Ahhhrrr got VRAM problem I guess :(

[+nanochess]

And replace the 74LS541 chips (for controller problems)

 

BTW, it's a good thing your VDP isn't fried, because if you get synchronization problems just out of the VDP pin, then it's fried.

[Jinks]

 

Excellent! well, there is a trick with the RF module, usually when you desolder the connector, you break the lines in PCB, check for continuity between pads and lines, repair them and it should work again.

 

Don't forget to check it is in channel 3.

 

Don't forget to replace the CMOS chip.

The RF never worked when it was soldered on before.

The lines all look good and have continuity on the rf module where I desoldered. what is the cmos chip?

The only other thing I see is under the daughter rf board right bewteen the cprq8304 and the capacitor there is a trace on the MB where is says 23. Right on the 3 the trace looks like it goes to the capacitor and then around the chip to somewhere. I think maybe to the cprq8304 chip but the trace is under the chip so can not tell. I guess it would be C68 and 23 on the video circut.

Any way to test the controllers before replacing the i/c chips? I think they may be bad.

[Jinks]

Ok my mb from c68 looks good according to the schematics. My RF daughterboard is rev F there is no location numbers for the components on the back side. Also noticed when installed in the case you would need something to reach the fhannel switch as fits in the case 3 inches.

[+nanochess]

The RF never worked when it was soldered on before.

The lines all look good and have continuity on the rf module where I desoldered. what is the cmos chip?

The only other thing I see is under the daughter rf board right bewteen the cprq8304 and the capacitor there is a trace on the MB where is says 23. Right on the 3 the trace looks like it goes to the capacitor and then around the chip to somewhere. I think maybe to the cprq8304 chip but the trace is under the chip so can not tell. I guess it would be C68 and 23 on the video circut.

Any way to test the controllers before replacing the i/c chips? I think they may be bad.

 

Expansion Module 1 for testing the controllers.

[Jinks]

ok

[+grips03]

I spent some time tonight trying to get a good process down to remove the VRAM chips.

 

Here is what I came up with.

 

Wear eye protection

Use a small flat blade screw driver and break the ceramic IC package of chip.

Use Xuron flush cutters from the top and bend the leg straight. This includes the part of the leg that was in the ceramic package.

Grab a straight pin

Apply the soldering iron at the base of the pin, same side as the pin

Pull the pin straight up

- repeat for each pin -

 

Go back and apply solder to all the pads

Use Hakko 808 or flux and solder wick to remove solder. You might need to do both sides of the pcb

Go back and use resistor leg or what other method you use to clean up the pads that still have solder stuck in the center

I was able to remove the chips with zero damage to the pads / traces this way.

 

edit: one damaged pad.

[Jinks]

I never damaged pads or traces they already were from corrosion. I need to get a solder sucker for when I do the controller IC chips. The needle to clean out the flux takes lots of time and can be risky to the contacts especially if you are too aggressive.

I loved dremeling the chips off. I went near the top by the pins and they come out in seconds. A 1/2" cut off wheel worked great. The chips came out in one piece with almost all the legs left in the board.

[+5-11under]

I do this:

 

Cut all the pins, right at the chip, with small cutters. Remove the chip.

Grab a pin (top side) with the small cutters. Heat the connection. Remove the lead with the cutters. Repeat for all pins.

Clean up with desoldering vacuum.

[Jinks]

Yup whatever works is best. Plenty of ways to do it. Thanks for all the advice without it my Coleco would have been scrap! I hope I can complete it with the video working someday. The IC chips will be a walk in the park compared to the ram chips. Now for potato chips.