Philips VG-8235 Burns fuse

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By Xan0ri

Master (168)

Xan0ri's picture

16-11-2020, 23:55

I am doing some progress here. Smile)
I've been going through IC's and components and just trying to get them to react, f.e LVA510. Then I suspect there was a problem with v9958 pins 50 & 51 and I resoldered them. Then, I found these jumpers ST1 & ST2. I removed jumper ST1 and just tried to boot -> The MSX BOOTED! ... Then it booted with both jumpers in. And then next time, it did not boot. But as I tried booting with different parts on and off, I've gotten it to boot several times now. Almost everytime msx boots successfully if I take the main powerconnector out of the mainboard, so there can be a discharge..?
Can anyone tell what are these jumpers? Do they have something to do with RAM or VRAM?
Do anyone of you have any ideas what would be the core problem? Why the manual discharge is needed?
Thanks in advance!

Here are some pictures:
https://ibb.co/f8JW3hB - Jumpers
https://ibb.co/MgPbftj - Successful boot
https://ibb.co/6r76Q8c - Leds

By Meits

Scribe (6049)

Meits's picture

17-11-2020, 00:16

The service manual says they're service jumpers.

By Xan0ri

Master (168)

Xan0ri's picture

17-11-2020, 08:37

Meits wrote:

The service manual says they're service jumpers.

I've must looked wrong pdf as I couldn't find it ehh... Thanks for the help. Maybe the jumpers are then not the main reason why booting up fails occasionally.
I could confirm that the problem is the power & electric discharge as 99% of time the msx boots after removing the PSU - motherboard connection for a while. Would be nice to understand now why this happens.

By Briqunullus

Master (202)

Briqunullus's picture

17-11-2020, 09:34

Progress! It looks like this machine will be fixable. I hope you'll find the missing piece of the puzzle soon. Good luck!

By Xan0ri

Master (168)

Xan0ri's picture

17-11-2020, 17:57

Briqunullus wrote:

Progress! It looks like this machine will be fixable. I hope you'll find the missing piece of the puzzle soon. Good luck!

Thanks! My current suspection is that maybe some capacitors are too old, hardly working anymore, and/or the external powersupply I made out of ATX psu is never actually stopping to send some current even I shut it off from the psu. There is still a wire jumper in atx motherboard connector making it to be always in ON -state (as I have no switch like on modern computer chassis). I ordered a PicoITX powersupply and will convert it for the msx as it can be then mounted inside msx. This MSX will be a combo of old and modern parts in the end I think.
I also played a bit of Penguin adventure from cartridge today and made my first basic listing in maybe 20 years.

By Xan0ri

Master (168)

Xan0ri's picture

20-11-2020, 11:58

I'm getting on with this project. As I already have video out from RF, I now try to get the video out from scart.
I have a cable that goes from scart to vga (also this is the way: scart -> vga) And my aim is to connect to a monitor with vga in. If I connect the cable the monitor reacts to it so cable is working and some signal going, but afterwards gives me a notify, there is no signal coming.
I think the cable has a wrong connection. I 've tried to understand from the schematics how the pinout should be but do not really understana. Can anybody lighten me up on what kind of cable I would need to connect to the monitor vga? Or should I somehow enable the scart from msx or something? As I said RF is working ok all the time.
Thanks Smile

By sdsnatcher73

Paragon (1212)

sdsnatcher73's picture

20-11-2020, 14:39

SCART to VGA is not common and will only work on CRT VGA monitors that support 15kHz signals. There is a list of more modern flat panel monitors that support 15kHz signals.

By Xan0ri

Master (168)

Xan0ri's picture

21-11-2020, 17:18

Happy to announce that this project is going on. The idea for SCART -> VGA started to seem bit too complicated worth the effort. So I went to a fleamarket and found a good older samsung syncmaster with all needed inputs and also a quality scart cable. And here we are with a working scart output with video and sound. I have also now ordered wozblaster enchanced and carnivore2 too & found from warehouse a 8gb compactflash UDMA. Also a ITX psu will be added as it can fit inside MSX as a powersource & I even ordered a bunch on 12v LEDS to pimp_the_ride. A picture:
msx_salamander.jpg

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