Oric Atmos query

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Vyper68
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Oric Atmos query

Post by Vyper68 » Fri Sep 26, 2014 1:17 pm

Hi there,
I am looking for some help and advice about an Oric Atmos i have just bought off eBay. I used to have an Oric in the 80's & 90's but it has been a long time since i have owned one. I decided to try and buy one off eBay for some retro fun.
The Oric i bought had no PSU so i bought a DC adapater it can output 9V @ 1A and the polarity can be switched and i have made it centre positive.
When i first turned it on i had a black & white screen of garbled characters and thought i had bought a broken machine.
I re-seated the ULA & ROM as everything else is soldered and couldn't feel any of the RAM chips getting warm. I thought i would give it one last go and it worked! - there is the same garbled black & white screen and then it goes to the normal Oric welcome screen. They keyboard works fine, as does the speaker and it's reporting the correct amount of memory free ( 37631 ).
So i thought it might be a dry solder joint, so i thought i would take a closer look at PCB. There is evidence of scratching next to the capacitor on the right of the heatsink but it does not look like it has been replaced.
So i flipped to board over and found this
ImageP1000567 by richiefarrell, on Flickr

Which is on the under side of the 6522 - has anyone seen this before? because i don't remember my Atmos having this and should i remove it?.
The other question i have is the heatsink is getting very warm quite quickly and i cannot remember how warm these things get anymore or if the power supply i am using is the cause.
And finally do you think the PSU connector needs re-soldering or should i leave it?
Thanks in advance guys.
ImageP1000569 by richiefarrell, on Flickr
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Re: Oric Atmos query

Post by Godzil » Fri Sep 26, 2014 1:41 pm

The resistor + capa is normal (even if the capacitor is not commonly put)

Look at the photos on this topic: http://forum.defence-force.org/viewtopic.php?f=23&t=919 there are a few of both side of the PCB, this atmos had nearly all known official reworks.

For your PSU/Regulator, can you measure the voltage output of your PSU, and can you set it to a lower value ? 6 or 7.5V should be fine.

And a 7805/7905 regulator can become really hot (that's why there is a heatsink) and is hard to damage (really hard)

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Re: Oric Atmos query

Post by Vyper68 » Fri Sep 26, 2014 1:54 pm

Thanks for the reply. Sounds like I am worrying about small stuff. Quite pleased it's normal.
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Re: Oric Atmos query

Post by Vyper68 » Fri Sep 26, 2014 7:24 pm

Can someone clarify the RAM on this machine as the chips are Hitachi HM4864P-2 not the 4164 i was expecting.
Sorry for being a noob but it's been so long since i got into Oric's i've forgotten everything. :oops:
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Re: Oric Atmos query

Post by Vyper68 » Wed Oct 08, 2014 5:30 am

Hi,
I need some more advice again. This Atmos I bought is being VERY temperamental. I get a black & white chequerboard effect before it boots to the Tangerine Basic screen. If I have left the machine off for a long time it freezes on the black & white screen until I power on & off a few times.
I think it might be a dry solder joint but cannot see any obvious ones ( my eyes are not what they used to be :D ). Is there anything else that might cause this? I don't think it's the RAM as if it was blown it would not work no matter how much I turned it off & on.
Any one got any ideas?
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iss
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Re: Oric Atmos query

Post by iss » Wed Oct 08, 2014 8:19 am

I have the same issue with an Atmos I recently bought.
Exactly as you said - it's very temperamental or 'temperature-mental' :).
One easy thing you can do is to replace the capacitor C21 (1uF) with new one.
capacitor.jpg
capacitor.jpg (12.34 KiB) Viewed 7062 times

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Re: Oric Atmos query

Post by Vyper68 » Wed Oct 08, 2014 12:33 pm

iss wrote:I have the same issue with an Atmos I recently bought.
Exactly as you said - it's very temperamental or 'temperature-mental' :).
One easy thing you can do is to replace the capacitor C21 (1uF) with new one.
capacitor.jpg

Thanks I'll give that a try & report back....Maplin here I come :D
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Re: Oric Atmos query

Post by Vyper68 » Wed Oct 08, 2014 1:55 pm

I was thinking if I am going to replace one electrolytic capacitor I might as well replace all of them.
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iss
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Re: Oric Atmos query

Post by iss » Wed Oct 08, 2014 2:23 pm

C21 is important for RESET signal else replacing all electrolytic capacitor is good idea.

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Re: Oric Atmos query

Post by Hialmar » Wed Oct 08, 2014 5:01 pm

A friend of my association told me that it was a bad idea to change capacitors if they are not dead.

There is a good chance that the new ones that you'll install will be of a worse quality than the ones you already have and therefore you'll need to change them more often.

For SMD (support mounted device) capacitors it's different because the risk is big of damaging the motherboard but there aren't any on Orics.
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Re: Oric Atmos query

Post by Chema » Wed Oct 08, 2014 5:34 pm

Curious, I've always heard changing ALL the capacitors in a vintage computer was a good practice to keep it living other 30 years... Anyway I didn't in my Oric. I'd probably break something in the process...

My oric also needs a couple of attempts to boot sometimes. But it always has...

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Re: Oric Atmos query

Post by Vyper68 » Wed Oct 08, 2014 6:43 pm

Hialmar wrote:A friend of my association told me that it was a bad idea to change capacitors if they are not dead.

There is a good chance that the new ones that you'll install will be of a worse quality than the ones you already have and therefore you'll need to change them more often.

For SMD (support mounted device) capacitors it's different because the risk is big of damaging the motherboard but there aren't any on Orics.
I understand what you're saying but wasn't there a problem with the quality of capacitors in the 80's & 90's fitted to computers and a lot went "bad" not just Oric's I'm talking about, PC motherboards, Atari ST power circuits, BBC Model B power supplies all had problems. So the new Panasonic branded capacitors I've bought will be better than the old ones....
Fingers crossed :wink:
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Re: Oric Atmos query

Post by Godzil » Thu Oct 09, 2014 9:57 am

Only the chemical capacitor need to be replaced as their live timespan is quite short.. (they the one like C21, the other brown one does not need to be changed, as most of them are only for decoupling, and this technology have a better lifespan.

Hialmar: I don't know where you ear that, but that not what I will tell nor will ear about this. Chemical capacitor have a really short lifespan, they are likely to fail quickly, and older one, like the one in the Oric, are quite dangerous because in case of failure they tends to explode are there is nothing to prevent them so (you know the cross embossed on newer chemical capacitor, this is for preventing an explosion)

And about CMS, if know how to do it there is no way to break anything, you just need to be gentle because they are more small.

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Re: Oric Atmos query

Post by iss » Thu Oct 09, 2014 12:27 pm

Totally agree with Godzil and when it comes to be 'gentle' here is what I do now:
Atmos.jpg
This is/was Atmos with the same power-on problem but I decide to desolder all chips and place sockets.
Important for me is to preserve the board but careful and gently I succeeded to preserve the chips too.
I tested desoldered ULA, 6502, 6522, AY-3-8192 and 8xRAM on other board (already with sockets) and ALL works :).
Now I'm wondering: if it's worth to remove really everything and to take high resolution pictures of the 'naked' motherboard?

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Re: Oric Atmos query

Post by Hialmar » Thu Oct 09, 2014 12:53 pm

Ahem maybe the Silicium guy was actually talking about other kind of capacitors (ie the brown ones Godzill is talking about). I'm not sure.

I'll ask him again when I see him.
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