Scott wrote:
> Checking power supply rails is the 1st thing I'd do too but with that ,if you can , check for power supply ripple.
> Older units are much more likely to have weak power supply filter caps.You'd need a scope or and RMS voltmeter to check for the ripple.
>
> If someone reworked some rectifiers try and find out WHY they quit.
> Resolder all the comps around the power supply section.
> W/o knowing more about the circuit , that's where I'd go.
>
>
Thanks for the reply. I've actually pulled the processor board on my
OB-8 in order to inspect for damage in the area of the bridge rectifier
that had been replaced, and I'm glad that I did. I'm amazed that I was
able to get seemingly normal voltage readings at connectors I and J.
I've uploaded a few photos for amusement and review. They can be seen here:
http://groups.yahoo.com/group/vintagesynthrepair/photos/album/1950312521/pic/list?mode=tn&order=ordinal&start=1&dir=asc
There is also quite a bit of what appears to be "rework" that has been
done to the board . . . Note the black wires running here and there in
the photos. Can anybody confirm that this work is not normal, and was
probably someone's attempt at a repair? Any further input on this would
be appreciated.
Thanks,
george
Message
Re: [vintagesynthrepair] Re: Troubleshooting an OB-8
2009-07-07 by Terje Winther
Thanks for the info.
I have justed serviced an OB-8 that showed the same problems regarding power, and especially the bridge rectifier. All black board area like your photos. The OB-8 I had in didn´t hvae the mods/straps like yours, but it did have some other added cables across several of the boards. Very unstable unit, and the mux chips got a little too hot for my taste. It will probably need another run of service to dig further in at the power problems.
Good luck with yours!
Terje
Den 7. juli. 2009 kl. 00.23 skrev gnw: