What could cause IC failure

[mrr19121970]

I picked up a eBay deal cheaply (36gbp):

A). VIC-20, 9v PSU, PET style datasette, VIC-1111 16kb expansion, RF module, joystick, 13 cassettes, handbook
B). VIC-20cr without badge, untested

The A VIC was declared and working, but seemed to turn itself off from time to time. This unit seems to have a dodgy on/off switch that makes a 'crackling' sound, that I assume needs to be desoldered, stripped and cleaned.

The B VIC powers up to cyan border and white screen. For me this is is described on Ray's page as:

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UE11		901486-01	ROM	BASIC
  Startup screen with borders but no characters. Disk commands do not 
work, but game carts still work.

I don't actually have a cart to test/prove this, but my question is what could cause the failure of the BASIC ROM? I've googled abit an I am not really any clearer here.

Any tips or suggestions?

[ken]

the most common failure I find when working on a vic20 is UE11then UE12 then memory
and for some strange reason I have found that the reset circuit on some are really flaky and needed repair , stuff like 10 to 20 second boot time

[mrr19121970]

Thanks for the reply Ken, how do you replace the ROM? With an original (used or new-old-stock), or an EPROM chip?

[ken]

it all depends , I usually replace with a pull from a parts machine , or replace with jiffydos
but UE11 and UE12 and (UD7) can be replaced with a eprom , with the use of a adapter
all depends on how you want to vic20 to look

[eslapion]

I can burn a kernal replacement on a MCM68764 which is a direct drop-in replacement for the ROM for 7$US.

There have been people selling exact replacement for the power switch since the same one is used on the VIC-20cr, C128, C64, 1541-II, 1581 and C64c.

[mrr19121970]

I PMed you for more details

[eslapion]

Any circuit exhibiting a temperature above 60C can suffer a substantial reduction in lifespan. The most vulnerable chip is the 6560, especially in older 2-prong VICs which have the voltage regulator inside the computer.

The 2364 ROMs used in PETs, VIC-20, C64, 1541 drive and SX-64 computers use energy inneficient NMOS technology so they consume a lot of power and dissipate lots of heat.

[mrr19121970]

...
The A VIC was declared and working, but seemed to turn itself off from time to time. This unit seems to have a dodgy on/off switch that makes a 'crackling' sound, that I assume needs to be desoldered, stripped and cleaned.

I desoldered and cleaned the soot out of the switch and used silcone spray to 'oil' the the plunger and refitted. Didn't cure the issue, strange crackling still (no smell of ions or burning). Shorted the switch with crocodile clip. Still went off and on, crackled (from what I assume is the 5v converter). Wife watching TV, so lights were dimmed, then I saw the sparks. Fuse. Removed & cleaned, and applied a little pressure to the contacts. Now all good on the 9 volt machine.

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

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Early VIC20 computers have a rather high input current and you need to
make sure the fuse is tight in the fuse holder. If it's loose in the clips,
the fuse and socket will get hot from the slight bit of resistance in the 
contacts. The resulting B+ voltage may be too low to run the computer 
properly and the fuse may eventually open due to the heat. Make sure the 
clips are clean of dirt and corrosion, and squeeze them together to make a 
tight fit before the fuse is installed.

Waiting for my new ROMs from elaspion.

[mrr19121970]

The 2364 ROMs used in PETs, VIC-20, C64, 1541 drive and SX-64 computers use energy inneficient NMOS technology so they consume a lot of power and dissipate lots of heat.

The 9v VIC is on now, idling. I can confirm hot (not burning) to touch. I'll heatsink these too.


KERNAL 39 degrees C
BASIC 36 degrees C
6502 29 degrees C
VIC 34 degrees C
CIA 2x 29 degrees C
CHARACTER 36 degrees C

[ken]

if getting a kernal , you want to get the correct NTSC or PAL version for your vic20

[mrr19121970]

PAL is ordered

[mrr19121970]

nothing

[Mike]

KERNAL, BASIC, 6502, VIC, [V]IA, CHARACTER < 40 °C [...] I'll heatsink these too.

At these temperatures, heatsinks are unnecessary, useless at the best. If anything, they just add heat capacity near the chip dies and so keep the ICs warmer even longer after the computer has been switched off. That doesn't mean the engineers at CBM actually didn't do anything to get excess heat off the ICs, most prominently the VIC: big ground plates in the PCB and the RF case also conduct away the heat over the chip pins. Witness the difficulty of any solder job on or near the RF case.

Another mechanism of chip failure hasn't been mentioned here thus far, and this one is mainly independent of temperature (cycles): moisture creeping into the chip packages in conjunction with poor die passivation. That will let the chip just rot from the inside.

[eslapion]

if getting a kernal , you want to get the correct NTSC or PAL version for your vic20

I made sure to ask for the exact part no to replace.

At these temperatures, heatsinks are unnecessary, useless at the best.

I second that. But in the early generations of VIC-20, I'm used to measure the 656X at close to 60C after an hour of operation. A heat sink is definitely recommended at that temperature.

My temperature acquisition method involves using a thermocouple with the case closed to avoid involuntary venting.

Another mechanism of chip failure hasn't been mentioned here thus far, and this one is mainly independent of temperature (cycles): moisture creeping into the chip packages in conjunction with poor die passivation. That will let the chip just rot from the inside.

I didn't know that one.

[mrr19121970]

No here is a dillema. 3 people 3 opinions:

Ray Carlson = yes

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

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It's advisable to install a heat sink on any IC that normally 
runs hot to make it last longer. The BASIC ROM next to the Kernal also runs 
pretty hot but I've yet to see one of those fail. That said, a heat sink is 
cheap insurance. 

Mike = No

At these temperatures, heatsinks are unnecessary, useless at the best.

elaspion = Maybe

I second that. But in the early generations of VIC-20, I'm used to measure the 656X at close to 60C after an hour of operation. A heat sink is definitely recommended at that temperature.