Hughes & Kettner Matrix 100 Head needs fixing

[MrKnStR]

Hi Folks,

first off, nice forum you got going there. I'm new to this whole amp fixing thing, though.
Well, lets get to the problem:

My Hughes & Kettner Matrix 100 Head's effects broke down on me. Usually, it forget's the last selected channel and switches to the clean channel.
The clean LED keeps blinking and trying to change the effects or channels won't work. Master Volume still works though.

BUT, when i power down/up the amp several times while holding down all the channel buttons (effects reset), it occasionally works again with a chance
to brake down at any time while playing. That also seems to be the case, when i leave it unplugged a long time and fire it up after that. I contacted a local HK dealer who told me it could have to do with the electronic filter stabilizing the current to the effects circuit board (german term "Siebung"). IMHO, this would indicate a problem with the internal power supply unit.

Why in hell does it work sometimes after the above procedure??
After what i've heard, this is a common problem with this series of amps, but i couldn't find any solutions on the net nevertheless.

Any hints or maybe a service manual would be very helpful. Could it be a bad capacitor or something similar?


Thanks alot in advance for any helpful contributions,
best regards,
MrKnStR

EDIT: I almost forgot, the amp itself is a refurbished one and the problem started after I accidentally left it switched on for two days or so. Maybe that wore parts down, but I can't imagine anything except the capacitors to wear down over time. I never cranked it up to full volume, so it's not a heat/overload issue.

[J M Fahey]

Start by asking H&K themselves some service info or at least the schematic.
Without that it becomes an impossible task.
Good luck.

[marinozzetto]

Hello guys, I am very new in this forum.
I found this very old topic, because I have exactly the same problem of MrKnStR: the channel swicthes by itself to CLEAN, and the related LED blinks instead of staying on. The effects don't work anymore until I switch off and on the amp.
I would be very lucky if MrRnStr is still following this forum maybe having solved his issue but..does anybody know how to solve this?

thanks a lot
Roberto (from Italy)

[g1]

  Do you have experience (and tools/test equipment) fixing amplifiers?
Schematic is available here:  http://elektrotanya.com/hughes_and_kettner_matrix_100_amplifier.pdf/download.html

[Explauracat]

I've just bought a second hand Matrix100 that has the same problem. I do have electronic experience in repairs, but need some help where to start looking for this problem. Any ideas??

[J M Fahey]

Yes, start by downloading and studying its schematic.

[Roly]

Fault: Selection of various Fx is intermittent, randomly reverts to "clean".

Looking at the circuits it seems that it uses a footswitch selector arrangement that might be a bit too cunning by half.

Looking specifically at the circuit for the "floor-board" (p32 of 35) it becomes apparent that H&K have devised a multi-way switching and indication system that requires only a two-wire interconnect to the amplifier.

We appear to have a four-way cross-latching circuit which works like those old mechanical "piano-key" selectors, press one down and whatever was selected before pops up, except here it's done electronically.

But how does it signal its state back to the amp?

Well it appears that the state other than "clean" draw different currents when selected (R10, 12 & 14), and that the amp activates whichever Fx is selected based on the current drawn by the footpedal (a very similar system is used for the front panel controls of most VCR's etc).

But it all goes through a 1/4-inch plug/socket!  These are not noted for their reliability of connection and certainly not the connector I would have used in this application, an XLR maybe.

What will happen if this connection is dirty and intermittent?  It will revert to "clean" because C2 to 5 are chosen to make sure it powers up to "clean" as the default, so any interruption to the circuit will be seen by the pedalboard as a power up reset.

So my primary guess at the moment is that this frequent problem is simply down to a dirty pedal connector - give the plug and socket a really good clean and I'll bet the problem vanishes.  While it certainly could be something to do with the supply to this section the footpedal connector has to be the most obvious and primary suspect.