Black Screen C64
 
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Black Screen C64

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(@robert-cadena)
Active Member Customer
Joined: 9 months ago
Posts: 8
Topic starter  

Howdy, 

I bought a c64 a while back and am trying to trouble shoot it, so I bought a Dead Test Cartridge ( https://diychris.com/product/commodore-c64-128-diagnostic-dead-test-cartridge-v1-1/ ) from Chris here and I'm getting odd results.  

Summary:

Real quick, without a cartridge the screen is black. With a cartridge, it sometimes immediately powers up to a pink color, sometimes orange, or a scrambled looking purplish color and a loud buzzing noise other times it powers up black (with noise). 

First Steps

First, an initial description of the symptoms and a quick troubleshooting I did before the dead test stuff.

First, I tried measuring voltages across the power rails and all the readings are as expected.

Fuse looks good.

I bought a new power supply ( https://www.amazon.com/gp/product/B086Z1ZWF2 )

RCA connector ( https://www.amazon.com/gp/product/B00M0FXP64/ )

And AV->HDMI converter ( https://www.amazon.com/gp/product/B0BQ6284ZD/ ) so I can try it on my Dell monitor.

But, I'm also testing the AV cable straight into the back of a Roku which has AV inputs and which I've made sure can handle PAL and NTSC by using another device.

I've removed the SID chip, the PLA, the 2 CIAs and powered it on to see if the blue screen comes on. One at a time, independently and together.  No dice.

Black Screen

If I power it on, the screen is black.

With dead test, see videos, sometimes solid colors (none the blue I expect) I'm attaching one video first and then another in a subsequent message.

To be thorough, I've waited on the dead test for 15+ seconds (minutes in some cases) in case it started to flash or for the diagnostic screen to come up.  Nothing.  It either stays in a single color, or it goes black.  I'm basing my expectations of the dead test behavior on the manual here: http://c64.rulez.org/capac/portal/wp-content/uploads/hardver/dead_test/781220_Manual.pdf

Thanks in advance.

 


   
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(@robert-cadena)
Active Member Customer
Joined: 9 months ago
Posts: 8
Topic starter  

Here's another video showing the behavior described above.


   
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(@administrator)
Member Admin
Joined: 6 years ago
Posts: 9
 

If there was an issue with the RAM you would see white flashes almost immediately after turning it on if you have the Dead Test plugged in. The C64 will absolutely not turn on without the PLA.

The issues you are having sound like they could be PLA related.

Do you have another PLA to try with? If you do, you can leave out the SID and both CIA's.

You can also remove basic and character when testing with the Dead Test.


   
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(@robert-cadena)
Active Member Customer
Joined: 9 months ago
Posts: 8
Topic starter  

Oh yeah, I mentioned an AV -> HDMI converter but, I think it's a poor converter: it always displays No Signal, and none of the solid or scrambled behavior I see on the Roku.  Hooking up a device with AV output I know works to the converter also shows a very poor quality display, so I think I just got either a crappy converter or that brand just sucks.


   
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(@robert-cadena)
Active Member Customer
Joined: 9 months ago
Posts: 8
Topic starter  

@administrator hey Chris, thanks for the reply.  I don't have another PLA with me, sadly. Guess I'll have to order one from you. I actually sent you this board and you added new sockets and it worked for you.... I think maybe my old power supply may have messed it up after you sent it back =(


   
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(@administrator)
Member Admin
Joined: 6 years ago
Posts: 9
 

@robert-cadena I just looked back through my e-mail. Looks like when you sent me the board I couldn't find any issues with it but then I recommended replacing the caps and socketing some of the chips more prone to failure. It's certainly possible that your PLA may have died. I would also try to remove all the chips that are in sockets and put them back in to make sure they are all socketed correctly.


   
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(@robert-cadena)
Active Member Customer
Joined: 9 months ago
Posts: 8
Topic starter  

@administrator yeah, I just tried that and still no dice.  I stumbled on this site https://www.pictorial64.com/fault.htm?id=u17_12  and it's kinda cool that they post pictures of symptoms and possible causes.  Looks like a solid pink screen is a symptom of a bad PLA. 

Ordering one from you.  I see you have a chip https://diychris.com/product/commodore-64-pla-906114-01-replacement-gal-version-fully-assembled/ and a Frankenstein-replacement thing https://diychris.com/product/commodore-64-pla-906114-01-replacement-gal-version-fully-assembled/ ... which do you recommend or is there any diff?  

 


   
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(@administrator)
Member Admin
Joined: 6 years ago
Posts: 9
 

@robert-cadena Not sure what you're referring to when you say Frankenstein-replacement. Both of the links go to the same place. The GAL PLA is a suitable replacement. I also have 82S100 compatible PLA's which are exactly the same as the original PLA's except these weren't manufactured by MOS and so they don't have the high failure rate. I purchase these as blanks and program them myself. https://diychris.com/product/commodore-64-pla-906114-01/


   
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(@robert-cadena)
Active Member Customer
Joined: 9 months ago
Posts: 8
Topic starter  

@administrator oh sorry, I was posting that via the phone and didn't notice that I was pasting the same link.  By Frankenstein I meant the GAL replacement vs the chip.  Other than that the GAL is cheaper.  I guess I'll go with the cheaper option for now.  Appreciate all your help, particularly on a Saturday =p 

 


   
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(@robert-cadena)
Active Member Customer
Joined: 9 months ago
Posts: 8
Topic starter  

SUCCESS! 😎 

I received my replacement PAL from diychris earlier last week and finally had a chance to pop it in and test it out over the weekend and … yup, just a bad PAL chip. This one worked straight away. Managed to run the dead test cartridge which you can see in the image. 

ran the diagnostics and it complained about bad CIA and a bad SID but it seems to work fine so far. 

so, all good now thanks!

 

This post was modified 8 months ago by Robert Cadena

   
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