Fourays: Testing Grey Market AY-3-8910 Chips

Finding out exactly what I received from China

Prior to today, I had done some cursory testing of a couple of the chips in order to prove a few points about how many I could integrate into a single system. But I still didn't know if all of the chips I have are real and/or functional.

Yesterday I did some further testing, but I realised my testing was not thorough enough and I came to the incorrect conclusion that the majority of the newly acquired chips were faulty. We'll fix that today.

Reference: One vintage genuine chip I already had

This chip is characterised by:

This is a legitimate General Instruments device, probably manufactured in September 1983. It works perfectly with both a 5V and 3.3V supply.

China shipment

Spoiler alert: I've written the test results on the bottom of each chip in pencil.

Shown all here with my GI chip also on the lower right side for comparison.

Top sides:

The bottom sides vary a lot and is best summarised thus:

Chip #Top side
Pin 1 mark		Bottom left
mould mark		Bottom right
mould mark		Bottom etching
1No---
2No---
3No---
4No---
5No8 14
(Indistinct)		--
6NoC2CJ
7NoSomething
unreadable		G3AH1PE1.1
8Yes-TN D6AA1KN51C2
9Yes-TN K3A98CE612C
10Yes5 E3TAIWAN-

All of these chips' pins were quite mucky or heavily tarnished.

Yesterday's test results

I tested all the chips yesterday with dirty pins and with only a 3.3V supply. In this setup, only one of the chips worked perfectly and another was mostly working but a bit intermittent. I pretty much accepted this as the result, given that I was comparing with my GI chip which also works just fine on 3.3V.

However, today started looking to see if I could source a few more chips. I have in fact placed another order for a batch of chips earlier today before it occurred to me that my test method may have been flawed.

Nevertheless, we can do better with testing the chips I have here, and I look forward to receiving perhaps a few more and testing those as well.

Preparation for another test round

Its not super clear to see in these photos, but this is a before and after of giving the legs a light filing to remove the tarnish and other dirt.

After that, a quick leg straightening and alignment and each is ready to be put in the breadboard for testing.

It was my intention to power the entire Fourays synth system from the 3.3V supply only. It turns out this is not entirely possible given yesterday's results. So, I also tested the chips with the recommended 5V supply.

Results

The only chip which is does not fully work is #5. It makes some crackly clicking noises when I request tones, but it is not making pure tones like it ought to.

All of the others work on a 5V supply. Chip #10 additionally works on a 3.3V supply.

I have my suspicions that chip #10 may be a later YM2149F or YM3439-D (CMOS) if it works reliably on 3.3V. I could test this by poking pin 26 to see if it drops an octave. In fact, all of the chips could be submitted to this test, it may be insightful. (But that doesn't explain why my GI chip works on 3.3V, that one is most definitely an old AY).

So, what do I do from here? I have to amend the schematic and PCB layouts a bit to send 5V to each AY chip, but I'm super happy that I do really have quite a few working chips now. This will be helpful if/when I decide to actually get PCBs made, as economy of scale will kick in and I could perhaps sell a couple of complete Fourays for a profit. In fact, doing this may well incentivise me to put in the effort with physical design and assembly to truly make this project the tribute to the AY that it claims to be.

The project continues ... 😄