Toshiba HX-10 Black Screen: What To Check?

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By RetroTechie

Paragon (1563)

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19-07-2012, 23:36

Rink wrote:

Bloody Samsung TV just reports "mode not supported" when this thing is plugged into the component input.

Don't suppose anyone can confirm what "resolution" the TMS9929A actually outputs YPbPr?

I'd guess that TV expects a signal with higher horizontal / vertical scan frequencies than what an MSX put outs. Which wouldn't be surprising given the typical use of component input on modern TV's.

As for 'plan C', check the Sony HB-75P service manual (MSX1 with RGB output, and LM1889 video encoder IIRC). But if a simple component replacement (that LVA510, a fried transistor or something) does the job and you have a replacement, I'd go for that even if it's an ancient part. Repairing an MSX1 is only worth so much trouble (very little for me personally, your mileage may vary).

Btw. if you try replacing that video encoder IC, be very careful not to overheat it when unsoldering! It would be silly to destroy a hard-to-get part, if it turns out that part wasn't broken in the 1st place. Shocked!

By Rink

Rookie (25)

Rink's picture

20-07-2012, 00:25

Still waiting for that LVA510 to arrive (Shanghai post, bah!) so just investigating different options in the mean time. SCART output seems to be the best other option at the minute; although the sockets are so big and ugly that i started trying to see if i could buy a Nintendo SNES/64/Gamecube multi av socket instead... can't unfortunately.

i almost bought another HX-10 today... but that would still leave me with one unit that isn't usable and I hate that. Wish i could say that every retro computing item i own actually works - but those that don't are in the queue to get fixed. Just seems a shame to have dead stuff.

By Rink

Rookie (25)

Rink's picture

24-07-2012, 21:09

Well, my chip arrived at last. I haven't tried it yet but will give it a whirl ASAP. Also just bought another HX-10, which was cheap due to having a fault in a different area so should have a working PAL encoder circuit I can transplant. Big smile

By RetroTechie

Paragon (1563)

RetroTechie's picture

24-07-2012, 21:39

Better try that first then (swap the PAL encoder boards, that is), to save yourself a dip IC replace in case problem is somewhere on the main board.

By Rink

Rookie (25)

Rink's picture

24-07-2012, 23:16

Yep, good thinking. Assuming the new PAL board works then I at least have one working MSX to play with while working out a replacement encoder and fixing whatever else is wrong with the other one. It never ends. Lol.

By Rink

Rookie (25)

Rink's picture

27-07-2012, 17:35

Right. I've swapped the PAL encoder board out for the one in the other HX-10 and it worked fine. So finally I have a nice, clean MSX to play on. LOL! Thank you for all the help guys.

At some point in the very near future, I'll try changing that LVA510 or continue with my own circuit design and see if I can resurrect that other one. Although it does have a problem with text - the display is fine but the actual characters themselves are all screwy.interestingly, the donor machine has a later serial number has the PAL encoder actually has fewer capacitors etc. on there.

By Rink

Rookie (25)

Rink's picture

28-07-2012, 12:49

Swapping the LVA510 got the old PAL encoder board working again (on the 'spare' HX-10).

So, does anyone know off the top of their head what causes this:

??? :)

I'm not overly fussed about dealing with this right now, but if it's simple (it's not going to be though, is it!?) then I might try and sort it out.

By Sky_hawk

Champion (267)

Sky_hawk's picture

28-07-2012, 16:31

looks like an eprom is either broken or, if it is socketed, it might be corroded. You can try removing it and reinserting any eproms it might have, and/or and logic ICs (74xx) near it.

Unfortunately, I seen to recall the HX10 does not have socketed IC's, in which case your best try is to replace the main rom eprom. ofcourse you need the content, but it is available online.

Gr,

Jan

By jltursan

Prophet (2561)

jltursan's picture

28-07-2012, 16:48

With a bad ROM, the HX-10 most probably would'nt boot to BASIC prompt.
Seems that there's a BAD VRAM ICs (4416), some characters have its bit 1 stuck to 0, there's also some others with bit 6 to 0. I don't know how they're mapped to their ICs; so it's a good measure to replace both VRAM ICs.

It's an easy replacement, you can use 4464 aswell, they're easier to find.

By Rink

Rookie (25)

Rink's picture

28-07-2012, 17:42

Nice one guys. I'll take a look at that.

Cheers.

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