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Attempting Intellivision repair


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Long story short, I narrowed down to the transformer. After popping the RF shield off and seeing a very clean board, I did a volt test. It's only getting 10.85 volts to the supply board. Then I started to check the ribbon connector. The first pin, if I recall, was fine. The next 2 were under the normal voltage. Before I could test the last pin, the transformer got hot enough to smell and I shut it down. The only thing that was warm on the supply board was the smaller of the 2 large caps. Right now I'm looking around on eBay for either a transformer or parts system.

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Scored a Partstellivision off eBay and it arrived yesterday. I swapped out the transformer and within 30 seconds, a small cap blew. So I swapped power supplies and so far, nothing burning up. The picture on channel 3 is scrambled lines while channel 4 has multicolored snow. I am open to suggestions on what to tinker with next.

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If not done already, have you checked to make sure the voltages to the 7805 and 7812 are correct and that both are outputting correct voltage? I believe on my Sears (Basically a 2609), that I had +10 going into the 7805 and something along the lines of +24 into the 7812. I've since swapped both out with comparable DC/DC converters but obviously the if the incorrect voltages aren't getting where they should it would prevent or take out the regulators affecting everything else downline of that.

 

As suggested, checking the voltage at the ribbon cable on the game PCB side will help determine this.

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Then at this point besides the small cap that blew on the power supply board, it has to be something in the logic on the main PCB. But I wouldn't know where to start exactly. I've tinkered with my Intelly a few times in that I did a cap kit on it and modded it for comp video, but nothing else.

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Tested 5 so far. The cart contacts so far are still shiny. I also sprayed a little bit of contact cleaner on the cart plugin and bent the pins down just a hair.

Have you checked the voltages at the board? Do all the ribbon pins and blue wire have continuity? Is the blue wire with the 2 pin Molex connected properly? Do you get a screen flash when you press reset or nothing at all?

Edited by HunterZero
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It sounds like you're working on an Inty 1. In case this helps someone else, I've built an Eagle schematic for the Inty II power board as it doesn't appear to be present in the service manual. I'm pretty certain that it's complete and correct, save for two specific items. I've made notes on the schematic detailing them.

Inty_II_Power_Board.zip

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That's definitely not right. You should be getting +5.6V from the wire connected to the 2-plug connector. According to the service manual, the voltages on the 5-wire ribbon cable should be, in order: +5V, +12V, +16V (unregulated), 0V (GND), -2.1V.

 

It looks like the cap that blew is C11 on the schematic. The Mattel service manual lists it as 0.22uF and the Sylvania one lists it as 0.1uF. I can't tell from your picture what the code on the blown cap says to be able to decode it. That said, that particular cap doesn't have anything to do with what you're getting out of the 2-pin connector: it's on the circuit that outputs +12V.

 

I would take a very close look at the transformer and switch assembly. My gut tells me that you've got a short in the switch. It's a triple-pole, single-throw switch. Off the top of my head it looks like a short between S1-C and one of the other two poles could cause you to see an overvoltage on the 5V/-2.1V part of the power board. The fact that you're not getting 16V on pin 3 of the ribbon connector also makes me suspect that the 12V/16V part of the board is losing current from a potential short in the switch or somewhere along that pathway.

Edited by JohnPCAE
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The "16V unregulated" reads about 22-25V without load IIRC.

 

Did you check voltages coming from the transformer? You should get:

 

Yellow Lead to Blue Lead - 18 VAC

Green/Yellow lead to any Green - 9.25 VAC

Green Lead to Green Lead - 18.5 VAC

 

No flash on reset means the STIC is not working. If you have a spare you could try swapping the STIC.

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No obvious issues visually with the board? Scorch marks? No broken small caps? Check the driver transistors near the CPU and electrolytics (although in my experience the SHOEI caps are quality and hold up well).

 

If you have a logic probe or scope you can start checking for clock/data pulses on IC pins. Since you have spares, try resocketing or swapping the CP1610, RA-3-9600 SRAM and PROM/SROM. Check the sockets themselves are good too.

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