c64 - ASSY 250425 Black Screen

Got an issue?
dpalmeira
Member
Member
Posts: 31
Joined: Sat Apr 16, 2022 11:03 am
Contact:

Re: c64 - ASSY 250425 Black Screen

Post by dpalmeira »

Hi banman, these docs are really helpful. I'll review these signals and compare with my working machine.

Repair and soldering video also is awesome! Great explanation, thank you so much.


banman
Member
Member
Posts: 290
Joined: Sat Jun 15, 2019 12:21 am
Contact:

Re: c64 - ASSY 250425 Black Screen

Post by banman »

Hi dpalmeira,


No worries.i hope it helps you.

Please let us know how it goes with you investigations. I will post more stuff I find.
I know the work is slow and tedious. There is no real rush really.

Keep your eye on the power switch. They can be very tricky.


TheRetroChannel
Member
Member
Posts: 2
Joined: Mon Aug 15, 2022 10:13 am
Contact:

Re: c64 - ASSY 250425 Black Screen

Post by TheRetroChannel »

Hey dpalmeria, I noticed you mentioned this a couple of posts back

"During the ICs pull of process always the pin 15 (S/LUM) of VIC II chip remains LOW (no signal)"

This doesn't seem right, and I think Adrian even mentions it in the video above the banman linked (although it may have been another recent one of his). The VIC-II should output a sync and white line regardless of what else is happening on the left half of the board. For example removing the PLA, MPU, SID etc will still result in a sync signal from the VIC-II.

I would be looking closely at the VIC-II. Does pin 14 (colour carrier) look correct? You may want to also the trace the output of pin 15 to make sure it is making it to the RF modulator. I think it goes through a ferrite bead and ends up at pin 2 (2nd from the right) of the RF modulator. Perhaps the luma/sync output is being held at ground by something, could even be something inside the RF modulator itself
banman
Member
Member
Posts: 290
Joined: Sat Jun 15, 2019 12:21 am
Contact:

Re: c64 - ASSY 250425 Black Screen

Post by banman »

Hi TheRetroChannel,


I like your YouTube channel!

I am leaning towards the idea that it is a broken track or a short on the PCB board. Maybe as you say in the RF modulator section.
dpalmeria has mentioned that all his main IC chips are functional. He tested them in a known good working C64.
TheRetroChannel
Member
Member
Posts: 2
Joined: Mon Aug 15, 2022 10:13 am
Contact:

Re: c64 - ASSY 250425 Black Screen

Post by TheRetroChannel »

Thanks banman. Yeah I agree there is possibly something wrong with the board. The VIC-II is not working correctly in it, and there's little point looking at the rest of the board until this part is figured out.

dpalmeira, I know you've checked the 12V regulator but have you also confirmed that 12V is making it to pin 13 and 5V to pin 40 on the VIC-II? It's very odd that the system appears to be mostly running but there's nothing on sync+luma. Can you post some pics of the underside of the board - specifically around the VIC-II and RF modulator area?
banman
Member
Member
Posts: 290
Joined: Sat Jun 15, 2019 12:21 am
Contact:

Re: c64 - ASSY 250425 Black Screen

Post by banman »

Hi dpalmeira,


I don't want to go on like a broken record..... I would like to retouch on the subject of the power switch not making correct contact and for that matter the wipers of the IC chip sockets too.

These can be a big source of issues. Especially when working with very old electronic devices like the C64.

I myself had a bad experience with a power switch that wasn't making good contact. All the voltages on the board tested okay yet I wasn't getting any video output. Only after pulling everything off the board did I realize the power switch was the problem. Evidently there was insufficient current to satisfy the start up requirements.

To further illustrate this Adrian had encountered a very similar situation in this video.



And again a problem with physical connections between components and the PCB board....

Post Reply Previous topicNext topic

Who is online

Users browsing this forum: No registered users and 0 guests