Oric 1 and Atmos - repair help needed - EDIT: Oric 1 works

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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Chema
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Re: Oric 1 and Atmos - repair help needed

Post by Chema » Sun Jan 08, 2017 12:21 pm

YuT666 wrote:Thanks, but what do you mean? The current what?
you have measure the voltage, which is fine, but could you measure the current ?
He means the amperage consumption. The usual multimeter has a mode to measure current in milliamperes.

I was thinking that it may be a good idea to some basic tests. You've measured the voltage. It would be nice to check if you have a valid phi2 clock (from the processor pin or in the expansion bus). You need an oscilloscope for that. You should have a 1Mhz signal with 1/3rd of the time as high. You should have a good clock input too at 1 MHz.

Then you could check the RES, NMI and IRQ lines, just in case any of them are forced low, hanging the processor.

If any of those fails it could give us a hint of the problem.

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Re: Oric 1 and Atmos - repair help needed

Post by YuT666 » Sun Jan 08, 2017 12:27 pm

Sorry, i don't have an Oszi.

Are there some other basic checks for a simple digital multimeter?

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Re: Oric 1 and Atmos - repair help needed

Post by Chema » Sun Jan 08, 2017 2:41 pm

Amperage and reset, IRQ and NMI lines can be checked with a multimeter.

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Re: Oric 1 and Atmos - repair help needed

Post by YuT666 » Sun Jan 08, 2017 3:02 pm

As i mentioned, i measured the reset pin (40) and this one is ok (first low for a second and after this high).

I'll test pin 4 (irq) and 6 (nmi):

Pin 4: 4,9 after a second

Pin 6: 4,0 after a second

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Re: Oric 1 and Atmos - repair help needed

Post by Godzil » Sun Jan 08, 2017 3:10 pm

4 Volt on NMI is a bit low (it should be ~5V), but high enough to be seen as a logic high weird, especially considering how NMI is connected in the Oric.

When you press the "RESET" button, does Pin6/NMI goes to 0? and if you move, without push, the reset button, does the voltage change?

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Re: Oric 1 and Atmos - repair help needed

Post by YuT666 » Wed Jan 11, 2017 9:02 pm

Sorry, i will test the things you've mentioned on friday or saturday. I'm really busy at the moment.

I received the clamps for the LA, so it should be a good help.

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Re: Oric 1 and Atmos - repair help needed

Post by YuT666 » Sat Jan 14, 2017 1:49 pm

Ok, here we go ...

Pin 6/NMI goes to 0 when i press the reset button and the voltage does not change, when i move the button (the same results with the Atmos).

Btw ... i received the clamps for my logic analyzer.

I bought some new Nichicon and Panasonic capacitors, but i've seen, that somebody changed the capacitors of the Oric 1 (the issue 3 board) in the past, 'cause there where new looking Rubycons there (all capacitors). The original C21 was a 1uf 10V and the new Rubycon is a 1uf 50V, so it should be a good one.

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Re: Oric 1 and Atmos - repair help needed

Post by YuT666 » Mon Jan 16, 2017 6:19 pm

So ... further hints are welcome.

I'll measure clk out of the ULA.

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Re: Oric 1 and Atmos - repair help needed

Post by iss » Tue Jan 17, 2017 9:43 pm

I'll second my suggestion to measure the resistance between +5V and GND tracks.
What VA-Ohm-meter do you have? You can use the diode mode to measure it too.
On attached pictures I used the cheapest meter I can found - the measured value
is from 160 up to 280 - on 6 different working boards (3x issue-3 and 3x issue-4).
If you have this value below 100 - this means definitely burned chip and I bet on faulty RAM.
20170117_220752.jpg
20170117_220927.jpg
And close up where you can measure it.
20170117_221627.jpg

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Re: Oric 1 and Atmos - repair help needed

Post by YuT666 » Sat Jan 21, 2017 4:47 pm

Ok, i got ...

Oric 1: 158
Atmos: 145

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Re: Oric 1 and Atmos - repair help needed

Post by YuT666 » Thu Jan 26, 2017 12:47 pm

Any more suggestions?

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Re: Oric 1 and Atmos - repair help needed

Post by Chema » Thu Jan 26, 2017 1:18 pm

Okay, with the risk of (again) saying something stupid...

Once discarded the PSU as source of problems, IMHO you've got a 90% chance of the problem being the memory. I say this because it is one of the most common issues, but as no chip becomes really hot, you have no way to tell.

Another candidate would be the 6502. Without changing it it is going to be difficult to tell, but we could try... The bootup sequence of the 6502 starts int the ROM. The CPU reads the vector at $FFFC and $FFFD and jumps there (in the atmos, this means jumping to $F88F) as I said, preparing the stack, setting the decimal flag, the interrupt flag and copying a table to page 2. Until that moment it does not access the RAM. As you have changed the ROM chip we could suppose there is no problem here, so if you have some activity in the address and data lines of the processor for a few cycles, then it is a good indication it is OK.

You now have a logic analyzer, so I bet you could monitor the address lines (for instance from the expansion port, easier to attach a probe there). It should not be difficult to see if they change as they should (more or less - a broken 6502 can also execute something before halting but again, this is just to make an educated guess).

Obviously, if there is no activity in the address lines, the 6502 is most probably dead.

If this works, then most probably it is getting stuck because the RAM is not working. One of the first tasks of the processor at boot is to find out the available memory by making read/write tests and to fill the memory with given patterns and the pointers start/end are stored in page 0. Wrong bits there and you'll get stuck in an infinite loop (though probably there would be activity on the address lines, because code is read from ROM, which we suppose is OK). Of course errors in reading writing in page 1 would be catastrophic, as the stack is held there...

This would, unfortunately, mean changing the ram chips just for testing this hypothesis. I am not sure if there is a way to test if memory chips are okay easily (such as measuring continuity between vcc and gnd or something like that) besides checking if they get hot. Besides I am not sure they always become hot if they are broken...

But there are still other things that could go wrong, such as broken tracks on the PCB, a broken 6522...

That is my 2 cent. Sorry for not being able to help further...
Last edited by Chema on Thu Jan 26, 2017 7:04 pm, edited 1 time in total.

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Re: Oric 1 and Atmos - repair help needed

Post by YuT666 » Thu Jan 26, 2017 5:27 pm

Don't worry Chema, I really appreciate your help.

It is strange (and a bit sad), that both Orics seem to have similar problems. I have to figure it out, what i should measure with the LA exactly, so the adress lines would be a good start.

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Re: Oric 1 and Atmos - repair help needed

Post by Silicebit. » Thu Feb 02, 2017 8:46 pm

Hi YuT666!

My personal opinion... Before check 6502, 6522 or ROM, I would check the RAM chips, in a 70% or 80% of cases, they are involved in the failures.

Changing RAM to an Atmos. In spanish only, sorry.
https://www.youtube.com/watch?v=6H5ygdk_eeE
Oric user since 1984. YouTube

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Re: Oric 1 and Atmos - repair help needed

Post by YuT666 » Fri Feb 03, 2017 8:01 pm

Thanks ... i'll try the piggy back method with some good 4164.

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