What could cause IC failure

[Mike]

In any case, U14 and/or U15 (both are 2Kx8 6116 SRAMs) in your CR VIC-20 then are likely the culprits.

I desoldered my U14 and U15 now. Sockets will be fitted tomorrow with the 40 pin sockets too.

I am right buying this? x2 ? (and maybe some spares for the future too). Alternative here

The RCA CDM6116AE3 should work, however I tried to find a confirming data sheet and didn't succeed.

The HM6116P-4 you pointed to as alternative definitely does the job. It's the same type I had fitted in my VIC-20 before I did the aforementioned VFLI mod.

[mrr19121970]

2 sets of 3 bought then. I have spares too. Thanks.

[mrr19121970]

Top tip Mike. This baby also seriously needs the s-video mod too. Here are the bad chips and my desoldered and socket in job. I am very proud.

[mrr19121970]

new memory chips arrived today. plugged in, still does not work. same symptoms as before

[mrr19121970]

Thanks to @Mike for your friendly and detailed mail about RAM and checking the traces. Sorry, I didn't have time to try what you suggested. I was fixing a C64 at the weekend, that had a CIA2 and 7406 logic chip issue (waiting on spares, but I guess this is fixed). This lead me to the thought, what if the VIA is holding something down? Remember my issue is white screen/cyan border. Avengers works. U14, U15, UAB1, UAB3, UB7, UD7, UE11, UE12 & UE10 all tested in another machine. So now this is what I tried:

Remove VIA2 : White screen, Cyan border
Remove VIA1 : White screen, Cyan border + CBM BASIC (no cursor)

Replace chips : White screen, Cyan border

Remove VIA1 : White screen, Cyan border + CBM BASIC (no cursor)

Replace chips (Swap VIA1/VIA2) : White screen, Cyan border + CBM BASIC with cursor <--- It works.

But the question is why? again a 7406 logic chip? I have the C64 test harness and diagnosis cart - but nothing on the VIC. How can I test? Update I connected SD2IEC and did a LOAD "$",8 - machine hung. SD2IEC didn't respond to userport reset either

http://personalpages.tds.net/~rcarlsen/ ... /vic20.txt

UAB1 6522 VIA INTERFACE, KEYBOARD-SERIAL
Startup screen normal, but no cursor. Keyboard doesn't work at all.
Partial failure: some keys "stuck" or don't work... may be a whole row
or column. Also may cause serial port (drive access) problems. Can
produce blank screen if shorted (remove to check).

UAB3 6522 VIA INTERFACE, JOY-USER-SERIAL-CASS
Startup screen normal, but drive access problems ("SEARCHING FOR... "
forever). One or more joystick positions don't work. No cassette or user
port access. Can produce blank screen if shorted (remove to check).

UB4 7406 LOGIC
Normal startup screen. Serial port (disk drive) access problems.

[mrr19121970]

Maybe I dreamed only about testing the VIAs in another machine?

The VIA1 is dead.

Case closed. Another VIC-20 saved from the landfill. Now I need to source a 6522, does it have to be MOS or can I take Rockwell too?

Update

Seems not without tinkering with PIN21 https://www.youtube.com/watch?v=BX_mTl3EiYM

[srowe]

Now I need to source a 6522, does it have to be MOS or can I take Rockwell too?

Rockwell 6522s are fine, when mine failed in the 1980's that all I could get. Still working now.

I think most other manufacturers should work as long as the IRQ/ is open-drain.

[mrr19121970]

How would I know if it is open drain? What's on your chips? There are loads of examples

R6522P
R6522AP
R65C22P2
R65C22P3

[srowe]

How would I know if it is open drain? What's on your chips?

The datasheets usually make it quite clear what the properties of the IRQ/ line are.

I've got a pair of R6522Ps, 1984 date codes.

[mrr19121970]

Thanks, this also confirms what i read here

On a slightly related note, the issues in GadgetUK164's video with Rockwell chips, I can't say I've had any problems. I've tested this on a VIC20 with a Rockwell R6522P, and they are fine, as expected. Also tested with the original CPU (a standard MOS 6502) and a Rockwell R6502P.

Update: As requested, I've also checked the Rockwell R6522AP, which is just their version of the MOS 6522A, which is a faster speed graded version of the MOS 6522.

I ordered 5x for 11 euro incl postage to have some spares. http://www.ebay.de/itm/171907254091

[eslapion]

How would I know if it is open drain? What's on your chips? There are loads of examples

R6522P
R6522AP
R65C22P2
R65C22P3

See:
http://www.westerndesigncenter.com/wdc/w65c22-chip.cfm

W65C22S/W65C22N Differences

•The W65C22S is lower power, faster and direct drive outputs with no current limiting resistors on outputs ports.
•The W65C22N is plug replacement of NMOS 6522 devices with current limiting resistors on output ports.
• The W65C22N does not have bus holding devices on the input, IO pins.
•The W65C22N IRQB is an open drain output that CAN be Wire-ORd, unlike the totem-pole output of the W65C22S (some customers have had to use a diode in series with the IRQB output when using the W65C22S in their systems that had Wire-ORd interrupts).

I could be wrong but I believe the difference is the same between Rockwell's R6522 series and R65C22.

[srowe]

I could be wrong but I believe the difference is the same between Rockwell's R6522 series and R65C22.

The datasheet I've found for the R65C22 says the IRQ/ line is open drain.

[mrr19121970]

Does anyone have any ideas how a dead or dying VIA1 would allow the screen/border to be displayed but stop loading/displaying char/basic roms?

Ray Carlson had no explanation.

[eslapion]

Does anyone have any ideas how a dead or dying VIA1 would allow the screen/border to be displayed but stop loading/displaying char/basic roms?

Ray Carlson had no explanation.

I suppose it could bog down the databus or part of the address bus.

I had a SID do that last year. It actually caused a black screen on a C64.