Smoke/Burning Smell (Guitar Research T64RS Head)

[ffaf 07]

I know, it's a cheap amp. That's why I opened it.

I can't find any schematics for the head, and I've looked EEEEVERYWHERE, so here's the basic drawing, and then the lowdown on what happened.



This was being played on for hours consecutively, so it probably burnt out.

The chip that's the problem is separated, with a 3 way input, and an 8 way output. (Note the red lettering...that chip.)

2 of the metal prongs, attached to the 8 wires output, are burnt.

With the chip taken out, and the open wiring, everything lights up (I'm not going to play on it in such a condition, but everything lights up.)

With the chip in, none of the channels light up, it turns on....but the chip burns. No sound comes out or anything.

Here's a link I read up on: www.geofex.com/ampdbug/smoke.htm

Any of you experts know:

- What chip it is?
- Where the problems coming from, if it's even from the chip? (Remember how it broke, might help answer this one)
- How to fix it / buy a replacement chip?

Thanks in advance for your help.

[ffaf 07]

it's not a relay board. it's called a PT60R. it's about and inch by two inches

[Steve Conner]

Sounds like that board is the power amp module, and the power amp chip on it burnt out. When these chips die they usually short out the power supply, and I guess that explains the smoke.

Try and spot the chip: it should be a lump of black plastic with about 15 legs and a metal tab sticking out that's screwed to a heatsink fin of some kind. Tell us the part number printed on the chip. PT60R isn't a part number of any power amp IC I know of, but Google says there's an amp called the Mega Amps PT60R that looks like the combo version of yours, so I guess you're giving us the number printed on the board.

The amp seems to be a generic chinese made thing that's sold under a few different badges. You could always try asking for a schematic of the PT60R at www.megaamps.com

[ffaf 07]

i have discovered that, and thank you for your help.

my next question: on the back of the preamp is printed



should i get a power amp IC that handles 120V and 100W? or one that handles 60W?

[Tom Phillips]

The 120V / 100W is the max power the whole amp draws from the AC line.
60W is closer to the possible power output into the speaker but my guess is that 60W is a very optimistic number. Hard to tell what the original PA chip was. Any luck in finding a part number on the chip itself?

[ffaf 07]

I could not find a part number on the chip itself. I don't have the part anymore. I have the printed circuit board, and i meltered the soder so that it would come out (it was a smooth operation, and i can soder the replacement back in.)

So if 120 V / 100 W is the max power the whole amp draws from the plug in the wall, a 70 V / 60W power amp would do fine?

because, my thought was, if I'm gtting 120 V / 100 W from the AC line, and all that power is running into 70 V / 60 W, then the chip would surely burn up again.


BUT, if i have a 120 V / 100 W chip, and the AC power is matched up, will that blow t 60 W speaker rating??

[Tom Phillips]

I could not find a part number on the chip itself. I don't have the part anymore.

Maybe someone will come up with an appropriate part number. There have to be more of those amps out there.

So if 120 V / 100 W is the max power the whole amp draws from the plug in the wall, a 70 V / 60W power amp would do fine?

because, my thought was, if I'm gtting 120 V / 100 W from the AC line, and all that power is running into 70 V / 60 W, then the chip would surely burn up again.

BUT, if i have a 120 V / 100 W chip, and the AC power is matched up, will that blow t 60 W speaker rating??

The power isn't "pushed" into the chip. The Chip "draws" the power it needs from the power supply. I'm not sure where you got the 70V you mentioned. I doubt that your amp has a 70V power supply. Also it's likely that the 60W output rating is marketing hype. I'd bet that the actual RMS output power is no greater than 30W.

I'm afraid there are just too many unknowns here for me to tell you what power amp chip to buy and solder in place of your old one. I recommend you keep up the serch for info on the amp or find someone who has one and is willing to look inside and tell you what the chip P/N is. Maybe someone will recognize the amp is you post some pics of the whole unit. Unfortunatly, it's not one of the amps that the average ampager would collect / restore / modify.

[ffaf 07]

The 70V is just because I've been looking at Power Amp IC chips for sale and the one that has 60 W also has 70 V. So if I had a 70 V, 60 W chip, would it "draw" 70 V from the possible 120 V the power amp provides, and therefore be safe?

but if i had a chip that "drew" 120V and 100W, which is the AC max, would it be too much for the 60 W speaker set up?

[Tom Phillips]

Your amp has a power supply that is designed to convert the 120V AC from the wall outlet to a DC voltage that the circuits inside the amp use. Without seeing a schematic or measuring the voltages in your amp I cannot say what the voltage is that your power amp chip uses.

There are efficiency issues and power losses in the circuits. Therefore, the power output to the speaker is much less than the power that is drawn from the wall outlet.

[ffaf 07]

Well, I could care less if this thing cakes out. So am I at least okay trying a 70V 60W power amp IC chip?

however, if this thing worked again i'd be more than grateful
hartke gt60 is the exact same amp, im pretty sure this chinese company is shipping them out under a couple of different names.

[Steve Conner]

You can't just go to an electronics store and ask for a "70V 60W Power Amp Chip" any more than you can go to an auto parts store and ask for a "100hp Replacement Engine" if your car's engine blew up. You need the part number of the old chip. If you tossed it out without writing down the part number (or it was burnt so bad as to be unreadable) tough luck.

[ffaf 07]

Well, regardless of part numbers, which I'm working on

which numbers are more appropriate.

look into this: http://futurlec.com/Philips/TDA7296.shtml

[fporfidio@optonline.net]

hey ffaf, i'm working on one right now. mine has a dead transformer. maybe we can help each other? can you read the ac voltages from the black center tap wire to the red wires? send me a pic of the ic that you think you need the number for and i'll see if it's legible on mine. my email is [email]fporfidio@optonline.net /email], Frank

[Enzo]

Hi Frank, welcome to the forum.

Always a good idea to look at the dates. This thread has been dead since 2006.