Faulty Laney HCM30R Guitar Amplifer

[gbono]

DO NOT put semiconductors in frig before soldering! You will induce thermal shock in the IC packaging/die and potentially damage the device during soldering.

You will need a solder sucker (vacuum removal tool) or solder braid/wick at the least. If you don't have these solder removal tools you run the risk of overheating the PCB traces during removal and you will not have nice clean open traces when you solder in the new IC.

Yes, I would check the continuity of the bridge rectifier when you have the chance. You may need to find a data sheet for the part since it may be impossible to check each "leg" of the rectifier bridge without this info.

good luck you can always buy more parts at RS spares ;-)

Ok got the lightbulb limiter info now.
I'll strip down the board this weekend and take out the tda2050 and then power up. This is a good easy starting point. I'm reluctant to take the nobs and screws off the front till I'm certain as it will invariably scratch off so paint etc. and don't want it in bits for to long.
I'll build a limiter if I have to go further.

Question. For replacing the TDA2050, am I going to be OK regards the soldering heat on the replacement. I'd considered cooling the new IC and heatsink in freezer then fitting and soldering. This would help stop the heat travelling up the pins. Have read that semiconductors very delicate. That goes for the diodes too then?

gbono
So was this wrong? or just worth checking. (understandable if you've got the meter out)

I've got photo's to post but I didn't bring them, I'll post tomorrow.
Also spent some time looking at circuit yesterday and have noticed it is ver.9346-3. It's just before the diagram
http://tremolo.elektroda.net/Firmowe.../HCM30R-CH.pdf
but the relevant parts look the same, only Laney direct would supply the actual one as I've looked everywhere.

Thanks for your very patient help.

[shadowfax]

DO NOT put semiconductors in frig before soldering!

Good job I mentioned that, you can sort of see where I was coming from though
I'll use solder wick. I'll try to clip on 'croc clip' and wire I have onto pins to act as heat sink.
These photos of circuit may be of interest. Closeup of D15, D16 added but prob. not needed.

[tubeswell]

I had to 'repair' one of these last year for one of the guys who used to play in one of the bands I'm in. (Turned out to be a loose-as speaker terminal lead clip - so I fitted a new clip). Those miniature IC op amps are really small and soldered directly onto the board - I was looking for (much bigger) TLO72s mounted into proper sockets. The teeny weeners in there are impossibly hard to get at unless you have a magnifying glass and a really fine-tip soldering iron. I have to ask - are these things designed so that they deliberately can't be serviced?

[shadowfax]

tubeswell think I can rule your particular problem out, anyway the IC's out now! Regards repair I've been suprised how relativily simple to get hold of componants are. That's in the UK though, Maplin's have made live easier for people by opening up so many branches. I don't think enough poeple try any more. Maybe now the world's poorer that'll change.

I've desoldered the tda2050 and re-assembled. I started it and switch light, and LED stayed on. No sound, no nothing. Tried turned dials up, volume etc, (didn't put Overdrive on) nothing. So from what I've been adviced here that must be promising.
Had to order IC and soldering iron gone, had to use portable gas one to desolder, which I will definatly not use to solder. Don't like them at all.

So if I'm right, transformer, power diodes, bridge rectifier ruled out now.
I'm safe to replace the IC without risk of it blowing new one, or should I really wait to use a 'light bulb limiter'.

Regards 'light bulb limiter' going from the diagram - the two earths shown, would be just joined, so using the mains plug earth. And '120 VAC recepticle' is just connection box/socket thats mains capable (120v or 240v the UK). Something like this BOX
Would 100w bulb be best. And plug fuse stays the same?
Cheers.

[52 Bill]

So if I'm right, transformer, power diodes, bridge rectifier ruled out now.

Probably yes, but you can check the power supply voltages with your meter before installing the new output chip.

[shadowfax]

Done a brief check, still waiting for IC.
D10,D12 23V and D11,D13 -23V, seems OK as looks like 25V on diagram (HCM30R-CH) it's close anyway and not too high??
Same on C44,C45
No readings for IC as its empty now, tried for C35, C39 before IC and nothing. Don't now if thats right, probably is.
Unfortunatly the diagram for this Amp doesn't have the handy 'TP' test points as on the Fender Amp one so it's harder to know whats right.

[52 Bill]

Done a brief check, still waiting for IC.
D10,D12 23V and D11,D13 -23V, seems OK as looks like 25V on diagram (HCM30R-CH) it's close anyway and not too high??
Same on C44,C45
Unfortunatly the diagram for this Amp doesn't have the handy 'TP' test points as on the Fender Amp one so it's harder to know whats right.

Yes, and the schematic also doesn't show how the power supply voltages connect to the rest of the amp.

The + & - 23 volts is correct, as the rating for the main filter caps is 25 volts. You can check the three low voltage supplies. The + & - 15 volts at D15 and D16 and the 5 volt supply at D17.

[shadowfax]

Great will do, ...... I think I did infact, but didn't note it.

[shadowfax]

Not sure about these:-
D15 16.2v, D16 -16.4v, D17 5.07v
D17 must be ok, but the other two varied abit rising slowly after start up. The readings are pretty settled, they may have risen after leaving on for a while but I wouldn't do that with the TDA2050 out.
Being over 15v concerns me, would that have damaged the TDA2050 or is 1v not enough. The resister for each diode would have to be burning hot to dammage diodes?? the damage was caused very quickly at start up not after being left on for ages, allowing for overheating.

If you'd suggest changing D15,D16 can I double check what to get
2 x 1.3W Zener Diodes 15v?
There is a close up photo of D15,D16 in earlier post, didn't like the look of 'em.
Don't want to waste new IC, but then it's not a major voltage difference.

[shadowfax]

BTW
(poss. readings at cathode marked pin, neg. at other pin)

These diodes are rated the same but they're look different and have differnent codes?
http://www.maplin.co.uk/Module.aspx?ModuleNo=19090

[52 Bill]

The slightly higher voltages can be a matter of the diode tolerance or your meter tolerance, don't worry about it.

These voltages only go to the pre-amp ics and not the power output chip.

[shadowfax]

Thanks for quick reply.
I had expected larger voltage differences than 1v but wasn't sure.
Sounds like its safe to try the new TDA2050, which I will do when it comes.
I'm tempted to ask if the preamp IC's could be a problem, but don't bother you would have said!
I'll try and attach what I can to the pins as a heat sink.
finger crossed........

[shadowfax]

It's working!

I'm starting to get over the initial shock now, had a few panics like forgeting to turn up the EQ dials, but after hours of testing it's still going.
I'm using a my Belkin surge strip now!

I'd had two repair quotes "£40+" and "phew.. from £15-£100+", which made it too much. I had a feeling it was do-able, but I'd really like to thank all the help I've had on this forum especially '52Bill' who got it straight away, I don't know your background but it looks like you really know your stuff.

When you DIY, as well as saving money, you can take more care on the job if someone isn't recommended then it's a risk. And I've learnt I bit along the way.

The amp seems to have servived intact. Unfortunatly I can't remember exactly how it sounded before, I wasn't listening as critical back then. It starts with a bump and settles down to a pretty quiet hum on clean, the overdrive channel increases the hum by 2-3x but that's seem usual. With headphones on I can detect the hum more, I would say that my little 'Kustom' 12w amp is quieter, but it's more basic. Guitar and leads I've ruled out, though there's pickup buzz that I want to reduce - that's the next job.

I'm not keen on taking it apart again just now, but is there any likely circuit damage (that I could sort out one day) that allow's it to work as it is now but could be causing 'noise'?

Cheers all

[52 Bill]

I'm not keen on taking it apart again just now, but is there any likely circuit damage (that I could sort out one day) that allow's it to work as it is now but could be causing 'noise'?

Glad to hear you got it up and running.

The noise could be "normal" or it could be a failing part like a filter cap or an ic in the preamp. If it hasn't entered the range of making the amp unusable, I'd live with it for now and see if it gets worse.

It could also be something that you did when working on the amp. Did you tighten all of the screws and ground connections? Double check any push on connectors?

[shadowfax]

Did you tighten all of the screws and ground connections? Double check any push on connectors?

Yep I was very careful to check. recheck, check again.... didn't want to mess up.
It may well be an existing problem it's a good amp but nothing fantastic, it's just that the 'Kustom' 12w sounds clearer by comparison.
So big caps C44, C45 wearing and not cleaning the AC power correctly? I suppose that I could wait for them to fail -if ever-. The pre-amp IC's are the many TL072 op amps that create the sound which is then boosted by the main TDA2050 for output. I think? So only takes a tiny sound problem in the pre-amp stage to be noticable later?

As I'm guessing it would be hard to pin down the problem IC -if at all- I think I will live with it, as you say it will get worse if it's a real problem.
Really good headphones pick out sounds you'd just not hear without them.

BTW I hope this encourages others to have a go if they have this problem and google away like I did.