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    A weird Issue

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    trb

    Posts : 61
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    Age : 51
    Location : France

    A weird Issue

    Post by trb on Wed May 18, 2016 8:04 am

    Hi GM36's friends

    I got a weird issue since few days:

    - the blue buttons on the control panel (FX access, Noise gate, etc.) and the ones at the back for power attenuator no longer work...
    - but with my Ipad, I can access to all midi features, as usual...

    I tried a "factory reset" procedure but no change for these buttons... weird ...

    Did some of you experienced such issue ?
    Thanks for your feedbacks.

    Bruno
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    bordonbert

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    Re: A weird Issue

    Post by bordonbert on Wed May 18, 2016 8:25 am

    Never come across this before TRB and it's very odd.  I haven't ever seen a GM schematic and can't say for sure but off the top of my head it smells as though the switches may work by maybe accessing relays or even the MIDI side of things and not the electronics direct.  For example, the TM has a power soak which is controlled direct from the switch.  In the GM it may be that the power soak is controlled via relays which are controlled by MIDI and by the switches, and that would be a very different configuration.

    As all of the switches have stopped working together, something in the power supply chain may have gone down which feeds all of that block of switching circuitry.  If the electronics which actually work the functions themselves is still powered up then the external MIDI control will be able to access it even though the local switches are not able to by whatever means they do so.  If you are able (i.e. have the skill and experience) to go inside safely, (DANGER: LETHAL VOLTAGES EXIST INSIDE VALVE AMPS), you could just try disconnecting any connectors from the board the switches are mounted on and connect them up again.  If this is caused by a little corrosion on the pins that should clean them up and start it working again.  Of course it could be something much more involved and may even be damage to the switch control circuitry.

    Anyone else able to throw some light onto this problem?  Am I talking total bo**ocks there?
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    bordonbert

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    Re: A weird Issue

    Post by bordonbert on Wed May 18, 2016 8:30 am

    Do the switches light up with their usual blue colour when they are pressed?
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    VoodooJeff

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    Re: A weird Issue

    Post by VoodooJeff on Wed May 18, 2016 9:09 am

    A couple of further questions: Do the buttons *function*, but not light up? Ie; if you press the button for the effects loop, does it turn on and off, just not light up?

    (2) Does it still do it with no midi device attached?

    It could be nothing more complicated than the power supply for the switch illumination (not betting on it, but possible), could be the midi card (some devices will default USB over midi if both are connected, and the midi card may be defecting to a similar command. Obviously not the right one. No USB here, but the failure may be similar)

    trb

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    Join date : 2014-07-26
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    Location : France

    Re: A weird Issue

    Post by trb on Wed May 18, 2016 9:15 am

    hi dears

    thanks for your quick feedbacks.
    When I press the front buttons there is no blue color appearing. And same for the back buttons, no orange color when pushing...

    In these few days, it had sometimes worked back, but when I power on again the day after, it no longer work... No chance today to make it work...

    @Borbonber: i'm pretty ok with someting with the power supply or relays, but I'm not sure to have a look inside...

    I can send it back to Thomann in my warrantee period.

    in the mean time any other ideas ?
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    bordonbert

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    Re: A weird Issue

    Post by bordonbert on Wed May 18, 2016 9:33 am

    Nope, sounds like it may need to go back to Thomann under warranty. In the meantime DO NOT open the end panels to have a look inside. You can void the warranty if you don't know what you are doing as there are tamper stickers on a few of the screws.

    With the intermittent nature of the problem from day to day it really sounds like something simple is at fault, like the contact somewhere in a connector I mentioned. This is a shame to have a problem like this on your new amp but if it is in the early stages of your owning it this is the period when most problems will occur. Every amp in the world has its share of problems. Don't let anyone tell you this points to H&K being unreliable in any way, it's just not true.

    Also bear in mind that if you have bought it direct from Thomann you have a European model with the mains transformer for their 220V. The UK 240V models can only be bought from within the UK, with the increased markup you will have noticed when you bought yours from Germany because we are all rich over here in comparison. king Officially we all use 230V now but in reality the UK uses 240V and Europe uses 220V. When we were "harmonised" all that happened was the tolerances were fiddled at both ends so there was an overlap so we could all say we used 230V. H&K may not be happy about that if you have to deal with them at any time as the UK mains voltage can technically go outside the recommended level but still be to national spec. I believe Thomann give the GM36 their own warranty so they can sell to the UK so you should be covered. I would find out about that situation just in case.

    trb

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    Re: A weird Issue

    Post by trb on Wed May 18, 2016 11:05 am

    I'm in France so no pb with 230V.
    It works like a charm with Ipad...

    edit
    @voodoojef: when I push the button, no color and no effect. no midi devices were connected like my FSB footswitch and Ipad.

    I think I'll send it back to Thoman (bought in 2014, under warranty)

    trb

    Posts : 61
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    Re: A weird Issue

    Post by trb on Tue May 24, 2016 4:51 am

    I was swapping my tubes for the factoty ones and.... it works again like a charm...!
    So swap back my personal tubes, and still works fine...

    So I postponed to send back the amp, and wiat for the next issue (warranty up to july 2017).
    Will keep you in the loop.
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    bordonbert

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    Re: A weird Issue

    Post by bordonbert on Tue May 24, 2016 7:13 am

    Glad to hear it's sorted itself out TRB but that sure is an oddity!  It is just possible that the problem is just a dirty contact in the valve base and either the TSC is affecting things when it detects something odd, or maybe a power supply is detecting something unusual about current draw for the same reason and shutting down.  That really is unusual.  Of course it could also be that the intermittent effect you described has just kicked out and it will drop out again soon.  I'll keep my fingers crossed for you.

    Thanks for coming back to us with this info.  Even though we don't understand why, we now know it is something else really simple to advise others to try when they get problems of this type.  It would help if we had the schematics for the GM36 but these are not out in the public domain yet.  It is very hard advising accurately on issues like this when you are working blind.  Logic is your best friend!

    As a piece of advice, if it happens again in the near future, swap your valves back to the originals just one at a time and try it after each one is replaced.  Start with the preamp valves in order V1 (with the cover), then V2 next to it, then go on to V3 and finally the output valves, one matched pair at a time.  This may take a bit more time but it's easy to run it up each time without putting the cover back on as long as you are careful to keep fingers away, and it will give you a suggestion as to where the problem may lie.  This could be due to a fault in particular valves (very unlikely as it does it with two valve sets), a socket, or the pcb joints around that particular valve.  Though it is not unknown, the infamous "dry" or "cold soldered" joint that sends people resoldering every joint in their amps almost never happens nowadays!  While lead free solder is an abomination, it takes a really poor piece of work to create that with automated flow soldering techniques.  My advice is not to be convinced to go down that route!

    Good luck and do keep in touch with us here.  We always love to have new members putting their own ideas and experiences into the pot for us all to share.

    trb

    Posts : 61
    Join date : 2014-07-26
    Age : 51
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    Re: A weird Issue

    Post by trb on Tue May 24, 2016 7:23 am

    Yes that's a good idea to test like this for the next issue (if there will be ...).

    WOuld like to have a scheme of the GM36 to better understand how is working.
    What's more, I would like to know how to improve the "bright side" of the GM36, like for example, with the cap value on the input jack... Very simple tweak to be done to tame the highs. Of course there are many others components making the bright feeling but, this one is a good starting point.
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    bordonbert

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    Re: A weird Issue

    Post by bordonbert on Tue May 24, 2016 8:03 am

    I can understand your need to work on the top end, the vast majority of us here who love the amp also reckon the GM36 is sometimes too prominent in that area. If you have a quick dig around amongst the other threads in this and the Tubemeister forum, (there aren't that many and it makes a nice half an hour browsing), you will find a lot of advice on speaker matching which is critical, valve selection which does have a useful effect, and other points including just what you said, the adjusting of tone with the loading cap.

    I run my own long cable system with a built in lineamp at the guitar end and a receiver box at the amp. This effectively removes all of the cable capacitance from the guitar, so the correct amount has to be added back. I have spent time playing around with the values and appreciate the way this can really affect tone. It's more than just treble cut, it's the pickup resonance frequency and is fundamental to the guitar's sound. My own feeling is this will help with your overall balance but won't help with any roughness at the top end as you are adjusting before the point where the problem occurs. You are going to get much more effect from speaker choice then valve choice which actually affect how the problem is produced, then altering signal details with guitar loading and eq in the effects loop.

    Other things to look for in the threads are Mitchell rings and anything on cabinets and the top end. This is a favourite topic of discussion on here and the info you will get is all sound and relates directly to your amp, not second hand common knowledge type of info which is never really accurate. This isn't a site where hopeful gurus post the stuff that they were told by other hopeful gurus who didn't understand it themselves. Guys who offer you advice are experienced and talk from a very balanced and sensible position.

    Regarding the schematic of the GM, not a chance! H&K are very tight with their control of these, just as they should be as a successful business with intellectual property to protect. The schematics and service documents are only released to their network of official service agents and they are instructed not to release them to others on pain of death. As far as I have seen they have stuck to that for the GM36. Unfortunately Wink .

    trb

    Posts : 61
    Join date : 2014-07-26
    Age : 51
    Location : France

    Re: A weird Issue

    Post by trb on Tue May 24, 2016 8:36 am

    Yeah Borbonbert, I agree.

    I checked the Mitchell ring foam, as I stated in another thread. A good effect, in addition to my tube swapping operation (all JJ with 5751 preamp).
    I finished with a foam disk (cdrom size) centered, works well, not too much muffled, less muddy than the ring. Installed on the G12M speaker in my 2*12 cab (other soeaker is the Eminence Cannabis Rex, a dark one).

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