AWA DSA-510 Amp

[tazelikechickn]

Hey Guys,

I am trying to repair a AWA DSA-510 Amp. I have a standby light on, but will not fire up when I press the switch. The switch etc is ok, but I would like to check out a schematic to see how it works.

Does anyone have access to a Schematic? I have tried all the sites that I know, but no luck.

Thanks for your help.

[David_AVD]

Does it use a switchmode or conventional transformer power supply?

[tazelikechickn]

Hey Dave,

It is just a standard transformer. It has power coming out (13 V & 6 V) and fuses are OK. No AC power to the bridge rectifier. The relay is not clicking on.

[David_AVD]

Check for open-circuit relay coil (it happens!) first.

Then move onto the relay drive transistor circuit.  Some amplifiers have a small value electrolytic capacitor that is charged via a separate diode off the power transformer.  If that cap dies, the relay won't kick in.

Other than that, check for cracked solder joints and any sign of overheated resistors (check their value).  That should get you started.

EDIT: Oh, so no AC into the bridge?  I missed that at first read.  Does it have another smaller power transformer?

[tazelikechickn]

No smaller transformer that I can see. I haven't really traced or done a lot of checks at the relay. I see a diode, a few caps and transistor nearby and will check that tomorrow.

Also haven't checked the relay coil or switch operation, but can't hear it click when the button is pressed. I gather it is not being switched. Another job for tomorrow.....

IDIOT ALERT!! I just realised that I was testing the bridge rectifier incorrectly. Damn you AC/DC! Once I checked the right terminals I got 29.7 Volts AC & 35.5 Volts DC - all good. I think I will have to check the relay next. I checked for continuity on the coil, but might have the wrong side. I will desolder it and check it off the board and it should power up with a 9 Volt battery I think?

I have included a photo that should make it easier to understand

BTW thanks for the help - it is greatly appreciated 

[David_AVD]

When you say it doesn't turn on, maybe you mean that the relay never clicks in and you get no audio from the speaker outputs?

If so, one of the amplifier outputs may have gone DC and the relay circuit is doing its job.

There will be two traces (call them A & B) going from the output stages (heatsink area) to the relay and another two going from the relay (call them C & D) to the speaker terminals.

The relay will be wired with one (normally open) contact between points A & C and another contact between points B & D.

What you need to do is measure the voltage on each of the two traces going to the relay (A & B) with respect to ground.  They should be close to 0V DC.  If not there is an issue with one of the output stages.

[tazelikechickn]

Great advice Dave,

I will check that when I get some time

[tazelikechickn]

Hey Dave,

I ended up removing the relay, powering it up and checking for continuity either side - all good. When installed, I can physically feel the relay click in and I have consistent power either side of the contacts. Yet it still stays in the standby mode, with the light staying on even when the button is pressed.

[David_AVD]

I'll see if I can check out a manual for you.

[tazelikechickn]

Much appreciated - thanks

[Rasz]

check power transistor/whatever is stabilizing voltage after the relay

[tazelikechickn]

Thanks Rasz,

I have checked the regulators & both positives and negatives are working correctly.

[Rasz]

ok, so you have +-15v healthy
lets go further, find +5V rail and check if its working
follow the voltage upriver

[tazelikechickn]

Hey Rasz,

Thanks for your reply.

The regs are -+6 & -+12. One thing I did note is that the main wiring loom going from the board to the switching board has 5V, G, M, P, 15V on it and I am only getting 12V at the 15V pin (5V OK - don't know what the others are).
At this point I'm not sure if there is meant to be 15V there as the regs are only meant to be 12V. Or am I barking up the wrong tree?

I have searched high and low for a schematic, but nuh - not gonna happen!

Any help is appreciated.

[David_AVD]

I have asked for the manual but may take a few days.

[tazelikechickn]

Thanks for your help guys.

In the meantime, I will try and follow the voltage trail.......

[tazelikechickn]

Hey David_AVD,

Have you had a chance to find a manual for the AWA Amp?

I have been doing some voltage checks, but am a little lost without a schematic.

Thanks

[David_AVD]

I chased up my contact earlier today but no dice.  Sorry.

[tazelikechickn]

No worries, thanks for your help anyway. Looks like I'll have to go 'old school' and use my brain!! Time is the worst enemy. I seem to forget what I have checked and what I haven't. I have taken photos and marked off what I have checked and this usually works, but just really busy at the moment. Why do we have to work? Why can't we just spent our time doing our hobbies?

I guess that's why they call it a hobby! 

Thanks again for your help.