"M.Joshi" wrote in message
...

Thanks for your reply Arfa - I have downloaded the schematic of the
protection IC and will take a look at the test circuit.

The shorted component is definately a zener as the PCB symbol indicates
(a diode symbol with two opposite diagonal tails). The zener measures
short in circuit and out of circuit too. I cannot seem to find any data
on it (W162). Do Japanese manufacturers use W to denote something?


Arfa Daily;2720819 Wrote:
"M.Joshi" wrote in message
...-

M.Joshi;2716810 Wrote:-
Hello,

I am trying to diagnose a fault with an Aiwa P30 DC Stereo Power Amp.
It is part of a mini separates system consisting of a separate tuner
and
pre-amp.

The power amplifier does not output any audio to the speakers from
either channels. I have checked that the startup relay engages and
both
the positive and negative power rails seem to be OK?

Any other pointers would be useful.

Thank you.-

I have investigated further - the gain sections appear to be working
fine. If I inject a 1KHz signal at the input on the RCA jacks, an
amplified version is present on one side of the protection relay. The
other side feeds the speaker output terminals. The relay is just not
switching for some reason? I have tested the relay out of circuit and
it does work.

The protection circuitry is built around a TA7137P IC.

I also found a zener diode which is measuring short circuit. The part
number is D162 - I cannot seem to find any data on this?

Thanks.




--
M.Joshi-

In what part of the circuit is this zener ? Are you sure it's a zener
and
not just an ordinary diode ? Have you checked it out of circuit to make
sure
that you are not reading across some parallel device ?

The relay might not be closing for one of two reasons. First, that it's

doing its job, and protecting your speakers from a DC offset at the
midpoint
of one of the amplifier channels. The first thing that you must do is to

determine if this is the case, by measuring with a multimeter set to a
DC
range, at the input side of the relay switching contacts, for each
channel.
You should do this with no signal present, and not expect to see more
than a
few mV - probably 15 mV maximum.

If there is no offset, then the chances are that the problem is around
the
7317 (that's 7317, not 7137 as you stated) protection IC. In my
experience,
it is seldom the IC itself which is faulty. Most often, it is one of the

components that defines the delay time before activation of the relay -

about four to six seconds for most amplifiers. The two components
involved
are a small electrolytic, and a high-ish value resistor feeding it with

charge current. Either of these components, when faulty, can cause the
IC to
malfunction in the way you are experiencing.

see

'TA7317P pdf, TA7317P description, TA7317P datasheets, TA7317P view :::
ALLDATASHEET :::' (http://tinyurl.com/3w8jszb)

and take a look at the test / application circuit. Look at the
components at
pin 8 for instance.

Arfa




--
M.Joshi

As I recall, the notation is short for WZ162 and would indicate a 16 volt
zener.
So...
I looked up a WZ162 using NTE cross refence software, and yes, it's a 16
volt zener, equivalent to an NTE 5025A.


Mark Z.