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Commodore PC10/20-III speed issue

M

Murugan

Member
Joined
Apr 21, 2013
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10
Location
Belgium
Hello there..

I had the chance to buy this cheap from a friend
My first PC was a PC10-III with dual floppydrives. I always wanted my first PC back and a month ago,I got this PC20-III (not the same config as mine back then but good and close enough).
I had to do some work and upgrades to it so I added a NEC V20 (modelnr is D70108C-10).
Checkit reports it as a V20 at 4,7MHz.
Using the speed.exe tool (I'm using version 1.2) that came with the original software, one should be able to change the speed to turbo and double (or with a keycombo).
Well....mine does nothing. I can run the command like speed -d but it seems nothing changes. Is it supposed to say something?
Checkit keeps reporting 4,7MHz.
Landmark System Speed Test 2.0 reports weird numbers. Version 6.0 hangs at 'calculating CPU speed'. When running Speed Test and doing the keycombo,sometimes the speed drops for a split second and then goes back to the one shown in my screenshot.
Installing the original 8088 seemed to change nothing.
Am I missing something here?

Thanks in advance...
 

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What BIOS do you have and have you tried another EPROM or another BIOS, like the 318085-06?
 
What key combo are you trying? Ctrl-Alt-Plus and Ctrl-Alt-Minus (on the numeric keypad)?
If the manual gives you that info, then I would agree with Ruud here - it could be a weird custom BIOS that doesn't have that functionality.

Just another [far out there] thought regarding the keyboard - is it the original one designed for that PC? If not, could it possibly be sending different scancodes? I never owned a CBM PC, so I don't know if the keyboards were standard full DINs and communicated the same as an IBM PC/XT, or were they like the Amstrad PC1512/1640 with their own proprietary standard? Just a thought.

Andy
 
What a great machine you have! It has Faraday FE2010A chipset and you can switch the clock speed with this combinations:

- Normal 4.77Mhz -- "Ctrl+Alt+S"
- Turbo 7.16Mhz -- "Ctrl+Alt+T"
- Double 9.55Mhz -- "Ctrl+Alt+D"
 
DOSDays said:
Just another [far out there] thought regarding the keyboard - is it the original one designed for that PC?
Click to expand...
The Commodore key board that comes with this PC is XT -and- AT compatible. The PC20-III accepts original XT "only" keyboards and in my case, even the AT2XT modules so I could use a KVM switch. FYI: my PC20-III also has a VGA card.
In short, I doubt if the keyboard is the problem.
 
Sorry for the late reply.
The BIOS is 318085-07. I don't have a programmer to try another BIOS version.
Ctrl-Alt-S/D/T does nothing,even on a original Commodore keyboard. Sometimes it reacts to the keycombo with dropping for a split second to 1.71MHz :/
 
Replacing the V20 back with the original 8088 was a good test step, for sure.
I'm starting to think you have a different hardware problem around the timer circuitry, or something causing an extra wait state.

Landmark 2.0's "CPU Clock" should show the actual frequency your CPU is running at, while the CPU bar further down gives you the equivalent speed compared to an original IBM PC-AT. So a CPU clock of 3.047 MHz isn't right.
To confirm, re-run Check-It and tell us the Dhrystones. An 8088 running at 8 MHz will come out at around 576 Dhrystones. A V20 running at the same clock should be more like 640 Dhrystones. An 8088 running at 4.77 MHz will be around 344 Dhrystones.
 
Last edited:
Checkit reports 379 Dhrystones. It says it's like 1.08 times faster than the IBM PC XT.
 

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That would be great!
Somehow I don't see the option to send you a PM. Do I need a certain amount of posts?
 
OK so I finally did something that I should have done from the beginning: removing the motherboard. It seems it had issues before and some attempted to repair it. I found this near the Char Rom. Did some quick continuity checks and the ones I tested,are good. It seems I will need to check that solderingwork now I presume?

IMG_20230621_102129.jpg
 

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