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Commodore 3016 scrambled screen

>>> Or i am doing it wrong..

No idea, unless you post the commands you are using and tell us what you don't think is working 😀...

Dave
 
Use the commands:

POKE 59426,n

Followed by:

PRINT PEEK(59424)

The POKE will output an 8-bit binary pattern to port B of the 6520. You can check the value of the bits on the 6520 port B with a multimeter or logic probe.

The value of n is in the range 0 through 255 corresponding to all of the combination of bits in a byte.

I would suggest using the individual values of 0,1,2,4,8,16,32,64,128,255 because they test each bit out individually.

You should see these bit patterns as voltages on port B of the IEEE488 6520.

You should also observe the same value back from the PEEK.

By the way, don't have anything plugged into the IEEE488 port whilst you are performing this testing.

If the outputs on port B of the 6520 work fine, it is probably a buffer (or three), but we can test these as well using the same POKEs and PEEKs...

Dave
 
It is starting to look like the 6520...

I would try a few other signals to make sure just before we call it.

 Dave
 
If you need the MC3446 port IC's there are (were) some excellent vintage new old stock ones for a good price at SH-Halbleiter in Germany.

Their website though has been under editing for a while, I'm concerned they might have closed. They have a massive array of vintage IC's & transistors. I bought a stack of TTL IC's with early 70's date codes from them and a number of rare parts.

In any case, here is their email:

info@sh-halbleiter.de

 
Hello,

Unfortunately my 4016 has stopped working. There is no screen.
CPU is OK. Pettester has all G's on screen. When i use the Diagnostic Clip there is a message A8-ADR BAD
Checked the 2114 and the dram's. Those seems to be ok.
 

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Address line A8 is faulty (stuck high, stuck low, ...).

Is the PETTESTER you are using mine or not? My PETTESTER screen should not be sat at a screenfull of G's - unless something has failed.

If it is an address line A8 fault, a NOP generator would be a good way to check the address lines out.

Dave
 
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