Colecovision PAL fix. No colors

[Zak]

Hello friends, I am repairing a Colecovision PAL version that gave a black screen. After an initial scan, I discovered that it was the BIOS that was dead. I replaced it and it revived, however no color. The tests I did to return the color, without success, were:

check voltages, are OK.
discarded TV and power supply, they work correctly with another colecovision.
Replacement of the complete RF modulator.
replacement of the two crystals.
replacement of cap70 and cap1
VDP video chip reflow

where can I continue?
I attached a video of the error.  Tnks!

 

Edited August 7, 2022 by Zak
add info

[marauder666]

I had one with incorrect colours, resolved by changing the CD4013 and the two CD4066. CD4013 and one of the CD4066 is related to generating the PAL colourburst signal which is passed to the LM1889 video encoder.

Start with those, they are dirt cheap.  After that I'd be looking at the LM1889.

 

Transistors Q20 and Q23 are also part of the PAL colourburst generation.

 

No guarantees without an oscilloscope to check the expected signals are where they should be.

Edited August 7, 2022 by marauder666

[Zak]

39 minutes ago, marauder666 said:

I had one with incorrect colours, resolved by changing the CD4013 and the two CD4066. CD4013 and one of the CD4066 is related to generating the PAL colourburst signal which is passed to the LM1889 video encoder.

Start with those, they are dirt cheap.  After that I'd be looking at the LM1889.

 

Transistors Q20 and Q23 are also part of the PAL colourburst generation.

 

No guarantees without an oscilloscope to check the expected signals are where they should be.

I get an oscilloscope today. I will be able to compare the values against a healthy CV. I will pay attention to Q20, Q23 and the U8 flip flop that divides the frequency of the crystal. tnks

[ChildOfCv]

U8 has nothing to do with color generation on PAL models.  Y3 works independently.  Q20 shuts down the color burst signal whenever external video is present.  So stop #1 for the oscilloscope is to make sure pins 17 and 18 on the 1889 have oscillation.  If not, check Q20.  Q23 forms a differential amp.  The collector and emitter have opposite phases as they amplify the colorburst signal.  U32B chooses which phase goes to the LEAD pin (1) of the 1889, by turning on one of the analog switches U30B or U30D. U32 should toggle for every scan line.

[Zak]

19 hours ago, ChildOfCv said:

U8 has nothing to do with color generation on PAL models.  Y3 works independently.  Q20 shuts down the color burst signal whenever external video is present.  So stop #1 for the oscilloscope is to make sure pins 17 and 18 on the 1889 have oscillation.  If not, check Q20.  Q23 forms a differential amp.  The collector and emitter have opposite phases as they amplify the colorburst signal.  U32B chooses which phase goes to the LEAD pin (1) of the 1889, by turning on one of the analog switches U30B or U30D. U32 should toggle for every scan line.

 

Tnks @ChildOfCv
update: I replaced Q20 and Q23 and nothing, still the same. Black&White (sometimes everything turns sepia).

something that I did notice, comparing the states of U32 with a logic probe against a healthy coleco, pins 1 and 2 are different.

 

healthy CV:

U32:1 -> LO

U32:2 -> HI

 

B/W CV:

U32:1 -> HI

U32:2 -> LO

 

other pins are the same.

I'm thinking of replacing U32 first, and then U30's to see if that fixes the problem. how about? Thanks as always for the great help.

[ChildOfCv]

U32 pins 1 and 2 are part of an unused flip flop.  The clock, S, and R pins are all tied to gnd.  The output is just whatever state it decided to be in that day.

 

Did you scope pin 1 of the 1889?  It should be a sine wave that flips phase at the end of each line, as signaled at pin 11 of U32.

Edited August 10, 2022 by ChildOfCv

[Zak]

15 hours ago, ChildOfCv said:

U32 pins 1 and 2 are part of an unused flip flop.  The clock, S, and R pins are all tied to gnd.  The output is just whatever state it decided to be in that day.

 

Did you scope pin 1 of the 1889?  It should be a sine wa

ve that flips phase at the end of each line, as signaled at pin 11 of U32.

 

 

1889 pin 1 ->

[ChildOfCv]

That signal doesn't look correct at all.  It should be a sine wave, not a square wave.  What's the time division setting on for that picture?

 

What does the output of either side of Q23 look like?

[Zak]

On 8/11/2022 at 11:03 PM, ChildOfCv said:

That signal doesn't look correct at all.  It should be a sine wave, not a square wave.  What's the time division setting on for that picture?

 

What does the output of either side of Q23 look like?

other time/div :

 

and Q23 E :

 

 

Q23 C :

 

 

 

next I will try replace 1889...

 

 

[ChildOfCv]

So far there's no reason to suspect the 1889.  If you use 0.2us time div on the scope, you should be able to see sine waves in the Q23 output signals.

 

But U30 is only giving highs and lows.  It's an analog switch where either Q23c or Q23e's signal should feed through to pin 1 of the LM1889.  But nothing is except highs and lows.  So U30 is my suspect.  Make sure it has proper power and ground, then check the gate pins (5 and 12) for proper high and low input signals.  They should be on at opposite times.

[ChildOfCv]

One quick test would be to remove U30 entirely then connect 1889 pin 1 to either pin 4 or 10 of U30's PCB holes.  Then see if the signal still looks well behaved.  Also, look for broken traces in this area.

[Zak]

22 hours ago, ChildOfCv said:

So far there's no reason to suspect the 1889.  If you use 0.2us time div on the scope, you should be able to see sine waves in the Q23 output signals.

 

But U30 is only giving highs and lows.  It's an analog switch where either Q23c or Q23e's signal should feed through to pin 1 of the LM1889.  But nothing is except highs and lows.  So U30 is my suspect.  Make sure it has proper power and ground, then check the gate pins (5 and 12) for proper high and low input signals.  They should be on at opposite times.

"So U30 is my suspect. "

 

YES YES YES,  @ChildOfCvyou got it right!

 

i replaced U30 with a spare IC and walahhh COLORS appeared. Then, when turning on the console, the logo appeared in black and white for a second and then came color. I corrected it in the modulator (pal modulator version) by removing the metal cover, it has two small potentiometers. Adjusting the highest one corrected that delay in the arrival of the color.

 

A big thank you to everyone who responded by helping: @ChildOfCv and @marauder666 for their predisposition.

 

#SOLVED

 

 

Edited August 14, 2022 by Zak