Pioneer Speaker Package subwoofer transformer.

[bamix]

Hey Guys,

I wasn't sure whether to post this in Audio or in Power Supplies.

Looking for some advice on a failed speaker package subwoofer. This Pioneer unit from a cheapo S-HS50 kit that came with my AVR dropped its lunch a while ago. I have pulled it apart and carried out some basic checks and it looks like the main transformer has failed.

I have 240VAC going in and nothing at all coming out. It has 3 wires coming out, 2 Yellow and a White at centre. I figure it is a centre tapped transformer but it has no marking or labelling on it at all that indicate what it is. I even pulled the end covers off and there was nothing inside there either. I have attached a picture for reference.

It only has an SF logo in a diamond with a part number below, SF-76E/282128E. Beneath that it says (Thermal Fuse Fitted 0115C).

According to my DMM I have no continuity on the primary (240V) side and I do have continuity on the secondary side between each Yellow and the central White wire.

So my question is, if there is no output and no labelling, how do I work out what the specification of this part is ?

I can't locate a repair manual on the subwoofer, the board number draws a blank too. I checked for anything screen printed on the board that might help. The only thing that was of any worth was a Bestar IC Relay BS-115C that is running a 24VDC Coil. Might this indicate that the transformer I need would be a 24-0-24 ?

I know it's a cheap, low level, poor performing sub but I just want to get it working again. So if anybody could humour me with some advice I would appreciate it

[eccerr0r]

Re: Pioneer Speaker Package subwoofer transformer.

Three things... first off if you can measure the size of the transformer, you can get a good guess at the volt-amps or watts the transformer can handle.

Then the other thing is show a good picture of the rest of the board, maybe someone can stare at the board a bit and make an educated guess at the voltage of the transformer. The 24V is a good guess from the relay, but maybe more clues can be gotten from the topology of the board, capacitors, zeners, etc.

With the voltage and the volt-amps a current rating can be estimated.

Third thing is how many watts this amp/speaker rated to handle? What's the rating written on the panel?

[bamix]

Re: Pioneer Speaker Package subwoofer transformer.

Thanks for getting back to me eccerr0r.

1. The dimensions of the transformer are: W80mm x H70mm x D95mm. Weight is about 2kg.

2. Photos are attached. If you need anything in more detail please let me know. I have a shot of all components for reference, power board and amplifier board.

3. It is rated at 180w with a 6.5" down firing speaker.

Thanks again.

[madan1]

Re: Pioneer Speaker Package subwoofer transformer.

+/-12V stand by which should not be affected by the big transformer fail
check the main caps ratings.. for sure the V is somewhere there, but not more

My guess is that the big transformer is used only to power the amp section. Everything else is powered constantly by the "stand by" board ( screw the power saving ).

[Khron]

Re: Pioneer Speaker Package subwoofer transformer.

If you have no continuity on the primary, odds are pretty good the thermal fuse went "poof".

If you're feeling cheap and/or adventurous, you could try gingerly cutting through the outside insulating tape, around the area the mains wires are - the thermal fuse is usually not buried too deep. Either bridge it, or replace it with a similar-rated one.

Do note that if you choose to replace it, the connections will need to be crimped, not soldered (due to it being a THERMAL fuse, y'know? ).

[bamix]

Re: Pioneer Speaker Package subwoofer transformer.

Thanks madan1.

The big caps are 50v 4700uF. I thought that too but at 50v it probably still leaves options of 12-0-12 to 48-0-48 so I didn't rely on that.

Yes, it sits in standby until it receives a low frequency signal and then it turns on. Feature of convenience I guess. Makes troubleshooting a bit more difficult though.

I agree with you, not a big fan of power saving. Have seen it cause many problems.

[bamix]

Re: Pioneer Speaker Package subwoofer transformer.

Thanks for the tip Khron.

I figured that might have been the case. 'Adventure' is my middle name so I will give it a go. Absolutely nothing to lose by trying that out.

I checked online at my local electronics outlet and they have thermal fuses at 77 and 133 degrees C. The transformer lists 105. To me that seems a little on the low side. Any opinion about moving to a higher fail temp ?

Thanks again. I will post the outcome of my 'open transformer surgery' when I have it on the operating table.

[madan1]

Re: Pioneer Speaker Package subwoofer transformer.

Make some pics of the bottom of the main pcb and the amplifier component ( from the pins look like a single-chip-solution ).

[bamix]

Re: Pioneer Speaker Package subwoofer transformer.

Hey Guys,

I have opened up the transformer end cap and cut away the tape and insulation to find the thermal fuse. See photos attached.

I checked with my DMM and good news is that the fuse is definitely open. However, I checked direct onto the primary windings past where the fuse is soldered and I get an open circuit there too

The only way I get anything in range at all is to go to the 2M Ohm setting on the meter so I am pretty sure that's not right.

madan1, I will take the pics you asked for and upload them next.

Thanks again.

[bamix]

Re: Pioneer Speaker Package subwoofer transformer.

madan1,

Pics requested of underside of the Power Board (IMG_3251_small.jpg) and Amplifier Board (IMG_3252_small.jpg) are attached.

Thanks.

[budm]

Re: Pioneer Speaker Package subwoofer transformer.

Since filter caps for the +/- supplies are rated at 50VDC, it is probably safe to say that the it may be running on +/-35VDC, so that means the transformer will be 24-0-24VAC.
24V x1.414 = 34V.

[petehall347]

Re: Pioneer Speaker Package subwoofer transformer.

Hey Guys,

I have opened up the transformer end cap and cut away the tape and insulation to find the thermal fuse. See photos attached.

I checked with my DMM and good news is that the fuse is definitely open. However, I checked direct onto the primary windings past where the fuse is soldered and I get an open circuit there too

The only way I get anything in range at all is to go to the 2M Ohm setting on the meter so I am pretty sure that's not right.

madan1, I will take the pics you asked for and upload them next.

Thanks again.

maybe it confused you like it does to me ..twist fuse wires together then check blue to brown wires ohms ..

[Agent24]

Re: Pioneer Speaker Package subwoofer transformer.

Maybe the transformer went shorted in the primary winding and blew itself as well as the fuse.

Or it could have been failing open-circuit, which would generate excessive heat.

[madan1]

Re: Pioneer Speaker Package subwoofer transformer.

madan1,

Pics requested of underside of the Power Board (IMG_3251_small.jpg) and Amplifier Board (IMG_3252_small.jpg) are attached.

Thanks.

and some of the components attached to the radiator

[bamix]

Re: Pioneer Speaker Package subwoofer transformer.

Thanks so much everybody for your kind consideration.

petehall347, you were right.

This time I checked at Blue and Brown and then used an alligator clip to join the 2 legs of the fuse together. Clip off = Open, Clip on = OK.

I will order 5 of these as replacements.

Hopefully the issue doesn't go any deeper than this one problem. I was concerned too as agent24 made mention about a consequential failure. madan1, if I still have any issues I will post the pics you made mention of. In that area I found some suspect solder joints on the board under magnifying glass so I touched them all up with the iron. I trust they are OK.

Thank you

Благодаря

Kiitos

[budm]

Re: Pioneer Speaker Package subwoofer transformer.

Leave the secondary of the transformer not connected, then use 40W lamp in series with the primary to power up the transformer (the thermal fuse bypassed) and see if the lamp will light up brightly or not.

[petehall347]

Re: Pioneer Speaker Package subwoofer transformer.

them damn things confuse me .. well they did for a few minutes .. i do this to find secondary voltages to order a new transformer .. new thermal fuses work sometimes if transformer is good ...
other factors blow them too like over-current on secondaries . thermal fuses are to protect against fire ... sometimes they wear out with old age same as regular fuses ...
always safety first .. use a current meter whilst testing and test for a few days ...

[madan1]

Re: Pioneer Speaker Package subwoofer transformer.

You are welcome , but I still insist on the pictures of the amplifier.. call it curiosity .
To me it looks like stk or something.. and since it is power directly from the main caps, the V will be easy to find in the documentation.

[Agent24]

Re: Pioneer Speaker Package subwoofer transformer.

Don't worry about what I said, since the primary is fine, the fuse probably just failed from old age.

[bamix]

Re: Pioneer Speaker Package subwoofer transformer.

budm,

I have a test socket that takes bayonet cap lamps but smallest I have available here is 60W. Is that going to create too much current draw for the test and potentially damage the primary side ?

I also have one of those Philips LED replacement globes for bayonet socket but it is 11W only.

Will either of these suffice ?