Top of the pile

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atari030
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Joined: Mon Feb 12, 2018 12:43 pm

Re: Top of the pile

Post by atari030 » Sun Apr 15, 2018 6:00 am

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.

atari030
Posts: 62
Joined: Mon Feb 12, 2018 12:43 pm

Re: Top of the pile

Post by atari030 » Sun Apr 29, 2018 7:19 am

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?

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exxos
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Re: Top of the pile

Post by exxos » Sun Apr 29, 2018 11:29 am

Have you scoped the colour out from tia? Possible bad switch yes... Easy to remove and link over for a test..
https://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxoshost.co.uk/atari/store2/ - All my hardware mods for sale - Please help support by making a purchase.

atari030
Posts: 62
Joined: Mon Feb 12, 2018 12:43 pm

Re: Top of the pile

Post by atari030 » Sun Apr 29, 2018 1:40 pm

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.

atari030
Posts: 62
Joined: Mon Feb 12, 2018 12:43 pm

Re: Top of the pile

Post by atari030 » Sun Apr 29, 2018 2:53 pm

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.

atari030
Posts: 62
Joined: Mon Feb 12, 2018 12:43 pm

Re: Top of the pile

Post by atari030 » Sun Jun 10, 2018 2:38 am

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.

atari030
Posts: 62
Joined: Mon Feb 12, 2018 12:43 pm

Re: Top of the pile

Post by atari030 » Tue Jun 12, 2018 1:01 pm

The MegaST PSU arrived. Looks like the board has a 5v short. Dammit.

atari030
Posts: 62
Joined: Mon Feb 12, 2018 12:43 pm

Re: Top of the pile

Post by atari030 » Sun Jan 19, 2020 11:59 am

Back to it....

I got sidetracked fixing and modding some A500's. :shock:

I bought an STe mainboard on a whim and its proved to be a bit of fun playing with it and that's peaked my interest again. I need a PSU and case bottom for it an she'll be back up and running after today's effort. I found an SMD-300 I had ripped out of an old PC, which was handy. I wanted a platform to mod and I only had one STe. Luckily I had one of the MC68HC000 CPU's as the original CPU was getting a bit hot. I'll have to order another now.

I recapped my STE PSU as it played up when I used it to test the new board and what a difference. System is stable and the picture is much better. The resistor is still pretty hot but it highlights how much of a difference it can make.

Turns out all my Mega PSU's react the same way on any ST/FM/e/Mega board, fan just stutters and stops, stutters then stops etc, etc. I'll just replace the guts with a better board. Next trick is repair the ram fault on my Mega4 once that is done.

And the old 130XE is a basket case. With the RAM disabled and/or a diag cart it just brown screens after replacing all the main IC's. I'll need more than a rainy afternoon for that one.

The 2600jr is still sitting on the same shelf.

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