PCB board is dead and apparently no longer supported by HK?!?

Hi all,

My 4yr old grandmeister 40 died about a month ago. I had noticed the volume cutting across all channels a couple of times and simply switching on and off seemed to immediately fix the issue.

However, while playing it completely died, all lights on and no errors showing but no sound at all.

Brought it to an authorised amp repair in south U.K. they diagnosed problem as faulty PCB board ( not the first they have seen with HK either).

They contacted HK for replacement part only to be told that the part it is no longer manufactured and hence the amp is not supported for repair with that fault. In fact they have no PCB boards left so I assume no new grandmeister 40s being made either.

They have not offered the repair shop (note this is an authorised amp repair dealer) any alternative either so that is it at the moment.  

Very disappointing service from HK, love my amp and the 2x12 HK cab but looks as though it was an expensive waste of money.

I would love to hear of any suggestions anybody might have about how to salvage the amp. If not it will end up for sale as parts I suppose.

Thanks for any help and advice on this.

Philip

Woah, that really is not what we want to hear is it? It is very surprising that a 4 year old PCB is now unsupported. I wonder if there is something more going on here. Can you give me any more info on the nature of the problem?

Do you know from the repair shop which PCB the fault was in? This is a key point in knowing how best to proceed. If you don't know you could contact them and ask. I assume you have paid them for the work so far so you have a right to any information they have found out.

Do every one of the valves light up and glow as they should?

With the amp in its faulty state, was there any noise at all coming from the speakers and I mean any slight background hiss or hum with your ear pressed against them? This could show whether the problem is right at the end of the chain, maybe around the output stages and power soak area. If it is earlier then I would expect there to be some power amp hiss and hum just audible.

A couple of things to try which might help to begin to tie down the area of the fault:

Assuming there is background noise, does it increase as you turn up the Master Volume control?

Put a guitar lead into the Fx Return socket and play directly into the power amp. Does that give any sound? If it does it shows the power amp and the power soak setup are working as they should.

Are you able to take a lead from the Fx Send socket into a different amp's Fx Return socket? That would show whether the preamp is still working.

This last is a bit of a punt. With a working amp turned up high, when any control is turned, say the Volume or Tones, you can hear a slight digital buzz as the control steps up and down through its values. Is there any sign of that? If this is in the digital area of the amp then you are up a gum tree I'm afraid. If it is in the audio areas then it may be fixable by a decent tech with an interest, though probably not economical for the service centre to do it.

Hi and thank you for the detailed reply.

The unit is still with the Amp Repair centre, they are trying to see if they can find any alternative solution and they are continuing to chase HK support, I have emailed HK support directly as well but they have not responded.

The only additional info that I had from the repair centre was : 'The tube flashover has done a lot of damage not only to the output stage but also the pre-amp'

Not sure if that helps you at all.


I can answer some of your questions though:

Do every one of the valves light up and glow as they should? Yes they did

With the amp in its faulty state, was there any noise at all coming from the speakers and I mean any slight background hiss or hum with your ear pressed against them? Yes very low volume and lacked bass, sounded very fuzzy, putting master volume on max made little or no difference. This was the same when using the Red Box in the amp

Assuming there is background noise, does it increase as you turn up the Master Volume control? only a tiny bit of difference in volume


This last is a bit of a punt. With a working amp turned up high, when any control is turned, say the Volume or Tones, you can hear a slight digital buzz as the control steps up and down through its values. Is there any sign of that? I never noticed anything like that.

That's great info you've given Phillip. It seems that the amp has suffered a "flashover" which basically means that the HT has jumped across a space, (usually on a PCB between tracks but sometimes between cables or terminals), and blown a lot of less tolerant components. The highest voltages are found in the output stage so I guess this is what they mean. The power amp HT has flashed over and damaged components around it and this has also travelled to the preamp section and damaged circuitry there. They share the same PCB so that is perfectly feasible. I would guess this certainly means a new PCB or a fair bit of time spent chasing down and replacing damaged components.

I can't be certain as I only have access to the GM36 service info but the preamp and power amp are on the same PCB for that model and the GM40D should have at least a shared family design at the basic level. We are looking at the "Mainboard" - most probably. I hope it has restricted the damage to that board alone, if it got into the digital control circuitry on the uProcessor PCB that is another level of complexity - and cost.

There is absolutely certainly nothing you can do yourself other than try to source a working PCB somewhere, and the phrase "hen's teeth" springs to mind. One thing I can help with is that H&K are notorious for not keeping up to date with emails and website messages. They are quick to respond to queries made publicly on Facebook! Search for Hughes & Kettner and look for "Product/Service" under their name. There are a few other sites based around the H&K name but that one gets you to them. Post your queries there and they usually respond pretty quickly. They aren't a massive industrial complex and the support staff are often out on the road at various events so they tend to use social media as a quick way of helping out.

I must admit this is the first time I have heard of this issue with any H&K amp, their designs are usually rock solid. Is there any suggestion of something getting into the amp and causing this? It hasn't had any any problem like amber liquid spilt on it has it? If this genuinely turns out to be a non-supported PCB issue after the relatively short time the GM40D has been available I am very surprised and disappointed with H&K. They usually are much more customer friendly than that.

I just found this online.  In the event of the service agent not being able to help this guy might.  Keld Ampworks Newark.  Be aware, I am NOT PERSONALLY RECOMMENDING this guy, I just found him when I searched for H&K GM40D flashover and he showed up as someone who is not afraid of tackling a modern amp like the GM40D.  He seems open about his rates, it's all there on his site.  Maybe worth checking out. If anyone has experience of his work let us know.

I took it on myself to contact Keld Ampworks and fill him in on your problem Phillip.  It may help us in the future to know there is a repair shop out there who will actually take on H&K amps.  He came back and asked if I can point him to any pics of the issue.

I think it is reasonable for him to need to see the state of the PCB before giving you a yes or no on whether he can help and if it is worth your while.  The flashover could be just a one off event because of something intrusive which just needs a repair and then a PCB clean, (a spillage of "lunatic's broth" is common but I have seen unlucky curious insects cause it too), or it could be that the PCB is physically burned beyond repair.

How are you sitting at the moment with the current repair centre?  Would you be able to get any pics of the damaged area which we could send to this shop for an opinion?



EDIT: This is a bit remiss of me but I should have pointed out that a flashover can possibly occur inside a faulty valve. The original fault may not have been caused by the amp itself. I would have thought that a valve fault would have blown the HT fuse though some other components like the TSC circuitry make faster fuses than fuses do! In this case, as it has spread to the preamp section, it sounds like it has been on the PCB itself but bear that in mind.

Hi BordonBert,

Thank you for going to so much trouble to investigate this.

In regards to usage the amp has had a very easy life, only used at home and certainly never had anything spilled on it.

I can ask the current repair centre if they can send some images of the PCB across to me and any test results that they have found so far. If they are not forthcoming then I can just get my amp back from them, will have to do that anyway at some point regardless of outcome.

That sounds good Philip. Pass them on here via the "Host An Image" icon above into a reply, or by using the "Add Reply" button which allows you to select and upload them directly. I can point him to the thread then.