Early 800 only showing B/W

[KLund1]

I have an early 800 that only shows B/W from the monitor jack. I have several other 800 boards and parts to swap out and test with. I have swapped out the power board, CPU, Memory, OS, and every socketed IC on the motherboard with known good working together parts. After every swap and test only B/W output. I put all the original parts on another motherboard, and i get color. SO there is something wrong with the main board itself. I can not see a visible damage.

For a while when I was swamping parts, I did not notice that the one of the 4 pin wire connections (J114) between the main board, and power board had come loose. The loose wire was the one closest to the front. I did a re-solder on it and still got the B/W output. Could that have damaged something on the main board while I swamping parts and applying power?

Just to be sure I swapped out parts again and still only get B/W. I even tried adjusting the red thing in the middle on the main board a 1/4 turn each way to see if that would change. nothing happened.

Suggestions on where to look for a fault?

Other Ideas?

Thanks

[ClausB]

How early? What's the 3-digit date code?

 

I think the red thing is the audio RF mixer tuner. The color pot is on the CPU board. Try moving that.

 

Also check the 12 V power supply.

Edited March 28, 2018 by ClausB

[SignGuy81]

You may want to follow this post here http://atariage.com/forums/topic/276641-atari-800-only-getting-black-and-white/ the guy I think is going to try a part and come back with results.

[+Nezgar]

Do you get colour from the RF output? The monitor jack outputs three video signals: Luma, Chroma, and Composite. Are you sure you're not getting signal from only the Luma output? Depending on your cable, it might only have a subset of the available combinations.

[+DrVenkman]

B&W is the Luma signal. If the monitor port is giving color through Composite or S-video, then the issue is with the RF modulator. If you still only get B&W through Composite and S-video, my suggestion is something with the 4050 hex buffer in the video circuit. Either the chip itself (less than 50 cents to replace with a modern part) or the socket.

[BillC]

B&W is the Luma signal. If the monitor port is giving color through Composite or S-video, then the issue is with the RF modulator. If you still only get B&W through Composite and S-video, my suggestion is something with the 4050 hex buffer in the video circuit. Either the chip itself (less than 50 cents to replace with a modern part) or the socket.

The color signal doesn"t pass through the 4050 buffer, that is only used for the LUMA and SYNC signals. After the Color signal reaches the 800 mainboard it passes thought several miscellaneous resistors and capacitors, and also 2 transistors in A104.

 

The mainboard portion of the 800 schematic is on pages 50 and 51 of the 400-800 Field Service Manual, with the video circuit at the bottom of page 51.

[SignGuy81]

The color signal doesn"t pass through the 4050 buffer, that is only used for the LUMA and SYNC signals. After the Color signal reaches the 800 mainboard it passes thought several miscellaneous resistors and capacitors, and also 2 transistors in A104.

 

The mainboard portion of the 800 schematic is on pages 50 and 51 of the 400-800 Field Service Manual, with the video circuit at the bottom of page 51.

 

Take a look at the post I referenced earlier. I didn't think to mention the 4050 chip either as well in that post to begin with. But apparently it can still affect the the signal, as well as Q105 which it doesn't directly pass thru. Take a look at page 158 of the same manual.

 

EDIT:

 

I just realized I misread the step and actually it the next step was supposed to be to check the color circuity and color delay circuit and R309, and only to swap the parts I mentioned if the screen didn't look like Figure 3-4(nothing to do with the color it meant the pattern on 3-4) so I see I misread that there.

 

EDIT:

Nope I believe I was right in what I thought it was referring to. The black and white manual was throwing me off but I remember now from the previous page you can see that when referring to figure 3-4 it keeps asking if it doesn't look like it can you adjust it to the right color so yes I do believe that is a valid step to replace those parts and they can affect the color.

Edited March 29, 2018 by SignGuy81

[KLund1]

THANKS everyone for all the good replies!!!!

 

One thing I forgot to mention is on power up the computer does go to Memo Pad but in B/W

 

 

ClausB - Thanks - the psu I use works well with all other 800's I have. I calibrated the CPU color pot when that board was in a working 800. The keyboard connection is only holes the cut end of the KB ribbon cable goes into. Also the cart sockets are green. Also the CPU card has a CTIA - no GTIA

Nexgar - The cable work perfectly with other 800's. I do not have away to test the RF output.

DrV - I have swapped out all the motherboard IC's and no change. What do you mean about the socket?

BillC & SignGuy81 - I do not have a salt cart to get color bars for fig 3.4. I do not have a scope as the flow chart on page 159 suggests I use next. I am also not that good at reading schematics. I do have my analog, and digital multimeters.

As I have motioned above I have swapped out all socketed parts with known working parts.

So it must be something that is soldered on the board.

[ACML]

THANKS everyone for all the good replies!!!!

 

One thing I forgot to mention is on power up the computer does go to Memo Pad but in B/W

 

 

ClausB - Thanks - the psu I use works well with all other 800's I have. I calibrated the CPU color pot when that board was in a working 800. The keyboard connection is only holes the cut end of the KB ribbon cable goes into. Also the cart sockets are green. Also the CPU card has a CTIA - no GTIA

Nexgar - The cable work perfectly with other 800's. I do not have away to test the RF output.

DrV - I have swapped out all the motherboard IC's and no change. What do you mean about the socket?

BillC & SignGuy81 - I do not have a salt cart to get color bars for fig 3.4. I do not have a scope as the flow chart on page 159 suggests I use next. I am also not that good at reading schematics. I do have my analog, and digital multimeters.

As I have motioned above I have swapped out all socketed parts with known working parts.

So it must be something that is soldered on the board.

If you have an SIO2SD or SDRIVE, you can load this SALT.EXE to test.

Atari SALT diagnostic CART v2.05 (1982).xex

[1050]

L110 appears to be bent at the very least, it's next

to A103 on the outboard side. It's supplying the

color clock and color adjust circuits so double check

that there is continuity across this inductor.

 

Was going to suggest that it could be that the color

clock oscillator isn't even working. Bad crystal, bad

transistors. But lack of power does that too.

[KLund1]

I'm back to this.
ACLM - thanks. I put that on my The Cart sd card. But in order to use it, we will have address the keyboard connection problem. Like I said this is a 1979, early 1980 machine. The keyboard is connects with the pins of the ribbon cable. major hassle to reinstall. I need suggestions for a part to deal with this. Sorry for the burly pic. but you can get the idea.

But If I follow the service manual flow chart as if I can see the color bars as gray I end up on page 7-10, box third from the bottom. (replace A103, A104, Q105) I have already replaces A103,104, several times. Q105 I think is a small black transistor. The text on it is so small I can't read it. What are it's values so I can see if we sell one at work (Fry's), and see if we have a connector for the keyboard.

1050 - Thanks. Those are two black things like L105 soldered together in a line but folded up and covered in plastic sheath. The connections look good close up. nothing touching that should not be. Continuity appears ok with my multimeter on resistance.

[Rybags]

There's no "colour clock oscillator" - this is an NTSC machine. Evidenced by mention that it's got a CTIA.

[KLund1]

I think I fixed the ribbon cable issue. I used one side of a round hole socket. See pic.

So I run the SALT test flow chart. and it takes me to page 7-11 where I need a scope I do not have not know how to use. Except I did skip the box where I change Q105 on 7-10

[BillC]

I'm back to this.

ACLM - thanks. I put that on my The Cart sd card. But in order to use it, we will have address the keyboard connection problem. Like I said this is a 1979, early 1980 machine. The keyboard is connects with the pins of the ribbon cable. major hassle to reinstall. I need suggestions for a part to deal with this. Sorry for the burly pic. but you can get the idea.

But If I follow the service manual flow chart as if I can see the color bars as gray I end up on page 7-10, box third from the bottom. (replace A103, A104, Q105) I have already replaces A103,104, several times. Q105 I think is a small black transistor. The text on it is so small I can't read it. What are it's values so I can see if we sell one at work (Fry's), and see if we have a connector for the keyboard.

1050 - Thanks. Those are two black things like L105 soldered together in a line but folded up and covered in plastic sheath. The connections look good close up. nothing touching that should not be. Continuity appears ok with my multimeter on resistance.

According to the parts list in the back of the Field Service Manual Q105 is a 2N3904 transistor, but this shouldn't be the issue since it's part of the Luma signal circuit after the 4050 and resistor ladder.

[KLund1]

So then what can be causing the B/W only output on the motherboard?

[BillC]

So then what can be causing the B/W only output on the motherboard?

It has also been asked whether you are using a confirmed composite video cable, there are monochrome only cables for the Atari 8-bits.

 

It would be helpful if you could test whether the RF output has color or is also B/W, if there is no RF cable attached the RCA connector for it is on the power board next to the RF modulator. If there is also no color signal on the RF it would indicate that the problem is likely before the output of A104.

[kb3wmh]

If you don't have a TV with an analog tuner you could pick up a VCR from Goodwill for a few dollars or from a yard sale. They are dirt cheap and can output a composite signal. If you get it from Goodwill you could donate it back when you are done with it, if you don't want the clutter.

 

Sent from my Nexus 6P using Tapatalk

[KLund1]

I went and dug out a VCR from the attic. Had to dig deep. Checked that it worked. Hooded it up to this ailing 800 and got B/W RF but since I have no cage on the motherboard I also got a lot of snow.

So this thing outputs only B/W from RF and Monitor.

I pulled yet another IC from another 800 from A104 and swapped it in. Got B/W. Just to be through I swapped in the A103. Got B/W.

I am pretty certain it is something soldered on the board that had gone bad. Or there is a short I can't see from some small dust.(I have used compressed air several times) possibly under a socket or the rows of resistors. Or it might be a bad solder joint.

I think maybe a run through the dishwasher (no worries, I have done this many times.) first before I warm up the soldering iron.

[SignGuy81]

I was looking back at the post I linked to with the same issue someone else was having and the schematic. For the other person I suggested looking at the 10pF cap inline with the color signal(I don't know if they tried checking/swapping it or not). It is the 10pF between R196 and pin 12 of A104. This cap is not labeled on the schematic other than the value.

Edited April 6, 2018 by SignGuy81

[1050]

1050 - Thanks. Those are two black things like L105 soldered together in a line but folded up and covered in plastic sheath. The connections look good close up. nothing touching that should not be. Continuity appears ok with my multimeter on resistance.

Just for grins did you double check for 11 volts there?

Sometimes an ohm check in circuit will bleed back

around and give the appearance of a connection

where none is actually there. It needs 11 volts

on both sides of L110 or no color.

 

There's no "colour clock oscillator" - this is an NTSC machine. Evidenced by mention that it's got a CTIA.

Sams seems to want to call it that too. Merican TV

repairmen have been calling it that from day one so

I don't think you can convince them that there is

no clocking going on here in the strictly speaking

computer sense of the word. Especially when that is

absolutely right. Ironical.

 

[KLund1]

I think that is c198.

I get 139nf on my meter. on the known good board I get 104nf. on 3rd good board I get 144nf.

On the good boards is is a fat yellow device. on the bad board it looks like a big diode, copper on the ends, gary in teh middle covered in clear glass/plastic. There are many of them in the places the yellows ones are on the good boards.

[SignGuy81]

I think that is c198.

I get 139nf on my meter. on the known good board I get 104nf. on 3rd good board I get 144nf.

On the good boards is is a fat yellow device. on the bad board it looks like a big diode, copper on the ends, gary in teh middle covered in clear glass/plastic. There are many of them in the places the yellows ones are on the good boards.

 

Is it possible for you to desolder one leg from both the good board and bad board of the caps and recheck them?

[SignGuy81]

Could you take a picture of the back of the whole board and also close up around A104(a couple inches all the way around) on the back side?

[KLund1]

I get 11.9V on both sides of L110

 

Pic is back of A104.

Waring up the iron

 

Again thanks for all the help!!

 

[KLund1]

I removed L110. I think I was careful. I had a heat sink between cap and solder points. Or I think I do not know how to use the cap function on my meter. without touching anything I get .093nf. When I touch the black probe to one leg, it goes .11nf. Then I touch the red probe to the other end and it stays at .11nf until I remove the red then it jump to many numbers over 1 to about 25 nf. Switching probes it stays at .093 until I lift one probe and it jumps to large numbers again

same with the good board L110

I check that voltage was zero before each test.

Now I do not get any reading fro the L110 on the third board.

aarrrr frustrating not knowing enough how things work.

Just tested a new in package ceramic cap and it measured right.

Is L110 a cap? it seems to hold a charge

Edited April 6, 2018 by KLund1