S
Sunny
Guest
Twenty odd years ago a friend gave me his Akai stereo preamp and
amplifier because they weren't working. They've outlasted everything
purchased since.
This Akai gear dates from the early seventies I believe. There was
nothing wrong with the preamp (PR-A04) when I got it, but the matching
amp (PA-W04) was dead apart from a faint glow from the LCD(?) VU meters.
The owner's manuals included full schematics (those were the days!), but
the 'Pulsed Power Supply' in the amp wasn't like anything I'd seen
before - although with the benefit of more experience, I think it might
be a full-wave rectifier followed by a PWM. It was clearly the problem,
so I dismantled the three layers of steel boxes it was in (I guess it
generates some EMI!) to get a look at the board. There was a burnt spot
and a missing trace, but I couldn't find any defective components to
explain the scorch, so soldered a wire to bridge it and powered up the
amp to see what would happen next. Believe it or not, there was a
popping noise and a spark from the repair area, but the VU meters came
up at full brightness and the amp then worked perfectly, and does so to
this day!
The volume and balance sliders on the preamp became problematic
(scratchy and sometimes missing one channel) about a year ago, and I
finally got around to them last week. These things are seriously
overengineered - multiple wipers mounted on rails, with the variable
resistance material layered onto relatively large PCBs, one for each
channel on either side of the wiper rails. There appeared to be little
chance of spraying contact cleaner far enough into the assemblies to do
any good, so I spent the better part of a day desoldering the things to
get them apart. The wiper contacts were still perfect, but the PCBs were
severely oxidised. I cleaned them with fine steel wool followed by pure
alcohol, and soldered it all back the way it had been.
We're enjoying Christmas night listening to our favourite tunes on my
30-year old Akai stereo, which sounds at least as good as it ever did.
It's been 'replaced' several times over the years, but the new gear has
always been tossed after failing in ways that could not be repaired due
to lack of schematics and/or available parts.
What to do if the Akai ever dies?
Sunny
amplifier because they weren't working. They've outlasted everything
purchased since.
This Akai gear dates from the early seventies I believe. There was
nothing wrong with the preamp (PR-A04) when I got it, but the matching
amp (PA-W04) was dead apart from a faint glow from the LCD(?) VU meters.
The owner's manuals included full schematics (those were the days!), but
the 'Pulsed Power Supply' in the amp wasn't like anything I'd seen
before - although with the benefit of more experience, I think it might
be a full-wave rectifier followed by a PWM. It was clearly the problem,
so I dismantled the three layers of steel boxes it was in (I guess it
generates some EMI!) to get a look at the board. There was a burnt spot
and a missing trace, but I couldn't find any defective components to
explain the scorch, so soldered a wire to bridge it and powered up the
amp to see what would happen next. Believe it or not, there was a
popping noise and a spark from the repair area, but the VU meters came
up at full brightness and the amp then worked perfectly, and does so to
this day!
The volume and balance sliders on the preamp became problematic
(scratchy and sometimes missing one channel) about a year ago, and I
finally got around to them last week. These things are seriously
overengineered - multiple wipers mounted on rails, with the variable
resistance material layered onto relatively large PCBs, one for each
channel on either side of the wiper rails. There appeared to be little
chance of spraying contact cleaner far enough into the assemblies to do
any good, so I spent the better part of a day desoldering the things to
get them apart. The wiper contacts were still perfect, but the PCBs were
severely oxidised. I cleaned them with fine steel wool followed by pure
alcohol, and soldered it all back the way it had been.
We're enjoying Christmas night listening to our favourite tunes on my
30-year old Akai stereo, which sounds at least as good as it ever did.
It's been 'replaced' several times over the years, but the new gear has
always been tossed after failing in ways that could not be repaired due
to lack of schematics and/or available parts.
What to do if the Akai ever dies?
Sunny