  Swap them back and then swap V1 and V3 and look for the same.  It is unlikely to stop under those conditions as the three valves are still in circuit but it should change if a preamp valve is faulty and is moved to a different place in the signal chain.  If you don't have an EL84 handy you could just try swapping the inner pair for the outer pair, (that is 1<->2 and 3<->4 numbered from one side to the other).  When you then engage the 18W selection on the power soak the inner pair are disconnected so if the problem goes away when you do that you have a suspect output valve in the inner pair, (or maybe even both in that pair).

If what the sound guy is telling you is true about his connections I can't see how he could have caused this.  And I'm afraid H&K will not supply spares such as the PCB boards to plain old users.  They will only release them to recognised service agents.  If you do find you cannot do anything yourself it will mean a trip to your friendly tech guy for a repair.  That could start as just investigation into what is wrong.  Having the unit in front of him would certainly make the diagnosis much easier to come up with.

Anyway, try some of the simple tests above and let us know what you find.