Thursday, December 22, 2011

AY8930 Initial tests!



Over concerns received about the possibility that the chips were fakes I decided to test a few of them right away  (Paypal customer is always right no? I might just get my money back if they are fakes)

So first thing I did was to place two of those chips on my Bagman arcade board, and the sound was just as one would expect a normal AY-3-8910 (the old version). So at least they are not broken CPUs or whatnot.

The concerns raised by my colleagues pointed towards  the possibility that these were just re-branded AY-3-8910 and not AY8930's, based on the date code (2008?? if 0830 is a date code I would admit its odd for a chip designed in 1990) and on the peculiar look of the Microchip logo, also that "TAIWAN Microchip" was weird and unseen before. (though this and that beg to differ).

So I undusted my AY protoboard that I used for chipsounds research, and placed a AY8930 that was previously tested OK in Bagman. Tried a few VGMX log files, (including intv_lock_n_chase.vgmx - one of my favorite games)

First interesting discovery was that the chip didn't seem to run at 3.57MHz but at half of that (1.79MHz, just ok for the right pitch of the intv register dump). I forgot that my protoboard was last populated with a YM2149F, which uses pin 26 for clock divider (input). and my jumper was already shorted. So at least if this is a rebranded chip, its a rebranded YM2149F and not a bare AY-3-8910, since the 8910 doesn't have this feature.

Started to check out the datasheet and made a little test VGMX file that plays a simple tone and pass through
A) all 32 values of volume
B) all 8 values of Duty Cycle (PWM)

Here's a lame 'instant video' of my setup and playing both Lock 'n' Chase and then, my test file on my protoboard:



The duty cycle changes are sadly NOT seamless. This is mentioned in the datasheet as well. "The new duty cycle value will take effect immediately. This may result in one period with a "random" duty cycle at the time the register is updated."

So much for maxYMiser -alike PWM without 90% cpu usage and/or IRQ reset tricks...

I haven't yet tried the advanced LFSR noise, but I'm pretty sure this batch of chip is legit. It wouldn't make sense to copy such a chip design when theres no real demand for it. Anything is possible though....

Until next time!

15 comments:

  1. Interesting read! Thanks for sharing, David.

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  2. Hi Seb.
    I dont mind sending you one or two for you to experiment. Still need to be 100% sure they are legit. This might mean decaping one for science. Lol. Microchip support has not being forthcoming so far.

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  3. Nice work! Looks like you had fun. :)

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  4. Those numbers (0830, 0338, 8916) on the supposed AY8930s look like they might be batch numbers in the event of a recall due to faulty manufacturing.

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  5. You're paranoid. :)
    ay8930 is not sid, they are not wanted, who would they fake? More than 8000 in Chinese stocks.

    I bought 4 pieces. Connected to my ZX Spectrum and everything is fine.

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  6. 1/10 of mine didnt work.
    they are rebadged, probably to look newer, its a standard chinese practice. you can believe what you want

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  7. My chips look a little different:

    AY8930
    8926CCA
    TIAWAN
    Microchip

    "/P" - wonder what that means.

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  8. i hope its TIAWAN and not TIAWAN, the date code look legit, care for a picture? Please send it to info and domain name plogue.com, ill make a new post with pictures of yours, my rebranded ones, and my legit one (i do have a 100% sure original from a 1990's arcade board)

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  9. As for the systematic rebranding of IC's from chinese resellers have a look at this:

    http://defensetech.org/2011/11/08/counterfeit-parts-found-on-new-p-8-posiedons

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  10. And more

    http://www.aeri.com/detection-of-counterfeit.asp

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  11. I bought lots of chips from ebay, and i got caught a few times. I have a few sellers that i trust, others on my ban list. (eproms, rams, opamps, sound chips) bought loads of different bits with various success rates.

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  12. would be interesting to see ban list plgDavid :)

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  13. Lets say white-list instead.

    For clearly used and recycled but NOT rebranded (eproms, vintage chips) I usually go to:
    http://www.ebay.com/usr/ic-china

    For new old stock (potentially re-branded but not systematically)
    best chances were with hkutsource jk_parts.

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  14. I prefer tested/recycled than untested/NOS, always.

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