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Commodore PET 2001-8 Question

daver2 said:
Monotech in NZ do a very nice 6550 replacement.

They have a 6540 coming along shortly (apparently). You can already see a photograph if you look on the website for the 6550.

Dave
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+1 for Monotech solutions.

Don't for forget that Lord Rutherford who split the Atom came from NZ as did the band Crowded House. And there was the Hamilton Jet invented there. And, apparently according to the once NZ Prime Minister, Robert Muldoon:
"when a Newzealander moves to live in Australia, it raises the average IQ of both countries"
 
Had already ordered a small batch of 6650's from Monotech in anticipation of needing some - sufficient to give me a couple of K of main memory and some video memory.
Too expensive to assume having to replace them all at this point.
I'll open another thread when stuff arrives and if I get stuck - likely as my previous experience with more 'modern' pets has always been a fairly easy RAM/ROM fix with more readily available parts.
 
First, thank you to Dave and Nivag for their help, time and patience in getting the PET working again! I appreciate it.

Secondly, can I now remove the RAMulator and put the 6502 back in and remove the Reset Switch?

Not sure if I mentioned this but the PET came with two Skyles Electric RAM boards. I am going to try to see if those still work.

It also came with a Skyles Electric RAM board that attached to the IEEE port. It also had a ROM board attached to it.

Any suggestions?
 
No problem.

If your PET is stable, then please feel free to remove the ROMulan card and pop the 6502 CPU back into the socket.

You can remove the reset switch/button also if you wish. Some people install the reset button internally as a permanent feature for when the PET dies again (not wanting to tempt fate)...

With regard to the Skyles boards, I would try and find the documentation for these cards first. Also, post photographs of the front and back of the cards.

Dave
 
What was the idea of the Skyles electric RAM boards; was it to replace existing RAM with the same amount of RAM with some other features (like say non volatility) or was it simply to add RAM to increase the total amount ?
 
I removed the temporary Reset switch and the RAMulator and the PET works great.

Here are some pictures of the Skyles Electric Works boards. I haven't re-installed them yet.
 

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The one board replaces the 6550 RAM with 2114 RAM. It is an 8K RAM board.

The other board didn't attach to the IEEE port but to the memory expansion connector. I will have to look up the part numbers on the board to see how much memory it contains. Each MM5257 chip is 4Kx1. So it looks like another 8K RAM.

Total appears to be 16KB.

Dave
 
I will correct my post #207. Each 2114 RAM chip is 1K*4 - so 8 2114 chips gives us 4KB.

I see you had two (2) card originally fitted for 8K.

If you are gong to try and fit the option RAM cards, I would suggest leaving the ROMulan plugged in - because you will want to thrash the RAM cards with PETTESTER!

Dave
 
I installed the Skyles RAM cards and got a random screen so I put the Monotech RAM back in and the PET works fine.
 
You only have 8 Monotech RAMs installed (first 4KB RAM) so you could install the Skyles cards one at a time in the bank of empty sockets in the next block of 4K.

You did install them into the correct IC sockets didn't you? They should only be fitted into a specific pair of RAM sockets.

The random screen will be as a result of the lower RAM not working. If course, if you had the ROMulan card installed with PETTESTER active it would have told you that.

The RAM card that fits onto the RAM expansion connector can only be tested if you have a complete 8K RAM on the main machine - otherwise you will not have a block of contiguous RAM.

Dave
 
I installed them in I4/J4 and I8/J8. This was the sockets they were originally installed in.
 
daver2 said:
The red LED was for use with special Commodore diagnostics. It does not light under normal circumstances. It may light if the PET is faulty (a very low probability though!). I had a little test program to illuminate it - but it is pointless (and this LED was not fitted to any future PET designs).

The 'random character' screen is the default.

it is actually good. It indicates that we have some heathy power supplies, the video circuitry (as far as it goes) is working - but the CPU is not working.

The CPU may not be working for a number of reasons though.

I will post some things for you to check presently.

Can you post a photograph of the 'random' screen. What may appear as random to you may not be random to an expert...

What test equipment do you have?

Dave
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I wish I would have read this before replacing the LED in fear is was faulty!
 
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