Aiwa P30 Power Amplifier Fault

If the amp is functioning to this level, maybe the audio input is missing? Have you checked the audio level going in? Flat wire connectors make this difficult, and I'm almost betting this unit uses them... grrr.

Mark Z.

When he says "startup relay", is he referring to a relay that turns on the main power transformer from a standby supply ? I'm not familiar with this model of Aiwa, but it occurs to me that it may also have an output relay that's not coming in ?

Arfa

Or.. maybe he means a protection circuit relay. I have no experience with this unit either, but it would be good/fantastic if people would take an extra freakin minute to type more details regarding their electronic problems.

These unclear questions generally take a few days of asking the OP for more info, to even get an idea of what might be taking place.

And, because the OP is posting from one of those gypo/clone DIY sites, he may miss seeing some replies.

-- Cheers, WB .............

On Sep 28, 8:08=A0am, "Mark Zacharias"

Hey OM:

I seen where peeps have left out the jumpers that go in the RCA jacks on the back the jumpers re feed the signal back into the amp for say you don't have an EQ that needs to be attached. To find out take a small screwdriver that will fit into the RCA jacks and with the volume cranked up all the way, poke the screwdriver in each jack to find out which one is inputting direct to the amp.

Once you hopefully find that jack the use a RCA cable to find the output just keep plugging the RCA cable into every jack until you find it don't forget the turn the volume back down though.

Been there done that that's my story and ima sticking to it.

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

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

Arfa

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

a

Yes, if W162 is silkscreened on a circuit board, it is likely to refer to a wire jumper. This would be consistent with a zero ohm reading.

Assuming the shorted zener has not caused collateral damage then matter of suck it and see to find a range of values that let the unit work and then pick the middle value to solder in

On Thu, 6 Oct 2011 21:23:10 +0000, M.Joshi put finger to keyboard and composed:

Is there an electrolyic capacitor in parallel with the diode? If so, then its voltage rating will put an upper limit to the rating of the diode.

Are there any similarly marked zeners elsewhere on the PCB? If so, then measure their voltages in-circuit and compare them against their marking codes.

- Franc Zabkar

--
Please remove one 'i' from my address when replying by email.

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.

The 'speaker' switches on the front panel are turned 'on', yes?

--Winston

Winston: Yes, I have tried different combinations of the A/B speaker selector switches!

Mark: I suspected that it was either a 16.2V zener or something similar. Thanks for checking the data book, I'll try a 16V zener.

--
M.Joshi