Tandy CoCo 2 Screen Issue (help Please)

[batboard]

I got a Color 2 with a box of cables, 8 games with manuals, 2 controllers, books ect... for 20$ on ebay, now, the title said untested, but the other stuff alone is more than 20$. I hooked it up, hit the switch and it made that wonderful (blink) sound and I get this half the time black and half the time scribbly whitish screen. I used the switch box and a coaxle connector, and both do the same. My 2600 works fine with it sooooo......hmmm. I cracked open the case and poked around and everything looks fine but the C36 capacitor has some brownish gunk around the base. I don't know if its just some 30 yr old glue or what, but it doesnt really look like a leak, and the components around it and the board look fine where it is, so I don't think the Cap is leaking. But maybe the cap is bad and thats why I get this screen........I don't have my Multimeter and oscilloscope with me, I just moved to NH and all my stuff is 2000 miles away, Winter is coming and I need something to do while barricaded in, Im from Florida....lol.....and really want to get this working....I took some video and put it on youtube for anyone to look at...hope someone can help me.

 

https://youtu.be/bfTxwCv8I0k

[R.Cade]

Untested means "broken, I couldn't get it to work" in eBay-speak.

 

I know that's not helpful to you, sorry.

 

It looks like you are getting a signal, but your TV just can't lock onto it. I would start by checking power everywhere on the board.

 

The brown stuff is just glue... don't worry about that.

Edited September 25, 2015 by R.Cade

[JamesD]

Replace the cable with a known good one.
After that... the most common things to die are the SAM, PIAs, RAM and CPU
A dead SAM can mess up the system clock so that would be my first guess. A bad clock crystal could also do it.

A bad PIA could mean the 6847 isn't getting configured right but I would think you'd have some sort of image.
Bad RAM would mean garbage on the screen but not like that.
A bad cpu would also leave garbage on the screen but you'd have screen borders and such.

[batboard]

I switched it to 3 and 4 when the channel select on the computer is on 3, the switched it to 4 and changed it back and forth. So i double checked. I figured the guy plunged it in and went , eh, and thats all it was, so I was hopeing it was just something he overlooked. But these things are like 40 caps, 5 ICs and a power supply....not much in them so it should be an easy solder fix something is bad. a 15 cent cap could just be the problem between a working CoCo and it going in the trash.

[batboard]

Replace the cable with a known good one.

After that... the most common things to die are the SAM, PIAs, RAM and CPU

A dead SAM can mess up the system clock so that would be my first guess. A bad clock crystal could also do it.

A bad PIA could mean the 6847 isn't getting configured right but I would think you'd have some sort of image.

Bad RAM would mean garbage on the screen but not like that.

A bad cpu would also leave garbage on the screen but you'd have screen borders and such.

 

I don't know where to get a cable. have to look i guess, and i can't test anything right now due to lack of equipment. Maybe I can just get my stuff shipped up here...But Im dieing to know it that big cap buy the power supply is leaking or what that gunk is.

[JamesD]

It should just take an RCA audio or video cable

[batboard]

Untested means "broken, I couldn't get it to work" in eBay-speak.

 

I know that's not helpful to you, sorry.

 

It looks like you are getting a signal, but your TV just can't lock onto it. I would start by checking power everywhere on the board.

 

The brown stuff is just glue... don't worry about that.

Sorry, I missed this when i was scrolling.....weird right, the only way i have to test power is to wet my finger and start probing.... , wasn't sure if someone might have run up against this before. sigh, I guess its stalemate till i get my meters and scopes and such up here. unless someone has a Coco2 they want to sell for cheap sucks because the other stuff is in great condition. Joysticks, games with manuals, even has 2 cords for the tape player, or maybe ones for the printer...