Help with two Orics

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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iss
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Re: Help with two Orics

Post by iss »

The problem here is definitely the CMOS 74HC04.
There is lot info in the net about the quartz oscillators TTL vs CMOS - random link here.

Interesting detail is that I've seen lot Oric's with 74F04 (Fast) and 74S04 (Schottky)
which makes sense but the 74LS04 is the original part.

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HigashiJun
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Re: Help with two Orics

Post by HigashiJun »

So you guys think it's better to stay with the 74LS04 ?

My actual Atmos (I'm still repairing) has a factory 74HC04 soldered in. As I think it's faulty, I'm about to replace it with the same reference.

I've also seen Orics with 74F04 (but not 74S04), but I heard somewhere that 74HC04 works flawlessly with oscillators...

What would be the best solution ?

Cheers.
HigashiJun

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mikeb
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Re: Help with two Orics

Post by mikeb »

HigashiJun wrote:
Fri Jun 12, 2020 3:49 am
What would be the best solution ?
The one that works reliably ;)

I don't know if Oric Products switched to using HC04's at some point, but the service manual says SN74LS04 as the part. It could well be that an HC04 will work (but may need an adjustment to other components e.g. resistor values) to work reliably.

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HigashiJun
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Re: Help with two Orics

Post by HigashiJun »

Thank you mikeb !

My bad, I have just realized that my Atmos has two factory ELCAP 74HCT04 (and not 74HC04)...

I think this chip is not a problem according to the following page:

http://ecomorder.com/techref/postbot.as ... dy&tgt=top

where it says that:
The HC series are C-MOS devices: 2 to 6V voltage range, fast logic

The LS series are TTL devices, 4.5 to 5.5V voltage range, slower.
standard logic.

The HCT series are also C-MOS, 4.5 to 5.5V voltage range and levels
compatible with TTL.
Sorry for the fuss...

Cheers.
HigashiJun

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protek
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Re: Help with two Orics

Post by protek »

I received the 74LS04 today (actually had to order another one because the first one apparently has gotten lost in the mail) and I can say with relative confidence that I now got two working Oric motherboards. With the help of 10 uF capacitor in the reset circuitry, board #2 now boots to basic by itself. At first, it seemed to boot better when power was connected from the mains side rather than the DC side, but eventually it started to boot consistently from the DC side too. Some caps perhaps not in their best capacity?

All in all, I’m calling board #2 fixed now. The only downside is that it doesn’t have an original ROM, but instead an EPROM, so using disk drives is out of the question. I also have only once casing and keyboard, so board #2 is bare. If anyone has a spare case and keyboard lying around that they might be willing to sell, please drop me a note. :)

Thank you all, especially Mike, for all the help, advice and patience! Fixing these two Orics has certainly been educating. Orics really are the kind of designs that you can get your head around.
Last edited by protek on Sat Jul 11, 2020 2:13 pm, edited 1 time in total.

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protek
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Re: Help with two Orics

Post by protek »

One thing that’s still puzzling me a bit is that I can’t get mikeb’s diagnostic ROM to run, at least on board #2. It’s just stuck on showing the thin vertical bars. It’s possible that I’ve got the ROM images mixed up and it’s iss’ ROM instead, as, although I can’t put my finger on it, it’s like I could hear a faint busy tone on the speaker beside the more constant tone.

Anyhow, I’ve been thinking about putting the diagnostic ROM onto a PCB, so that I don’t have to pull the ROM every time I want to test it.

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Chema
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Re: Help with two Orics

Post by Chema »

Congratulations for a full repair of both systems!!!

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mikeb
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Re: Help with two Orics

Post by mikeb »

protek wrote:
Wed Jul 08, 2020 9:56 am
It’s just stuck on showing the thin vertical bars.
Vertical like | | | or the "other vertical" like -- ---- ---- I've had that problem before with reports! :)

If it's coarse (character block sized) bars, like a usual Oric startup, these are usually horizontal. Vertical coarse bars I know nothing about. iss may have done them, I don't know?

If it's FINE (pixel sized) vertical bars, like you get a flash of when Oric boots, it looks like grey, then that's the RAM test going through, leaving 0x55 (010101) on the screen. It should clear that to a blank screen and announce the ROM version/Press NMI to continue.

No noises of any note are made until much later into the tests. (See the order of service in the Diagnostic ROM pdf).

For original ROMS, cases and keyboards you might get some from @Steve M ... any still left?

https://forum.defence-force.org/memberl ... ofile&u=35

Glad you're getting them working, it's all certainly more understandable and repairable than modern tiny, multilayer, surface mount, no service-guide, no-schematics stuff :)

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protek
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Re: Help with two Orics

Post by protek »

Image

Like these. Well, maybe they’re not so thin. More like jailbars.

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mikeb
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Re: Help with two Orics

Post by mikeb »

OK those are coarse vertical bars (character block sized), and I didn't put any of *that* in the test ROM :)

I suspect that if you've got a (known) working Diag Rom, and there's no sign that it got into the RAM test, it could have failed at the first hurdle (it tests a couple of low/zero page bytes first to see if I can get a pointer to index through RAM) -- if that failed, there's no point trying to test RAM.

The Diag-Rom instructions PDF mentions that it will lock up the processor in a tight loop, with A0/A1 pulsing (HERE: Jmp HERE! -- 3 byte loop) and A2 upwards will be static with an "error code" to try and show what I think failed.

Quick poke at page zero (#0000,#0001):-

"If the test runs and fails it exits with status code 1 (Quick RAM test fail). As described, the address lines will be in a stable state (A15-A8 high, A7-A2 will be 000001, A1-A0 pulsing)."

Full RAM test (#0002-#02FF,#0400-#BFFF)

"If the test runs and fails it exits with status code 2 (Full RAM test fail). As described, the address lines will be in a stable state (A15-A8 high, A7-A2 will be 000010, A1-A0 pulsing)."

I can't test the top 16K, it's hiding.

cslee_work
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Re: Help with two Orics

Post by cslee_work »

In my debug, A1 was flatlining. After removing one of the address mux chip, A1 started toggling.
So after replacing the address mux, my Oric booted up.

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