Hi Tony,
Have been out of pocket for a few days ( building a parade float).
Back now.
--- In xpantastic@..., "Tony Cappellini" <cappy2112@...>
wrote:
I went through all the DC voltmeter measurements in the service
manuel. Everything looks good (to me) except for Step 3, +5M text.
On the right side of D4 (as I am facing the Processor Board,
sometimes I measured 6.6 v, other times I measured 3.9 to 4.9 volts.
I suspect there is a bad solder joing on D4, so I will reflow this.
6.6 V seems very strange for the memory power supply. The battary
might need changing.
If you are re-flowing the + side of this circuit ( M+5V) you better
make sure you have an un-grounded soldering Iron. If not
the +Mem supply will be shorted to ground and then the MEM will be
lost.
Hope I caught you in time.
I notice in the Xpander schematics D4 exsists twice. One is a diode
at the top edge of the board the other is an LED for the LFO. Now I
am sure you know the difference between a diode and an LED but I
thought I would mention it. This was changed in the M12 schems.
I looked at C3 and there is some dry dusty residue on the negative
side of C3.
There is less residue on the negative side of C1.
If this is shiny brown, this may be soldering flux. This should
always be cleaned off the circuit board.
After about 5 - 10 years this will eat the solder and cause problems
These caps are old, so I might as well just replace them all at the
same time.
There are 4 more electrolytic caps on the PS board, but their leads
are right up against the PCB, so I can't see if they are leaking.
I have not seen this in Oberheims, but many times in old Korgs /
Rolands.
It will be worth the money to have all the voices re-capped.
Good Idea, I am thinking off doing this myself. When I change my
battary.
In a previous email you referred to a RARE DAC. The service manual
references several whose part numbers look like easy to find
components to me.
Which rare DAC are you referring to?
Well, I be talkin about U811 the main DAC which feeds the voice
board. The MP7614C-4 was mad by EXAR and is obsolete per their web
site, and the HS3140C-4 was made by SIPEX and is also obsolete.
I suppose with digging you can find this part out there somewhere
(repair shop or part house which specializes in obsolete parts but
you will pay quite a bit).
Good Luck
Karl
