Colecovision repair?

[iridude]

Is there a manual or a site on what Vram chips, etc what voltage they should be and what pins to check? 

[ChildOfCv]

There's a technical service manual.  But if it turns out to be video RAM, your best bet is to buy the full replacement kit from console5.com

 

What errors are you seeing?

[iridude]

I haven't tried anything yet. The power switch I looked at and for sure someone tried to fix this. However, none of those  two sliding parts those small things that go into switch. Can I use aluminum foil or something else to see if I get something at least? Or not a good idea? I for sure need a new power switch which I ordered. In meantime just trying to see if I can get anything to work.

Edited March 12 by iridude

[ChildOfCv]

If you only need a temporary replacement for the switches, then make a jumper connection.  You can just unplug it to turn off the power.

[iridude]

You have article on making a jumper connection? Thanks

[ChildOfCv]

Just solder wires between the appropriate pins of the switch.

[iridude]

I think pins 1 & 3 are the 12V source and 2 & 4 are the +5v source. I would put a jumper wire at 1&3 (12v) and 2 & 4 (+5v) correct?

[ChildOfCv]

I guess that depends on how you count the pins

 

By this numbering system, use 2-3 and 5-6

[iridude]

Ok it seems I have power now what should I check I have what it says on my tv no signal.  I am guessing rf but not sure what to check to see if I get a voltage.

 

I went to colleco tech manual and did following:

 

Check voltage on board and power supply all looks good there

 

U9:36 nothing with logic probe. However, I have no cartridge in not sure if that makes difference here or not.

 

U9:17 - 24 does something on logic probe assuming good

 

U9:33 shows +5v volts to be exact 4.96

 

U9:40 seems good

 

U9:34 high on logic probe

 

U7:13 high on logic probe

 

It says now check U7 and U1 does that mean those chips maybe suspect and should be replaced? I am confused on this. Thanks

 

Edited March 14 by iridude

[iridude]

I did check u24 and I’m getting nothing on this pin with my logic probe which I think is pin  number 13. What does u24 do?

[iridude]

I tested u1 now pin 11 showing 5v. Not sure if I am doing this correctly but I have a meter with hz and put red lead on pin 6 and ground on rf shield and shows nothing

[ChildOfCv]

2 hours ago, iridude said:

Ok it seems I have power now what should I check I have what it says on my tv no signal.  I am guessing rf but not sure what to check to see if I get a voltage.

 

I went to colleco tech manual and did following:

 

Check voltage on board and power supply all looks good there

 

U9:36 nothing with logic probe. However, I have no cartridge in not sure if that makes difference here or not.

They have to mean oscilloscope for that pin.  That's an analog output.  It's the B/W part of the composite signal.

 

Quote

U9:17 - 24 does something on logic probe assuming good

That means the rest of the system is doing stuff.  Not necessarily the right stuff, but it's doing stuff.

 

Quote

It says now check U7 and U1 does that mean those chips maybe suspect and should be replaced? I am confused on this. Thanks

When the system doesn't work, any chip is suspect

For U7, make sure pin 12 is low and pin 10 is high.  Make sure pin 6 is low.  Pin 4 should be high/low pulsing, but mostly high.  Pin 2 should be pulsing.  Pin 8 only pulses when you use the roller on a SAC or the trackball in trackball mode.

 

U1 is the CPU.  There are no simple checks for that.  But if the address and data lines are doing their thing, then it may be okay.

Edited March 14 by ChildOfCv

[iridude]

I checked U7 pin 12 is low; 10 is high and pin 6 is low; pin 4 is pulsing; pin 2 is pulsing. I guess this looks ok.

 

What else should I check? I am getting no input signal on my tv. thanks

 

I am guessing rf modulator. Not sure how to check this though

Edited March 14 by iridude

[iridude]

I checked u10 through u 17 and read somewhere that pin 14 of the ram should be pulsing.

 

my probe shows this. All the ram chips show this. Is it possible all the ram is bad? Could this cause a no signal issue though? 

 

 

Edited March 15 by iridude

[ChildOfCv]

7 hours ago, iridude said:

I did check u24 and I’m getting nothing on this pin with my logic probe which I think is pin  number 13. What does u24 do?

U24 is used for joystick input.  If the system isn't querying the joystick, you won't see anything going on.

[ChildOfCv]

6 hours ago, iridude said:

I tested u1 now pin 11 showing 5v. Not sure if I am doing this correctly but I have a meter with hz and put red lead on pin 6 and ground on rf shield and shows nothing

The clock will be 3.58MHz.  Your meter probably doesn't read that high.

[ChildOfCv]

Also, your PCB looks quite dirty.  Maybe you should wash it off.  Make sure it's thoroughly dry again before plugging it in again.

[ChildOfCv]

3 hours ago, iridude said:

I checked u10 through u 17 and read somewhere that pin 14 of the ram should be pulsing.

 

my probe shows this. All the ram chips show this. Is it possible all the ram is bad? Could this cause a no signal issue though? 

No, lack of signal is different.  The video chip still creates a raster image even if the RAM is bad.  If you have a composite mod handy, connect it to pin 36 of the video chip and see if it creates a B/W image on the TV in AV mode.

[iridude]

I don’t have that mod but I was thinking of buying the one at console5 with Trss are all the av mods the same? I heard some won’t work the Atari’s expansion module. Example I would connect red wire to pin 36 and ground to a ground and should get a b/w image. 

[iridude]

I tried something so the switch for channel if I put it in middle I get picture but has sound but it has lot of noise. Only getting signal on channel 4 this switch not supposed to be in middle correct? At least getting signal now

 

[iridude]

Can the switch be fixed? Best way to remove the RF Box? Not sure how much heat is needed. Seems like 4 tabs holding the box in place.

[iridude]

Would a A/V mod upgrade fix the channel switch? Like is channel switch needed after upgrade?

[ChildOfCv]

10 hours ago, iridude said:

I don’t have that mod but I was thinking of buying the one at console5 with Trss are all the av mods the same? I heard some won’t work the Atari’s expansion module. Example I would connect red wire to pin 36 and ground to a ground and should get a b/w image. 

Composite mods would work.  I would suggest this one:

https://console5.com/store/colecovision-composite-av-video-mod-kit-ntsc-consoles-coleco-vision.html

It has the least impact on the rest of the system.

[ChildOfCv]

9 hours ago, iridude said:

I tried something so the switch for channel if I put it in middle I get picture but has sound but it has lot of noise. Only getting signal on channel 4 this switch not supposed to be in middle correct? At least getting signal now

 

It could be tuning.  Around the center of one side of the board there should be a hole in the board.  That hole gives access to the channel tuning adjuster.  There should be a ferrite slug with a hex head there.  It should not be broken, crumbled, etc.  If it is, then you probably won't be able to tune your RF output properly.

 

But you can still install the composite mod to make all of that irrelevant.