Commodore 64 weird situation

[flaviosr]

Hello,

brief summary of the situation:
. 6510 ok
. VIC-II (6569R3) ok
. black screen
. with a "dead screen card" BLACK SCREEN
Any ideas?

Thank you very much

 

[rittwage]

It's not weird at all. Almost any fault in a C64 results in "black screen".

Always start with the PLA.

 

[flaviosr]

Shouldn't the card "turn around" a dead PLA?

 

[flaviosr]

Ok. The card cannot turn around a dead PLA...

 

[robert_sissco]

I have also seen (never personally experienced) where a faulty SID can cause this as well. Since the 64 can boot without it, and easy test would be to remove the SID chip and then try powering it on.

 

[RobertB]

I have also seen (never personally experienced) where a faulty SID can cause this as well.

That happened to one of my SX-64's. After Ray Carlsen replaced the SID, the screen was fine.

Truly,
Robert Bernardo
Fresno Commodore User Group - http://www.dickestel.com/fcug.htm
Southern California Commodore & Amiga Network - http://www.portcommodore.com/sccan

 

[robert_sissco]

That happened to one of my SX-64's. After Ray Carlsen replaced the SID, the screen was fine.

Funny, I learned of this on The 8-Bit Guy's SX-64 video. I mean he tested in a breadbin 64 and had the same issue so it isn't exclusive to the SX-64, I just find it funny that is where both were encountered.

 

[ClassicHasClass]

The SID in the SX-64 seems to be unusually vulnerable to damage. It can get fried by just plugging in a video cable at the wrong time (which is why I always connect an external monitor to mine with the power off) - I've blown a SID that way myself, and I've certainly heard of others.

 

[robert_sissco]

The SID in the SX-64 seems to be unusually vulnerable to damage. It can get fried by just plugging in a video cable at the wrong time

Good to know. I always do the same with any of my computers cause I thought it was common sense, but good to know that a common cause is found to try and avoid it

 

[rittwage]

That's the same on any C64. The SID is not protected in any way from external damage.

 

[flaviosr]

The PLA has been replaced with a good one (it was bad).
If I remove the SID the screen remains black.
I have discovered some issues on the 5V rails... the RAM does not receive the right voltage (something around 1.5). Just discovered and then I had to leave. Any suggestions on what to check?

 

[rittwage]

If not the power switch, something is pulling it down (short).

 

[flaviosr]

VR1 and VR2 are bad (this C64 is really a nightmare)... I have VR1 but I am missing VR2... I buy some of both and then I check again.

 

[robert_sissco]

VR1 and VR2 are bad (this C64 is really a nightmare)... I have VR1 but I am missing VR2... I buy some of both and then I check again.

I had a C64 where the video was bad due to a damaged RF modulator, a dead VIC, and a dead PLA chip, replaced all of that, had faulty RAM, 4 of the 8 chips were failing (it would boot but the memory was always short). FIXED that and then the keyboard started failing. The CIA chip had cracked traces under it, and this was on top of a broken ground pin on the edge connector on the user port. Someone dropped this one on the corner back by the user port (the case was smashed back there) so I think that explains the CIA and RAM faults, and the RF modulator was rusty inside (not sure how), but yea some of these boards can just keep throwing fault after fault.

I ultimately just bought a SixtyClone board of the same assembly number, desoldered all the chips, moved them to sockets on the SiztyClone and it has been a work horse ever since.

 

[gertk]

Another common fault where multiple chips are fried: a bad power supply.
Always check voltages from the supply before connecting it.