Help with two Orics

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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protek
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Re: Help with two Orics

Post by protek »

I may have suggested this, or may have forgotten, but once it is powered up, what happens if you briefly short (with a wire) CPU pin 1 (VSS) and 40 (Reset)?
Lo and behold! That did it! Thanks, Mike!
Image

So I guess I’ll need that cap

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Chema
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Re: Help with two Orics

Post by Chema »

And Mike did it again! :D

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kenneth
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Re: Help with two Orics

Post by kenneth »

Two Orics reborn :mrgreen:

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protek
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Re: Help with two Orics

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Now I’m tempted to find a case and keyboard for this mainboard also, as I got two boards but only one case and keyboard.

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ibisum
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Re: Help with two Orics

Post by ibisum »

Mike, you get a virtual beer bought for you. Nice one!

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Dbug
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Re: Help with two Orics

Post by Dbug »

Maybe we could actually get him delivered an actual real beer, not sure if there are services that can do that where he lives :)

But yeah, this type of help is much appreciated, thanks a lot Mike !

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HigashiJun
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Re: Help with two Orics

Post by HigashiJun »

Well done !

:D
HigashiJun

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protek
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Re: Help with two Orics

Post by protek »

I’d love to buy you a beer, Mike. Thanks once more for all the help and advice! I’ve learned a lot of the inner workings of the Oric.

I’m still waiting to get the new capacitor for C21. I did notice that in many cases, board #2 will require 1-2 reset cycles before the TV even gets a signal on the RGB port. Once there is a signal, the next reset cycle will put the system into correct state.

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mikeb
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Re: Help with two Orics

Post by mikeb »

kenneth wrote:
Tue Jun 02, 2020 10:58 pm
Two Orics reborn :mrgreen:
From "Do ULA!" to doula :)

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mikeb
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Re: Help with two Orics

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Dbug wrote:
Wed Jun 03, 2020 9:45 am
But yeah, this type of help is much appreciated, thanks a lot Mike !
protek wrote:
Wed Jun 03, 2020 11:48 am
I’d love to buy you a beer, Mike. Thanks once more for all the help and advice! I’ve learned a lot of the inner workings of the Oric.
Beers not necessary, though thanks for the thought :)

More than happy to know that Orics are getting back up and working.

It always helps to start with the basics, in this order :-

[*]Are all the bits there? Any physically broken/squashed bits? Signs of previous repairs?
[*]Power supply -- is 5V everywhere it needs to be? What current is being drawn?
[*]Clocks - 12MHz clock into ULA, 1MHz clock out?
[*]Reset -- give it a hard kick.
[*]Unusually hot/cold DRAM chips after powering on.

Because all of the above will kill any attempts to fault-find, or cause weird symptoms, or overlook the obvious :)

I've got a spare Oric board that boots successfully, but quite often will get a phantom keypress at bootup. It never does it after a manual-wire reset as above, so I think that one is just on the edge of needing to be done :)

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protek
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Re: Help with two Orics

Post by protek »

I swapped the capacitor. I couldn’t find one with 1uf 10V rating, so I went one with 1uF 50V rating, which turned out to be the same as the original was. The original’s packaging had darkened as if it had run really hot at some point.

The new cap didn’t solve the boot issue, though. Board #2 still requires several reset cycles to get a signal on the TV and eventually a proper display. I probed the reset signal and it stays constantly high.

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mikeb
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Re: Help with two Orics

Post by mikeb »

protek wrote:
Thu Jun 04, 2020 6:08 am
I swapped the capacitor. I couldn’t find one with 1uf 10V rating, so I went one with 1uF 50V rating, which turned out to be the same as the original was. The original’s packaging had darkened as if it had run really hot at some point.

The new cap didn’t solve the boot issue, though. Board #2 still requires several reset cycles to get a signal on the TV and eventually a proper display. I probed the reset signal and it stays constantly high.
The 1uF 10v to 50v shouldn't be a problem (usually, uprating like that makes fitting it difficult!)

The reset signal being constantly high is odd. I'm not sure how exactly you'd measure that though, as at power on, the reset line will go from 0v (unpowered) to 5v (powered) almost as fast as the 5v rail does.

It might appear to be high from the moment of power on, but if you scope the 5v rail AND reset line at the same time (if a CRT: in "chop" mode, not "alternate" mode!) and trigger it correctly, and have a storage option .... (!) you'd see :-

Code: Select all

_____/~~~~~ (POWER)
______/~~~~ (RESET)
But it bothers me you say you get NO SIGNAL to the TV at power on, until some number of resets? The ULA never sees the reset signal (not connected), and runs from power on (all the time), so you should at least get a stable, but junk, picture when Oric doesn't start (like when the boards were first "broken" :)

If you really get nothing, at all, then the ULA may not have it's clock (12MHz) coming in, which can be caused by IC21 (two segments) not oscillating -- some people have replaced this chip with related types and had success ( I forget if it was 74LS to 74HC or vice versa)

If you are missing picture, worth checking what's happening at Pin 7 (ULA 12MHz clock in) and Pin 14 (ULA 1MHz clock out). Also, pin 16 (ULA Composite Sync out) should have a nice 15.625KHz pulse train (64usec) with interruptions every 20ms (50Hz) showing horiz and vert sync is being produced.

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protek
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Re: Help with two Orics

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But it bothers me you say you get NO SIGNAL to the TV at power on, until some number of resets? The ULA never sees the reset signal (not connected), and runs from power on (all the time), so you should at least get a stable, but junk, picture when Oric doesn't start (like when the boards were first "broken" :)
Well, the screen isn’t completely blank. There is some moving garble, not pure static but something that the TV isn’t able to sync with. Getting a stable, junky picture requires a few reset cycles.

I got a 74HC for the IC21 as there weren’t any LS ones available at the local electronics shop. I did try the HC in my working board and that worked without a hitch in that.

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protek
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Re: Help with two Orics

Post by protek »

Anyhow, here’s board #2 up, close and personal:

Image

Image

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protek
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Re: Help with two Orics

Post by protek »

I forgot to tell where I got the reset pin being high. I used my logic probe for that. I didn’t see any change in that during the power cycle.

The board is behaving a little better now, booting to a stable junk picture most of the time. I wanted to try the diagnostic ROM, but I just can’t get a stable picture with that, even after reset. I should probably install the diag ROM into a PCB, so that I could connect it into the expansion port.

It looks like i’m facing the same symptoms as in this blog: http://blog.tynemouthsoftware.co.uk/20 ... uitry.html

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