Functional VDP Test (TMS9129NL) with Arduino

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Van Briqunullus

Champion (512)

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02-10-2020, 14:59

Great video. I've also been wondering why they even would bother faking these chips. The numbers are low, the margins are small. I guess the profit is being made higher up the chain. Someone introduces a couple of hundreds of fakes and tries to supply those ebay sellers. Maybe they even supply batches of multiple fake chips at once to increase the numbers. Anyway, they will be long gone before the scam comes out. In that sense, those ebay sellers may be victims as well.

Van meits

Scribe (6502)

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02-10-2020, 16:32

If those ebay sellers wat to sell genuine chips, they should perform the aceton test before they advertise them.

Van llopis

Resident (55)

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06-10-2020, 10:21

Meits wrote:

If those ebay sellers wat to sell genuine chips, they should perform the aceton test before they advertise them.

I agree. They could do that with a random sampling and find out the legit distributors. But it's clear that they rather not know. The whole system is really messed up :-(

Van Grauw

Ascended (10582)

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06-10-2020, 12:48

The acetone test does not tell you if the chip is a real one. Unfortunately even genuine chips are often relabeled. I have received at least 8 of those (4 YM2608s and 4 YM2610Bs).

If they would throw away everything that doesn’t survive acetone, they would throw away a lot of real (and in scarce supply) chips. The only way to know for sure is to test the chips, and given the wide variety of chips offered, that seems rather impossible for them to do.

Additionally, if one seller did do that, they would have to up their prices significantly, and would probably lose almost all their business because other sellers wouldn’t follow suit. If buyers on eBay get the choice between 2 listings of a chip, one 4 euros the other 16 euros, both claiming in the description that “it’s genuine, believe me”, you can bet that people will pick the former.

Simply put it is not economically viable to test the supply of old stock and pulls before sale.

Van GregZone

Supporter (1)

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10-09-2021, 10:23


Then I connected the video signals (Y, R-Y and B-Y) to a GBS-8200 VGA converter board with 470 Ohm resistors between signal and ground.


My VDP generates the same heat when on the breadboard, so it would be normal

The component inputs on my GBS-8200 are terminated with 75ohm resistors to provide the normal 75ohm video input load, effectively paralleling your 470ohm resistors!

If yours is the same, then connecting the TMS9929 outputs directly to the GBS-8200 Y, R-Y, B-Y inputs would certainly explain your VDP getting hot!

I believe the TMS9929 video output pins should only be driving the 470ohm load, so a simple transistor buffer (or a video buffer IC), should be used to drive the 75ohm GBS-8200 inputs.
Without this you will be excessively loading the output pins, which would certainly account for overheating and potential early failure.

Please check the input termination on your GBS-8200 to see if this is the case.

Hope this helps.

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