Commodore 64, Powers on but no A/V

[sheath]

So I bought a Commodore 64 "as is" and loe and behold it won't display anything over Composite or Antennae, but the power light comes on.  I've checked everywhere over the last month and haven't found any tutorials for this particular problem.  Can anyone point me in the right direction?  I am fairly certain I bought the later model of the original C64.

http://www.ebay.com/itm/361470198150?ul_noapp=true

[eidis]

 Hi Sheath!

Judging by the provided link, you have an early C64. The most common faults are bad PSU, PLA and RAM. More info can be found in the following links:

C64
https://www.c64-wiki.de/index.php/c64

C64 CHIPS and COMMON SYMPTOMS 9-28-07.
http://cbm8bit.com/articles/ray-charlsen/article35

Keep the scene alive!
Eidis

[Hojo_Norem]

Judging by the provided link, you have an early C64. The most common faults are bad PSU, PLA and RAM. More info can be found in the following links:

The part of the PSU that usually goes bad is the +5VDC line.  It should be easy to test using a multimeter.  Another common failure is the fuse.  It's an old fashioned long style glass fuse rated at 2A (I think).  This is responsible for the 9VAC supply in the C64.  On the longboards (which will most likely be what's in your c64) the 9VAC gets rectified into a second +5VDC supply that feeds the SID and VICII and a +12VDC supply that also feeds the SID and VICII.  It also supplies the power to the datassette interface.  If the fuse blows then it will stop all operation.

On the shortboards (the found in the c64c), the VICII runs off the single psu supplied +5VDC supply, so if the fuse goes all it does is kill the sound and tape but the machine will otherwise power on and be somewhat functional.

One thing to note, if the 5v supply in the psu has gone bad then there is a good chance that it may have also fried the RAM.

We can advise more it you can give us a shot of the board inside your machine, or at least the part number printed on the PCB.

[sheath]

Thank you both, I checked the fuse and it looks fine, and the power light comes on.  I'll check the links to see if they have these exact symptoms.  All of the chips on the board are socketed like old bios chips, so if I just need to find a replacement chip or two I can do that too.  Thanks again, I'll give a progress report as I continue reading and troubleshooting. 

The C64 is supposed to have a start up screen without any tapes or carts loaded right?  I don't have anything to test it now.  Does it play a sound too?  Because I haven't heard any audio yet.

[ApolloBoy]

It's supposed to go to a BASIC prompt when it boots up, it won't play any audio unless you program it to.

[Hojo_Norem]

A dead CPU, VICII or PLA pretty much guarantee a black screen dead c64.  Dead ram may also, but I've heard of machines with faulty ram showing something at least.  I'm not 100% sure on the CIA's either.  Depending on which one, a dead CIA will either kill disk drive access or the keyboard and joystick ports.

You could try blind typing this program to generate some sound, if your are 100% certain that you have your audio connected properly (and for the SID's sake, only plug/unplug audio cables when powered off... or any cable for that matter.)

(BTW, the C64 by default starts in uppercase mode, so you don't need to hold shift or use shift lock while typing alphanumericals.  The program is a slightly cleaned up version of one found in the c64 user guide.)

10 S=54272
20 FOR L=S TO S+24:POKE L,0:NEXT L
30 FOR L=15 TO 0 STEP-1
40 POKE S+24,L
50 POKE S+4,129
60 POKE S+5,15
70 POKE S+1,40
80 POKE S,200:NEXT L
90 POKE S+4,128
100 POKE S+5,0
110 GOTO 30
RUN

[sheath]

I cleaned out the VIC chip's pins with rubbing alcohol and cleaned and blew out the connector, now I get a black screen instead of no signal.  So that's progress.  I'll use the guide above and hopefully find a board diagram online so I can clean the other chips that are known to cause a black screen.  Thanks for the program, I'll try that next to see if I get audio.

[eidis]

 Hi Sheath!

All of the chips on the board are socketed like old bios chips

Have you tried reseating all chips ? You might also try checking for continuity. It could be that somewhere is a broken trace.

Keep the scene alive!
Eidis

[sheath]

I haven't reset all of the chips, just the PLA and VIC.  The fellow from the UK who helped me is confident it is the PLA and shipped me another one.  I'm waiting on it to arrive.  Currently the machine powers on and displays a black screen.  I have a multimeter but don't know what to test with it.  I also got in this book that should help if I have any further problems.