Pravetz 8D: loading tapes?

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Symoon
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Pravetz 8D: loading tapes?

Post by Symoon » Mon May 21, 2018 9:10 am

Hi,

I bought years ago a Pravetz 8D. At the time, I tried to load tapes and it didn't seem to work.
Tried again today, to see if Novalight would work on it, but same result: zero loading, any source, standard format, tried two players, various sound volume... All my other Orics load nicely anything.

Is there a specific tape format for the Pravetz? Or a problem and I should open it?

Thanks!
(Will try to SAVE something, IIRC it worked)

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Re: Pravetz 8D: loading tapes?

Post by Symoon » Mon May 21, 2018 11:01 am

Ok, CSAVE works fine, but I can't load again what was saved.

I opend the case and saw nothing special except a RAM chip that was badly inserted. Fixed that; no change.
:cry: :cry: :cry:

Will post photos later, if needed.

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Re: Pravetz 8D: loading tapes?

Post by iss » Mon May 21, 2018 11:12 am

Hi, Symoon,
Is there a specific tape format for the Pravetz?
Definitely there should be NO difference in tape data format.

From what I remember Pravetz-8D was 'famous' with its bad tape input - permanent 'ERROR FOUND' :evil:. And when I found the Oric resources on the web around 2010, I was really shocked how you Oric guys are using the tapes at all :shock: . Anyway...

The first possible difference can be in the analog part of the hardware - schematics are equal:
Oric-8D-tape-in.jpg
but it's possible during production some batches to were built with random parts - simply what they have available on stock. IMO this is very unlikely, but who knows...

Next is the ROM - and here is difference for sure exactly in the tape related code (not counting the obvious changes in the message strings and character definitions)!
It starts at #E4B6:
Oric-8D-ROM-diff.jpg
Here are bytes:

Code: Select all

Oric Atmos:
E4B6     8e b1 02 a2 09 20 c9 e6  9d a7 02 ca d0 f7 20 c9  e6 f0 0a e0 10 b0 f7 9d  93 02 e8 d0 f1 9d 93 02
Pravetz-8D:
E4B6     a2 09 20 c9 e6 9d a7 02  ca d0 f7 20 c9 e6 f0 0d  9d 93 02 e8 e0 10 d0 f3  20 c9 e6 d0 fb 9d 93 02
And quick disassembly view:
Oric-8D-disassm.jpg
May be you can find what exactly is wrong here...

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Re: Pravetz 8D: loading tapes?

Post by Symoon » Mon May 21, 2018 12:05 pm

Thanks ISS for such a detailed reply! So apprently, I won't have to buy another Pravetz!
That's too bad, really. But that explains maybe why there was a specific need/design for a disk drive.

I'll try and check if it could be a software thing (If it's hardware... I'm ignorant ;) )

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Re: Pravetz 8D: loading tapes?

Post by Symoon » Mon May 21, 2018 2:00 pm

iss wrote:
Mon May 21, 2018 11:12 am
Next is the ROM - and here is difference for sure exactly in the tape related code (not counting the obvious changes in the message strings and character definitions)!
It starts at #E4B6:Oric-8D-ROM-diff.jpg
Here are bytes:

Code: Select all

Oric Atmos:
E4B6     8e b1 02 a2 09 20 c9 e6  9d a7 02 ca d0 f7 20 c9  e6 f0 0a e0 10 b0 f7 9d  93 02 e8 d0 f1 9d 93 02
Pravetz-8D:
E4B6     a2 09 20 c9 e6 9d a7 02  ca d0 f7 20 c9 e6 f0 0d  9d 93 02 e8 e0 10 d0 f3  20 c9 e6 d0 fb 9d 93 02
May be you can find what exactly is wrong here...
Actually, it just seems to be the usual two ROM 1.1 different versions. The early version (starting with STX $02B1) checked if there were parity errors during the synchro sequence, which is likely, leading to "errors found" message on non-data bytes. This was fixed in a later ROM 1.1 version; it seems to be the case here ;)

So the problem must be elsewhere!

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Re: Pravetz 8D: loading tapes?

Post by iss » Mon May 21, 2018 5:29 pm

Symoon wrote:
Mon May 21, 2018 2:00 pm
...This was fixed in a later ROM 1.1 version...
... and this shows exactly the moment when Pravetz was stolen! :D

Here is how the analog part looks by me:
P8D.jpg
An easy test can be if the ROM is on socket to change it with normal Atmos ROM and check how loading works.
I'll do this test asap and will post the result.

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Re: Pravetz 8D: loading tapes?

Post by Symoon » Mon May 21, 2018 6:22 pm

And here's mine. The ROM is not socketed here.

Not sure what they're used for, but we clearly don't have the same chips, at several places :shock:
IMG_9347_pravetz_Symoon.JPG

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Re: Pravetz 8D: loading tapes?

Post by iss » Mon May 21, 2018 8:38 pm

Very interesting exemplar! I think it's one from the latest produced - they were without RF modulator and your's is without the PAL encoder chips. Else nothing suspicious in the hardware.
Can you only check the resistor matrix (the red rectangle) if it has "10k" label?
20180521_220345.jpg

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Re: Pravetz 8D: loading tapes?

Post by Symoon » Mon May 21, 2018 9:49 pm

Thanks! There's also a chip on my board which is not on yours, just above the sound chip?

Sadly I'm away from the computer for a few weeks now, and I didn't take any picture showing the resistor in detail. We'll have to wait!

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Re: Pravetz 8D: loading tapes?

Post by iss » Mon May 21, 2018 10:16 pm

No hurry, take your time. :)
Else the chip 1ЛБ00ШМ is equal to 74LS00 and it's on your PCB because you have ROM split in 2x8k PROMs (2x7864) by me it's only one PROM and the 74LS00 is not needed. I'll try to make my board as yours with the same PROMs and will check how tape loading is working.
When you can, please, check if SLOW works?

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Re: Pravetz 8D: loading tapes?

Post by Symoon » Sat Jul 07, 2018 11:21 am

Sorry for the long silence, I had taken pictures but got my camera stolen, along with a computer and an external hard drive (and more). Most was backed up luckily, except the photos for the last 6 months.
At the moment I'm still busy sorting things out, will be back more active when they get back to normal!

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Re: Pravetz 8D: loading tapes?

Post by Chema » Sat Jul 07, 2018 12:23 pm

Ouch! Sorry to hear that....

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Re: Pravetz 8D: loading tapes?

Post by NekoNoNiaow » Sat Jul 07, 2018 3:31 pm

Damn, that sucks, hope you manage to find backed up versions.

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Re: Pravetz 8D: loading tapes?

Post by Symoon » Sat Jul 07, 2018 3:46 pm

Thanks guys. Luckily the computer was 100% backed up (on another similar one), the hard drive was backed up something like 4 weeks before and I hadn't stored any recent work on it, just downloads and other. Only the camera SD card was backed up in October...
I wasn't so lucky with all the work I did on paper... But so it is, it could have been worse.

Spending time buying things again, creating new backups, and administrative things (lost some official papers too).
Watch you luggage in French trains, especially when they're still in the station - guys climb in, watch for distracted people, and steal luggage. I was watching a video on my phone and they took my bag that was right above me...
Anyway, I'm off topic ;)

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