Hi , I’m Max from London UK. This forum is a great resource which I much appreciate! Working on my old Sony WM-D6, need some help regarding DC converter which is faulty. Looked at threads here and found mine is a different earlier version so I think it’s worthwhile to document it here for future reference. Will appreciate help from anyone with knowledge/interest in this. Thanks
As was suggested by Valentin I checked the transformer for continuity and it seems fine. Also replaced the input inductor and checked the pnp transistor and the caps. All tested fine.
It's not clear if this DC-DC converter is really different than the one in the service manual or its just a slightly different PCB layout. Note that it is the NPN transistor that goes bad in these DC-DC converters, not the PNP one. I recommend using the FMMT491ATA as a replacement, as it can handle higher current than the original and it's widely available. The BC817 suggested in the D6C thread will also work, but since a better one is available I see no point in using a lower spec one. @Mister X Please move this thread to the walkman section.
From what is written here the scheme is reversed on the diagrams found on the net WM-D6C convertitore c.c./c.c. fisso | Forum di Stereo2Go
Yes, in the WM-D6C service manual it is reversed, but on the WM-D6 manual it is drawn the correct way. The voltage divider for the negative feedback is at the output, that's the easiest way to figure out which is the input and which is the output. I attached the D6 DC-DC converter schematic for reference.
this is correct... @Valentin reversing the output with the input creates a lot of confusion you should create a corrected file and make it available every d6c diagram that you find on the net the converter is reversed sorry for the pun
Hi. This schematic is very helpful thank you Valentin. The strange thing is if you look at the first photo I posted, it seems like there is no NPN transistor! All I can see is a couple of diodes. Also not clear to me how to test the zener diode (right in the middle with a missing chipped bit). Thanks
This is a good idea. Will come back with updates about this later on. The error is in the service manual itself. It's not the only one to be found in SONY service manuals, I came across others over time. @maximin The circuit needs to have 2 transistors to be regulated. One is part of the oscillator and one an error amplifier. Now I realise, your NPN transistor is missing. That's why your DC-DC converter doesn't work. Attached a picture with where it should be soldered. The replacement is FMMT491ATA. For reference, a zener diode starts conducting at 0.6V when forward biased (just like a regular diode), but when reverse biased it will start conducting at the zener voltage (5.6V in this case). You can't test it with a multimeter, as the compliance voltage of the diode tester is not high enough to bias the diode. It needs to be tested with a variable supply and a current limiting resistor.
Thank you Valentin! So this D6 was never operational? That is very strange. It looks as if this tr was never fitted. How is that possible? I will find this transistor and report here. Thanks.
The transistor was fitted before, as there is a burn mark I can see in the middle of that red glue line. The presence of the red glue is also the telltale sign the transistor was there, as this glue is used to hold the components onto the board for wave soldering. It's hard to say exactly what happened, if someone removed that transistor before or it simply fell off when you disassembled the can. You can check to see if the legs of the transistor are still in those blobs of solder. However, at this point it's not too relevant what happened.
Hello maximin, Great news and I sure enjoy my Walkman and the students in my classroom get a kick out of it mine is one the earlier ones of a diffrent model . I need to pick up a later one I do have a Panasonic with Auto reverse thou but it's not a Sony ! Sincerely Rich
