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    GM36 Store switch LED lights without being touched and amp goes quiet.

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    GtrPat

    Posts : 3
    Join date : 2018-07-19

    GM36 Store switch LED lights without being touched and amp goes quiet.

    Post by GtrPat on Thu Jul 19, 2018 3:28 pm

    I love this amp. Twice today my GM36 "Store" LED came on without being touched and the amp went quiet. Pushing switches and making adjustments had no impact on this condition. shutting the amp off and on brought it back to life. I use this amp frequently for shows and am concerned that I may be headed for reliability issue.

    The amp also has recently been shutting the output off and lighting the speaker kill switch once or twice per show. Pressing the speaker kill switch does not bring the audio back. Again shutting the amp off and on restores operation. It did this about a year ago and I replaced the EL84s. It worked fine for quite a while before starting to do this again. So I replaced the EL84s yesterday (Apex matched quad) and now when testing it before our next show this "Store" LED issue pops up.


    Anyone have a similar experience? Any thoughts on a cause or what this indicates? And more importantly is there a solution that I might perform myself? I know which end of the soldering iron not to grab.


    Thanks,
    Pat
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    RedCreep

    Posts : 2
    Join date : 2018-06-23

    GM36 Store switch LED lights without being touched and amp goes quiet

    Post by RedCreep on Wed Aug 29, 2018 2:46 pm

    Hi Pat,

    I'm having the exact same problem with my GM40. Just at random moments the store LED comes on, everything is silent and completely locked. It requires a power toggle to reset.
    It happened a few times yesterday during our rehearsal; very annoying!

    Did you get your problem solved and if yes, how?

    I just performed a factory restore and up till now the problem has not re-appeared but that is only 30 minutes or so.

    It might have to do something with our name ....

    Kind regards,

    Pat
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    bordonbert

    Posts : 1089
    Join date : 2015-01-28
    Age : 98
    Location : Southern England

    Re: GM36 Store switch LED lights without being touched and amp goes quiet.

    Post by bordonbert on Wed Aug 29, 2018 5:42 pm

    The GM36 is the only version whose schematic has escaped into the wild I am afraid but there is virtually the same setup in areas like this as far as we know at the moment.  The Store and Fx Access LEDs are on unique lines from the microcontroller and the Store and Fx Access switches share a single line.  They seem to simply pull the voltage on the line down to different levels which the controller then responds to.  The three lines are not involved in any way with any other area other than telling the microcontroller what you want it to do and displaying the acknowledgement.  If the Store switch, Fx Access switch and the LEDs work as they should in their normal usage that should show that they are ok.  Does the Store/Fx Access system work as it should under normal conditions?

    The two phases of your problem as you describe could be linked at least with one causing the other.  Your speaker kill coming on could definitely have been caused by the output valves so a new set would not have hurt at all.  Let's assume that has now been cured with the valve replacement.  It is possible that during that "episode" the programming could have been corrupted.  I would start by doing as Pat has done, perform a factory reset on the whole amp.  I'm sure you already know this but make sure that you have backed up your custom voice patches first!  The reset will wipe any custom voices you have created and replace them with the factory versions.  If this does not stop the problem then we have to assume it is a hardware issue and, if that is in the microcontroller board, it can only be fixed by qualified service personnel with access to the parts which you would not have.  If the amp is still under warranty then it should be covered under that.  That is as long as you have not invalidated the warranty by removing the sides or base cover incorrectly?  If not it could be a fairly expensive fix I'm afraid.

    Try a factory reset first and see if that solves the problem.  If it is currently happening pretty regularly you should know pretty quickly whether you have sorted it.
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    RedCreep

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    Join date : 2018-06-23

    gm36-store-switch-led-lights-without-being-touched-and-amp-goes-quiet

    Post by RedCreep on Mon Sep 03, 2018 3:26 pm

    Just to give some feedback.

    I'm still skeptical but after I gave my GM40 a 'factory restore' the problem has not re-occurred. This includes a full gig (fortunately) and a couple of evenings of playing and leaving the amp on for hours.

    Fingers crossed .....

    The whole process of back-up, factory restore and re-load presets is very straightforward and fast.
    I did loose my 'global' settings but that was a quick fix.
    I'm using midi channel 1 exclusively for the GM40 while using omni for the intellifex in the effects-loop. Both expression pedals on my midiboard (ART X-15) transmit at channel 2 exclusively.
    Not using any continuous controls on the GM40, just channel switching and on/off. I miss the range-ability on continuous controls on the GM40.
    After the factory restore the GM40 was reset to midi-omni.

    Thanks for the reply.

    I would be interested to know where to get the GM36 schematic. When I google for schematic GM36 I get the lay-out of a bus ! And, can you believe it, they have a GM40 model as well!

    Pat

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    bordonbert

    Posts : 1089
    Join date : 2015-01-28
    Age : 98
    Location : Southern England

    Re: GM36 Store switch LED lights without being touched and amp goes quiet.

    Post by bordonbert on Mon Sep 03, 2018 7:48 pm

    Glad it's stabilised Pat.  A factory reset is a useful thing for any unit with pre-programmed responses like the GM40.  It is asking a lot for computer style sections to work in close proximity to 400V electronics without the occasional glitch.

    I'm afraid we have to work within the parameters of not upsetting H&K in our posts.  While we are supporting their products as best we can we have built up a fair bit of goodwill which gets us some very useful information and advice regarding the technical aspects.  We can't give out any details of H&K schematics in our public posts, they are very protective of them as you can imagine.  They aren't a mass producer like Fender or Marshall who almost openly offer the schematics to their playing fan base.  The best I can say is that some of them are available on different forums.

    When you say "range-ability" do you mean the "useful usable range" of those controls in the audible sense?  If so I would guess you would include the basic tone controls in that.  Many of us feel the same.  I have found that the more you sort out your speaker choices and get some lower end back into the system right up to the mids, the more that aspect opens up.  I can confirm that in theory there is nothing wrong with the tone control setup at all.  Have a search for the thread where I set up Spice models of each stage of the amplifier and looked into how they do what they do.  The curves are still available on my hosting site.  The tone controls got an absolutely clean bill of health.  I just think that in an amp with virtually no bottom end being produced at all the Bass control is going to make precious little difference even though it might give a full range of boost down there.  After all 10 x 0 is  scratch  errrmm  bom   still 0.

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