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Random Characters Issue on a COMMOODRE PET 2001

dave_m said:
Stéphane,
This is wonderful. You have done a great job with this computer. Your PET have given you some very hard problems which you have overcome with patience and nerves of steel.

Dwight is one of our best troubleshooters. He can fix anything.
-Dave
Click to expand...

Hi
I always find it challenging to debug through email. Instructions have to
be concise and often the person at the other end doesn't give complete responses.
Stéphane was better than the average though.
Trouble shooting is all about understanding what the circuit should do and
what to expect.
For me, it is always fun. I enjoy the hunt!
Part of trouble shooting is to always have two parts in your head.
Part one: guess as to what is wrong
Part two: a method of proving that guess is right or wrong
Early on, my guesses were far off but as time goes on, one must
be flexible and except that guesses are just that and move on.
Use all the information to refine the guess until there is no other
choice.
Dwight
 
MikeS said:
Sounds like he's got the business (CBM) keyboard
Click to expand...

Mike,
Right, I missed that, but I think he originally had a 901447-24 editor ROM for a graphics keyboard installed. In any event, would any of this effect the "return key"? In addition to changing the editor ROM, he may have an issue with the keyboard scan logic as Anders mentioned.
-Dave
 
Thank you Mike and Dave! I was so happy to finally get my screen back to life!
One more step toward healing for my PET ;)!

Fixing the screen was quite an adventure because even with the great assistance and excellent advices from Dwight, it was a real discovery!

I must say I have learnt a lot and I have a real admiration for your expertise.

Talking now about my keyboard mapping, these are in details the two ROM sets I have :

Original one (that came with the PET, but in a second time!) :
D9 901465-22 1880
D8 901474-02 2080
D7 901465-21 2080
D6 901465-20 1880
D5 901465-19 2280

When I use those ships, I get the TIM, not the BASIC welcome screen.
(There is something wrong with this set, but I do not know what ???)

Spare one (coming from an ebay lot) :
D9 901465-03 0980
D8 901447-24 1180
D7 901465-02 0980
D6 901465-01 0980

And finally the set Dave kindly sent me.

When I use those set of ships, I get the BASIC welcome screen, but the keyboard mapping is wrong.
(So they should be working fine, but they do not fit with my PET.)

I am sorry the first time I asked I totally forgot to mention about my keyboard and I realize I got you in a wrong direction.

Is there a way to "combine" the two sets to get a working and fitting set ?
(Oups ! Did you get this ? ;))
 
sbo said:
Talking now about my keyboard mapping, these are in details the two ROM sets I have :

Original one (that came with the PET, but in a second time!) :
D9 901465-22 1880
D8 901474-02 2080
D7 901465-21 2080
D6 901465-20 1880
D5 901465-19 2280

When I use those ships, I get the TIM, not the BASIC welcome screen.
(There is something wrong with this set, but I do not know what ???)

Spare one (coming from an ebay lot) :
D9 901465-03 0980
D8 901447-24 1180
D7 901465-02 0980
D6 901465-01 0980

When I use those set of ships, I get the BASIC welcome screen, but the keyboard mapping is wrong.
(So they should be working fine, but they do not fit with my PET.)
Click to expand...

No, I do not think they can be combined.

OK, it looks like a previous owner upgraded to V4 and one of these chips is bad. V4 assumes there is a CRT controller chip (6545) on the mainboard so I am surprised it works so well.

The second set from ebay is V2 and came with an editor for the graphics keyboard (901447-24).

What you need to try first is a V2 editor for the business keyboard (901474-01) programmed into a 2716 EPROM as Mike mentioned. Can anyone in Europe send one to him? I can but it would take 11 days.

There still may be another issue with the keyboard scanning.
 
Last edited:
Dave has it right; the second set is BASIC 2 but the Exxx ROM is for the PET keyboard instead of the CBM version.

The first set is indeed BASIC 4 but there are versions for models with and without a 6545 CRTC, and that set should work in this CBM3xxx.

Once Stephane gets his computer working (or maybe he can use his friend's) he could plug those V4 ROMs one by one into one of the spare sockets and create some checksums to see which one(s) is/are bad.

Boy, first Dwight and now Chuck; are we attracting new members into the let's-try-to-fix-your-PET community? ;-)
 
I can program the 901474-01 image onto a 2716 and send to Stèphane. If I do it tonight, I can post the chip tomorrow and with a bit of luck it arrives in the beginning of next week. However I wonder what is the best way to send a pre-programmed EPROM, stuck into a bit of pink foam and some antistatic bag around?

I wonder about the spare ROM set from eBay. It suggests you should have four sets of ROMs as the motherboard I sent had a working set of ROMs onboard, minus the fact it contains the wrong kind of Editor ROM.
 
carlsson said:
I can program the 901474-01 image onto a 2716 and send to Stèphane. If I do it tonight, I can post the chip tomorrow and with a bit of luck it arrives in the beginning of next week. However I wonder what is the best way to send a pre-programmed EPROM, stuck into a bit of pink foam and some antistatic bag around?

I wonder about the spare ROM set from eBay. It suggests you should have four sets of ROMs as the motherboard I sent had a working set of ROMs onboard, minus the fact it contains the wrong kind of Editor ROM.
Click to expand...

Hi Anders,

Yes you're right ! I totally forgot about the set of ROMs onboard.
What do you think I should do now ? Try to find a compliant set of ROMs ? I have searched the Web, but it seems to be quite rare and hard to find ...

If it does not take you too much time and effort, programming the 901474-01 image onto a 2716 seems to be the fastest solution.
But if it is not possible for you, don't worry, time does not matter, and I will do my best to find an alternative solution.

I will send you my spare set of ROMs ; they will be more useful to you than they actually are for me.

Thank you,
Stéphane.
 
If you like, you can send me all your original V4 ROMs, the spare set of chips you got from eBay and perhaps even Dave's EPROMs if you have no other use for them. Then I can read all ROMs and compare to binary images to see which are good and bad from each set, and complement either the V4 set or the V2 set on the board I sent you with the suitable Editor ROM.
 
carlsson said:
If you like, you can send me all your original V4 ROMs, the spare set of chips you got from eBay and perhaps even Dave's EPROMs if you have no other use for them. Then I can read all ROMs and compare to binary images to see which are good and bad from each set, and complement either the V4 set or the V2 set on the board I sent you with the suitable Editor ROM.
Click to expand...

Great idea !
I will send you the sets of ROMs ASAP. just let me know about the shipping cost for the return.

Thank you,
Stéphane.
 
Sounds like everything is well in hand; you're a good man, Anders!

But I do want to mention again that if you had to, and have a working PET with a spare socket, then you could easily use the PET itself to identify a bad ROM.

@ Anders: Any word on what happened with that PET in Italy?
 
MikeS said:
Once Stephane gets his computer working (or maybe he can use his friend's) he could plug those V4 ROMs one by one into one of the spare sockets and create some checksums to see which one(s) is/are bad.
Click to expand...

Mike,
While we are waiting for ROMs to be sent back & forth, let's look at PET BASIC programs that will do some kind of sum check on ROMs placed in the $9000 address ROM slot.

This one will do a modulo 256 sum of the bytes.

On a PET, this little program takes an incredible 96 Seconds to run.

Code: 
10 for i = 0 to 4095
20 let dat% = peek(36864 + i) rem base address is 9000H
30 let sc% = sc% + dat%
40 if sc% >= 256 then let sc% = sc% -256 rem modulo 256 sumcheck
50 next i
60 print "sum check = " sc%
 
As a matter of fact we just had a friendly little contest in the Club100 Tandy M100 group to see how short/fast/fancy a one-line checksum program could be...

Now all we need is a corresponding program for the PC to generate the checksums of the binary images and then a little batch file to enter them into my Excel sheet with all the ROM numbers and descriptions ;-)

Simple enough for a one-off to check a given ROM though.

Tell you what, Dave; you publish a checksum of a known good ROM and we'll see if someone can identify it ;-)
 
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