Sick VIC

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sausage_toes
Vic 20 Newbie
Posts: 4
Joined: Wed Apr 20, 2016 11:17 pm

Sick VIC

Post by sausage_toes »

Poor VIC, he's done the technicolor yawn all over the front of his video screen.
Image

Typing blind disk commands has no apparent effect with a 1541 connected.

Jupiter Lander seems to work
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Keyboard input works with cartridge inserted. I've pulled the ROMs and re-seated them in their sockets, but it did not help. Any idea which chip(s) I should investigate/replace for a garbled screen but game cartridge working?

He's an older style VIC with the 2 prong 12 VAC power transformer, actual output seems to dip to 9 VAC under load with VIC switched on.
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Assembly No. 324003 1981 COMMODORE INTL

The large capacitor near the power regulators is showing sings of corrosion. Looks like a 4700 mic 16v axial electrolytic, does anyone know the mouser or digikey part no replacement for these?

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Also need to know the correct size, voltage and amps for this fuse, again a vendor part number if you know it.

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srowe
Vic 20 Scientist
Posts: 1325
Joined: Mon Jun 16, 2014 3:19 pm

Re: Sick VIC

Post by srowe »

Welcome to the forum.

From Ray Carlsen's excellent repair guide

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

The first suspect is
UB7 6560-101 VIC VIDEO/AUDIO
White or blank screen, garbled or no video, screen full of (or few
random) "garbage" characters. "Blind" disk commands may still work.
Partial failure: Dark or smeary image, loss of color, garbled or no
sound, game paddles or light pen doesn't work.
but if cartridge games work then I wonder if that's the case.

I'd certainly suspect the BASIC ROM

Code: Select all

UE11		901486-01	ROM	BASIC
  Startup screen with borders but no characters. Disk commands do not 
work, but game carts still work.
The large capacitor near the power regulators is showing sings of corrosion.
That's concerning, does it look like electrolyte has leaked? Is the can bulging? If it's failing/failed that could certainly cause damage to system.
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mrr19121970
Vic 20 Nerd
Posts: 873
Joined: Tue Jan 19, 2016 9:22 am
Location: Germany
Occupation: IT service manager

Re: Sick VIC

Post by mrr19121970 »

As I mentioned on Lemon64.com I really feel you will struggle without a working mainboard to test your ICs.
UB6 LM555 TIMER POWER-ON SYSTEM RESET
Will not reset on power up. May produce garbled or random screen
characters-graphics, or screen may start up "frozen". If drive resets
when computer is powered up, this chip is OK.

UB7 6560-101 VIC VIDEO/AUDIO
White or blank screen, garbled or no video, screen full of (or few
random) "garbage" characters. "Blind" disk commands may still work.
Partial failure: Dark or smeary image, loss of color, garbled or no
sound, game paddles or light pen doesn't work.

UC2 74LS04 LOGIC
Screen character colors incorrect (scrambled). If very bad, entire
screen becomes garbled with flashing characters, vertical bars and
random colors.

UE1-UE6 2114 or TMM314A SRAM MEMORY
Blank screen. Partial failure: less than normal "3583 BYTES FREE" at
startup, sometimes will produce "garbage" screen or screen freeze after
warmup. Shorted chips may get very hot. NOTE: UE1 is used to generate
character color.

UD7 901460-03 ROM CHARACTER
Startup screen characters missing (just blocks or flashing lines where
characters should be
) and alphanumerics missing from games. Game carts
that use mostly graphics characters may look normal while running.

UD8 and UE8 MPS65245 or MOS65245 or 74LS245 TRI-STATE LOGIC
Blank screen. Partical failure: garbled video or audio. see UB7
Did you try a userport reset with a 1541 drive attached?
Kakemoms
Vic 20 Nerd
Posts: 740
Joined: Sun Feb 15, 2015 8:45 am

Re: Sick VIC

Post by Kakemoms »

According to the Vic-20 Friendly Computer Technical Manual its a 4700uF / 16V Electrolyte capacitor..

I am trying to find out more about the ferrites that were used in the Vic-20, but they are all specified as "ferrite"... Not a very good manual.

Edit:
For a capacitor you can use this 4700uF 16V electrolytic from http://www.newark.com:

Manufacturer: VISHAY
Newark Part No.: 14M6694
Manufacturer Part No MAL213815472E3

Its slightly smaller but it will fit (original is around 37mm I think).

Edit: This is a better fit with 38mm length and 4700uF 16V:

Manufacturer: VISHAY
Newark Part No.: 04R7586
Manufacturer Part No MAL211815472E3

It also has a long lifetime (8000h) but at a cost..
sausage_toes
Vic 20 Newbie
Posts: 4
Joined: Wed Apr 20, 2016 11:17 pm

Re: Sick VIC

Post by sausage_toes »

Awesome working tracking that cap down thank you! However, @ $8.11 + $20 shipping is a bit steep, I'll have to keep looking for an alternative.

Kakemoms wrote:According to the Vic-20 Friendly Computer Technical Manual its a 4700uF / 16V Electrolyte capacitor..

I am trying to find out more about the ferrites that were used in the Vic-20, but they are all specified as "ferrite"... Not a very good manual.

Edit:
For a capacitor you can use this 4700uF 16V electrolytic from http://www.newark.com:

Manufacturer: VISHAY
Newark Part No.: 14M6694
Manufacturer Part No MAL213815472E3

Its slightly smaller but it will fit (original is around 37mm I think).

Edit: This is a better fit with 38mm length and 4700uF 16V:

Manufacturer: VISHAY
Newark Part No.: 04R7586
Manufacturer Part No MAL211815472E3

It also has a long lifetime (8000h) but at a cost..
sausage_toes
Vic 20 Newbie
Posts: 4
Joined: Wed Apr 20, 2016 11:17 pm

Re: Sick VIC

Post by sausage_toes »

User port reset? I assume there are pins to short for this?

With Carts working, I thought that would eliminate the VIC chip, RAM and TTL as suspects as I thought a Cart would only replace/mask the ROMs, is that not the case?
mrr19121970 wrote:As I mentioned on Lemon64.com I really feel you will struggle without a working mainboard to test your ICs.
UB6 LM555 TIMER POWER-ON SYSTEM RESET
Will not reset on power up. May produce garbled or random screen
characters-graphics, or screen may start up "frozen". If drive resets
when computer is powered up, this chip is OK.

UB7 6560-101 VIC VIDEO/AUDIO
White or blank screen, garbled or no video, screen full of (or few
random) "garbage" characters. "Blind" disk commands may still work.
Partial failure: Dark or smeary image, loss of color, garbled or no
sound, game paddles or light pen doesn't work.

UC2 74LS04 LOGIC
Screen character colors incorrect (scrambled). If very bad, entire
screen becomes garbled with flashing characters, vertical bars and
random colors.

UE1-UE6 2114 or TMM314A SRAM MEMORY
Blank screen. Partial failure: less than normal "3583 BYTES FREE" at
startup, sometimes will produce "garbage" screen or screen freeze after
warmup. Shorted chips may get very hot. NOTE: UE1 is used to generate
character color.

UD7 901460-03 ROM CHARACTER
Startup screen characters missing (just blocks or flashing lines where
characters should be
) and alphanumerics missing from games. Game carts
that use mostly graphics characters may look normal while running.

UD8 and UE8 MPS65245 or MOS65245 or 74LS245 TRI-STATE LOGIC
Blank screen. Partical failure: garbled video or audio. see UB7
Did you try a userport reset with a 1541 drive attached?
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mrr19121970
Vic 20 Nerd
Posts: 873
Joined: Tue Jan 19, 2016 9:22 am
Location: Germany
Occupation: IT service manager

Re: Sick VIC

Post by mrr19121970 »

Connect pins 1 and 3 with a 1k ohm resistor
Kakemoms
Vic 20 Nerd
Posts: 740
Joined: Sun Feb 15, 2015 8:45 am

Re: Sick VIC

Post by Kakemoms »

sausage_toes wrote: Awesome working tracking that cap down thank you! However, @ $8.11 + $20 shipping is a bit steep, I'll have to keep looking for an alternative.
Try ebay. Search for VISHAY capacitor 4700 16V. Numerous hits and maybe some of them are near you?
sausage_toes wrote:User port reset? I assume there are pins to short for this?

With Carts working, I thought that would eliminate the VIC chip, RAM and TTL as suspects as I thought a Cart would only replace/mask the ROMs, is that not the case?
I think he means that the drive is resetting when you switch on your Vic-20.

Kernal/Basic uses zeropage and first page memory a lot. So you could try with a Cart that uses the kernal to see if that's the problem (e.g low mem). No Cart masks the ROM, it can only occupy RAM1/2/3 and/or BLK1,2,3 and 5 areas (and in seldom cases IO2/3). Most Carts are 8KBytes and go into BLK5 ($A000-$BFFF).

In some cases its not the chips that are the problem, but the solder of the chips. Some Vic-20'ies had very poor soldering on their chips, so try refilling such poor solder points if you find them. I even had this problem with my 1084 monitor in which a solder had simply cracked (nearly impossible to see).

Poor soldering from manufacturer:
Attachments
Vic-20-poor-solder.png
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