My Oric and its modifications

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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Chema
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My Oric and its modifications

Post by Chema » Tue Jun 10, 2014 10:45 am

Hi guys.

I was quite sure my Oric did not have any modifications from the service bulletins because when I converted it from Oric-1 to Atmos it was done at the shop with the DIY kit.

However, as usually happens to me, I completely overlooked the fact that there was a problem with the keyboard (some keys did not work) so it was sent for repair.

And, of course, they applied some modifications. So, here are some pictures from my Oric motherboard. I'd like to be sure which modifications were made and which weren't. I recognize the one described in the service bulletin 1 (from http://www.48katmos.freeuk.com/servman.pdf) related to the overheating of the sound chip, and also I think I have the modification 56 for improved cassette loading, though I think they speak about pin 8 of the VIA when it should be pin 18.

EDIT: Dbug, isn't there a way to make pictures appear in a reduced version when browsing the forum and at the original size just when clicking or something like that? (Yeah, I am begging for such thing...)
compside.jpg
Component side
compside.jpg (1.45 MiB) Viewed 5026 times
trakside.jpg
Track side
trakside.jpg (1.39 MiB) Viewed 5026 times
Have you noticed the loose pin on the condenser in the lower-right part of the component side (near the VIA)? I am pretty sure it should be soldered to pin 18, and it could well be making contact with pin 19... Should I solder it at its correct position?

Here is a detail of this part:
compside2.jpg
compside2.jpg (1.53 MiB) Viewed 5026 times
Thanks for your help!

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Re: My Oric and its modifications

Post by Godzil » Tue Jun 10, 2014 11:27 am

If you look at my "disapearing" Oric where I've made photos of the PCB:

Image

The capacitor is connected between ground and 18, and yes this is tape related (pin 18 is CB1 which is tape_in. and pin 8 have nothing to do with tape :D)

On the other side, yes you are right, the resistor on the PSG is the "anti-overheat patch" and the resistor near the ULA is more strange to me as it just add another resitor in // of one of the OpAmp in, but if the sounds work correctly, there is no reason to change this (there is no service bulletin about this patch..)

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Re: My Oric and its modifications

Post by Chema » Tue Jun 10, 2014 12:14 pm

Godzil wrote: The capacitor is connected between ground and 18, and yes this is tape related (pin 18 is CB1 which is tape_in. and pin 8 have nothing to do with tape :D)

On the other side, yes you are right, the resistor on the PSG is the "anti-overheat patch" and the resistor near the ULA is more strange to me as it just add another resitor in // of one of the OpAmp in, but if the sounds work correctly, there is no reason to change this (there is no service bulletin about this patch..)
I wonder what the result would be if the capacitor were wrongly in contact with pin 19 (CB2)... Alas! it is clearly unsoldered now, so I might re-solder it to the correct position. I was able to load tapes quite correctly anyway, but who knows...

About the PSG modification it is ok to leave it there, I guess, though I cannot hear the sound through the Oric's internal speaker. Probably a broken speaker or something like that, as I am able to hear the sound through external (with volumen control :) ) speakers.

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Re: My Oric and its modifications

Post by Godzil » Tue Jun 10, 2014 1:15 pm

If you have access to an oscilloscope or a multimeter we can test the sound output or your HP.

Connecting it to CB2 (pin19) may cause problem with the PSG and the printer port, as if the toggling speen on the CB2 is too quick, the capacitor may led to lost toggling (some sort of aliasing).

I can't remember the value of this capacitor, but I think it's the C19 on the Issue 7 schematics ( http://regmedia.co.uk/2013/01/21/oric_4.jpg )

A 2.2nF could be "harmfull" to the signal starting from 200 or 300KHz. I don't know the frequency used on CB2, but it could cause nice problems :)

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Re: My Oric and its modifications

Post by Chema » Wed Jun 11, 2014 1:22 pm

I correctly soldered the capacitor to pin 18. And I did not break anything in the process, it seems. I should test it when loading things from tape, but anyway it does not correct my issue with Zip'n'Zap or Pulsoids. As a side point the synth music at the beginning of Quintessential sounds as horrible noise in my Oric. And, did you notice that I have a Rockwell processor and a Synertek 6522 VIA?

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Re: My Oric and its modifications

Post by Dbug » Wed Jun 11, 2014 1:31 pm

Chema wrote:I correctly soldered the capacitor to pin 18. And I did not break anything in the process, it seems. I should test it when loading things from tape, but anyway it does not correct my issue with Zip'n'Zap or Pulsoids. As a side point the synth music at the beginning of Quintessential sounds as horrible noise in my Oric. And, did you notice that I have a Rockwell processor and a Synertek 6522 VIA?
In my experience, problems with digitized sound sounding horrible is due to some models of AY/YM having different volume levels.

It's actually easy to measure: Use a multi-meter on the audio out, and play volume from 0 to 15.

If you get log values, it's correct. If you get a linear volume increase, it will sound like crap because the digit code is using log conversion tables to rebuild an equivalent of an 8 bit sample value by combining the volume of the 3 channels using conversion tables that takes into consideration that the volume is not linear.

I experienced that once on my Atari ST, I burnt my YM-2149, and I replaced it by a "pin compatible" model, most of the old musics sounded about the same, but anything that expected fine volume changes just sounded VERY LOUD OR LIKE A VERY SCRATCHED VYNIL LP :)

PS: I tried to change some settings about the image sizes, but it does not seem to work.

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Re: My Oric and its modifications

Post by Godzil » Wed Jun 11, 2014 1:47 pm

You may also try to change the chemical capacitor on the audio path, who knows

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