Ronald wrote:
On Feb 23, 6:42 am, "Mark D. Zacharias"
wrote:
I've replaced the diodes, still no change. I got a schematic off
the internet. finding a short in the 15 volt line is tough. my
thoughts if I unsolder the parts in the line it should resolve the
short. Replace them one by one until the short shows up. Sounds
logical?

-Ron
If the 15 volt reg gets hot, it seems to me there's some IC or
other loading it down. I'd sub in an external 15 volt or so and
see what gets hot.

Mark Z.

I just got a schematic for it. Traced back to the diodes on the dc
power board. Gonna replace them tommarow. Odd readings on the
diodes, in diode test i tested it both ways one reading of 1.1 and
.5 and a few just .5 in one direction. my guess from my repair
work on pinball machines .4 - .6 is ok diode but could possiable
failed diode. But I'm replacing them with new ones. to ensure a
rebuilt power supply.

-Ron

That's why I recommended subbing in an external 15 volts or so (with
the unit turned off and unplugged) and see what gets hot. Much
quicker and easier. Helped me fix many a unit. These pieces are so
complicated that tracing everywhere that 15 volt line goes would
take way too much time and effort.

Mark Z.- Hide quoted text -

- Show quoted text -

should I tap anywhere in the 15 volt line? chassis ground or pcb
ground.

-Ron

The way I would suggest is to remove the 15 volt regulator (positive 15, I
assume) and connect the positive lead from the power supply right there or
at the capacitor which would usually follow. The ground of the power supply
would connect to chassis ground. If the supply is adjustable, you can start
at a lower voltage.

The shorted or leaky part is probably on the DSP board or an input switching
IC near the inputs, or maybe one or more bad op-amps.

One thing. If it's really a dead, dead short, i.e. zero point zero ohms,
then just feeding your power supply into it might not reveal anything, since
some resistance is necessary in order for the bad part to generate heat.
This is pretty rare but I have seen it happen. However, your regulator IC
would probably just shut down if this were the case.

Mark Z.