Identify Transformers for Surround Sound System

[telecomguy]

I have a Philips surround sound system that now needs new transformers as I attempted a capacitor fix that went south. The transformers have the following markings: R7249T 6HC (and the C is underlined)

These are 4 pin transformers on the AC inlet. Anyone know a manufacturer I should be looking at? If you google search that part number you'll just find my post on Fixya...

I don't have the input ratings handy but can post them later if it helps. Thanks for any help/advice. <tg>

 

[ScottyUK]

If it is vintage Philips, then there's every chance that it is a Philips component. They divested most of their component businesses about 10-15 years ago so if it is 'new' Philips then it is probably from China. If this gear is really worth saving then first try a Philips repair centre. If you get no joy see if you can figure out what the transformer was from the silk screen layer on the board and look for an alternative. It is probably possible to rewind the transformer if you're desperate. I haven't done it for a long time because it is both fiddly and frustrating, although it is rewarding too if successful. Small transformers are usually harder to re-wind than bigger ones in my experience.


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If we learn from our mistakes I'm getting a great education!

 

[IRstuff]

How do you know you clobbered the transformers? Unless you're running huge amounts of power, it's unlikely that you killed a bunch of wire.

TTFN
faq731-376

 

[telecomguy]

IRstuff, smoke, sparks, little wires sticking out in non-production fashion... P

Bought on Craigslist for $100. Ran for a while just fine with a long warmup cycle and buzz when powering up. Once it came on the sound system worked great. Finally stopped getting beyond the buzz phase so I searched and found the do-it-yourself solution was to replace some undersized capacitors ($3 at RadioShack). Unfortunately I replaced the wrong ones. When I applied power I was immediately made aware of my error. Thought I'd spend another few bucks to fix it, else I'll be buying a new system.

 

[IRstuff]

With that much damage, there's probably more latent damage that's not even obvious from visual inspection. You burned out the power transformer!! Where did all that power go, besides the transformer? I'd be amazed if the amplifiers aren't cooked as well.

TTFN
faq731-376

 

[telecomguy]

Fair enough. Thanks for the feedback.

 

[telecomguy]

Just remembered I didn't have the power supply board connected to the system at the time I plugged in the AC cord so damage is isolated. By chance I did a search for some of the numbers silkscreened on the PCB and found it:

http://www.ebay.com/itm/Alite-Vance...663?pt=LH_DefaultDomain_0&hash=item4cfd6f909f

The parts I know I fried are at the top left. Looking at the board I now see the ref des are L101 & L102 (indicating they may be some kind of inductors rather than transformers?).

In any event, for $26 I'm just replacing the board to avoid having to chase other issues. Thanks again for the help.

 

[ScottyUK]

If that is a switching power supply - which it looks like from the photo - then bear in mind that some desings are intended to work correctly only when a minimum load is present. Operating with no load usually causes mis-operation like poor regulation, sometimes it seemingly has no ill effects, sometimes the PS just doesn't do anything, and sometimes you get a firework show.


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If we learn from our mistakes I'm getting a great education!

 

[Comcokid]

A educated guess given the picture and your description is that you burned-up some input inductors that are part of a input line filter.

Remove the parts, measure the diameter of the wire to get the wire gauge, cut the wires off the bobbin with a xacto knife and count the 'loops' to get the turns-count, then start re-winding.

Now, I'm assuming that since they are marked as "L" that they are single inductors, but they might use "L" as a designation for common mode chokes or differential mode chokes, in which case you will have two windings as if they were transformers. The picture does show two sections on the bobbin, so they may be chokes. In that case you will have to determine the direction of each winding when you rewind to get the filtering right, and determine which pin went to which coil since there will be a coil on each power input line for a total of two coils and four connecting pins.

 

[telecomguy]

Yes, they are the double winding version. That's what made me think they were transformers. The silkscreening under the part (once removed) shows two coil diagrams across the two sets of pins. I guess I could re-wind, but like IRStuff said, who knows what else I may have damaged so I've ordered that new one. And thanks ScottyUK. That may be what happened. The caps I replaced may not have caused the problem. It could have just been that I applied power without a load.

Thanks all,
<tg>