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Re: Top of the pile

Posted: Sun Apr 15, 2018 6:00 am
by atari030
I removed the 2600 AV mod and replaced with one based around the 2n3904 and no dice, still black and white. Looks like I need to replace the TIA. Win some lose some. I must say, it is nice and sharp though. I might do the same mod to my 2600 DV.

Re: Top of the pile

Posted: Sun Apr 29, 2018 7:19 am
by atari030
Well, that didn't go as planned. All my IC's arrived, changed out the Freddie, basic and Sally in the 130XE. Still red screen. Tried a BASIC cart as well, still red. Sigh. Time to invest is the syscart. Probably need to change out RAM, I'm betting.

My TIA also arrived, socketed and replaced that, no change. Replaced the 4050, no change. Checked resitor values from the TIA to 405, all appear to be correct. Next trick will be to check continuity, but, I think I'm chasing a red herring. If I switsh the B/W switch there is no change in the output, it is black and white. But, I do get a flicker of colour bleed every now and then. What I can't work out is how the BW switch actually works.

What I am starting to think is that either the BW switch is rooted in some way, or, maybe the colour bleed pot. Any idea's, Chris?

Re: Top of the pile

Posted: Sun Apr 29, 2018 11:29 am
by exxos
Have you scoped the colour out from tia? Possible bad switch yes... Easy to remove and link over for a test..

Re: Top of the pile

Posted: Sun Apr 29, 2018 1:40 pm
by atari030
I replaced the TIA, jumping the switch was a thought, I will do that in a sec. Googling around shows some interest in electrolytics which I am still investigating. The original mod I used was using a 3 variable resistor ladder, the one I just wired in was essentially this one;

http://vintagegamingandmore.com/installation-guide-jr/

Except, I soldered the components directly to the motherboard (I hate mess). Both mods produce black and white. I seem to recall that before I boxed this thing it was producing colour with the ladder mod, till I tried to tidy it up a bit more. Could be a coincidence. My memory of what I did is a bit hazy after so many years.

Re: Top of the pile

Posted: Sun Apr 29, 2018 2:53 pm
by atari030
The switch is just a switch, it seems. It isn't DPDT. Pins 1 and 2 are bridges, so pin 3 goes to ground when the switch is thrown. Now the 500k colour adjust trimpost has just committed seppuku. Next to replace........ I can't say I'm not learning anything about the 2600.

Re: Top of the pile

Posted: Sun Jun 10, 2018 2:38 am
by atari030
Bit of an update. Slow on the repair front lately.

I have a MegaST PSU on the way so I can start work on my 4MB model. I think I will install a Gotek in it rather than try and find a big button floppy. That should arrive on Tuesday.

I have replaced the Freddie and MMU in the 130XE, still no dice. I will have to either buzz it out or get a syscheck cart. Patience isn't a virtue I have, so probably buzz it out when I get time. THis one is proving to be a real tough nut to crack.

2600 Jr has progressed in that I am pretty certain the fault is in the PAL clock generator somewhere. I buzzed out the TIA and everything is where it needs to be. It could be a resistor, but I'd doubt it. Possibly the crystal, I think. I could have bought another 2600, but that's not the point. :)

Onwards and upwards.

Re: Top of the pile

Posted: Tue Jun 12, 2018 1:01 pm
by atari030
The MegaST PSU arrived. Looks like the board has a 5v short. Dammit.