[sdiy] . . . and now, the power supply (was Akai AX80 Voice 4 DCO2 issue and AX80 Voice 8 PWM over-modulation before that)

james meagher w.james.meagher at gmail.com
Wed Jul 18 00:53:15 CEST 2012

I'm having trouble figuring out exactly what this Diode is:

It's listed in the AX80 Service manual as PSU D5 - 10D1   FA-1   F15
100/1.0A . . . but it clearly says 9K on it. 9K what???


On Tue, Jul 17, 2012 at 2:31 AM, Bob Weigel <sounddoctorin at imt.net> wrote:
> On 7/17/2012 1:21 AM, random variate wrote:
>> VFD
>> Vacuum Fluorescent Display
>> Rarely do the tubes go - built to last - but regulators and supporting display board chips.
>> On 17 Jul 2012, at 04:53, "james meagher"<w.james.meagher at gmail.com>  wrote:
>>> Just when you thought a day might go by where I don't post about my
>>> Akai AX80 restoration . . .
>>> So, with the tact switches, keys, Voice 8 issue and memory back-up all
>>> dealt with, and the Voice 4 DCO 2 problem just awaiting a part, I
>>> decided to actually enjoy the AX80 for a few minutes this afternoon.
>>> I'd just finished swapping IC22 and IC24 to ensure that the Voice 4
>>> problem was indeed IC22 (now the problem appeared on Voice 7 and Voice
>>> 4 worked flawlessly), and installing a new memory back-up battery,
>>> when I settled in to create a patch or two. Less than five minutes in
>>> all the LCD displays died (I know they're not really LCD . . . vacuum,
>>> something, something - can't remember the name). Just 100% dark.
>>> Everything else continued to function as it should.
>>> I opened her back up and began probing about. Visually everything on
>>> the LCD PCBs (heretofore referred to as FLD Operations PCBs) looked
>>> A-OK. Eventually I found that the cable harness (P1 on the FLD board
>>> and P4 on the PSB) that runs to the Power Supply PCB, and should
>>> provide the FLD board with  +5V, GND, -40V, was instead metering at
>>> +5V, GND, -5V. What happened next I'm not too proud of.
>>> I decided to start metering around the Power Supply to see if I could
>>> figure out why only -5V and not -40V was going to the FLD board. The
>>> transformer showed to be supplying the correct values to the PSB. D5
>>> metered as I expected it would. Then a fly landed on my face and I
>>> think that in my spastic reaction the probe very briefly connected IC5
>>> Pin 1 (should be 5.6V) and pin 2 (GND). I didn't think much of it
>>> until a second later when R2 began to melt and smoke before my eyes. I
>>> immediately powered off and unplugged the machine. Visual inspection
>>> shows that there is also a black spot on the underside of R3.
>>> My original suspicion was that the problem would reside with C18 or
>>> C23 - but I didn't get that far with my probing before the meltdown.
>>> So, obviously I've not had the board back on since and I'm unsure how
>>> to proceed. Obviously R2 and R3 need to be replaced - but I'm more
>>> than a bit hesitant to replace only them and then turn it back on. I'm
>>> feeling inclined to replace everything on that path to the FLD
>>> Operations board and CPU PCB . . . Is this overkill or not enough?
>>> There are also all the components that lead to the Voice PCB. Nards.
>>> I think I'll go to bed early tonight.
>>> James
>>> _______________________________________________
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>>> Synth-diy at dropmix.xs4all.nl
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> btw everyone should read my repair notes on my website to avoid damaging the mux chips...was just talking to someone else about this same thing..
> --
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