need help in repairing sony hbf700 strange problem

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By Retro Rob

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03-05-2022, 00:52

Maybe somebody here can help me ,repair bas passed on my problem ,i own a sony hbf700 with 2+ and 7mhz expansion works fine with a rom cardridge but when i load the same game rom from disk the graphics on the screen start to automatically mix up after little running time

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By Manuel

Ascended (19053)

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03-05-2022, 09:03

Which game? How do you load it?

By Retro Rob

Supporter (14)

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03-05-2022, 09:10

Nederlands kan ook
Stop er een originele konami rom in zoals nemesis 2 gaat alles goed
Vervolgens laad ik een gekraakte konami uit 1988 die altijd gewerkt hebben dan gaat het fout na korte tijd en beginnen de graphics een eigen leven te leiden

By Manuel

Ascended (19053)

Manuel's picture

03-05-2022, 09:18

Sounds like a bad crack. Has it always worked on that same machine? Or did it stop working after you changed something to it?

Note that this is an English language forum.

By Retro Rob

Supporter (14)

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03-05-2022, 10:12

i have 2 hbf700’s and a turbo-r , I will test that specific sony this evening with different roms and there crack versions to see if there is a change , i did not change anything to the machine myself i bought it this way some years ago on marketplace forgot to test it intensifly , i am starting to think thats why it was sold but on the other hand there could be disks gone bad after all these years

By meits

Scribe (6527)

meits's picture

03-05-2022, 10:20

Disks and (oftenly bad) rom hacks are a recipe for strange things.
Still, VRAM could be bad.
If you have two Sonys, the same problem should occur on both machines.

By Retro Rob

Supporter (14)

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03-05-2022, 10:26

Thanks for now i will set them up in the evening and do some tests ,i will let you know the results

By mcolom

Champion (276)

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03-05-2022, 12:34

This reminds me of a problem I had a loooong time ago with my MSX-1.
It got damaged probably because of inserting/removing a cartridge with the computer on, but the problem was quite curious. All text modes worked fine, but SCREEN 2 modes didn't. After a few seconds after being in SCREEN 2, the graphics started to get corrupted, as if the VRAM internal pointer was erratic.

I've tried to reproduce the problem by tweaking with openMSX's code, introducing errors in the VRAM chips, but I didn't manage the obtain the same effect. I thought at first that it could be the VRAM chips, but now I tend to think that something inside the Toshiba T6950 related to graphic modes broke. Honestly, I don't really understand it, because I'd expect that any internal hardware piece (like latches, memory access registers, etc.) related to graphics mode is also used in text modes. But that's what happened.

Anything, your problem Retro Rob is probably less exotic and simply related to bad dumps, as meits said.

By Retro Rob

Supporter (14)

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03-05-2022, 21:32

After some testing I have come to the conclusion the computer seems ok i think the drive and or some disks are not 100% some games it loads ok on both and seem to work fine ,some are broken or deformed on the first sony but load ok on the other sony some disk are almost certain broken

By gdx

Enlighted (5815)

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05-05-2022, 03:04

It could be the disks or drive that have gone bad after all these years or the software that doesn't support 7mhz turbo mode because even if the Main-ROM has been modified, it performs direct access to the VDP.

mcolom wrote:

This reminds me of a problem I had a loooong time ago with my MSX-1.
It got damaged probably because of inserting/removing a cartridge with the computer on, but the problem was quite curious. All text modes worked fine, but SCREEN 2 modes didn't. After a few seconds after being in SCREEN 2, the graphics started to get corrupted, as if the VRAM internal pointer was erratic.

You are right, inserting/removing a cartridge when the computer is on can broke the VDP. I had this issue with a HB-F700.

By Retro Rob

Supporter (14)

Retro Rob's picture

03-09-2022, 01:04

Turns out corrupted copy’s seemed a factor then it turned out the problems where only in some screen settings and in the final step of diagnosis the real problem was oxidized contacts of the sockets that contain the vram chips when lifting and returning the chips all problems where gone

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