Identifying Part from Schematic

[mikay786]

Got this Monitor Audio FB212 subwoofer, which unfortunately the previous owner has absolutely butchered the power board. Never seen such negligence

Problem started out as a hum and original owner proceeded to change main caps with some ebay jobbies which blew spewing guts out all over board. That and hes changed the bridge rectifier as the one fitted is not the original. After the replacement main caps blew he took them out and put back in the old ones.

So as it stands only the bridge rectifier isn't original (he says its the same specs but don't really trust anyone who has done this to the board)

Visually as far as i can see there is a blown resister, which I've identified as a 100k Resistor from schematic. (Position R3)

So what I'm trying to figure out is what the original bridge rectifier was from the schematic but following / reading them is a bit beyond me at present.

Looks like its maybe "BD1 BD254", not sure if that's a part number or what?

[paulstef]

Re: Identifying Part from Schematic

http://media.digikey.com/pdf/Data%20...5,25,35(W).pdf Maybe similar to this one.

400V, 25A.

[CapLeaker]

Re: Identifying Part from Schematic

sounds like a 25A 400V bridge rectifier.

[mikay786]

Re: Identifying Part from Schematic

Thanks, ill test the one fitted to see if it still works.

just noticed in the schematic the main caps are supposed to be 10000uf 80v, and the ones fitted (which owner said were the originals) are 4700uf 80v!!

and the bridge rectifier fitted is a KBPC2501, which is 25a 100a, so wrong part again?

[paulstef]

Re: Identifying Part from Schematic

Thanks, ill test the one fitted to see if it still works.

just noticed in the schematic the main caps are supposed to be 10000uf 80v, and the ones fitted (which owner said were the originals) are 4700uf 80v!!

and the bridge rectifier fitted is a KBPC2501, which is 25a 100a, so wrong part again?

Yes this rectifier has 100V peak reverse voltage.
You could remove the bridge rectifier and measure the output voltage of the transformer if you are uncomfortable with it. From the voltage ratings of the other caps it may not be a problem.

[mikay786]

Re: Identifying Part from Schematic

http://uk.rs-online.com/web/p/bridge...fiers/2278643/

something like this better? (I'm going to put back in 10000uf 80v caps too)

[budm]

Re: Identifying Part from Schematic

For R3 100K resistor to burn up like that I would check ZD1, D1, Q23.

[mikay786]

Re: Identifying Part from Schematic

Alright looks like I'm going to need a replacement transformer

Did what budm suggested in another thread, disconnecting the transformer from the main board and fault seems here. Is literally exploding fuses.

Theres no spec on the unit itself, but I have gathered from a quick google that's its a

600VA Shielded Transformer (http://www.widescreenreview.com/news_detail.php?id=6387)

5 Primary Side Cables (115-230v)
6 Output Cables

From the marking on the board thankfully its gives values.

2 x 55ac
2 x 12vc
2 x GND

2 X 12vc going to 2nd bridge rectifier RB154 (BD2 on schematic)
2 X 55ac going into the main bridge rectifier GBPC2504W (BD1 on Schematic)
2 X GND going into ground

Any advice on a replacement?

[budm]

Re: Identifying Part from Schematic

Boy, you sure run into bad transformers. This may be hard to get.
Any label or sticker on the Transformer?
I wonder if it is truly 55V-0-55V, that would make the +/-77VDC (55 * 1.414) power supply for the power amplifier section, the filter caps are only rating at 80VDC and since it is not regulated power supply, that Voltage can easily goes over 77VDC.

[budm]

Re: Identifying Part from Schematic

BTW, where did you get the diagram from? Are there any more info or more pages of the service manual?

[mikay786]

Re: Identifying Part from Schematic

There's nothing on it apart from sticker saying 185230533, lucky it has markings on the board or would have absolutely nothing to go on.

I feel this is going to be difficult!

[mikay786]

Re: Identifying Part from Schematic

I got it from avforums, someone posted it up on there. Not been able to find anything else.

[mikay786]

Re: Identifying Part from Schematic

What is this, inside the primary side

says

17 AM
033A5

[budm]

Re: Identifying Part from Schematic

That is the thermal protection device in case the transformer winding gets so hot that it may catch on fire, this device will cutoff the power to the transformer winding. That device should show <1 Ohms between the two leads.

[mikay786]

Re: Identifying Part from Schematic

I don't think that's the problem as is blowing fuses, just done a continuity test and all the primary cables have continuity between them!

[mikay786]

Re: Identifying Part from Schematic

are there any less powerful options if this original is too hard to replace?

[paulstef]

Re: Identifying Part from Schematic

Just to make sure, you tested the primary side also disconnected , right? There is still a switch and a capacitor on the primary side which could be at fault.

[mikay786]

Re: Identifying Part from Schematic

No, I didn't. You mean the film caps and the ac selector?

[paulstef]

Re: Identifying Part from Schematic

No, I didn't. You mean the film caps and the ac selector?

Yes, just to make sure...

[mikay786]

Re: Identifying Part from Schematic

tested the filter caps and they seem fine, kinda of torn the transformer apart now !! well just the outer layers to see if there was a short up top.

Well another lesson for the future, ill see if I can put it back together later and tried without connecting to switch. Erm would I just wire directly to the socket bypassing the voltage selector?