My son learned a valuable lesson (I think) and broke his stereo. I am
hoping one of you can offer me some help on maybe fixing it.

Here's the deal: against my advice, he snuck the stereo outside and
plugged it into a 12v to 120v convertor in his car. Eventually he
brought it back inside and claims it worked, but I am not certain he is
telling the truth - the car convertor may have killed it. Anyway, all
the thing will do now is click when you plug it in (I think it always
did this so it is normal) and there is power to the LED next to the
main power button on the front, but it will not do anything when you
try to use the power button. In other words, it won't turn on. I am
not sure if the power supply is damaged or if there is a board problem.
I have checked the fuses and they are ok.

Can anyone offer any advice on this?

I do have background in fixing solid state pinball machines so I do
have access to a DMM. However I don't really know where to start on a
stereo per se. I do not have schematics.

Being that I was once young and stupid also, I would like to try and
help him out. This was a fairly pricey stereo when new and it is
definitely worth salvaging. Thanks in advance - John

paragon66x wrote:
My son learned a valuable lesson (I think) and broke his stereo. I am
hoping one of you can offer me some help on maybe fixing it.

Here's the deal: against my advice, he snuck the stereo outside and
plugged it into a 12v to 120v convertor in his car. Eventually he
brought it back inside and claims it worked, but I am not certain he
is telling the truth - the car convertor may have killed it. Anyway,
all the thing will do now is click when you plug it in (I think it
always did this so it is normal) and there is power to the LED next
to the main power button on the front, but it will not do anything
when you try to use the power button. In other words, it won't turn
on. I am not sure if the power supply is damaged or if there is a
board problem. I have checked the fuses and they are ok.

Can anyone offer any advice on this?

I do have background in fixing solid state pinball machines so I do
have access to a DMM. However I don't really know where to start on a
stereo per se. I do not have schematics.

Being that I was once young and stupid also, I would like to try and
help him out. This was a fairly pricey stereo when new and it is
definitely worth salvaging. Thanks in advance - John

If the fuses are really good, this is a bad sign, given what you have said
about using the 12 to 120 converter. Possibly a bad power transformer.
With the receiver unplugged, use your DMM to measure resistance (ohms) at
the AC switched outlet on the rear panel. This outlet directly parallels the
main transformer primary. If the transformer primary is OK, and there are no
blown fuses or other open circuit, then the resistance should be very low,
probably less than 1 ohm, since it is a large transformer. If it's in the
100 ohm range or greater, you are measuring only the primary of the standby
transformer, and the main transformer may be bad. Possibly a thermal fuse
opened inside the transformer.


Mark Z.

Mark D. Zacharias wrote:

If the fuses are really good, this is a bad sign, given what you have said
about using the 12 to 120 converter. Possibly a bad power transformer.
With the receiver unplugged, use your DMM to measure resistance (ohms) at
the AC switched outlet on the rear panel. This outlet directly parallels the
main transformer primary. If the transformer primary is OK, and there are no
blown fuses or other open circuit, then the resistance should be very low,
probably less than 1 ohm, since it is a large transformer. If it's in the
100 ohm range or greater, you are measuring only the primary of the standby
transformer, and the main transformer may be bad. Possibly a thermal fuse
opened inside the transformer.


Mark Z.

Hi Mark - there is no switched outlet in the back of the stereo. It
has the main plug hard-wired in and various jacks for speakers and what
not, but no other place for any AC plug to go into. This is one of the
"mini-stereos" with the CD player, cassettes, etc, all in one self
contained unit.

I do currently have the main cover off and notice when you plug it in,
it makes the "normal" click after a couple of seconds (at least I think
that is normal), and one of the belt drives on a cassette motor jogs
forward for a split second. After that, the light to the main power
button LED is lit red, but the power to the system will not come on.
With that said, what else do you recommend? Thanks - John

paragon66x wrote:
Mark D. Zacharias wrote:

If the fuses are really good, this is a bad sign, given what you
have said about using the 12 to 120 converter. Possibly a bad power
transformer.
With the receiver unplugged, use your DMM to measure resistance
(ohms) at the AC switched outlet on the rear panel. This outlet
directly parallels the main transformer primary. If the transformer
primary is OK, and there are no blown fuses or other open circuit,
then the resistance should be very low, probably less than 1 ohm,
since it is a large transformer. If it's in the 100 ohm range or
greater, you are measuring only the primary of the standby
transformer, and the main transformer may be bad. Possibly a thermal
fuse opened inside the transformer.


Mark Z.

Hi Mark - there is no switched outlet in the back of the stereo. It
has the main plug hard-wired in and various jacks for speakers and
what not, but no other place for any AC plug to go into. This is one
of the "mini-stereos" with the CD player, cassettes, etc, all in one
self contained unit.

I do currently have the main cover off and notice when you plug it in,
it makes the "normal" click after a couple of seconds (at least I
think that is normal), and one of the belt drives on a cassette motor
jogs forward for a split second. After that, the light to the main
power button LED is lit red, but the power to the system will not
come on. With that said, what else do you recommend? Thanks - John

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.

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

Oh and as far as it turning on normally, I am not sure if I am
misleading you or not. The thing doesn't turn on. When you press the
power button it doesn't do jack. When you plug it in though it does
put power to the power button LED and it looks like there is fire going
to the cassette motor too as it lunges forward a bit. But that's all
she does other than make the click after plugging it in, but I don't
know what that click means - just seems like it always did that. John

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.

Mark - It may take me a day or two to digest your last post - it's
pretty deep for me. I will actually be traveling the next couple of
days for work so it may be a while before I can look into what you
posted. I should be able to reply by the coming weekend. Thanks - John

paragon66x wrote:
Mark - It may take me a day or two to digest your last post - it's
pretty deep for me. I will actually be traveling the next couple of
days for work so it may be a while before I can look into what you
posted. I should be able to reply by the coming weekend. Thanks -
John

You can e-mail me direct at:



and reverse the domain name.

Mark Z.