Identifying a diode value, conductive glue strikes again!

[mikay786]

Re: Identifying a diode value, conductive glue strikes again!

Anyone know how to identify polarity of the diac? Does the brown mark on the lead mark the negative?

Forgot to check when taking out and photos are too blurry!!

[CapLeaker]

Re: Identifying a diode value, conductive glue strikes again!

A diac has 2 diodes in opposite directions. So it doesn't matter what way around.

[budm]

Re: Identifying a diode value, conductive glue strikes again!

http://www.learnabout-electronics.org/diodes_07.php

No polarity.

[mikay786]

Re: Identifying a diode value, conductive glue strikes again!

Thanks, must be something else then. Replaced the toshiba mosfets and now powers up fine and isn't blowing fuses but not getting any sound.

Will check to see if the pot is causing it as with the last ma sub.

[mikay786]

Re: Identifying a diode value, conductive glue strikes again!

Edit, is there anyway to test diac to see if it's doing its job with power on?

[budm]

Re: Identifying a diode value, conductive glue strikes again!

So are now getting the DCVs for the pre-amp section to run?
There should be another board for the pre-amp SECTION.

[mikay786]

Re: Identifying a diode value, conductive glue strikes again!

I'll have to check when I go back up.

There's two other boards, 1 where the ac comes in where there's a little transformer and a few other bits and the other number 2 board which is connected to all the back panel switches and pots and inputs.

I assume number 2 board is the preamp board? It's connected to the volume dial via lead and the volume dial does light up so power is going to that board.

[budm]

Re: Identifying a diode value, conductive glue strikes again!

I'll have to check when I go back up.

There's two other boards, 1 where the ac comes in where there's a little transformer and a few other bits and the other number 2 board which is connected to all the back panel switches and pots and inputs.

I assume number 2 board is the preamp board? It's connected to the volume dial via lead and the volume dial does light up so power is going to that board.

That is correct, the second board has the same function as the other sub you worked on with bad pots, it should have the +/-12~15VDC to run the op-amps.

[mikay786]

Re: Identifying a diode value, conductive glue strikes again!

I'll check its properly shortly, thanks

[mikay786]

Re: Identifying a diode value, conductive glue strikes again!

So checked board, its a little different to the last one I worked on as has two connectors (plus another one for volume dial)

The one of the right coming from right hand board has multiple voltages, 8v, 15v, 8v. If I measured correctly, red lead on red pin and black lead onto the 3 white pins.

The other connector on the left has 12v from the red pin and black pin closest to it.

[mikay786]

Re: Identifying a diode value, conductive glue strikes again!

Just an update on this as had put it aside for a while as was stuck and had more pressing things to do.

Anyhow I bought a surround sound system that had the same sub in it so went back to the faulty one.

Anyhow ive basically narrowed the fault down to the main board, the one with the big caps and have ruled out the diac. Just switched over main boards and was working, switched over diac and fault persists.

Fault being it stays in standbye mode, so could be a starting cap / relay?

I'm going to swap over larger caps which ones lid looks to have popped off just to rule them out.

[mikay786]

Re: Identifying a diode value, conductive glue strikes again!

Ohh and the diac was a DB3 by ST electronics. The one from the working sub was a blue and had text on it.

[mikay786]

Re: Identifying a diode value, conductive glue strikes again!

Giving up on this as is likely one of the many surface mount components on the underside.

Virtually swapped all components bar the transformer from the top side and no luck, just standbye. Put all the components taken out from the faulty unit and put into the working unit and that still works fine.

Theres two relays and on the working unit you can hear the first relay and then a second later the second relay kicks in turning the unit full on.

On the faulty one you hear the first relay but the second relay doesn't sound. Ive switched relays over and no difference. Relay is in connected to shitloads ofd components on the underside which ive had a measure of a few diodes which seem fine. Theres some sort of controller chip which may possibly be the cause but is beyond my capabilities.