Need help with my oric 1

If you want to ask questions about how the machine works, peculiar details, the differences between models, here it is !
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Gotang
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Need help with my oric 1

Post by Gotang »

Hi guys thanks for letting me join the forum after a bit of help
got my first oric 1 from ebay and yes you guest its broken
now I have marked all the chips I have replaced or tested but I'm scratching my head abit now ive swapped the cpu with a one from a working vic 20 not that have a working icu and I know its not that regulator even changed and a few recaps but I still get this black and white check screen on boot any idea where I should be looking next all help welcome have a multi meter and no other roms so bit stuck can lend a rom out of a friend's machine but I just don't think it's that mem chips are cold to touch cpu and chip under it get a warm but nothing more
over to the oric jedis lol
all help very welcome can't wait to get this working and have a mess about.
oh no sound from speaker or keyboard when powered on psu all good and scart rgb cables all tested on my mates oric
gotang
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mikeb
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Re: Need help with my oric 1

Post by mikeb »

You could start here, grab the PDF and the .ZIP pack of images.

http://oric.signal11.org.uk/html/repairguide.htm

On the plus side you seem to have a stable decent picture, and while that's an unusual arrangement of bars, that could be down to the specific type of DRAM chips used -- at least it's orderly, not chaotic garbage or blank screen!

The basic and important stuff -- look for any missing components, any pins bent inside the rear 34 way/20 way connectors. Does it look like anyone's already had a go at repairing it? ;)

Make sure you have 4.9v to 5.0v on the 5v rail (measure across any 74LSXX chip in the usual corners, e.g. pin 7/14 or 8/16).

You've clearly got a functioning 12 MHz clock (otherwise, no picture!) and so it's quite likely the CPU has a 1MHz clock to work with.

Is the CPU getting a reset? Some of the Orics are getting long in the tooth, and don't get a proper power up reset. Using a small piece of wire, CAREFULLY short pin 1 and 40 on the CPU (6502) to apply ground (p1) to ~RESET (p40) and see if it starts up -- if so, a small electrolytic capacitor is the likely fault, easily replaced.

The DRAM being stone cold is not conclusive that they chips are ok, but sometimes you do get lucky and find that 1 of 8 of the chips gets hot, quickly, after power on. There are other ways they can die, so it may still be a RAM fault.

Gotang
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Re: Need help with my oric 1

Post by Gotang »

Hi thanks for that have tryed all your suggestions but I'm even more confused now if I take ic5 and ic 6 out I get the same screan so it's deff not them also have tested ic7 on friends machine works spot on so not that
getting 4.9v on the 74lsxx chips so power getting there also tested rom
No one seems to have worked on the board and nothing missing I can see that resister on bottom looks like it's been done at factory?
Not sure what to try next lol
Any other help really welcome
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mikeb
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Re: Need help with my oric 1

Post by mikeb »

Gotang wrote:
Mon Aug 24, 2020 2:09 pm
Hi thanks for that have tryed all your suggestions but I'm even more confused now if I take ic5 and ic 6 out I get the same screan so it's deff not them also have tested ic7 on friends machine works spot on so not that
getting 4.9v on the 74lsxx chips so power getting there also tested rom
No one seems to have worked on the board and nothing missing I can see that resister on bottom looks like it's been done at factory?
Not sure what to try next lol
Any other help really welcome
OK, never mind digital logic, can I check yours ;)

If you take IC5 and IC6 out (that's the CPU and VIA gone) you will still get a startup picture like that (as the picture is produced by: Power supply, 12MHz Clock, ULA, Multiplexers, DRAM chips). So a non-responding 6502, a 6502 that didn't get reset properly, a 6502-1MHz that is too slow to work (must be a 6502A) and a host of other problems could look like that too.

IC7 (ULA) is fairly bullet proof, it's rare a fault actually comes from the ULA being bad.

Seeing the back of the board -- yes that resistor is likely a factory mod (I've got a 2k2 resistor in similar spot on mine).

In a way, I'm happy that your 6502 CPU and 6522 VIA are in sockets, usually the 6502/6522 and Sound chip (8912) are all soldered in. Then it is a real pain to chip-swap! However, I think that means someone has already desoldered the 6502/6522 and put sockets in. Was this you, or a previous owner? I don't think any native Orics left the factory with socketed 6502/6522 (anyone want to provide a counter-example?)

It is possible that damage has been caused in doing this, just be aware. It would mean that you would need to check that each of the 40 pins on the CPU and VIA do actually connect to ALL the places they are meant to, in case of a broken trace or broken through-plated hole. It's a nuisance, but it can happen with these old boards and bad luck!

I do think someone has already replaced the electrolytic capacitor by the 7905 regulator and to the left of the ULA (C8, 10v 100uF and C1 220uf 10v) because they look small and modern, and the soldering on the back is non-original. Definite signs of flux/scraping! :)

I can't tell from the picture, BUT, it looks like there may be a solder bridge between one leg of C1 and Pin 37 of the ULA (the track passes right under the + leg of C1 on the back) -- can you check that and make sure it's NOT shorting (bad soldering!). If it is, that will cause trouble as Pin 37 is part of the row/col address bus to the DRAM multiplexer chips.

Note that C1 goes to the speaker, then to ground. This would really put a spanner in the works if that short is real, rather than just on the picture.

I've marked where I mean on attached picture. Check it, but clean it up anyway just in case.

There may be more lurking. IC8 and IC20 are quite important in getting the row/addresses from the ULA to the DRAM, and they have been known to fail.
Suspect joint
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mikeb
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Re: Need help with my oric 1

Post by mikeb »

Gotang wrote:
Mon Aug 24, 2020 2:09 pm
if I take ic5 and ic 6 out I get the same screan so it's deff not them also have tested ic7 on friends machine works spot on
On this point: Did you find out if IC5 and 6 work in a friend's machine? Or are theirs soldered in, so you couldn't test this :)

From the factory, I think the ULA and the ROM are the only socketted chips. Sockets cost money, and reduce reliability a little. If they are not needed, they tend to be left off for production stuff. For home build, or repairs, use sockets -- it makes fault find and repair easier.

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Vyper68
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Re: Need help with my oric 1

Post by Vyper68 »

I agree with Mike 6502A/6522A were soldered in, with sockets the case doesn’t close unless you modify it inside and there are what look like solder splashes on the underside where the 40pin sockets are. Is there any value in swapping out the BASIC 1.0 and fitting an EPROM of you test ROM Mike?
It also looks like there is minor damage under the sockets where the old CPU & VIA were removed so no telling what they are like underneath the sockets :(
Bazinga!

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Re: Need help with my oric 1

Post by Gotang »

Hi guys I've put the sockets in and tested all traces they are all spot on and I recapped the board as well as stated with the marks on chips all fine I know photos don't really show in the light but none are shorting added some more pics so you guys can see when ever I work on machines I allways recap and test every thing to make sure no broken vias or traces my friends machine it stock and don't want to remove chips etc any chips I change I always when possible put sockets in to help with future diags etc and yes the case closes with the sockets in think I will push forward and just change the memory just to rule this out need to source some any tips on newer memory chips oh and yea the board will get a clean down to remove solder paste etc when finished
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Vyper68
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Re: Need help with my oric 1

Post by Vyper68 »

If you can burn a copy of Mike’s test ROM and swap out your Basic ROM that will tell you if you have a RAM fault.
Bazinga!

Gotang
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Re: Need help with my oric 1

Post by Gotang »

Fitted sockets and had some 4164s not sure if the are comapable sthink they should be but ordered some 4864s to put in getting this now
feel I'm getting a little closer lol
Any thoughts
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Gotang
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Re: Need help with my oric 1

Post by Gotang »

Vyper68 wrote:
Tue Aug 25, 2020 3:45 pm
If you can burn a copy of Mike’s test ROM and swap out your Basic ROM that will tell you if you have a RAM fault.
Don't have a rom burner bud

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mikeb
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Re: Need help with my oric 1

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Gotang wrote:
Tue Aug 25, 2020 2:54 pm
any chips I change I always when possible put sockets in to help with future diags
Sockets: OK -- just wanting to check the history of the board. As long as you're sure all the traces are good (otherwise you could be on a wild goose chase fixing a faulty component you'll never find. I fully support the socketing motivation, and recommend it myself. If a chip has to come out to be tested/replaced, put a socket in. The case does close with sockets (I'm not sure who started that rumour!) as I've got an ATMOS that had to have the DRAM jacked up on sockets to get it working.

When you recapped, it does look like C1 is shorting to the next track. Not solder paste, or flux, but actual joined across. I'm lazy, and leave flux behind too, but not solder splats!

Note that the DRAM may appear faulty if the two multiplexer chips I mentioned have a fault. IC 8 and 20.

The change of chips does seem to have changed the display, now you've got Morse code (!) ..-.-.- ??

The diag ROM may not help you that much at THIS stage, because if there is a RAM fault (or the appearance of such, so that reading-writing memory doesn't work), it will very quickly give up and issue an error code. It's basically the first thing it checks -- can I write/read two locations of zero-page memory? If not, I can't even make a 16-bit pointer to test the rest. Time to cry!

It would however show you the processor was running, as having probed RAM and failed, it goes into a tight loop in ROM to keep things spinning along.

Edit To Add: Your new pictures show the DRAM as "-2" (200ns variant). Are these "from the factory"? -- can't see a date code to make me think they've already been changed. "-15" 150ns (or better, -1 = 100ns) are recommended. Whether it's 4164, 4864, shouldn't matter, as long as it's a compatible pinout, and 1 x 64k sized (or 1 x 16k for the Oric-1 16K experience) but they do need to be fast enough to get the data out under Oric's triple-access per cycle timing.

This is why the 6502 must be an "A" variant, although it's running at 1MHz, it's expected to get the job done in an effective timing of 1.5MHz to leave space for the ULA to access memory twice more in each clock cycle. Slow DRAM need not apply.

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Re: Need help with my oric 1

Post by Vyper68 »

I’ll get my coat :lol:
Bazinga!

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Re: Need help with my oric 1

Post by Gotang »

Order a few of them chips case faulty c1 is fine it's just the photo going to leave the oric till the new parts arrive git a atari mega st to sort tomorrow lol I'm a gluten for punishment :D
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Re: Need help with my oric 1

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Vyper68 wrote:
Tue Aug 25, 2020 6:53 pm
I’ll get my coat :lol:
No no, grab popcorn! Things could get interesting! ;)

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Re: Need help with my oric 1

Post by Vyper68 »

mikeb wrote:
Wed Aug 26, 2020 5:32 pm
Vyper68 wrote:
Tue Aug 25, 2020 6:53 pm
I’ll get my coat :lol:
No no, grab popcorn! Things could get interesting! ;)
I’ve just been sent a old issue 2 Oric-1 to fix and it’s going to be a doozy - garbage on screen and whine from the speaker. So I have my own project now :D
Bazinga!

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