Denial

CR VIC20. Sometimes it starts fine, 3583 bytes free, when I power on. Other times there seems to be a video signal but all black, like it is not coming out of reset. Seems to go in phases - starts every time for a while, then not at all for a while. Any ideas what to look at? When it is working seems to be perfect - nice video quality

I have the same problem. Curious to know what it is as well.

Do any of you 2 guys have a reset button ? See if pressing it will start your VIC.

I suspect the 555 is no longer doing its job properly. Sometimes it can be caused by the chip itself but most often by the large capacitor attached to it.

I have a memory expansion with a reset button - can try that.

Yes - pressing reset button on the memory expansion does 'boot' the VIC-20, so I guess there is something funny going on with the 555 timer circuit, as you say.

Same thing here, the reset button gets it working.

I'm learning a lot about the VIC this week

Well, that was easy enough!

In both cases the 555 is longer doing its job either because of the chip or, more likely, because the electrolytic capacitor is dead.

I have two VIC-20s that need attention - a PET-style keys machine which is consistently slow to reset and this CR machine which sometimes resets fine (and quickly too) but then has phases of not wanting to reset at all on power up. I guess I should put in an order for some capacitors.

Yes, Change the capacitor next to the 555. I had 2 Vics that were slow to start and that fixed them. Both 1uf capacitors in each VIC-20 were the same make and colored orange. I also had one VIC-20 with the 1uf orange colored capacitor on the VIC-1 sound output that was bad causing low volume.