Last ATMOS finally repaired !

If you want to ask questions about how the machine works, peculiar details, the differences between models, here it is !
How to program the oric hardware (VIA, FDC, ...) is also welcome.
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HigashiJun
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Last ATMOS finally repaired !

Post by HigashiJun »

I've been struggling to repair the last ATMOS I won on Ebay some time ago.

To tell the truth, I had no much time to spend on it and this naughty boy was particularly reluctant to get back on feet...

Here are two pictures of the mainboard, as I added sockets for every IC in order to be able to easily change any defective one:

1.jpeg
2.jpeg

Everything works fine now but I have to make some deeper tests to be completely sure.

As you can see, I kept the heatsink just for the looks since my ATMOS doesn't need it any more.

Thanks to iss and one of his old threads, my Cumana Reborn works great with my own burnt ROM 1.22. The Hitachi HN4827128G EPROM is really worth it.

I however noticed two strange things while repairing my ATMOS:

- One of the two AY-3-8912 PSG I tried only produced PING and ZAP sounds. SHOOT and EXPLODE had no effect. Does it mean the chip is defective or damaged ?
- The ATMOS booted normally with its original ULA, but the "checker board pattern" had some artifacts. The boot screen is normal with the actual ULA. Does it also mean the original ULA chip is damaged ?

Any clues are welcome.

Cheers.
HigashiJun

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Dbug
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Re: Last ATMOS finally repaired !

Post by Dbug »

HigashiJun wrote:
Thu Oct 01, 2020 2:32 pm
- One of the two AY-3-8912 PSG I tried only produced PING and ZAP sounds. SHOOT and EXPLODE had no effect. Does it mean the chip is defective or damaged ?
PING and ZAP use the normal three channel generator, while SHOOT and EXPLODE are using the noise generator, so maybe something happened there.

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HigashiJun
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Re: Last ATMOS finally repaired !

Post by HigashiJun »

Dbug wrote:
Thu Oct 01, 2020 3:31 pm
HigashiJun wrote:
Thu Oct 01, 2020 2:32 pm
- One of the two AY-3-8912 PSG I tried only produced PING and ZAP sounds. SHOOT and EXPLODE had no effect. Does it mean the chip is defective or damaged ?
PING and ZAP use the normal three channel generator, while SHOOT and EXPLODE are using the noise generator, so maybe something happened there.
Interesting.

I didn't know there was a noise generator in the Oric... I thought every pre-made sounds were generated by the PSG.

Could you tell me where this sound generator is ? I think it's dependent on the PSG as a simple PSG chip exchange made everything work normally.
HigashiJun

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mikeb
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Re: Last ATMOS finally repaired !

Post by mikeb »

HigashiJun wrote:
Thu Oct 01, 2020 4:07 pm
Dbug wrote:
Thu Oct 01, 2020 3:31 pm
HigashiJun wrote:
Thu Oct 01, 2020 2:32 pm
- One of the two AY-3-8912 PSG I tried only produced PING and ZAP sounds. SHOOT and EXPLODE had no effect. Does it mean the chip is defective or damaged ?
PING and ZAP use the normal three channel generator, while SHOOT and EXPLODE are using the noise generator, so maybe something happened there.
Interesting.

I didn't know there was a noise generator in the Oric... I thought every pre-made sounds were generated by the PSG.

Could you tell me where this sound generator is ? I think it's dependent on the PSG as a simple PSG chip exchange made everything work normally.
The noise generator is one of the features built into the 8912 PSG chip. It is possible it is damaged, swap the PSG to find out for sure.

I did come across a fault on an early Oric where ZAP sounded lumpy (it wasn't a falling tone, but came down distinct notes rapidly). Seems like some of the low order bits of the "pitch" being requested were not being understood.

I think that PING/EXPLODE and SHOOT are purely the PSG being set up to produce a particular tone (or noise) and the envelope generator programmed to make it fade out as needed. ZAP is different, as the BASIC ROM has to keep re-writing the pitch to make it fall, which is why ZAP holds up the interpreter until it is done!

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Re: Last ATMOS finally repaired !

Post by mikeb »

HigashiJun wrote:
Thu Oct 01, 2020 2:32 pm
- The ATMOS booted normally with its original ULA, but the "checker board pattern" had some artifacts. The boot screen is normal with the actual ULA. Does it also mean the original ULA chip is damaged ?
The checkerboard pattern is an illusion created by the particular brand of DRAM chips you use. The factory originals lead to the classic three-white-bars on black. Aftermarket replacements can produce all sorts of patterns, including total random garbage. As long it clears off the screen, and is replaced with a functioning TEXT/HIRES mode I'd say you're in good shape.
Last edited by mikeb on Fri Oct 02, 2020 5:27 pm, edited 1 time in total.

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HigashiJun
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Re: Last ATMOS finally repaired !

Post by HigashiJun »

mikeb wrote:
Thu Oct 01, 2020 5:21 pm
HigashiJun wrote:
Thu Oct 01, 2020 2:32 pm
- The ATMOS booted normally with its original ULA, but the "checker board pattern" had some artifacts. The boot screen is normal with the actual ULA. Does it also mean the original ULA chip is damaged ?
The checkerboard pattern is an illusion created by the particular brand of DRAM chips you use. The factory originals lead to the classic three-white-bars on black. Aftermarket replacements can produce all sorts of patterns, including total random garbage. As long it clears off the screen, and is replaced with a funcitoning TEXT/HIRES mode I'd say you're in good shape.
Thank you mikeb for your explanations !

In my case, changing the ULA makes some garbage appear on the boot screen. The boot pattern itself remains the same (as memory chips are not replaced).

That's why I think the concerned ULA has a slight issue and makes this garbage visible on the screen.
HigashiJun

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