Speaker Protection board from Ebay

[hd220]

Has anyone any experience with these boards?
I picked up a couple of these reasonably cheap from ebay seller zoe_tsang. He sent the following connection diagram which I do not really understand. He says he doesn't have a schematic (typical of Chinese sellers) but ignored a request in the same email to clarify the connections.
(I know, buyer beware of buying from China on Ebay but they were cheap so not much is lost other than experimenting time.)

The second picture is of the connection diagram the seller sent after I bought it last year.

[Mooly]

Have you looked at the data sheet for typical application ?
http://www.datasheetcatalog.org/data...ec/UPC1237.pdf

It needs a supply ! which will feed into the diode as marked. The diode means you can feed either AC or DC into the PCB.
Identifiy the ground connection.
Identifiy the inputs from the amplifier.
Identifiy the relay connections.

Easy

[kavermei]

入 means 'in', 出 means 'out'.

[hd220]

Thanks Mooly and kavermei;
(Apologies for the camera phone pictures below - not always clear with closeups).

The boards I have are labeled in English. The relay speaker connection side is clear and connections per the diagram I drew.
The +32V VCC+ (as labeled) connection is clear as is the GND, assuming one wanted to use DC to power the board.

There is an "AC 28" hole which connects to the transformer. What about the other side of the transformer? Where does it connect to? if it is the "GND" point, it doesn't work, the relays are open.

I'm not normally this blind to this, I do have some electronics experience but either the board is faulty (which I am doubting) or I am missing something.

I do have the datasheet and at first glance it wasn't helpful.

[kavermei]

It's hard to tell for sure without a schematic. If you could trace out the circuit diagram from the PCB traces, I'm sure we could tell you in a second.

[hd220]

kavermei:
My point precisely which is why I asked for a schematic. Lots of these boards are being flogged by several sellers and I thought perhaps someone on diyAudio might have come across it.

I'll attempt to trace it. It is double sided with some of the traces underneath the relays which I'll pull out if need be. At that point I should be able to figure it out and post it here for the diyAudio community for reference.

[prairiemystic]

I would use the UPC1237 IC datasheet for a schematic, if you Google it

[AndrewT]

Hi,
it is likely that the AC in is a detect loss of AC and disconnect speakers.

The PCB is likely to be powered by the two adjacent pads using DC.

[kavermei]

Originally Posted by AndrewT

Hi,
it is likely that the AC in is a detect loss of AC and disconnect speakers.

The PCB is likely to be powered by the two adjacent pads using DC.

Yes, that is quite likely, the purpose being to avoid the 'thump' in the speakers at power-off.

[hd220]

OK, so I've traced the circuit. It is virtually identical to the datasheet's typical application schematic. Very minor changes. I've redrawn it to make more sense. The amp L and R channel outputs are sampled by the two 56K resistors connected to UPC1237's pin 2. Any DC there and the relays open I guess.
Also, I think Andrew T and kavermei are correct, the AC connection detects loss of AC. Question remains, what is the other side of the winding connected to? It may not be (and isn't in my case) the PSU circuit ground.

The board is powered by VCC+/GND, not that or AC IN as I originally thought.

So, the schematic is attached for diyAudio community's reference.