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| | Previous Messages | Posted By
MIK
on 2022-01-31
02:27:45
 |  Re: White - Yellow - Gold PCB
Thanks Ulysses, nice to know what these extra components are. Thanks again! 
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Posted By
Ulysses777
on 2022-01-30
13:24:20
| Re: White - Yellow - Gold PCB
@MIK
Those extra components are protection diodes added to the serial port, see this for details.
There is a revision of the Plus/4 PCB (ASSY 250455) that has these diodes as standard, all other boards were optionally modded at the factory.
@Gaia
Those are the brands from the C16, here's some more from the Plus/4:
Matsushita: FF 00 FF 00 for 128 bytes, then 00 FF 00 FF for next 128 bytes etc.
Micron: 00 FF 00 FF continuously.
Motorola: 00 FF 00 FF for 256 bytes, then FF 00 FF 00 for next 256 bytes etc.
OKI: FF x 64, 00 x 64, continuously.
Siemens: same as Fujitsu.
Toshiba: same as OKI.
There are supposedly other boards with Mostek, NEC and Sharp chips.
There are occasionally other values at boundaries, but they are never consistent values.
I also have an oddball Plus/4 which has Toshiba chips on bits 0, 2, 3 and 6, and TI chips on bits 1, 4, 5 and 7, and the powerup pattern on that is: $4D x 64, $00 x 64, $FF x 64, $B2 x 64 
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Posted By
MIK
on 2022-01-30
06:22:06
| Re: White - Yellow - Gold PCB
Looks like my Rev.A that displays the early Vegas Jackpot has Hitachi ram, pleased about that as chips from Japan are more regarded as the best quality. I put the game in the picture as no one else is going to do that so you know it's mine.
Just above the PLA you can see some extra components or whatever it is... extra wire/jumper that I was going on about. I thought it was the other Rev.A but turns out it's this one.
I never resized my picture so you can see it better I hope and as it's large I'll add a link instead.
Piccy: mik_c16_rev_A.jpg
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Posted By
Gaia
on 2022-01-29
16:39:11
| Re: White - Yellow - Gold PCB
Thanks Ulysses, this was really insightful! In fact, I have just added these RAM brands to YAPE's options... I seem to recall there has been another odd one that even had $7F and $80 as startup values at certain boundaries. Perhaps Matsushita, but I am not sure anymore...
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Posted By
MIK
on 2022-01-29
13:09:39
| Re: White - Yellow - Gold PCB
Very interesting info there. I had no idea of the different ram type's and have been very lucky not to have any ram chips die or else I would of looked in to it more. I might open my working Vegas C16 and take a look, and check out my others at some point. Thanks!
Hollywood Poker is a strange one. The only way I could get it to fully load correctly on Plus4 was to load it via the machine code monitor, or like you say it doesn't load properly if the normal LOAD command is used.
The tap images on this site come from my copy. Yape btw ignores the fact you might use the BASIC LOAD command and instead reads the first few bites to get the memory locations it was save from, and so Hollywood Poker loads fine in Yape just using the normal LOAD in BASIC.
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Posted By
Ulysses777
on 2022-01-29
10:03:52
| Re: White - Yellow - Gold PCB
The Vegas Jackpot loading bug is caused by this somewhat mangled BASIC line:
POKE65298,PEEK(55298)OR2
Which means that if bit 2 of 55298 ($D802, which resolves to $1802 on the C16) is on, then it selects ROM instead of RAM for the character set, causing the bug.
And the contents of $1802 on powerup is dependant on the make of RAM chips fitted. The Fujitsu chips, starting from location 0, alternate as $FF,$00,$FF,$00 and so on, which means that $1802 powers up as $FF, causing the bug. Whereas TI chips powerup with 128 $00s, followed by 128 $FFs, so $1802 powers up as $00, and does not cause the bug.
Coincidentally, all my Rev.B boards have Fujitsu chips and all my Rev.A boards have TI chips.
The only odd one out that I have is my 116, which has Hitachi chips, which alternates as $FF,$FF,$00,$00 for the first 128 bytes, then switches to $00,$00,$FF,$FF for the next 128 bytes, then switches back and so on. This does not have the above bug.
The only physical difference that I know of between C16 Rev.A and Rev.B boards is the routing of the COLOR and LUM lines from the TED chip. On Rev.A, they run under a corner of the RF modulator housing, requiring a piece of clear insulating tape between the housing and the PCB. On Rev.B boards, these lines are routed away from the modulator housing.
Another game that has a bug caused by RAM powerup status is Hollywood Poker. If $5381 powers up as $00, then the datasette will not stop running after loading side 2.
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Posted By
MIK
on 2022-01-29
01:43:04
| Re: White - Yellow - Gold PCB
@Ulysses777
In a galaxy far far away was the last time I had them open, sorry. I wrote the REV on a small white label and stuck it on the underside of the case to save me opening them and so I knew what they were. But glad you recognised what I was going on about from what I said. 
None of the Rev.B's I have will display this early version of Vegas Jackpot nor will any Plus/4, and from memory I have 1 Rev.A that won't either but I recall this Rev.A might look more like a Rev.B.
There 'may' be some extra soldering, some wire jumper on the Rev.A that the game does display properly on.
My spare C16's are stored away safely but I believe they are all UK made.
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Posted By
Gaia
on 2022-01-28
16:53:55
| Re: White - Yellow - Gold PCB
My take is that it depends on the RAM startup pattern (which in fact depends on the type of RAM chip...). In case the startup pattern is an alternating sequence of $00 and $FF then the loading screen is corrupted, in case it's more like $00, $00, $FF, $FF alternating in 256 byte blocks, then it is fine...
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Posted By
Ulysses777
on 2022-01-28
15:56:34
| Re: White - Yellow - Gold PCB
I have one C16 PCB with yellow lettering (a Rev.B), the rest of mine have white lettering.
@MIK, these C16s of yours that don't work with the early Vegas Jackpot loading screen, do they happen to have Fujitsu RAM chips?
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Posted By
MIK
on 2022-01-28
12:38:22
| Re: White - Yellow - Gold PCB
No idea, check out the revision which will be printed as Rev.A or Rev.B. Anything different to the norm might be Rev.A as there are at least 2 versions in the UK. One Rev.A I have I call it the Shaun Southern revision as it is the only one to display early versions of Vegas Jackpot properly, my preferred C16 LOL.
From my own experience...
What you might count as rare for Commodore mother boards are the removable chips. Rare being the Gold and Silver alloy coloured ones which were once said to be heat resistant back in the day, but as we know most 8bit chips do die and fry.
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Posted By
Retroshire
on 2022-01-28
06:32:24
| White - Yellow - Gold PCB
I found different colors of print in the Main PCB of a C16 and/or Plus/4.
The white one very oft, the yellow a little less, but only once the gold color print.
How rare are these gold printed PCB's?
I have one for the C16 and also one for the Plus/4
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