Hi guys, I'm new here and to amplifiers in general. For a few weeks now i have been googling mad trying to figure out what has happened to my precious super chrome amp :/ The fans were making a lot of noise and the two bulbs below the analog gauges blew so i figured i would give it a bit of an overhaul during spring break. I soldered in new leds, and installed new fans. A few days later I reinstalled the once working unit to find that it no longer works. Frustrated, I removed the top cover and found that i dropped a screw inside, possibly shorting something out on the board, and none of the analog gauges would move although the unit powers up fine. In testing with my fluke 233/a, I slipped and shorted out the negative and positive speaker outputs and after a loud spark, the analog gauges now work fine, weird, and now theres no power at all to the output speaker terminals, WHAT do I do now? I believe the output Fets are bad, total guess though, 1RFZ44N. Can these be tested in the unit or do I have to remove them? I found a great website but to get further information theres a 60$ charge and the amp is so old its probably not worth it to be spending 100s of dollars. Thanks guys, any help would be deeply appreciated!
What site charge $60 to get onto the site?
Have you read the basic amp repair tutorial (link in sig line below)?
The IRFZ44s are in the power supply. They are not the output transistors. The output transistors aren't likely FETs, they're likely bipolar transistors.
Have you read the basic amp repair tutorial (link in sig line below)?
The IRFZ44s are in the power supply. They are not the output transistors. The output transistors aren't likely FETs, they're likely bipolar transistors.
Can you post a picture of the complete amp and one of the board? I think I've been through this on one of these.
OK, some pics and a bit more info. After giving the board another hard look, i found what looks like a deep gash seen in picture 1. Im thinking that this is maybe from the screw? its pretty deep though and maybe this was the original problem. Yes I have read the basic tutorial and I found it to be fantastic! Thats the site that charges to get into the more advanced stuff, probably for good reason too. I tried using the basic tutorial but all my readings were nowhere close to what should have been, I'm thinking this is because I tested them in circuit right? None of them said OL. And sorry , i didn't mean to called them by the wrong name.
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That's probably a factory mod. The boards are difficult to scar like that.
That's not a site. It's a DVD (non-video) tutorial.
Did you check all of the output transistors to see if any were shorted?
That's not a site. It's a DVD (non-video) tutorial.
Did you check all of the output transistors to see if any were shorted?
These things were kind of hinky(technical term). Every one that I've ever worked on had shorted outputs and 1 leaking rectifier on the positive rail. You have to remove them from the board to check them. I don't which failed first. But it always accompanied bad fans.
We're the meter lights originally LED's or bulbs? I can't remember which one mine had.
We're the meter lights originally LED's or bulbs? I can't remember which one mine had.
Wow thanks, you guys are great. Thanks for the fast responses. I did test them, but I tested them in circuit, so I'm not confident in the results because everyone tested bad. I will start pulling them off and get back here with an update! Thanks again
OK, so I finally had some time to sit down and test this unit further. The TIP35C and TIP36C BJTs both test according to the basic amplifier repair guide, I tested these in circuit. Although I pulled one 35C and one 36C to test them for reverse bias as it seems impossible in circuit and they also passed. Following this I pulled one of the Z44Ns and tested it as well and it passed, which also seems impossible to test in circuit. I removed all of the rectifiers, two dual positive and two dual negative according to the data sheets, and they pass all tests as well. Should I pull all the Z44Ns to test them individually?
and the meter lights were originally bulbs in which i switched to led, could this effect anything? seemed harmless.
Did you use a resistor in series with the LED's? This caused me trouble once before. When I switch bulbs for LED's, I use 6 volt LED with a 1k ohm resistor.
If you haven't found anything bad yet, reassemble it. Does your power supply have an amp meter? If so, try to power it and see how many amps it draws. If not, power it through a 7.5 amp fuse and see if it blows.
Is there an IC on the board numbered TL494 or 594? I can not remember.
If you haven't found anything bad yet, reassemble it. Does your power supply have an amp meter? If so, try to power it and see how many amps it draws. If not, power it through a 7.5 amp fuse and see if it blows.
Is there an IC on the board numbered TL494 or 594? I can not remember.
Yes, i used a resistor with the led and it lights up fine, I'm pretty familiar with leds. I will reassemble within the next few days and also i don't have an amp meter. I will try the 7.5 amp fuse trick and see what happens. The board has a Hyundai chip. GL494 0024. Could this little chip be causing me all these problems?
If it won't power up after you assemble it, post the voltage on all of the pins of that chip. Look up the data sheet to know what pin numbers are which. That is the PWM IC for the power supply. It could have failed. But not likely. The voltages will tell more. Do you have a scope?
I will definitely check that out once I get it all back together. Its very weird that all the Fets are OK, kinda wish I found something by now. I do have a scope but only have minimal experience using it, a one semester electronics class in college. I will report back when i have results. Thanks again, your help is invaluable!
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