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PET 2001 B Garbled letters all over screen!!!!

andrewj

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I recently aquired a Pet 2001 B and when I power it up all I get is garbled letters all over the screen! Does anyone know what might be causing this?? Would really like to get it goin any help would be great!
 

MikeS

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I recently aquired a Pet 2001 B and when I power it up all I get is garbled letters all over the screen! Does anyone know what might be causing this?? Would really like to get it goin any help would be great!
First of all, what's a 2001 B? Not a 2001-8 by any chance?
- What are the numbers on the RAM and ROM chips?
- Does it have the built-in cassette player?
- Where are you located?
- Browse the Commodore section and you will find a number of threads about the same problem.

The first step is always to Carefully remove and replace all socketed chips, or at least slide them sideways in their sockets. If you do remove them, be very careful not to bend any pins when you put them back.

Good luck.
 

andrewj

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pet 2001 8

pet 2001 8

yes its a 2001 8 . the numbers are 6540 and 6550. Ive reseated all the chips and still same result just random characters all over the screen. It doesnt have a built in cassete player. Im located in regina saskatchewan canada. Im very novice at all this but like my commodores so trying to learn all I can. Thanks for any info.
 

deathshadow

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Most common cause of garbled random letters on old machines is bad RAM. Unfortunately I believe the RAM is soldered down to the board so it's not exactly easy to test for. Commodore never were much of ones for socketing components that were actually prone to dying -- they just socket all the stable stuff.

Hell, most PET 2001's used Ceramic ram's... check them over, see if any have visible cracking. (switching to plastic wasn't just about cost)
 

MikeS

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yes its a 2001 8 . the numbers are 6540 and 6550. Ive reseated all the chips and still same result just random characters all over the screen. It doesnt have a built in cassete player. Im located in regina saskatchewan canada. Im very novice at all this but like my commodores so trying to learn all I can. Thanks for any info.
Hmm, nasty. It's quite likely that one of those chips is bad but, being non-standard, they're going to be hard to test even if you had the right equipment. Not only that, but it's going to be a problem finding replacements if you need them.

No chance there's somebody close to you with the same machine that you could swap with?

Let's see if anybody else comes up with any bright ideas; if not, as a last resort you could send them to me and I could check them out for you and maybe have a replacement if necessary.

If it turns out that you need a RAM or ROM chip there are various adapters available, including one that sits underneath the CPU and replaces the entire set.

What are the Commodore numbers on the 6540s? Something like 901439-07 etc.
 

MikeS

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Most common cause of garbled random letters on old machines is bad RAM. Unfortunately I believe the RAM is soldered down to the board so it's not exactly easy to test for. Commodore never were much of ones for socketing components that were actually prone to dying -- they just socket all the stable stuff.

Hell, most PET 2001's used Ceramic ram's... check them over, see if any have visible cracking. (switching to plastic wasn't just about cost)
Pretty well all 2001s had RAMs & ROMs in sockets; makes it convenient, but also a common source of trouble because they were pretty crappy.

Actually, bad ROMs are more often the cause of a dead PET, unless the bad RAM happens to be in page 0.

And although they probably do exist I've never seen any ceramic 6540s or 6550s; I assume the ones in this one are all plastic?
 

andrewj

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2001 8 pet

2001 8 pet

The chip numbers are as in order from left to right sitting in front of the computer
02 4 2181 023 5180 HN462532G(which apears to be a replacement chip on an adapter board of some sort also has 1982 SEW B2/3 $FIX on it) 0220680A 021 3280A

020 3980A then at the back right of the board one more 6540 0101978A
 

MikeS

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The chip numbers are as in order from left to right sitting in front of the computer
02 4 2181 023 5180 HN462532G(which apears to be a replacement chip on an adapter board of some sort also has 1982 SEW B2/3 $FIX on it) 0220680A 021 3280A

020 3980A then at the back right of the board one more 6540 0101978A
You can sure make something simple look complicated and hard to read... ;-)

They're definitely in the wrong sockets; presumably one socket is empty as apparently someone's already replaced two of the ROMs with that adapter.

Note that the board has numbers along the front which number the sockets 1 - 7, right to left.

The ROMs should be:
1 - 020
2 - 022
3 - 024
4 - 025
5 - 021
6 - 023
7 - 026

It looks like you're missing 025 and 026 which is the upper 4K of memory; try that adapter in socket 4 and if that doesn't work try it in socket 7.

Hmm, looks like our spamming friend is back...
 

andrewj

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2001 8

2001 8

Ok I rearanged the chips this morn and yes slot 7 is empty. Nothing has changed but at least these are in order now..thanks.
I also noticed this morning that when i wiggle the wires going up to the monitor the screen can go blank..wondering if maybe the problems up there with that area ??? Would I be able to replace the roms or reprogram??
 

MikeS

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Ok I rearanged the chips this morn and yes slot 7 is empty. Nothing has changed but at least these are in order now..thanks.
I also noticed this morning that when i wiggle the wires going up to the monitor the screen can go blank..wondering if maybe the problems up there with that area ??? Would I be able to replace the roms or reprogram??
Did you try the adapter in slot 7 instead of 4?

Didn't think that would fix it but it was worth a try; looks like someone (you?) pulled the ROMs and then didn't know the right locations, but presumably wouldn't have pulled them in the first place if there wasn't a problem. You can't reprogram them since ROMs are permanently programmed, but you can replace them with EPROMs just like someone has already done with that 2532 and adapter replacing the 025 & 026 ROMs. Of course you'd have to know which one(s) (if any) need to be replaced, but unless you make an adapter to read them in a 'normal' reader the only way to read and check them is in another 2001 using those chips.

IC sockets and connectors were a common problem, so the connector inside the monitor is probably a little loose or oxidized; nothing to do with your main problem though. If you open up the monitor to tighten and clean the connector, be careful not to damage the CRT (and of course turn off the power first!)

Also check the main power connector from the transformer and capacitor; they often overheated and oxidized (and turned brown from the heat).

Where are all the other PET experts? No other suggestions?
 
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dave_m

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Where are all the other PET experts? No other suggestions?

You are doing too good to need us!

Does anyone have the link to the person that sells the total ROM replacement unit?

I have the link to the person that sells a 6540 adapter including the replacement 2716 (see below). The price is probably way too costly if all 7 chips are needed.

Maybe Andrew should take you up the the kind offer to test the ROMs and just order the one he may need.

http://home.comcast.net/~medasaro/6540rom.com/home.html
 

andrewj

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I would like to take you up on the offer to test the ROMs. Its likly where the problem seems to be. Id need your address and I'll get them in the mail.
 

MikeS

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Does anyone have the link to the person that sells the total ROM replacement unit?
I'm sure that when I first saw it there was an assembled version available for sale that used a '512 EPROM, and I think someone in fact just installed one but I can't recall who or where, but all I can find now at a quick look is a flash version and it's not clear whether assembled versions are still available:
http://vic-20.de/x1541/hardware/petram.html
I think Anders might have some experience with this board (or its predecessor).

I have the link to the person that sells a 6540 adapter including the replacement 2716 (see below). The price is probably way too costly if all 7 chips are needed.
As a matter of fact Jim Brain sells an adapter that lets you replace a 6540 with a 27xx chip with jumper options to select a bank out of up to 512KB. I used one to put a 2764 into the character generator socket to permit selecting alternate character sets, and another one contains a 27256 which holds both BASIC 1 and the upgrade BASIC switch-selectable; that does involve a half-dozen or so connections to the MB however.

I see that he only lists the bare board for $1.50, but I think he will still sell assembled versions for less than $10.00 ea., not including the EPROM; I've bought several assembled units myself. Note that it uses an SMT chip and several SMT resistors.

http://www.jbrain.net/products/ROM%2del-6540.html

Maybe Andrew should take you up the the kind offer to test the ROMs and just order the one he may need.
No problem; if it turns out that one or more ROMs are bad I might have a 6540 replacement anyway; if not I can put a 27xx in one of JB's adapters.

I'll PM you (Andrew) with my address; keep in mind that although it's likely it's not certain that it is in fact a bad ROM or, if it is, that that's the only problem.
 
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MikeS

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Sorry, I have never used either of Nicolas' various boards. I've only read about them and met him in person.
Ah, OK. I thought I'd just recently read on one of the PET forums that someone had installed one, and thought it might have been you. Do you remember a version that used a 27512 instead of flash RAM, or am I dreaming that?
 

dave_m

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As a matter of fact Jim Brain sells an adapter that lets you replace a 6540 with a 27xx chip with jumper options to select a bank out of up to 512KB.

http://www.jbrain.net/products/ROM%2del-6540.html

Mike,
Thanks for the Jim Brain information. I tried to find it previously but could never get to the page with the board info. He should work on making his website easier to navigate.
-Dave
 

MikeS

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Mike,
Thanks for the Jim Brain information. I tried to find it previously but could never get to the page with the board info. He should work on making his website easier to navigate.
-Dave
Amen! (Are ya reading this, Jim? ;-)

No, not Giles' most excellent board; I'm pretty sure I just read about someone using a purchased board, probably from Nicolas, but maybe I was dreaming it...
 

MikeS

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I would like to take you up on the offer to test the ROMs. Its likly where the problem seems to be. Id need your address and I'll get them in the mail.
One other thing to check in the meantime is page 0 RAM; try swapping ICs I1 and J1 with a pair from elsewhere, e.g. I8 and J8.
 

MikeS

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Does anyone have the link to the person that sells the total ROM replacement unit?
I had a reply from Nicolas: he did indeed sell assembled units at one time but these days he doesn't have the time; he does however have the PCBs, GALs and flash chips and I'm thinking of ordering a couple of sets and resell them at cost in assembled form in case someone without soldering skills needs one. We'll see...

Note that it replaces the ROMs AND the RAM, and with a different GAL program can also be used in VICs, disk drives, etc.

I have the link to the person that sells a 6540 adapter including the replacement 2716 (see below). The price is probably way too costly if all 7 chips are needed.
I have a couple of Jim's version of this and could supply a single ROM replacement if necessary.
 
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