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WM-D6C DC-DC converter fixed

For many of us it is very famous problem. Reversed DC polarity and … 
There were many discussions on this topic. Here I would like to discuss two possible solutions, with simple TO-DO for everyone

1st. possibilty

Replace whole converter by modern type, sold here and there on eBay. You can find various 5V to 12V converters, or even anything to 12V converters. They’re small, much smaller than the original one. They’re more efficient. They can deliver more power. So why not to use them easily?
The answer is simple – they inerfere with internal circuits of D6C. You need to build ground shielding around it. More, their output voltage isn’t “clean” enough and it requires another filtering. Impossible? No, it just requires some time spent. Does anyone have experiences?

2nd. posibility

Repair the old one. Is it easy? Yes and no. The most difficult part is to remove the converter from PCB and open the original shield. It is difficult but everyone will know how to do it as soon as he tries.
I will rather describe how to troubleshoot the circuit that is inside.

Here is crop from service manual. It is just symbolic circuit and it has some basic mistakes. But it is very good start point.

Transformer and transistor on the left side create oscillator. Diode on the top is rectifier. Transistor and diodes on the right create stabilizer. When you reverse polarity, three parts can be burned – the ones marked with red letters and transformer. However, the wire on the transformer is much thicker than on the 33uH coil, that’s why it will survive. In most cases, it is necessary to replace both red parts:

1. Inductor: in blue circle (33uH, bigger version)

2. Transistor: in blue circle.

Instead of hard to get 2SD1048 you can use BC817 as 1:1 replacement. Well, the older one is little stronger (700mA vs 500mA) but in this application it doesn’t matter that much.

It is good to have right soldering station to be able to solder SMD parts. Or ask someone who can.

I hope you find this article useful. Any comments are welcome.


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Wow and Flutter – my know-how


I would like to post my experiences regarding typical problems with tape speed variations. I have fixed about 200 walkmans from Sony, Panasonic and Aiwa. However, I collect and repair only full-metal body autoreverse models made cca. after 1989. But most of my observations are valid for any model.

Many people think that these problems are related mostly to wrong belt used, but my experiences are little different. So here is my knowledge listed in the lowest to the highest probability order.

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Sony DD series step-by-step repair guide for dummies

Sony DD series (direct drive) walkmans are very popular among portable cassette players because of their high quality construction, excellent fully analog sound quality – and great timeless design.

Although they’re well built, they will not work within specs without proper service. Because they’re 30+ years old, most of them will have some common issues by now.

In this manual I will give very detailed step-by-step instructions on how to fix all common problems – and recommendations on maintenance tasks to do, to avoid future problems. With the help of this manual you should be able to do proper service on any DD unit. I’ve fixed more than 200 DD units and will present my know-how and best practices, discovered through the years. I will try to make it as complete as possible.

This manual is suitable for everyone with at least basic technical skills. Experienced technicians will also find useful information here.

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Panasonic RQ-S series walkmans – complete step-by-step repair guide

Dear all walkman fans,

from time to time I read here in various posts, how difficult it is to fix those small ultra narrow walkmans and bring them back to the specs. I must say it is not true. Most of them were designed to be serviced easily. Yes, they’re small, sometimes just little bigger than the cassette itself. But after you open them, you will see that there all is perfectly organized and parts are not that small as one could expect. From my experience, they’re much easier to fix than most bigger devices, such as boomboxes. Why? Boomboxes are made of plastics, their construction is cheap, with mix of wires, etc.

Continue reading Panasonic RQ-S series walkmans – complete step-by-step repair guide