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    GM36 Randomly Switching To Silent Mode

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    PatF

    Posts : 5
    Join date : 2016-01-19

    GM36 Randomly Switching To Silent Mode

    Post by PatF on Tue Jan 19, 2016 7:35 am

    My GM36 is almost 2 years old. I love this amp and use it for live shows almost exclusively. Recently it has started randomly switching to silent mode (speaker with a line through it switch lights up) 10 to 30 minutes after power up. I can't find any other indicators. The only way I have found so far to get it out of silent mode is to cycle power. Once that is done the amp functions fine for the rest of the show. My concerns are that it is doing this more and more frequently, it has to be a glitch or some sort of trouble indicator and then there is now the nagging concern now that this thing is going to interrupt a show at some point way worse than it already does...

    Any thoughts or insight to this behavior would be greatly appreciated. Thanks in advance for any help solving this. My first email sent to H&K support a couple of months ago has gone unanswered...not like them...
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    bordonbert

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    Age : 97
    Location : Southern England

    Re: GM36 Randomly Switching To Silent Mode

    Post by bordonbert on Tue Jan 19, 2016 8:41 am

    I can't find this in the manual but I'm sure I read that the amp kicks into this mode when there is an output problem as a protection mechanism, and mine did this a couple of times when I was new to it and playing with my speaker setup.  I think that disconnecting the speaker when live was detected and it went into this mode.  A couple of things to do to get background info:

    Have you checked out your output valve bias with the "magic plectrum"?  This is always good to monitor occasionally.

    Have you tried using a different speaker cable, (possible shorting or open circuit)?

    What speaker setup are you using, (possible impedance too far out of range)?

    We would point out here that getting on to the H&K Facebook site is a better way of talking to them.  They seem to monitor and respond better there than by plain email. Try here:  H&K Product/Service

    Anyone else offer any thoughts as to the switching?




    (EDIT:  Why am I showing your avatar in the personal section of my post?  Are you seeing the same thing out there?)
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    PatF

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    Re: GM36 Randomly Switching To Silent Mode

    Post by PatF on Tue Jan 19, 2016 11:26 am

    Thanks for the quick response to my post.

    I recall something to the effect of it being a safety feature too, but haven't run across it again in researching this issue.

    I will check the output tube bias...haven't done that as there haven't been any trouble indicators that I've seen so far besides this behavior.

    Haven't tried a different speaker cable either I made it so I am confident it should be OK and for that reason alone I will check it out.

    Relatively new 16 ohm Warehouse Guitar Speaker in a new cab. It looks (wiring & mounting) and sounds OK nothing but good tone throughout shows.

    I am baffled that the amp does this shortly after warm up and then performs flawlessly for the rest of the show then one to ten shows later it does it again. I really don't want to lose my confidence in this amp.

    I will do some more digging and have posted on the Facebook page as advised. Thanks again.
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    PatF

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    Re: GM36 Randomly Switching To Silent Mode

    Post by PatF on Tue Jan 19, 2016 3:56 pm

    Speaker and cabling are good. Magic pick revealed that on pair of the quad was biased considerably different from the other and that one of the tubes in one pair were was way off from the other other. Replaced with a matched quad I had on hand. I have to wait and see if the problem reappears now.

    Thanks for the suggestion.
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    bordonbert

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    Re: GM36 Randomly Switching To Silent Mode

    Post by bordonbert on Wed Jan 20, 2016 7:27 am

    Aha!  I would say that could well be significant.

    One thing I have found with my own is that this can be reported and for some reason, when you reseat the valves, it clears.  I had the same experience as yourself, the outer pair read as a good match but the inner reported a massive difference between its two valves.  I swapped the inner and outer pairs to try to get more life out of them with the 18W power soak on, (outer pair are switched off), while I sourced a new set and, what do you know, they then all reported to be perfectly in balance again.  I reckon it could be down to simple corrosion on the pins which got cleaned up with the wiping action of pulling out and pushing back in.  You could try replacing all of the original valves and checking again just to see if that's the case.

    How often are you gigging and rehearsing?  Will you be using the amp in a non critical way at gigging volumes before your next gig?  And what power soak setting do you generally use.  If it's 18W or below then you only really need a good pair in the inner slot to prevent this from happening.
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    PatF

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    Re: GM36 Randomly Switching To Silent Mode

    Post by PatF on Wed Jan 20, 2016 9:25 am

    I use the amp gigging and rehearsing 3 to 4 times weekly. I do use it with the red box most of the time. So I should know if this solved the problem within a week or two max. I read about the potential or suspected corrosion issue(s) of tube pins or sockets in another thread however once the original tubes were removed I never put them back in. Next time I have the amp open I'll try that. BTW the two el84s that were out of were the active ones when the red box is engaged.

    Thanks for sharing your knowledge and experience. I'll update in a few weeks if no issues occur before then.

    kurowan

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    Join date : 2016-02-01
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    Re: GM36 Randomly Switching To Silent Mode

    Post by kurowan on Mon Feb 01, 2016 10:18 am

    hello, my amp had the same problem , because of faulty MIDI module happily under guaranteed. Hoping it helps you in.
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    PatF

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    Re: GM36 Randomly Switching To Silent Mode

    Post by PatF on Mon Feb 01, 2016 11:04 am

    Well I thought it was OK for a while...but it did it again last night. After changing the el84 tubes it ran fine for lots of rehearsals and several gigs then last night it did it again. Exact same symptoms: early on within 20 to 30 minutes it switches to silent mode and has to be power cycled to get out of silent mode and then runs fine for the rest of the night. Anyone know of any good service centers in Southwest Florida???

    ConradK

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    Join date : 2015-09-09

    Re: GM36 Randomly Switching To Silent Mode

    Post by ConradK on Tue Mar 01, 2016 10:34 am

    Hey PatF

    Did you get this sorted? My amp has started doing the same thing. It plays fine for hours and then suddenly i am experiencing volume drops (sounds like a bad cable initially)

    It first appeared when i was using the volume pedal and eq pedal through the loop - (i am using the correct volume pedal) and it has worked for months in this configuration and then suddenly it started misbehaving.

    I have subsequently stopped using anything the effects loop and it semeed to stop however last night it reappeared (playing through the front of the amp)
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    bordonbert

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    Re: GM36 Randomly Switching To Silent Mode

    Post by bordonbert on Tue Mar 01, 2016 1:24 pm

    Do you mean the volume pedal was in the loop with the eq pedal both acting directly on the signal, or was it a midi one acting to control the Volume knob?

    kurowan

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    Join date : 2016-02-01
    Location : France

    Re: GM36 Randomly Switching To Silent Mode

    Post by kurowan on Tue Mar 01, 2016 2:21 pm

    https://youtu.be/cnsqz4Wz74c

    If this is the same problem as in the video I returned the amp and they replaced the card "uC and Digit Pot Board" that was defective.
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    bordonbert

    Posts : 815
    Join date : 2015-01-28
    Age : 97
    Location : Southern England

    Re: GM36 Randomly Switching To Silent Mode

    Post by bordonbert on Wed Mar 02, 2016 9:00 am

    Excellent news. It did sound like a digital control issue rather than anything to do with the basic amp. Good to hear H&K sorted it pdq.

    Did you other guys get to the root of your problems too?

    ConradK

    Posts : 81
    Join date : 2015-09-09

    Mine is going back to to the dealer this week and then onto h and k to sort - ill be back in touch

    Post by ConradK on Thu Mar 03, 2016 5:22 am

    Mine is going back to to the dealer this week and then onto h and k to sort - ill be back in touch

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