Hit Bit w/broken graphics

Resident (61)

17-07-2003, 00:41

Does anybody know if it would be easy to fix or replace the graphics chip of my Sony Hit Bit HB75-P? I unintentionally inserted one cartridge in each slot, and afterwards the graphics are distorted.

This happened back in 89 when I was a kid, and fortunately my father got me an SVI738 as a replacement for christmas that year. But now I would like to repair it and start playing with it again.

Any help appreciated. Thanks!

By MOA

Champion (293)

17-07-2003, 00:52

Trying to find a new one is easier

Otherwise try to contact Texas Instruments for a new videochip (or did Yamaha also make the MSX1 version? It's a TI-something, I think... and Yamaha made the v9938 for MSX 2 which was backwards compatible with the TI-chip.)

Worst case: your VDP is embedded in some other chip. In that case: forget it or get a replacement for that 'other' chip

Hmm... Somehow I have this feeling that my post is not much of a help!

By anonymous

incognito ergo sum (116)

17-07-2003, 01:08

I don't think VDP's were embedded in MSX1's :/
The chip you need is a Texas Instruments TMS9918 or 9928 or 9929, depending on NTSC or PAL and RGB or composite. As far as I know the 75P has a RGB SCART connector. Anyway, the number is on the chip
If you're lucky it's in a socket, otherwise you'll have to do some (de)soldering.

By pseen

Resident (61)

19-07-2003, 16:14

Thanks for the quick replies!

Any idea where I can get the mentioned chips, and what they will cost me?

By anonymous

incognito ergo sum (116)

19-07-2003, 18:28

I'm sure you can find suppliers on the web, no idea of the costs, but it can't be much.

By Manuel

Ascended (19300)

19-07-2003, 19:09

Note that the VDP may be broken, but also the VRAM may be broken and the VDP not.

By MOA

Champion (293)

19-07-2003, 21:18

Note that the VDP may be broken, but also the VRAM may be broken and the VDP not.

Makes sense! Can you tell us what really happens on that screen of yours, pseen?

It's not that hard to write some VRAM test programs, btw. Maybe someone can write some VDP/VRAM test tool...?

By pseen

Resident (61)

20-07-2003, 12:24

Yes, it does make sense that the RAM may be broken, and not the chip.

What happens is, I get a very distorted picture, where blocks of pixels seem to be displaced and copied around on the screen. You can barely make out the outline of the Konami logo when playing a cartridge, for instance. I'll see if I can get some pictures up!

Again, thanks for the interest!

By pseen

Resident (61)

25-09-2013, 20:38

OK, a 10+ year bump. Hope I'm not out of line...

A small update: I opened the HIT BIT and had a look. After pulling two plastic clips, removing a rectangular alu heat sink and rubbing off some blue gooey heat conducting material, I found the chip. GuyveR800 was right, it's a TMS9929. I suppose the eight chips right below it are the video RAM chips. Seeing as none of them are in sockets, I'll probably wait a few more years before I try to desolder and replace them...

By Marq

Champion (387)

25-09-2013, 21:05

TestRAM from here: http://www.alsoftware.com.br/adrianpage/index.php?page=msxsoft&section=util could give some hint, in case you see enough of what's going on...

By pseen

Resident (61)

25-09-2013, 21:12

Awesome, will try to give it a go!