Aiwa CD/Stereo power problem

[TA7205]

Hi;

I have a Aiwa CX-NA508U (3 CD/tuner/tape etc)
in for repair. The thing will just sit there dead.

The power supply appears to be up +35v at output transistors.

5V present, micro has toggling waveforms and appers to
be alive.

Occasinally, when I plug it in it lights up and starts to function fine.
And will continue to work until unpugged again.

I have tried flexing the PCB, pulled and wiggled data cables, used
hot/cold treatment. Does not respond.

Does anyone have experence with this model ?

Thanks,
Rick

[CLSNOWYOWL]

Yes, I have seen quite a few of these models, but this is an unusual symptom
for this model.

Since the symptom is unusual, please let me ask you some questions about the
device in for repair. Have you done a visual inspection of the device to try to
determine if the unit has been dropped or has ay kind of corrosion or moisture
damage? Perhaps there is a hairline fracture at the PCB or at one of the
interconnecting cables? Could you have any damage to the display driver board
or some of its connections (perhaps the digitron driver is bad)? You may have
to completely disassemble the display PCB, power supply pcb, and other PCB's to
determine if the unit had either been dropped or has a significant defect.

Just a thought... How are all of the solder connections on these interconnects,
chips, power supply, and other critical components? You might have to check the
bias voltage levels on the transistors that turn onthe microprocessor. The
transistor may get voltage, but the forward bias may not be there off of the
emitter or collector o the transistor. also, check for leaky caps. in the power
supply that have high ESR. You may have a leaky or margianlly bad capacitor or
transistor that is either sometimes causing the device to come on briefly, but
not coming up full, which may be causing the device to go into shutdown mode.
Also, check your 12 volt supply, too, not just your 35 Volt or 5 volt supply.

Good luck and I hope this helps.

Charles Lucas

Subject: Aiwa CD/Stereo power problem
From: ta7...@aol.com (TA7205)
Date: 8/2/01 1:47 PM EST
Message-id: <20010802144737...@mb-mp.aol.com>

[Mark D. Zacharias]

I've seen 10uF capacitors bad in the power supply which can cause this
symptom. they're located on the main board, near the rear of the unit, near
the rectifier diodes. Part of a voltage doubler supply for the display.

Mark Z.

"TA7205" <ta7...@aol.com> wrote in message
news:20010802144737...@mb-mp.aol.com...

[leeppp]

"Mark D. Zacharias" <mzach...@kscable.com> wrote in message news:<ezoa7.11619$Jg.11...@typhoon.kc.rr.com>...

Remember, 10 mics and lower will read high on ESR meter..look at
"worst case" ESR chart to be sure. I had a weird finely cracked
vertical feedback resistor in tv that could only be found by using
freeze spray and watching it arc!!! The pro`s gave up on set as a
"tough dog" not worthy of any more wasted time.It turned out that
resistor was installed with NO strain relief and finally gave up after
a few yrs. LEE