A bit more info...
If this should turn out to be a more complex problem then there is not a lot you will be able to do. H&K have a policy of not supplying spares to anyone but one of their approved repair centres. You would have to at least deal through one of them. And of course that depends on where you are based. In Europe things are great as H&K are German. Here in the UK it isn't too bad, tiny island nearby and all that. In the US things may be a bit more difficult with the distances involved.
In your message you described symptoms of craziness due to a MIDI issue. If you had other devices in the chain that sounds like it may have been your MIDI channels getting confused so the amp was responding randomly to signals that were not meant for it. That may have passed and gone and things have sorted themselves out but have you performed a factory reset since then? Problems like that one could maybe be due to glitched software, and that can happen with just the slightest of errors in the installed code. You could try that just to rule out software corruption as a factor. It isn't highly likely but it is a possibility after such a strange problem. Bear in mind, you will lose all of your current settings and any precious presets!!! Don't do it unless they aren't important or you have made a backup off the amp through the app.
For the record the MIDI messaging and control section is completely separate from anything signal related, it doesn't even touch it, and MIDI circuitry is made bombproof in terms of its affecting things like power supplies. You can short out MIDI lines without any fear of damage being caused inside the amp. (Don't try putting 100V across there to test that, there are always limits!
) It is only connected to the digital processing system to pass on decoded messages and it is that software based side which orders the changes in the amp. The switching in the analogue signal circuitry then acts on them. So I find it hard to see the MIDI area as a factor in this other than having possibly messed up the software and even that is a stretch.
All that said, if the amp is working as it should with the loop disengaged then the basic functionality is fine.
A simple thing, does the LED in the Fx Loop switch turn on and off as it should? That LED is in the signal line from the switch to the processor so it will give us an indication as to whether the switch is working and whether it is sending the correct signal or not.
I couldn't pick up on whether the amp worked with the loop engaged with that switch and with the patch cable across the loop sockets. Do you get sound like that? That would confirm whether there is a problem with the buffer or not.
The problem has to be somewhere around the signal line in the loop. We wouldn't be talking about the small Effects Board, that is only for the amp's own internal effects and not external pedals. It is in circuit all of the time with no switching in and out involved. The things that could be involved would seem to be the Fx Loop switch which engages it, the Send buffer, the Loop Send and Return sockets, and the solid state switching IC which controls the whole selection process. These should all be checked out by the simple tests we have mentioned which you can set up. So get these tests done: the Fx switch LED on/off action, signal from the Send socket into other amp, signal from other amp Send or a pedal into Return socket. The results of those tests should tell us whether there is something more serious wrong.
Just for info, the loop is engaged by a solid state switching IC which selects and passes on either the unaffected signal or the signal returning from the loop to the following preamp circuitry. The signal sent to the Loop Send socket is hooked up constantly, whether the Return signal is selected by that IC is what engages the Loop. The chip also performs other changes to the preamp circuit setup which have nothing to do with the loop and won't be involved. There is a LOT of switching of tonal circuitry going on due to channel selections and it is all controlled by a series of these switches. The changes take place in the preamp section on the micro-controller and digi-pot board. These switches are complex 16 pin surface mount chips and not relays so are not easily replaceable without special SM rework tools. I wouldn't touch that side of things myself without a proper station in a workshop, and I had a career of doing work like that at a high level!
If you can, add a factory reset which will reinstall the software back to its original level to the tests you have lined up. It's a good thing to do from time to time for any amp of this type. Answering those couple of simple questions will help too.
Home
