Determine power transformer outputs (SQR-6650)

[djim]

I've been trying to revived my Sony SQR-6650. I've determined that the Power Transformer's secondary outputs have failed.
While I have a service manual, it does not detail the outputs in value or schematically.
Its Secondary wires are a pair of Red to the power board, a pair of Blue to lamps, a single Violet to the power board, and a Black lead to common ground.
The lamps are rated at 8 volts, so I can guess at the Blue wire values.
A block diagram indicates that the Power Supply board is supposed to provide +24, -17, and +15 v to the Amp board, but I don't know how to translate that for the Red and Violet wires off the secondaries.
Any suggestions or info is much appreciated.

 

[Soundfield]

I've been trying to revived my Sony SQR-6650. I've determined that the Power Transformer's secondary outputs have failed.
While I have a service manual, it does not detail the outputs in value or schematically.
Its Secondary wires are a pair of Red to the power board, a pair of Blue to lamps, a single Violet to the power board, and a Black lead to common ground.
The lamps are rated at 8 volts, so I can guess at the Blue wire values.
A block diagram indicates that the Power Supply board is supposed to provide +24, -17, and +15 v to the Amp board, but I don't know how to translate that for the Red and Violet wires off the secondaries.
Any suggestions or info is much appreciated.

Very unusual for all of a transformer's secondary winding to fail. But if that is the case, what do you hope to achieve? It is very, very unlikely you'll be able to find a replacement transformer with the same voltages, VA per winding and physical size unless you rob one from an identical unit (in which case the actual ratings don't really matter as you can just swap them).

 

[par4ken]

Look at the schematic to determine the DC voltage out, then work backward. A bridge rectifier when the output if filtered will produce DC voltage 1.414 times the AC secondary voltage. Simply divide the unregulated DC output voltage by 1.414.

Looking at the SQR-4750 schematic from hifiengine it shows +26 and -26 diving the output stage, working backward 26÷1.414 = 18.4V or about 36 Volts center tapped.

The SQR-6650 is higher powered so the voltage would be higher than that.

Unlikely that all the secondary's would fail, more likely the primary has opened up, check for fuses, switches, power cord and anything else in the primary path.

 

[Soundfield]

Unlikely that all the secondary's would fail, more likely the primary has opened up, check for fuses, switches, power cord and anything else in the primary path.

Yup, agreed, but he's pretty much stuffed either way. A duff transformer is about the worst thing that can befall a bit of vintage kit. Practically no chance of finding a suitable form, fit and function replacement (unless, as I said, you cannibalise another identical unit).

 

[quadsearcher]

SAMS Photofact Where the pros shop for Photofact manuals, Quickfact manuals, service manuals and owners manuals | SAMS Technical Publishing lists that model as covered in a book, MHF-76. Since they reverse-engineer schematics, they often have detailed voltages measured on a live unit, and might have included secondary AC voltages. They are available via phone or website to confirm this model is listed correctly in their cross-reference and they sell reprints. That still doesn't tell us the rated current, because open-circuit voltage readings will be higher, but physical size is an indicator. I also ran across an original Sony manual for that model that someone has for sale (ebay?).

That said, old-school repair techs have been known to repair some transformers (sometimes there is an internal fuse/thermal link, definitely not for the inexperienced to attempt). Since it is unlikely to say the least that all secondaries have opened at the same time, it is more likely the primary that is open, and consistent with the usual failure mode of a power transformer. What resistance do you read across the primary? It should be low.

Oh, I see you do have a service manual, is it original Sony? If so, look up the Sony part number for the transformer in the parts list, very unlikely to be in stock anywhere, but I've found very old parts listed on their site sometimes. If you could attach a picture of the schematic, just the transformer area, I'd like to see it.