Recent content by mch

The picture in post 1 of the pet with almost exact repeating faults is usually caused by faulty video ram chips, as pointed out by Radix above. I would recommend MBH2114 Tesla video ram chips sold on ebay by ELEBOZ a seller in Chech Republic. Any I have bought have all worked 100%, and they are...

If you have a good fuse, the next item to check is the line filter. This is a small silver barrel unit the size of your thumb hidden behind the transformer. It has 2 blue wire and 2 black wires coming from it. 40 years ago this filter was needed to stop the pet from interfering with TV...

First thing to do is check the fuse with a voltmeter. PET power supplies are very robust

after inputting the code by Dave_m to test the 6520 at UB16 (post 411 on topic "3040 2 red lights") the 6520 is good. After inputting the test code from the Osborne Book mentioned above, EOI is good and all other control lines are bad. EOI only uses the keyboard 6520. The other control lines all...

I am waiting for MC3446 chips before proceeding further. As a matter of interest the book "PET and the IEEE-488 Bus (GPIB) " published by Osborne /Mc Graw Hill has a GPIB Diagnostic test at the end of the book to test Data Bus, NDAC, DAV, NRFD, ATN and EOI. Except for the DIO Data bus tests...

After amending program as pointed out by Dave_m in post 18, i get 3.14 volts on UA20 pin 10. This is NDAC out to IEEE-488 port at JI. all other readings were >4.0 volts. i ordered 3 MC3446 buffers from Littlediodes in UK for £11.99 each plus £1 postage which seems a good price to me. I have...

After inputting the above program, I get following results dav: 0 nrfd: 0 ndac: s/b 0 is 1 atn: no transition detected dio: in = 0 out = 255 : 11111111 in = 1 out = 255: 11111111 and so on in = 2,4,8,16,32,64,128,255 out is always 255 followed by same eight 11111111 Computer is 8032. It...

Hello to VCFED. I have been reading the posts about Commodore Pet and the fantastic help given to members who need help. We first started using a Pet in the 1980's running an accounts preparation program called Auditman. This program was supplied by Computers Services Midlands (CSM) in...

https://archive.org/details/1980-03-compute-magazine/page/n93/mode/2up?view=theater see above link for a description of Rabbit, used to speed up cassette loading etc. Adko has already posted above information. Michael