power supply question NMS8280

By msxrestarter

Master (224)

msxrestarter's picture

19-11-2005, 11:35

I have a problem with the power supply of my 8280.
This problem seems to be quite usual and I've read some documents on how to fix the powerdiodes, but mine doesn't seem to have them inside.
In stead there's some kind of transistor mounted.
Is this an modification by the former owner(s) or did philips altered this themselfs to optimize the power supply ?
users.telenet.be/msxrestarter/voeding8280diodes.JPG
Can someone give me the output values the power supply normally provides, so I can check what is wrong. Maybe I'm mistaken and the problem isn't with the power supply at all.
How do I check these values and which voltage must I measure between wich color cables ?
I would like to know the color code of the four main power cables as well.
There is a yellow,black,blue and red cable connected to the output of the power supply.

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By Repair-Bas

Paragon (1149)

Repair-Bas's picture

19-11-2005, 12:02

I miss the diodes and the -12 volt power IC looks not so good.
The power IC on the side of the computer is normal.
In the 2nd and 3rd series of the 8280 you can find this.
Place new diodes (6A) and a new 7912 voltage IC.

There is also a 256 kB memory mapper in this computer.

By msxrestarter

Master (224)

msxrestarter's picture

19-11-2005, 12:27

Ok, thx Bas. I thought that the transistor on the side maybe replaced te powerdiodes.
Just removed te print of the power supply so I could have a look at the backside, and indeed someone has removed te diodes but didn't replace them.
Just to be sure, the IC you mean is marked on the print as 'IC1052' wright ?Question

By Repair-Bas

Paragon (1149)

Repair-Bas's picture

19-11-2005, 12:33

Yes, IC 1052

But if you replace the diodes look on my site.
This is the best way to mounting them

http://www.bas-ditta.info/verkoopenlinks/images/msx%20001.jpg

By msxrestarter

Master (224)

msxrestarter's picture

19-11-2005, 12:43

So it's better to mount them higher, I mean further away from the print, so the cooling is better I suppose ?
If I'm reading right the diodes on the pic are A8's.
Is this even better then the A6's you mentioned before ?oO

By msxrestarter

Master (224)

msxrestarter's picture

19-11-2005, 17:52

Just had a better look at the picture and saw I got it wrong.
Diodes are indeed A6 8 DC Big smile

By Repair-Bas

Paragon (1149)

Repair-Bas's picture

19-11-2005, 20:22

Let me know when you put in the new diodeds.

By msxrestarter

Master (224)

msxrestarter's picture

25-11-2005, 18:52

Just put in the new diodes and IC 7912 and he's running again. Boots up normal, diskdrives work fine, cartridge slot are working an also internal 256Kb memory mapper is OK.

users.telenet.be/msxrestarter/diodebrug%20met%20nieuwe%206A%20diodes.jpg

But there's still something wrong with the video input. When I connect my camera to the video input I can't get a clear image on the monitor screen.
Seems like the signal is disturbed somehow. The image does come on the screen but there's a black diagonal stripe and also a horizontal 'rainbow' stripe which covers a part of the image.
The picture below is taken when camera is turned on/off.

users.telenet.be/msxrestarter/geen%20signaal.jpg

This is a picture of the screen when the camera is set to a white piece of paper.

users.telenet.be/msxrestarter/wit%20papier%20in%20beeld.jpg

I don't know where to start in solving this new problem. Maybe it's an known problem for 8280's who's power supply have been broken ?:-?

By msxrestarter

Master (224)

msxrestarter's picture

28-11-2005, 19:59

Does nobody got a clue where to start in solving this problem ?

Would love to get it working 100% again Crying

By HansO

Paladin (672)

HansO's picture

28-11-2005, 21:30

Does nobody got a clue where to start in solving this problem ?

Would love to get it working 100% again Crying

Not really a clue, but with an oscilloscope and the service manual you will have a chance. The circuit diagram is quite good.

It looks like the sync signal is not getting through.

By msxrestarter

Master (224)

msxrestarter's picture

28-11-2005, 23:18

Thx Hans for your reply.
I've just downloaded the service manual and will try to study it as good as possible.
I'm a real novice at this so I probably need some more help to get started.
First I'll have to get my hands on an oscilloscope to start the testing.
Problem will probably be how to connect the oscillospe in the wright way without damaging the msx.
Maybe it's a good idea to post a new topic about the video input problem when I got stuck or need some more help in reading the circuit diagram and/or connecting the scope.Smile