Hi folks,
for sentimental reasons I took a chance on an old A60, £49 inc. P&P. It is the last, 1985 model, smaller transformer and RCA phono sockets for turntable. CD input.
It powers on but no output and speaker fuses are blowing. Also there is a distinct resonance to the case when it is on. No noise, just vibration.
The power supply fuses are fine. When I got it I noticed that the white block that fits in the M.C. option slot was back to front. Hopefully nothing else is wrongly wired! I have only done 6 measurements so far, across the four diodes D204-7 and capacitors C209/10. They all measure around 40v.
Where to start. Any suggestions other than the obvious landfill suggestions welcome.
cheers
for sentimental reasons I took a chance on an old A60, £49 inc. P&P. It is the last, 1985 model, smaller transformer and RCA phono sockets for turntable. CD input.
It powers on but no output and speaker fuses are blowing. Also there is a distinct resonance to the case when it is on. No noise, just vibration.
The power supply fuses are fine. When I got it I noticed that the white block that fits in the M.C. option slot was back to front. Hopefully nothing else is wrongly wired! I have only done 6 measurements so far, across the four diodes D204-7 and capacitors C209/10. They all measure around 40v.
Where to start. Any suggestions other than the obvious landfill suggestions welcome.
cheers
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TIP3055 power transistors are cheap, plentiful and RS should have the tiny, replacement ZTX653/753 driver transistor types so you should be covered for spares, barring further issues. It seems the previous owner/tinker was a bit too adventurous for his/her skill level. That's nothing new and I've been there too, thinking I could reason out problems when I couldn't, so don't be afraid to ask or google the problem for testing hints, at least.
The distinct vibration is a worry, though. Have you checked the ground continuity to mains (protective earth) ground? Do you have +/-35VDC at the power supply rail fuses? 40V seems too high for the transistors.
The distinct vibration is a worry, though. Have you checked the ground continuity to mains (protective earth) ground? Do you have +/-35VDC at the power supply rail fuses? 40V seems too high for the transistors.
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Yes, the vibration was a worry. However, having replaced the power supply cables in the correct way the vibration seems to have gone. I managed to find some photos of the interior online, and from these, with some amount of squinting, I could see that the MC option block was back to front and that the black and white power supply leads were connected back to front. Its a pity that the three way connector block was made symmetrical! (a couple of pictures attached to highlight problem areas). I am not sure yet what the consequences of these being inverted would be.
One outstanding issue, the sound through my AKG 550 headphones is very tinny. But the sound via a pair of KEF Q100s was fine.
Cheers
One outstanding issue, the sound through my AKG 550 headphones is very tinny. But the sound via a pair of KEF Q100s was fine.
Cheers
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