paragon66x wrote:
If it seems to turn on normally, with the speaker relay coming on
after the usual delay, and just no display, there is a chance that
only the -30 volt line for the display is down (or some other
section of the power supply). There is a 100 ohm fusible resistor on
the power board, R901, near the large connector which goes to the
main board. This resistor could be bad.

There is also a separate fuse board, and there could be bad fuses
there - don't recall if you said you had checked those.


Mark Z.

I actually checked the "hidden" fuses on the power supply board above
the transformer a while back. I went ahead and removed the power
supply from the stereo again tonight, removed the fuses again and they
checked ok for continuity. I then checked the resistors on the board
and they seemed to check within tolerance - one of these was the R901
you speak of. I went ahead and checked the switching diodes (they
seemed ok) and the two 1N002 diodes. One of the 1N002's (D902) tested
kind of odd so I pulled one leg out and it checks out the way it
should. When I put it back in the board it cheked out the same as
before across the ends - ".051" and it didn't matter which way I had
the black and red leads of my DMM. As you probably already know these
should ideally check between .4 - .6 one way and "OL" the other. So I
am not sure why this diode is reading this way, but I did notice one
of the traces is going to a small transistor Q901, but I do not
recognize this as one I know how to check/ meter out The numbers on
it are C107 (top line) and M131 (bottom line). On the same trace
going the other way it leads to an OMRON 5VDC black box (not sure if
its function). Does this diode reading sound suspicious or like
soemthing else on the board is causing this goofy reading?
Considering I pulled one leg out and it read ok I beleive the diode
to be good. Other than this, I don't readily see anything that looks
out of the ordinary. Any other ideas for me to try? I will leave
the power supply on my bench overnight. Thanks for your help this
far. John

Well, sorry we got off track. These models can be tough sometimes (well,
most of the time it seems).

Generally speaking - one must confirm the standby status first. The DC
voltage derived from the standby transformer, usually 5 volts. The reset
line to the microprocessor should rise smoothly and pretty quick from 0 to 5
volts when the power cord is inserted. The crystal should be running. If no
scope is available, the DC voltage on the crystal should be about 1/2 of the
5 volts. There would be a relay turn-on line from the micro which obviously
should fire when you press the power button.

I'm concerned about that relay firing when you plug it in, though - doesn't
sound right to me.

Although your model is somewhat different, there is a history I should make
you aware of.

On the HCD-GX450 and 250 models there was an issue with the flat cable which
connected the main board on the side with the front panel. Somehow even
though these were new units, sometimes there were bad or intermittent
connections where this cable plugged in, both at the main board and at the
front panel side. Caused a variety of unusual symptoms INCLUDING one I saw
where the relay fired upon plugging in, but would not turn on.

Sound familiar?

Mark Z.