A problematic Oric 1

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.
rh74
2nd Star Corporal
Posts: 20
Joined: Mon May 17, 2021 8:53 am

A problematic Oric 1

Post by rh74 »

Hi there people, Marco's writing from Italy. I have joined this forum since I am a lucky owner of some Orics two of them with some problems I'm trying to fix. Obviously, and that's the reason why I joined you, I'm facing some issues I'm not able to solve even after trying everything I can and I read in you previous posts. Ok let's go in order. The problematic Orics are both Oric 1, one of them is an initial version (gray badge) and the other is a more recent model (colored badge). With them I own also an Atmos that is working perfectly. Let's start from the Oric colored badge (I left the gray one for another post since it seems having different issue).

This is the current status as I turn it on:
IMG_20210517_084736.jpg
If I try to reset the 6502 I'm generally greeted with a different pattern, even if the most common is the following one:
IMG_20210517_084816.jpg
I can't hide my favorite one is the Atari ET pattern:
IMG_20210517_084858.jpg

Some times after turning it off an on again (an old workaround as you should know... :lol: ) I obtain a most common pattern usually tied to bad RAM chip (see the next post for image).

The mainboard was already tweaked with main ICs removed and socketed (again next post for image).

Unfortunately the backside is not in what I could call a "good state" (same as above).

Since the backside status I passed all the connected PIN between CPU/VIA/ULA and related components searching for broke tracks, but they are good. Other things I tested so far:
  • 6502, swapped with a spare CPU (1541 is the donor): same results
  • 6502, placed the original one in an Apple ][: working
  • 6522, swapped with two different IC again from the 1541: same results
  • 10017, swapped with the working Atmos one, other Oric 1 and a spare 10017 from ebay: same results
  • RAM, tested with Arduino, found two failed and replaced with compatible and tested ones
  • ROM, tested with ROM reader, swapped between Oric 1s, swapped with Atoms one: same results
  • IC8, IC20, IC21, tested with IC tester, seems good
  • Clock, measured I found 12MHZ, 1MHz, 0.86MHz where expected
Now my next tests will be boot with diag ROM but without CPU/VIA/ULA inserted (as I understand from i ss YouTube video I should still have a tone) and checking the reset button since it is not currently working (could it be defective?). Any further help, advice, hint will be very appreciated.

P.S. I hope I broke no forum rules... In that case, my apologies.

rh74
2nd Star Corporal
Posts: 20
Joined: Mon May 17, 2021 8:53 am

Re: A problematic Oric 1

Post by rh74 »

Here the missing images.

Common pattern:
IMG_20210517_084837.jpg
Mainboard front side:
IMG_20210517_084930.jpg
Mainboard back side:
IMG_20210517_085004.jpg

User avatar
Dbug
Site Admin
Posts: 3683
Joined: Fri Jan 06, 2006 10:00 pm
Location: Oslo, Norway
Contact:

Re: A problematic Oric 1

Post by Dbug »

I myself suck at electronics, so I will let the knowledgeable people to answer :)
And welcome.
rh74 wrote:
Wed May 19, 2021 11:59 am
P.S. I hope I broke no forum rules... In that case, my apologies.
There are no many rules, basically:
- Respect other people and what they are doing
- Sometimes people answer fast, sometimes nobody post for a couple of days, just wait and don't get angry, it happens :)
- The whole point is to be a useful resource over a long period of time, so post to the right place, with titles related to the issue, posted in English

And I guess that's about it really.

Good luck for the repairs!

rh74
2nd Star Corporal
Posts: 20
Joined: Mon May 17, 2021 8:53 am

Re: A problematic Oric 1

Post by rh74 »

Dbug wrote:
Wed May 19, 2021 1:48 pm
And welcome.
Thanks, it's always good to be a part of such enthusiastic people
Dbug wrote:
Wed May 19, 2021 1:48 pm
Good luck for the repairs!
I guess I'll need it... :D

User avatar
Chema
Game master
Posts: 2809
Joined: Tue Jan 17, 2006 10:55 am
Location: Gijón, SPAIN
Contact:

Re: A problematic Oric 1

Post by Chema »

Welcome! I'll also let other users with more experience in electronics answer :)

However, the usual culprits are RAM and RAM multiplexors, and you already tested those (make sure the ram is of the correct speed, was it 100ns?). My only (probably lame) idea is, based on the state of the back of the board, that there could be a cold or broken solder in one of those chips that have been socketed. It could be tricky to spot and may escape the usual continuity test (due to the pressure made with the tester probe).

Anyway, good luck too!!

User avatar
iss
Wing Commander
Posts: 1277
Joined: Sat Apr 03, 2010 5:43 pm
Location: Bulgaria
Contact:

Re: A problematic Oric 1

Post by iss »

Welcome @ DF-forum!
And congrats for your Oric machines and the obvious skills you have :).

About the the repair: the first thing that I would recommend is to re-check the RAM and if possible use faster chips 150ns.
If you can borrow from somewhere another 8-chip set (all from the same manufacturer) and test with it.
In my experience I have had cases when a simple random swap RAM chips places makes Oric to boot.
Another option is to use diagnostic ROMS (which you already found) - my ROM is very simple but robust and requires the absolute minimum working chips, @mike's ROM is more advanced and can more diagnostics - use both :).
At end you can test all tracks continuity - it's boring long work but it definitely helps!

Can you measure the resistance between +5V and GND rails? (Don't forget to disconnect the PSU first!)
Measure twice (it's safe!):
- connect red probe to +5V and black probe to GND;
- connect black probe to +5V and red probe to GND.
and post your readings?

rh74
2nd Star Corporal
Posts: 20
Joined: Mon May 17, 2021 8:53 am

Re: A problematic Oric 1

Post by rh74 »

Chema wrote:
Wed May 19, 2021 2:20 pm
make sure the ram is of the correct speed, was it 100ns?
They should be the same speed. I removed a couple of Hitachi IC to be replaced with Germany ones. Serials are the same HN4864P-2. Afaik P-2 should indicate the speed. Anyway I already have a complete set of Germany ICs, I will try to set them in each sock.
iss wrote:
Wed May 19, 2021 4:50 pm
And congrats for your Oric machines and the obvious skills you have :).
Well I shouldn't say that here... I'm a Commodore guy. But with the years I found some less known systems more charming like Dragons, Alice, ATOM, and so on. I think Oric did a good job, probably a more reliable components would help, but still they are nice computers.
iss wrote:
Wed May 19, 2021 4:50 pm
If you can borrow from somewhere another 8-chip set (all from the same manufacturer) and test with it.
See above. I should also search for some socketed RAM chips in other computers. I will check. Just to be sure, what does identify the speed? The number after P, am I correct?
iss wrote:
Wed May 19, 2021 4:50 pm
Another option is to use diagnostic ROMS (which you already found) - my ROM is very simple but robust and requires the absolute minimum working chips, @mike's ROM is more advanced and can more diagnostics - use both :).
I was not aware of the existence of two separated ROM images, and I'm pretty sure I cocked Mike's one... Please, can you point me to your ROM image?
iss wrote:
Wed May 19, 2021 4:50 pm
At end you can test all tracks continuity - it's boring long work but it definitely helps!
Yeah sure. I tested from top mainboard side, sock to sock, but probably I should test them solder to solder to be sure there's continuity. I will keep these as last test.
iss wrote:
Wed May 19, 2021 4:50 pm
Can you measure the resistance between +5V and GND rails? (Don't forget to disconnect the PSU first!)
Ok, I found information about the GND rails, but I'm not sure about the track. Should I cut them before reading values? And just to be double sure, is the GND Rails the one connecting PIN 14 of RAM ICs and other sparse ICs pins?

It seems it was a good idea join you, I have already some more test to do. I'm sure we'll find a way to repair the little one. Thanks!

User avatar
iss
Wing Commander
Posts: 1277
Joined: Sat Apr 03, 2010 5:43 pm
Location: Bulgaria
Contact:

Re: A problematic Oric 1

Post by iss »

rh74 wrote:
Wed May 19, 2021 5:22 pm
Ok, I found information about the GND rails, but I'm not sure about the track. Should I cut them before reading values? And just to be double sure, is the GND Rails the one connecting PIN 14 of RAM ICs and other sparse ICs pins?
No track cutting! Here is what I mean:
oric.jpg
For a working board the readings should be roughly ~250 Ohms.
If the difference is more than +/-50 Ohms (i.e. <200 or >300 Ohms) there should be something broken.

Here is my DIAG ROM.

User avatar
Vyper68
Flying Officer
Posts: 130
Joined: Mon Sep 22, 2014 4:18 pm
Location: Hurworth, UK
Contact:

Re: A problematic Oric 1

Post by Vyper68 »

Is there a reason TR1 was removed? The state of the back of the PCB means broken tracks and vias are the most likely source of the problem. It would need tracing and testing.
You could fit a test ROM just in case it’s an IC but it might not be the actual chip and be the tracks connecting the chip to the board.
Bazinga!

rh74
2nd Star Corporal
Posts: 20
Joined: Mon May 17, 2021 8:53 am

Re: A problematic Oric 1

Post by rh74 »

iss wrote:
Wed May 19, 2021 10:23 pm
For a working board the readings should be roughly ~250 Ohms.
I gave it a really super quick try yesterday but not over the pins you are suggesting (took a +5v and a pin 14 of a RAM IC). It said 170 Ohm... This evening I'll try taking measure on ROM IC.
Vyper68 wrote:
Thu May 20, 2021 6:38 am
Is there a reason TR1 was removed?
Yes there is. It had a broken leg. I read from the scheme that TR should be involved in tape signal, so I just removed it for the moment. BTW problems were there also with the TR in place. Anyway I need some quiet time to mount a new BC547.
Vyper68 wrote:
Thu May 20, 2021 6:38 am
The state of the back of the PCB means broken tracks and vias are the most likely source of the problem.
That's what I am afraid of. I saw in this forum high quality images of a naked board. In you opinion would it possible to replicate it to be printed on new PCB? Since the first day I had this Oric I'm wondering about this option. Tracks are very bad and it would take less time to solder everything on a new board than to find micro cracks in the tracks.

User avatar
Vyper68
Flying Officer
Posts: 130
Joined: Mon Sep 22, 2014 4:18 pm
Location: Hurworth, UK
Contact:

Re: A problematic Oric 1

Post by Vyper68 »

I cannot remember who did it off the top of my head but one of the guys on here created a new main PCB as a like for like copy, or he had some bare PCB’s. I’m pretty sure they were new ones so someone might have the Gerber files to have some new boards made.
I had some Spectrum PCB’s made in white from JLCPCB a couple of years ago and they were really nice. I used it to build a new Spectrum after my Issue 2 died and I use it as my main Speccy now. So if we had the files we could order some from there.

TR1 goes to the 6522A Pin 19 if you want to check that at some point.
Bazinga!

User avatar
iss
Wing Commander
Posts: 1277
Joined: Sat Apr 03, 2010 5:43 pm
Location: Bulgaria
Contact:

Re: A problematic Oric 1

Post by iss »

rh74 wrote:
Thu May 20, 2021 11:28 am
iss wrote:
Wed May 19, 2021 10:23 pm
For a working board the readings should be roughly ~250 Ohms.
I gave it a really super quick try yesterday but not over the pins you are suggesting (took a +5v and a pin 14 of a RAM IC). It said 170 Ohm... This evening I'll try taking measure on ROM IC.
It doesn't matter where to measure (that's why I said power rails).
The 170 Ohms are too low, so there should be problematic chip, broken (or shorten) tracks.

rh74
2nd Star Corporal
Posts: 20
Joined: Mon May 17, 2021 8:53 am

Re: A problematic Oric 1

Post by rh74 »

Well known apart (IC8, IC20 and IC21), are there other crucial ICs I should check? As you can see in photos just the 8, 20, 21 and 24 are socketed. I was going to remove the remaining ones, but if I can start from the culprit one it would be great.

User avatar
iss
Wing Commander
Posts: 1277
Joined: Sat Apr 03, 2010 5:43 pm
Location: Bulgaria
Contact:

Re: A problematic Oric 1

Post by iss »

Other DIP14/DIP16 chips are not directly involved to the booting, except the main 12MHz clock generator which obviously works (you have stable picture). So it remains the sound chip (AY-3-8912) - I never saw a broken one but who knows.
The main suspect remains RAM chips :( and broken tracks.
One easy thing: check/replace the capacitor C21. You can short quickly its pins to "emulate" reset.
Else an oscilloscope will help a lot :).

rh74
2nd Star Corporal
Posts: 20
Joined: Mon May 17, 2021 8:53 am

Re: A problematic Oric 1

Post by rh74 »

iss wrote:
Thu May 20, 2021 5:09 pm
The main suspect remains RAM chips :( and broken tracks.
I know... :(
iss wrote:
Thu May 20, 2021 5:09 pm
One easy thing: check/replace the capacitor C21. You can short quickly its pins to "emulate" reset.
Already changed. The previous one was already changed, but once I removed and measured it, it showed a smaller capacitance than the nominal one.

iss wrote:
Thu May 20, 2021 5:09 pm
Else an oscilloscope will help a lot :).
There is... 8)
Untitled.png

Post Reply