Amplifiers that are a total pain in the arse to repair and reason(s) why ?

Telejester

I'll be in honest in saying I had a solid state Laney combo back in the 80s before I owned a    quite wonderful Peavey bandit 65. The Laney was a pile of junk, but I would be expecting a monumental leap in quality with the lh20 head.

DJH83004

I've only worked on one Lionheart l20h and from memory it had the classic thermistor fault in the heater supply circuit, which I replaced with a fuse, oh and it did have a tatty handle for reasonably new amp

ICBM

Well, after all that the Valve King wasn't too hard to repair - Peavey don't have spare PCBs though, so it's lucky it was!

The burned-out component was a resistor not a diode, and it was in the valve-monitoring part of the circuit rather than the 'Vari-Class' - although it had the same result (no output) since the circuit shuts down the amp if the bias is outside the correct range - or if it thinks it is because one of the resistors has burned out…

It's sort-of a good idea, but it still strikes me as unnecessarily complicated and likely to cause more problems than it solves - particularly as with a major power valve short, it fed the full HT into a 15V part of the circuit with rather predictable results! The dead valve also took out its pair, and the phase inverter valve… I'm not sure how but I find it hard to believe it's a coincidence. But after cleaning the board, replacing the missing resistor with a conventional 1/4W one (which should show the small scale of all this) and fitting some new valves, it all - somewhat to my surprise - seems to work fine.



I still wouldn't buy one though.

Edit - bugger, that didn't last long! Ran for about ten minutes then redplated and shut itself off again. At least the new resistor didn't burn out so it's not exactly the same fault again. The next question is what else is wrong with it...

ICBM

I'm going to add the Fender 'Pro Tube' Twin to this list - the early-2000s one with a deeper cabinet than normal and extra chassis screws in the cabinet.

I have to change the Presence pot on one - it's had a bash and the shaft was bent and wouldn't turn properly, and of course when I tried to straighten it I got to about 90% of the way there and then it snapped off.

Replacing the pot is a nightmare - to do it properly you have to remove the front PCB which holds all the pots… so far so normal, but this one is joined to the main PCB with about 20 short solid wire jumper links, so to get the board out, either I'm going to have to cut every one of these and solder them back together afterwards (I don't really like doing this) which is still quite a big job, or to avoid that the only other way is to remove the main PCB as well, which is a *huge* job.

So I've decided to bodge it - by destroying the old pot above the board, soldering some flying leads to the solder pads and fitting a chassis-mount pot through the hole. I'm not proud of this, but the owner is just trying to sell the amp and I don't really want to cost him the thick end of a hundred quid's worth of work when I can do it for thirty. It's lucky it *is* something I can do this way rather than something where there would be no choice...

DJH83004

No shame in that IC, I have soldered flying leads onto pots & PCBs many times, particularly when the pot is a special and unobtainable, or the amp is borderline to repair or scrap.

Gassage

Lazy J cos I have to drive to Jesse's to get it sorted and then inevitably have to put a deposit on an amp.

kipple

ICBM said:

kipple said:

Do you have any experience of problems with Fender 15 watt EVH 5150III LBX. It runs on EL84
Do you know anything about build quality reliability .Is it easy to work on

Do you know can the Amp be biased when it is time to change tubes or does it need tubes that fall within a certain range.

Sorry, I don't have any experience with them at all.

It doesn't look particularly fun to work on…

https://www.gitarrebass.de/wp-content/uploads/2016/03/EVH-5150-III-innen.jpg

There's a trimmer at the right hand side of the pic (blue, partly hidden by a cable tie) but I don't know if that's a bias control or not.

Just in case anyone has a 5150III LBX
I finally got around to checking out the Trimmer pot shown in the picture and it is definitely A Bias trimmer pot. I biased the Amp yesterday using the trimmer pot.
Cheers Ian 

jpfamps

ICBM said:

I'm going to add the Fender 'Pro Tube' Twin to this list - the early-2000s one with a deeper cabinet than normal and extra chassis screws in the cabinet.

I have to change the Presence pot on one - it's had a bash and the shaft was bent and wouldn't turn properly, and of course when I tried to straighten it I got to about 90% of the way there and then it snapped off.

Replacing the pot is a nightmare - to do it properly you have to remove the front PCB which holds all the pots… so far so normal, but this one is joined to the main PCB with about 20 short solid wire jumper links, so to get the board out, either I'm going to have to cut every one of these and solder them back together afterwards (I don't really like doing this) which is still quite a big job, or to avoid that the only other way is to remove the main PCB as well, which is a *huge* job.

So I've decided to bodge it - by destroying the old pot above the board, soldering some flying leads to the solder pads and fitting a chassis-mount pot through the hole. I'm not proud of this, but the owner is just trying to sell the amp and I don't really want to cost him the thick end of a hundred quid's worth of work when I can do it for thirty. It's lucky it *is* something I can do this way rather than something where there would be no choice...

That amp is indeed a total sod.

I've seen several that motor boated when the fx loop return level was turned up due to poor filtering.

The design hangs 8 (yes eight!) triodes of one power supply node, which is asking for trouble.

Removing the main PCB is a major undertaking.

Danny1969

On my bench at the moment, AER AcoustiCube 3 . This thing costs a fortune.  There's 2 faults, hum with no input jack inserted ...






well that was easy, jack socket switched contact is bent and doesn't ground when lead is pulled out. The other fault is a bit of a bugger, when the second channel is switched to line where's no signal. Now the switching seems to be logic gate or flip flop triggering many relays all over the board, never seen so many relays in an amp and no idea why it needs to be this complicated bearing in mind the 3 different amounts of gain needed to reproduce mic \ line and Piezo 

Disassembly isn't too bad, the IDE cables are glued but only require a some gentle heat to release. If you bend the front panel slightly you can remove the pre amp PCB without taking out the rear PCB first. It's a mixture of thru hole large component and a lot of SM but nothing tiny

Unless anyone's see and done this fault before and can help @ICBM it looks like it's gonna be a long afternoon hunting down the fault 

ICBM

Sorry, nothing I can help with. I don't remember ever having to work on any AER amp, except a very early one for a blown speaker.

jpfamps

I've worked on a few AERs, but as they don't supply schematics, and are often very complex, I usually swerve them.

It does help we work opposite Westside Distribution, so can send people over to them.

ICBM

Another one... not actually difficult to work on, but still a total pain in the arse to repair.

Roland KC-880 keyboard amp.

It has top-mounted controls, which as you probably know by now I dislike - one of the reasons why is that it's far too easy to damage them, if something gets put/dropped on top of the amp. This one has had something heavy dropped on it by the look of the panel, and it has smashed the master volume pot.

No problem you would think - except that it's a PCB-mounted *5*-gang pot!! So not only extremely difficult to unsolder without damaging the board - although my usual method of carefully destroying the pot should work, it will be very time-consuming - but good luck finding that... I'm sure I've never even seen one before. I'll try Roland but past experience suggests they won't have it in the UK, if at all.

WHY?! Surely even in a stereo amp - which this is - a dual-gang should be all it needs? This just seems like needless complication for the sake of it.

Worse, the owner needs it for an important gig next week... so the simplest solution is just to jam the remains of it in the full-up position, solder across the top two pins on each gang to make sure, and call it a field repair, since it still has individual channel volumes .

jpfamps

ICBM said:

Another one... not actually difficult to work on, but still a total pain in the arse to repair.

Roland KC-880 keyboard amp.

It has top-mounted controls, which as you probably know by now I dislike - one of the reasons why is that it's far too easy to damage them, if something gets put/dropped on top of the amp. This one has had something heavy dropped on it by the look of the panel, and it has smashed the master volume pot.

No problem you would think - except that it's a PCB-mounted *5*-gang pot!! So not only extremely difficult to unsolder without damaging the board - although my usual method of carefully destroying the pot should work, it will be very time-consuming - but good luck finding that... I'm sure I've never even seen one before. I'll try Roland but past experience suggests they won't have it in the UK, if at all.

WHY?! Surely even in a stereo amp - which this is - a dual-gang should be all it needs? This just seems like needless complication for the sake of it.

Worse, the owner needs it for an important gig next week... so the simplest solution is just to jam the remains of it in the full-up position, solder across the top two pins on each gang to make sure, and call it a field repair, since it still has individual channel volumes .

Have you tried Chipquik?

https://uk.farnell.com/chip-quik/smd1/removal-kit-smd/dp/1850214

It's a very low temp solder and flux that is really aimed at SMD work, but I also use it sometimes for through hole components, especially getting the DPDT switches off MXR pedals as the traces are verrry thin.

It's not cheap, but it's great at getting components off the PCB without damaging the traces.

My default method before this was similar to yours, cut the component down so that the pins can be removed individually, apply some flux and leaded solder and remove the pins one by one.

Danny1969

ICBM said:

Another one... not actually difficult to work on, but still a total pain in the arse to repair.

Roland KC-880 keyboard amp.

It has top-mounted controls, which as you probably know by now I dislike - one of the reasons why is that it's far too easy to damage them, if something gets put/dropped on top of the amp. This one has had something heavy dropped on it by the look of the panel, and it has smashed the master volume pot.

No problem you would think - except that it's a PCB-mounted *5*-gang pot!! So not only extremely difficult to unsolder without damaging the board - although my usual method of carefully destroying the pot should work, it will be very time-consuming - but good luck finding that... I'm sure I've never even seen one before. I'll try Roland but past experience suggests they won't have it in the UK, if at all.

WHY?! Surely even in a stereo amp - which this is - a dual-gang should be all it needs? This just seems like needless complication for the sake of it.

Worse, the owner needs it for an important gig next week... so the simplest solution is just to jam the remains of it in the full-up position, solder across the top two pins on each gang to make sure, and call it a field repair, since it still has individual channel volumes .

Ha ha, that's exactly how I fixed the last one that came in to me. Heavy amps those too ! right pain in the arse to lug about

ICBM

jpfamps said:

Have you tried Chipquik?

https://uk.farnell.com/chip-quik/smd1/removal-kit-smd/dp/1850214

It's a very low temp solder and flux that is really aimed at SMD work, but I also use it sometimes for through hole components, especially getting the DPDT switches off MXR pedals as the traces are verrry thin.

It's not cheap, but it's great at getting components off the PCB without damaging the traces.

I will have a look, that sounds useful.

Danny1969 said:

Ha ha, that's exactly how I fixed the last one that came in to me. Heavy amps those too ! right pain in the arse to lug about

Very - the side handles are horrendous, there's too short a gap between the crossbar and the top so they try to break the back of your hand. Very poorly designed amp in so many ways.

I'm actually hoping that the 'field repair' is sufficient to make it unnecessary ever to do the proper job... or see it again. But I have a feeling that it will be back like a bad smell.

shady

What no JTM60/JCM600 stories? I actually really liked my 3x10 JTM, although it did start to quietly crackle intermittently just before I moved it on. 

ICBM

shady said:

What no JTM60/JCM600 stories? I actually really liked my 3x10 JTM, although it did start to quietly crackle intermittently just before I moved it on. 

They’re actually not hard to work on, despite being an utter pile of junk. In particular, changing the transformers is a piece of cake .

A chap I know had the 1x15” one, that sounded nice too - he used it for a long time before he finally got fed up with it breaking down, after its second OT failure.

Kalimna

Out of interest, what is it about the JTM series that makes them unreliable?

shaunm

Kalimna said:

Out of interest, what is it about the JTM series that makes them unreliable?

The JTM45 Reissues I believe are pretty good. Is this correct @ICBM ?

ICBM

Kalimna said:

Out of interest, what is it about the JTM series that makes them unreliable?

Stupid physical layout with poor cooling - actually *heating*, the hot air from the power valves goes straight up into the chassis - poor transformers, plastic valve sockets which melt, fragile speaker jacks, flimsy speaker cables, crap pots, power resistors which desolder themselves...

An object lesson in how to build an amp badly. And the vinyl comes off the flimsy MDF cabinets easily and snags the chassis when you're trying to work on them.

shaunm said:

The JTM45 Reissues I believe are pretty good. Is this correct @ICBM ?

Totally different amp from the JTM30 and JTM60.

All the reissues are extremely well-built and reliable.