Re: Electronic keyboard repair (I hope)

On Thu, 13 Dec 2007 09:42:34 GMT, "Arfa Daily" <arfa.daily@xxxxxxxxxxxx> wrote:


"Puddin' Man" <puddingDOTman@xxxxxxxxx> wrote in message
news:3vb1m3hji8uitvdn2upc2odt61tqvkpa1b@xxxxxxxxxx
On Thu, 13 Dec 2007 01:11:59 GMT, "Arfa Daily" <arfa.daily@xxxxxxxxxxxx>
wrote:


"Puddin' Man" <puddingDOTman@xxxxxxxxx> wrote in message
news:lrt0m39p1tm52rkgnasl8mgijpgk8ptmec@xxxxxxxxxx
On Wed, 12 Dec 2007 15:42:10 -0600, jakdedert <jakdedert@xxxxxxxxxxxxx>
wrote:

You need to find the main power supply board, and trace forward from
where there. That board (or portion of the main circuit board where the
DC adapter connects) is where the excess voltage is regulated down to a
level that the actual circuits use.

Power supply board:
Takes input from batt. or converter
Connections:
Black wire - screws to alum. kb frame
"to HP" - 3 element, goes to speaker
"to DM" - 4 element, goes to 1684 PN1 (lg. board)
elements are labeled DG +5D AG +5A
+5D and +5A measure 5v DC to black wire
"to SW" - 8 element, goes to switch/volume board
elements are labeled E 5v B T M S E E
M measures 15v DC to black wire

The two large boards (2 x 12+ ") are labeled 1684 PN1 and 1684 PN2
with markings for the voicings, various effects.

Any help?

Thx,
P


"+5D" will be the 5v digital supply - ie the 5v supply for the digital
electronics, and "+5A" will be the 5v analogue supply. "DG" and "AG" are
the
corresponding digital and analogue ground returns for those two supplies,
so
will be the references to measure the supplies against.

That's a big help. I had no idea how they code such stuff.

You really need to
be able to measure the +5D supply with a reasonable amount of accuracy -
to
at least 0.05v.

To what extent will such an accurate measuring device empty my po' wallet?

Goes without saying that if I get 5v from +5D when it plays and 0v when
it freezes, I've likely found my problem?

Thanks,
P

Weeeelll, yes ... But more likely, it would be something like 4.9v when
it's working ie just limping along on the lowest threshold that the micro
can work at, and 4.7v when it's wrong. With digital electronics,
particularly older garden variety such as this, a few decimals of a volt are
enough to make the difference, which is why you need a meter that can read
to half a decimal.

Ouch.

Such a meter is not expensive, and if the one you have,
even if it is a $10 job, is digital, then it should be capable of this level
of resolution.

It's analog.

I spotted a Sears Craftsman dig. meter on sale $30 but sez
"DC accuracy to 0.7 percent for accurate measurements."
Not sufficient for the job?

The trick is how *accurate* it actually is, and that is
something that you can't really know without comparing it to a 'standard' or
someone else's much more expensive meter. I am shortly to be away for a few
days, so will only get back on here another time or two. There are lots of
others on here who should be able to help you through this. Good luck with
it, and hope you manage to get a result.

Your help is -very- much appreciated.

I continue to try to measure differential voltage between the ekb when
working and when "frozen". Just measured both putting the meter under
the microscope of my eyeball. If there was any difference at all, there
was a snatch-hair more voltage when "frozen". Reading was like 4.9 v.

Dunno where to go from here. Any help most welcome.

Cheers,
Puddin'

"Well, there's two trains runnin'.
Ain't neither one goin' my way.
One run at midnight,
the other run just before day."
- from "Still A Fool", Muddy Waters, maybe 1949
.

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