I just noticed these are a mix of 721 and 704, i will need to sort these out.

I guess Tiido around here would be interested in those.

HammysHangout wrote on 2026-07-16, 01:29:

I recently came into a bag full of YMF721-S OPL4 Chips, anyone have a easy way to maybe test?

Contact Serdaco. I believe he wanted to make a WaveBlaster module with such chips, but couldn't get the stock required.

Keropi and Marmes will also likely be interested.

i ordered a TQFP 100 to Dip adapter so i can build out a tester to test them.. I tried looking for github or project files that used these chips to built out a tester, and the only thing i found was by Adrian -> Looking for help wiring up YMF704C and looks like he got it working, and that would be a perfect build to test the 704 chips.

I am wanting to test them first , really wasn't posting a "need to offload these"

if Keropi , Marmes, Serdaco, Tiido are interested in them , i maybe persuaded to sell a few "as-is" but they are not in the best shape, the person i bought out just had them all in a bag loose, so the pins got a little bent up.. ( he was like "all that stuff is obsolete and not useable" ) - i would love to build out a tester of sorts to at least test basic functionality i think both of them have MPU Support.. then second would be trying to build out maybe an isa adapter with a tqfp 100 zif socket.

*grabbyhands* I would very much like a portion of these chips. 25 of them will allow to perfectly complete the batch of YMF71x sound cards I'm making and close that chapter. Years ago I started these cards but for variety of reasons it has gotten delayed and in part of only being able to buy non-functional fake chips... I made the card with YMF704 or 721 on them in mind, to give the Yamaha pairing the datasheets want you to have and this would allow that original goal to be achieved without seeking donor hardware to harvest parts from.

There actually can be a lot of missing pins on these chips, from my measurements, all the ones listed "No Connect" in the datasheet actually are those so no secret pins unfortuately...

Making a test adaptor isn't gonna be too hard but you need something that can send MIDI data either as regular MIDI UART signal or via parallel IO interface, such as being MPU401 on an ISA card. You will need to make an address decoder and also a bus buffer for that since the chip has very weak IO drivers that are unable to drive ISA bus directly. But some MCU will defnitely work for that. MIDI UART is simplest, although it won't allow to test the OPL3 part of it. You also will need an audio DAC or a transmitter chip like DIT4096 for easy connecting it to some SPDIF capable device.

So, i did sort, i def have 25+ of each chip... I would just hate to ship you 50 chips, and they get lost, are bad, etc.

do you have a blank sound board missing a 704/721 that i could install two chips on?

more pictures..

I think I have a couple cards that I can send so you can play with. I recently moved and things are still a bit all over the place but I'll try to locate the "fun retro hardware" box and get some photos of the cards.

Chips getting lost would definitely be a tragedy but tracked packages usually don't get lost no I am not all that worried about that happening... and if there are a bunch that don't work, the plastic bag did what it does well 🤣 (but I am still closer to the original goal~).

The photos look amazing ~

EDIT: Found them ! I still have to test them to verify they function, which will take a bit of effort as I must assemble a test computer too, but that will happen in the coming days.

* The lower card should be ready to go when YMF704 or 721 is soldered on.
* Higher card is missing YAC516, which I may or may not be able to find. It also has modification done to allow talking from ISA bus which is slightly faster than MIDI UART way but it needs the small wire connected to one of the pins on YMF704/721, the board designer has forgotten to route this trace and as a result, the function will not work at all without the patch wire. You can easily revert things back to UART mode, my clearing the various solder bridges when compared to the lower card.

Selfishly I'd love for these chips to find their way to Tiido, because I've always wanted one of his cards 😅