Hello guys,
My Kenwood amp just broke down a couple of weeks ago. I loved it so much that I don't want to throw it away, even though my closest prior experience to DIY audio is building a PC. I hope you can help me with troubleshooting. I have a voltage meter at the ready and am ready to fix this thing.
The problem: The speakers don't work and even the power-light at the front doesn't glow up. I can only hear a faint humming from inside the machine. The speakers get 0 sound.
Already checked: the 3 fuses I found aren't burned out.
My question:
How do I start troubleshooting? My idea is to measure the voltage from the power inlet and one step further every time it gives enough voltage. But I have no clue as to what voltage there needs to be at what point.
Instruction manual: https://www.vintageshifi.com/repert...e.php?pdf=Kenwood-KAF-1030-Service-Manual.pdf
Pictures:
My Kenwood amp just broke down a couple of weeks ago. I loved it so much that I don't want to throw it away, even though my closest prior experience to DIY audio is building a PC. I hope you can help me with troubleshooting. I have a voltage meter at the ready and am ready to fix this thing.
The problem: The speakers don't work and even the power-light at the front doesn't glow up. I can only hear a faint humming from inside the machine. The speakers get 0 sound.
Already checked: the 3 fuses I found aren't burned out.
My question:
How do I start troubleshooting? My idea is to measure the voltage from the power inlet and one step further every time it gives enough voltage. But I have no clue as to what voltage there needs to be at what point.
Instruction manual: https://www.vintageshifi.com/repert...e.php?pdf=Kenwood-KAF-1030-Service-Manual.pdf
Pictures:
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Ohh... I see that your 'name' follows the theme :the 1030 Kenwood Amp!
I used to have one, still have it, an older model where the preamplifier section was on the PCB behind the panel... Well, I separated them and use only the power Amp section. It never gave any problem and I really abused it... Only one time the driver transistors became hot and started to smoke because I didn't connect the ground wire and I said "whhops I did it again" but it recovered well... The protection circuit works and the muting circuit, unused, at the input, doesn't bring any harm, despite some 'audiophiles' might think that it'muddens the sound'...
I used to have one, still have it, an older model where the preamplifier section was on the PCB behind the panel... Well, I separated them and use only the power Amp section. It never gave any problem and I really abused it... Only one time the driver transistors became hot and started to smoke because I didn't connect the ground wire and I said "whhops I did it again" but it recovered well... The protection circuit works and the muting circuit, unused, at the input, doesn't bring any harm, despite some 'audiophiles' might think that it'muddens the sound'...
Thanks for the reply. Yeah I created an account for this amp 🙂
I am looking up what I can do with the preamp and power amp. Do you think it is a good way to go about it measuring voltages everywhere, starting from the power chord?
Today I just want to find whatever is broken so I can buy a new part and fix it. Weird thing is, nothing looks broken or burnt.
I am looking up what I can do with the preamp and power amp. Do you think it is a good way to go about it measuring voltages everywhere, starting from the power chord?
Today I just want to find whatever is broken so I can buy a new part and fix it. Weird thing is, nothing looks broken or burnt.
Update:
Whatever I did, the amp wouldn't turn on. Until I just dust-sprayed it. It turned on: led lights lighting up, seemingly fixed. I connected the speakers to try if those would work, and with a soft click the amp shut off again 🙁 Now it won't turn on again, with or without speakers.
Whatever I did, the amp wouldn't turn on. Until I just dust-sprayed it. It turned on: led lights lighting up, seemingly fixed. I connected the speakers to try if those would work, and with a soft click the amp shut off again 🙁 Now it won't turn on again, with or without speakers.
Hmmm... I'm not well versed into amplifiers... Not really into it, but it seems, if it 'clicks', that some protection is working : one possibility is some DC at the input, so a preamplifier fault. First you should divide the two sections, and each has its sub-section(like this forum 😛😱)
Update:
Just blew a fuse in my face. Now I know how to not measure voltage. Don't unplug a cable and use the meter to complete the circuit. That's not how to do that I guess.
Just blew a fuse in my face. Now I know how to not measure voltage. Don't unplug a cable and use the meter to complete the circuit. That's not how to do that I guess.
Oh well... Now I'll tell another tale of This amp: I changed the PS capacitors and I didn't check the polarity (....strange?!)so one ended in making a 'ppzzffzffffh' and a column 9f white smoke 😀🙄
Hah glad I'm not the only one making bad mistakes. This is seeming to be one of the most difficult things I've ever tried. Now can't check the voltage since the fuse on the power board is blown.
Next try: take it all apart and search for anything that looks burnt or broken.
Next try: take it all apart and search for anything that looks burnt or broken.
Update: Nothing at all looks burnt or broken, apart from the fuse I blew by short circuiting the thing just now. If anyone has any tips for a layman, that'd be awesome. I can supply pics of any part if requested.
FWIW, failed semiconductors seldom look burnt, neither do small capacitors or resistors. Only larger, high power resistors and semis may have the mass to become hot for long enough to glow brightly before burning out, scorching the PCB etc. and an obvious sign that whatever the resistor is connected to, is probably where the actual fault(s) lies. That's why you follow schematics and test, not just replace what you guess is faulty and switching on again to see what further damage you can cause.
There is something of a clue here in that the amp uses Sanken Darlington type power transistors which are known problems as they age. The internal emitter resistor burns out and they are effectively toast, as you can't bypass the chip resistor. Its possible that the protection relay which connects the speakers, is de-activated according to such a fault detection so maybe that's why you don't hear anything? Try this basic test before you create more faults.....
1)Remove all connections from the amp and turn volume control down.
2)Turn your voltmeter to a high DC range and connect it across the selected A or B pairs of speakers (that's for R channel then L channel output terminals) and power up. You can reverse the probes if you read negative volts and if you read only low or no voltage, switch the range down to where you can measure something that should only be in the range of around 20mV.
The amplifier has protection circuits that likely have done as they should - i.e. prevent you from blowing your speakers when an amplifier fault is detected. So we're testing for a DC fault voltage at the output. If there is no relay "click" after you turn the power on, this is likely what's happened, so listen and measure as a check for the type of problem.
3) Construct a DBT (that's "dim bulb tester" or "lightbulb limiter" - Google is your friend) and do it with safety, maintaining any 3-wire earth connection in mind to protect the amp from further damage when testing under power. You don't want to continue blowing parts every time you power up but it's a chore in some places to still find a suitable, say 60W incandescent lightbulb. I can buy quartz halogens of 70W rating no problem but in some places, it's not so easy.
4) Run all further tests with this DBT inline - don't risk turning your amp into a wreck.
There is something of a clue here in that the amp uses Sanken Darlington type power transistors which are known problems as they age. The internal emitter resistor burns out and they are effectively toast, as you can't bypass the chip resistor. Its possible that the protection relay which connects the speakers, is de-activated according to such a fault detection so maybe that's why you don't hear anything? Try this basic test before you create more faults.....
1)Remove all connections from the amp and turn volume control down.
2)Turn your voltmeter to a high DC range and connect it across the selected A or B pairs of speakers (that's for R channel then L channel output terminals) and power up. You can reverse the probes if you read negative volts and if you read only low or no voltage, switch the range down to where you can measure something that should only be in the range of around 20mV.
The amplifier has protection circuits that likely have done as they should - i.e. prevent you from blowing your speakers when an amplifier fault is detected. So we're testing for a DC fault voltage at the output. If there is no relay "click" after you turn the power on, this is likely what's happened, so listen and measure as a check for the type of problem.
3) Construct a DBT (that's "dim bulb tester" or "lightbulb limiter" - Google is your friend) and do it with safety, maintaining any 3-wire earth connection in mind to protect the amp from further damage when testing under power. You don't want to continue blowing parts every time you power up but it's a chore in some places to still find a suitable, say 60W incandescent lightbulb. I can buy quartz halogens of 70W rating no problem but in some places, it's not so easy.
4) Run all further tests with this DBT inline - don't risk turning your amp into a wreck.