Repairing a black screen of death on an Intellivision II?

[Akito01]

Thankfully I do have a replacement unit already, but I'm reluctant to toss out my previous console because the casing itself is in lovely condition and I just installed a completely new RF modulator in it.

 

How I managed to kill this unit was due to a misadventure while trying to mess around with the composite mod I had installed. Without knowing for absolute certain, I think what happened is that the top of the mod circuit (the bit where the +5v wire is connected, that runs to the +5v source on the daughter board) came into contact with the naked back end of where the power cord is inserted (I now use electrical tape, but before I just had a bit of card that must have moved out of position).

 

The fact that I was willing to mess around with the innards while the power cord was connected should be evidence of my ignorance, thus I come to the boards to seek feedback on what is the likely cause of the current black screen problem, and the most likely solution. I know it isn't the fuse, because that is clearly intact, and it seems to power on normally based on the red LED and the fact that it is giving a signal to the tv (even if it is a blank screen). The unit worked before, though the quality of the picture had been slowly getting worse over time -this lead me to replacing the RF modulator, which installed fine and clean, but the same black screen comes up regardless of old or new modulator. I'm assuming there is some bit on the daughter board that gave out, possibly a capacitor? That looks like a nightmare to replace given how tightly everything is packed in in there. Replacing the daughter board entirely seems like a potential solution, but this particular model of INTV II has the daughter board affixed to the mother board by a ribbon cable and definitely looks different in other ways to the daughter board I have in my new replacement unit, which is connected by pins and can be removed and inserted back very easily.

 

I suspect there may be no clear or easy answer to my problem, but again, I feel I have to ask since I really don't have it in me to toss out this machine.

[Purdy]

A cry for help but no answers yet so I'll let you know we aren't ignoring you Akito!

Firstly let me say that I have no experience of Inty 2 so I'm definitely not the best person to give advice!

Having said that, someone has to give you encouragement so here goes....

 

I'm sure you know that if things are as you say, some serious damage may have occurred to sensitive components in your unit.

As you say you can't be sure what actually happened, make sure first that it isn't something more trivial...such as a dirty cartridge slot which has chosen this moment to play up. Otherwise:

 

I don't know how much experience you have, but you will need some diagnostic tools and skills, plus some soldering/desoldering skills to even attempt to carry out a repair.

As a first check it would be necessary to test the system voltages at the proper test points.

You can find some info here: http://console5.com/wiki/Intellivision_II#Schematics

 

Having done that, if you followed the troubleshooting procedure shown in the Service Manual you would probably need to replace hard-to-find components.

And I imagine that the ICs are mainly soldered to the board...so you won't have a 'plug in and try' option.

 

My advice to you if the above looks at all daunting would be to pick up a cheap, externally crappy Inty2, remove it's innards, and fit them to your console.

Then put the whole episode down to experience.

[Akito01]

Yeah, the third option is certainly the most logical. I do have a voltmeter, and I'll likely give that a try and see if I can nail down the problem area. Some of the ICs on this board are removable, thankfully, and not soldered in. I think this will have to be a project for next weekend, but if there is something more going on than a capacitor replacement, then realistically the best I can probably do is save the case and rescue my fresh RF from the now useless motherboard (its only because that RF modulator went in so nicely is why I thought it was worth a shot to try and rescue the rest of the machine).

 

One of my first soldering projects was replacing the capacitors on my TurboDuo to restore its CD audio. I was proud of myself on that one (compare the price of a couple capacitors to a replacement TurboDuo). Since then I have successfully put composite mods into an Atari 2600 jr, INTV II and ColecoVision. I still wouldn't rank my skills are particularly adept, as most of those are fairly simple projects.

 

Not to switch the topic too wildly, but I noticed something strange about the video output on my replacement INTV II. Although I promised not to mess around too much with this unit, that didn't stop me from taking out the composite video circuit from my borked unit and installing it in this new one. Aesthetically I was really happy with the result since I have the AV ports properly mounted on the case, where I originally had wires sticking out the back. Now, the RF video output is very nice and clean, and my LCD TV has no problem with that video source. Now, I usually use AV2 as my preferred composite input on this TV for my retro consoles. The quality of the composite video going into AV2 was really bumming me out -it was much darker and fuzzier that what was outputting on my original INTV II. But, as I discovered by accident, if I switch the TV input to AV1, I suddenly get video from my INTV that is every bit as bright and clear as from the RF! Thus, I plug the video cable into input 2, the audio cable into input 1, and everything is golden. But, why is this happening? I suspect that there may be too much voltage going into the video circuit, which is why this bleedover signal is crisper than at the input source? I should likely go and try plugging my machine in my CRT TV in the other room and see how that goes. I know from my experience with the RetroGen Genesis-to-SNES adapter that my LCD TV chokes on that very strong video signal, but my CRT plays that device perfectly fine.

 

The +5V is being tapped from TP 7 on the daughter board, which from the schematics, is listed as '+4.85 to +5.15 VDC'. I originally tried to use TP 8, since that is listed as '+5VDC/on', but it is apparently a control pin, and when connected to the composite circuit, causes the INTV to turn on immediately when plugged into power and only display a black screen. There are apparently other places to draw +5v, but the mother board gives no specific indications of where these would be. I'm aware of that point between U12 & U13, but that spot is a bit too precious too try with my mediocre skills. I doubt there is a better spot than the TP 7 pin, but that begs the question of whether excessive voltage is actually the problem. This leaves building another circuit but trying different resistor variables, perhaps? The one I have now is very by-the-book, according to the widely available specs for the INTV composite mod.

 

Ah, at this point I'm rambling a bit. If it works, it works, even if it is in a very unorthodox way.