Presentation and faulty MSX

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Par ran_79

Supporter (6)

Portrait de ran_79

29-03-2021, 20:55

Hello everybody, let me present myself,
just acquired a sony msx hb-75 and want to learn and have fun with MSX.
The computer works well but it has vertical lines in each 3 input modes: antena, AV and RGB. Also hear static noise on speaker in the three modes.
Can you guide me to where to watch for the failure? I attach some pics about it.
Thanks for any advice in advance Smile

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Par sdsnatcher73

Paragon (1740)

Portrait de sdsnatcher73

30-03-2021, 05:45

Welcome! I’ve seen this or similar issues pop up on the forum before. I don’t think your HB-75 is faulty but the HB-75 output is somehow a little different than other MSX or computers/consoles in general. It seems to be more of an issue on (relatively) modern LCD TVs. What screen are you using?

Par Wild_Penguin

Hero (638)

Portrait de Wild_Penguin

30-03-2021, 12:02

I don't know where to look for errors, but I do know for certain my HB-75P doesn't have these errors. I think sdsnatcher73's suggestion to try on another monitor is a good one. Many modern LCD TVs do a poor job showing analog signals (and there are huge differences among them); an analog display is usually best, but more expensive TVs might do a better job with analog signals in general; my projector does a surprisingly good job, with low latency!

If you haven't yet, the first step would be to open the unit and look for obvious defects. The capacitors near the +5V and +12V regulators do at least sometimes fail (mine had exploded!). If you have a multimeter, it is easy to measure these voltage lines, and IMO worth it since PSU issues are kind of common.

Actually,it is possible even without opening the unit to measure from the cartridge slot - just be sure you have something which can be easily connected to the slot (a bare cartridge PCB for example), but if you don't, it is way easier to measure by opening the unit.

EDIT: The only specialty with the HB-75P is that it has an RGB output. But it is not perfect, it will always have a blue tint to it. I think I've red somewhere it has to do with how difficult it is to derive RGB from the TMS9929 in general, and this is the reason why RGB is kind of rare in MSX1 machines in general - but I don't remember where I red this, so I'm not sure. It's composite and RF outputs don't have anything special AFAIK - but I could be in the wrong...

EDIT2: Another msx-user-tip: did you know about https://www.msx.pics/ ? It's way better than, for example, postimg.cc, and contains only msx pictures - doesn't have any annoying ads or spam/ad "messages"! But one downside is that it requires registration for posting. Just FYI, you can use whatever image hosting you want ;)

Par ran_79

Supporter (6)

Portrait de ran_79

30-03-2021, 16:56

Hi sdsnatcher73, and thanks! Indeed, I'm using a LCD TV, a Samsung from 2009.

Par ran_79

Supporter (6)

Portrait de ran_79

30-03-2021, 17:05

Thanks Wild_Penguin! For now, I have not another TV to try on, but seems very possible this TV is the cause and not the computer as you both say. Both voltages are ok, and I changed one cable from 220v configuration to 240v, which make it less hot, so I'm thinking about closing it and use it with RGB that looks far way better than AV in another computer that has not those lines. And test it with another TV when I can.
Will use msx.pics from now on, thanks again!

Par Alexey

Guardian (3074)

Portrait de Alexey

30-03-2021, 17:10

This machine outputs a composite video signal, so it doesn't matter what monitor you are using. If the firmware's screen is corrupted (and judging from the screenshots - it is), then either the BIOS or the RAM/VRAM could be faulty.

Par ran_79

Supporter (6)

Portrait de ran_79

30-03-2021, 19:01

Thanks Alexey, for give more light to it. just have seen a video on YouTube that is about this model and the author complaints one time and another about how fragile traces are on this board. Think I won't dissolder anything if it doesn't get worst, because I think I can easily damage it.
https://youtu.be/SknAQpC26oo

Par Manuel

Ascended (17779)

Portrait de Manuel

30-03-2021, 20:26

Sorry, but I don't think the firmware screen is corrupted. Is it, ran_79?

Par ran_79

Supporter (6)

Portrait de ran_79

31-03-2021, 03:47

Hi Manuel, and thanks for reply. Characters are not swapped for others, neither a chunk is missing, neither tere are random pixels, if that is what you meant.

Par sdsnatcher73

Paragon (1740)

Portrait de sdsnatcher73

31-03-2021, 05:13

That is probably what Manuel ment. I don’t think it is an issue with broken RAM/VRAM. The composite signal in this machine is probably what causes this effect. RF is created from the composite video and audio and RGB uses composite for sync, so both are affected as well. Try to get a 20” 4:3 LCD TV, in my experience they handle the signal well. I am sure with some determination you can find one for €5 or €10 (which is what I paid for mine).

Par Alexey

Guardian (3074)

Portrait de Alexey

31-03-2021, 11:04

It would be better if the TS could post the image of the whole screen, not just a part of it.

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