Colecovision Black Screen and Hum

[Ianr757]

I just got in a nonworking Colecovision that I thought I'd try and repair. Upon initial inspection, the console would power on, but the screen was black and there was a hum/sustained beeping noise every other power cycle. I tried the Atari expansion module and it worked fine, so I thought it was going to be either the RAM, VDP or both. Well, after replacing all RAM ICs using the 5v memory mod, and the VDP with a spare, it still has not improved. Any ideas of where to go next? Thanks!

[Ruggers Customs]

You check the cpu?  Normally I would say power supply first but I assume you've checked that already.

 

Black screen with a tone is either going to be your cpu and or the vdp most of the time.  

[Ianr757]

8 minutes ago, Ruggers Customs said:

You check the cpu?  Normally I would say power supply first but I assume you've checked that already.

 

Black screen with a tone is either going to be your cpu and or the vdp most of the time.  

Aha, I was leaning towards the Z80, just didn't know if it would make a difference since the expansion module works. Thanks for the tip! And yes, the power supply is just fine, so it must be the Z80. I'll swap it out and report back.

[Ianr757]

@Ruggers Customs Success, it's alive! Turns out the original VDP was fine, just the Z80 and maybe the RAM (which was going to be modified anyway). Thanks so much for the help!

[Ruggers Customs]

22 minutes ago, Ianr757 said:

@Ruggers Customs Success, it's alive! Turns out the original VDP was fine, just the Z80 and maybe the RAM (which was going to be modified anyway). Thanks so much for the help!

Awesome, good job!

[CrazyBoss]

if its the VRAM it will still give you a "boot screen", but it can have problems like wrong text or damaged graphics, not sure if the "main" ram is bad, for Colecovision (and all other tms99xx systems) its normaly the VRAM that goes bad.