Help with two Orics

[protek]

Greetings! A fresh Oric owner and a new member reporting for duty! I recently acquired one Oric and a spare mainboard. Both were fixer-uppers.

First board had no RAM, CPU, ULA, ROM or VIA, but there were sockets for all the missing chips. I got new ULA, CPU and VIA and borrowed 4164 RAM chips from my spare Spectrum, and the ROM from the other Oric mainboard. I checked the 5V line to be within tolerances. The image I’m getting on my Amstrad GT65 is as below. It is also buzzing.


The other one had all the chips accounted for, although I knew it was not working. I got a set of new 4164 RAMs and installed those on sockets. Also removed the ULA, put a socket and tried the new ULA. This one makes a chime (relay click?) upon startup. Picture is as below. 5V line is all right.


Which of the two boards is a better canditate for revival, and what would be the next thing to check out? I have a multimeter and logic probe that I can use.

Thank you in advance!

[iss]

Welcome, protek!
I would start with the first one (which has sockets) - at least good text chars are visible.
I tried my crystal ball but no insights...
Can you post pictures of the PCB and your power adapter (mainly its label with data about voltage and current).
You measured 5V line and it's good - you mean the thick track on the PCB, right?

[protek]

The PSU is a modern, switching multi-voltage adapter that outputs 9 V at 1 amp at least. I’ll provide pics of the board and the PSU. Can’t remember exactly where I measured the voltage but can do it again from the 5V rail.

[ibisum]

More amps required! I use 1.5A ..

[protek]

No worries. It outputs 1.7 A at 9V

[protek]

Here are the pics:


Don’t mind the missing ROM. It’s on the other mainboard atm





The 5V line reads -4.96 V, and in case you’re wondering, the PSU is positive center.

[iss]

IMO everything looks nice and nothing suspicious.
Are this tracks OK or it's because the low resolution of picture:

Tiedosto_002.png (93.69 KiB) Viewed 6078 times

You can check also if the insulator under the 7905 is firmly placed and doesn't short tracks.

[protek]

The traces are all right. It’s just some grime on top of them.

[protek]

It’s been a while...

I spent some time today troubleshooting the Orics. I desoldered the CPU and VIA from board #2 and tried the new chips on that. It shows different kind of garbage but still not booting, so I put the new chips back into board #1.

Board #1 that showed some random characters in my pics, usually boots to garbage for maybe a second before the display shifts and shows the characters among the garbage. It doesn’t have the boot fix on the ULA like board #2.

I’ve tried probing the data lines on RAM and other ICs. One of the RAMs (IC13) didn’t show any activity on DI. All the 4164s are new, so I really don’t think those are the suspects.

I also burned a new ROM and tried it on board #1. No change save for random characters changing to other random characters.

I gather the ULA, or ULAs are all right since I get characters on display. I think the Basic ROMs are all right too, since they really do not affect the behavior of either boards. Of course I can’t say for sure as I don’t have a working system to try the chips on.

I could use some advice in regards what to try next.

[iss]

I could use some advice in regards what to try next.

Take a look in THIS thread about diagnostic ROM's and lot of repairing info.

[protek]

Thanks! I’ll be sure to check that out.

I’ll just burn the diagnostic ROM image onto an eprom and put it in place of the Basic ROM?

[mikeb]

One of the RAMs (IC13) didn’t show any activity on DI.

DI/DO are tied together on each DRAM chip. You should see activity on all of the DI/DO pairs, if it's stuck low or high, then something is faulty on that one data line.

If the DRAM chips are new, and socketed, swap the "stuck" one with a neighbour. Does the stuck line move with the chip? (bad DRAM) or stay put? (other fault on board).

If the DRAM chips are new and not socketed, kick yourself for not socketing the DRAM

Remember to peer into the Expansion socket in case a pin is bent/conductive debris

[protek]

I tried the diag rom. Board #1 gives me a nice, clean busy tone and nice, pretty consistent jail bars on the screen.

With board #2, it does give the busy tone, but its more high-pitched and mixed with the constant high-pitch tone that plays when it’s on. Also the screen is more garbled and changes with the busy tone.

@mikeb: Yes, I do always put in sockets if I remove an IC.

@iss: My Salora says hi to your Finlux.

[protek]

Okay, here’s the current situation with board #1. I got a batch of 8264 RAM chips and a couple of 74LS257s. I swapped out all RAM and IC8 which was socketed. I am still getting the picture above. Forcing a reset gives a blue color to some of the brackets shown. I now also got activity on all the RAM chips’ data lines, or at least the probe shows them high. Can’t really tell if it’s pulsating or not.

To summarize: based on iss’ diag rom, I should have a working CPU, VIA, AY and speaker. I suspect my ULA, or both of them are also working as they yield similar results on this board and display clear characters on screen. The regulator supplies a good voltage to the power rail. IC20 is soldered directly to the PCB and if there isn’t anything else I should try first, I’m going to desolder that and put a socket and a new 74LS257 in its place.

EDIT: One thing I noticed after changing the RAM and IC8, that there’s no longer any buzzing coming from the speaker.

Also, when I compare my latest screenshot to the original taken when I had it connected to the Amstrad green monitor, I notice that both pictures seem to show the same random characters but the black/white pattern is now different.

I’ve got a gut feeling that I’m maybe a one component away from getting this thing sorted.

[protek]

One thing worth mentioning is that the new RAM chips are marked MB8264-20, so I assume they would be 200ns. Is this too slow for the Oric?

My 4164 are marked KM4164B-15 (150ns?).