PET / IEEE-488 interface woes

[SiriusHardware]

I know folks who ordered MC3446 from Cricklewood in the UK in the last couple of years, when they were first ordered they were about 4 GBP each, then the next time about 6 GBP each. While all the MC3446 devices ordered from Cricklewood worked, it may be useful, and cheaper, to try to diagnose the health of all three of your original MC3446 ICs first.

Remove them all in one piece, fit them in sockets and move them around to see where any faults indicated by the diagnostic programs move to when the chips are moved around. You could find that you only need one or two replacements.

 

[Hugo Holden]

I get most of my harder to find vintage IC's from S-H Halbleiter . I just landed some MC3446 IC's as spares for my PET, original Motorola parts with 83 date codes. Halbleiter stock a large range of vintage semiconductors & IC's.

 

[mch]

I get most of my harder to find vintage IC's from S-H Halbleiter . I just landed some MC3446 IC's as spares for my PET, original Motorola parts with 83 date codes. Halbleiter stock a large range of vintage semiconductors & IC's.

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 dealt with them before and recommend them.

 

[SiriusHardware]

Wow, that's quite a high price but may be worth it if they are the real thing.

The ones from Cricklewood have crept up a little more but are not quite as expensive as the ones from Littlediode at the time of writing this (Start of September 2022).

Integrated Circuits Base Numbers Beginning With M | Cricklewood Electronics

Visit Cricklewood Electronics for Professional CCTV Systems that give full security to the homeowner. We offer high quality Home Security CCTV Systems.

www.cricklewoodelectronics.com

 

[Hugo Holden]

Wow, that's quite a high price but may be worth it if they are the real thing.

The ones from Cricklewood have crept up a little more but are not quite as expensive as the ones from Littlediode at the time of writing this (Start of September 2022).

Integrated Circuits Base Numbers Beginning With M | Cricklewood Electronics

Visit Cricklewood Electronics for Professional CCTV Systems that give full security to the homeowner. We offer high quality Home Security CCTV Systems.

www.cricklewoodelectronics.com

The ones from Halbleiter are only 5.95 Euro which is about 5 GBP and they are vintage stock that Halbleiter have, they are not resellers., so they are better value than little diode parts. And fairly close in price to the Cricklewood ones.

 

[dave_m]

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.

OK, that did not bring out a problem.

Let's try again. Delete the STOP you put in at line 330.
Add a stop at line 360

360 if ndac = 1 then print"s/b 0 is 1":stop: goto 400

Check the voltages at UB16 pin 39, UA20 pin 11, UA20 pin 10, and UA20 pin9. They should be Low but but if UB16 pin 39 is High, then the UB16 PIA may be bad. If pin 39
is Low and any of the others is High, then UA20 the MC3446 may be bad.

 

[mch]

OK, that did not bring out a problem.

Let's try again. Delete the STOP you put in at line 330.
Add a stop at line 360

360 if ndac = 1 then print"s/b 0 is 1":stop: goto 400

Check the voltages at UB16 pin 39, UA20 pin 11, UA20 pin 10, and UA20 pin9. They should be Low but but if UB16 pin 39 is High, then the UB16 PIA may be bad. If pin 39
is Low and any of the others is High, then UA20 the MC3446 may be bad.

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, all the other tests are short and are very similar in nature and easy to input (e;g. NDAC test has only 9 lines.)
After you finish the NDAC test just do CURSOR UP and make a few changes to the code previously entered to carry out the DAV test, and do the same for NRFD, ATN and EOI. So it will not matter that you might not be able to save your test program as you can do these tests in a few minutes. You can print out the complete test on one page.

There are links to this book on this site.

 

[Hugo Holden]

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, all the other tests are short and are very similar in nature and easy to input (e;g. NDAC test has only 9 lines.)

That is a good suggestion to all those with the PET. I looked on ebay and there are a number of copies there too, so I bought one because I'm fond of paper books.

 

[mch]

That is a good suggestion to all those with the PET. I looked on ebay and there are a number of copies there too, so I bought one because I'm fond of paper books.

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 use the 6522 chip for either input or output.. NRFD uses 6522 for both input and output. So on replacing the 6522 chip the SD2PET loaded perfectly. I was amazed. Thanks to Dave=m for his code to test the IEEE 6520 and all our other experts.
Amazon have a copy of the Osborne book for sale at £936 and will deliver to Ireland. I think Hugo is right about paper books but I will wait for a better price.

 

[Hugo Holden]

There are a good number of the books on ebay for reasonable prices.

I'm glad you found the fault.

I had a keyboard PIA failure in my PET where it was like a ghost typing on the keyboard. It was unusual, more interesting than a dead IC, so I didn't throw it away, I put a label on it saying "Ghost Writer". Maybe I will put it back in the PET one day for an unusual fault Demo and see if it will type out the next week's Lotto numbers.