C64 Black screen on power on

Wolfy

Away with the fairies...
AmiBayer
Joined
Jul 2, 2011
Posts
651
Country
UK
Region
Devizes, Wiltshire
I was given a breadbin 64 about 3 months ago that has the above issue.
To start off, it has a small tag attached indicating it has been to a repair center at some point...
Now it is still in it`s box so I am sorry for being vague, anyways, upon opening and visual inspection of mobo I noticed one of the ICs that sits horizontal as opposed all the other IC`s that sit vertical had it`s pin 1 bulging slightly, took out the IC and the leg had been bent up under the chip, streightened with care, replaced and still black screen...
(should have wrote down IC id...!)

Anyway, fast forward to now, and I have another working C64 :) so the question I would like to pose is... what order should I start swapping ICs?

Fankoo!
 
My money would be on PLA chip followed by VIC.

Pla is labeled 906114-01 and is at u17

The vic is at u19 and is probably the horizontal ic you found

Sent from my GT-I9100 using Tapatalk 2
 
Black screen means lack of signal from an important chip, regardless the computer.

On 64, PLA, VIC and CPU.

If you see garbage, then the most common problems are the on-off switch making bad contact (specially the 5V part) and one of the ROMs goes to digital heaven. Only then RAM chips.
 
Hmf.
Well C64 #2 actually turned out to have same issue as C64 #1 so I now have 2 of em with the same symptom.
(I shall learn to not get excited when someone says "it works" )

Anyway I have opened both:
C64 #1
Assy 250425
Majority of IC`s are socketed so removed one by one and cleaned the legs with IPA and reseated... and still black screen.

C64 #2
Assy 250407
Other than SID and VIC all IC`s are soldered direct onto board, so only removed and reseated these 2.
Upon power-up I was greeted by the bordered C64 screen but the inner area was black and the border was on first power up was purple, then second power up all black, third power up cyan border, fourth gave a fast flash of a full screen of yellow garbarge text on black screen then now just black every power up.
(I am of course not wildly toggling the power switch...)
When I had the coloured borders there was no text or suchlike on the screen.

I have not tried swapping the vic chips yet...
 
http://www.faime.demon.co.uk/retro/cbm.html

http://personalpages.tds.net/~rcarlsen/cbm/c64/

Both pages indicate that you may have a bad RAM chip. Turn the 64 on, leave it on for ten minutes with the cover open and check the temperature of the chips.

If one 4164 id abnormally hot, it is the culprit. Second suspect are the ROM chips.

Just after checking if those chips are not the culprits you can blame the PLA.

A good measure for 64 users is using some small heatsinks glued with thermal pads over the hot chips, even on Europe! That's mandatory for people living in hot countries as mine.
 
Thanks RKauer!
I was unsure if it was safe to leave on but will get round to taking apart the C64 that has shown most life (#2) and will follow advice of checking for hot ram chips.
 
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