Early 800 only showing B/W

[BillC]

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.

The Sobola schematics show this as C161, and that is the only 10pF capacitor I found listed for the main PCB in the Parts List in the back of the Field Service Manual

[BillC]

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

Page 203 of the Field Service Manual lists L103-L112 as Ferrite Bead Inductors but doesn't give any value, Atari part# CO14384.

[1050]

Is L110 a cap? it seems to hold a charge

Nope, L part of L110 means it's an inductor so should

read as a short piece of wire would. Dead short

included.

 

Other issues with .xxnf measurements could be just

parasitic capacitance of the test leads. Such a low

value would regularly just be ignored by a more

knowledgeable engineer - the value is so picayune as

to not matter in any case.

 

I can't find a value for it either using Sams. I'm

leaning towards 10mH since there are two transistors

getting power thru it among other needs. Same size

powers the SIO READY line in the XL series L10 there.

Only value found for it is on the schematic. Parts

list shows it, but like the 800 parts list, the value

isn't there. At least they are consistent.

[KLund1]

Finally figured it out.

I just followed the service manual steps. When I encountered soldered in part to swap out, I did so very carefully. Then do a test on both boards I was using for testing. This take a lot of time. removing boards from both motherboards, desolder both parts, swap, resolder, install boards again, test, repeat. When I got to X101 swap, I GOT COLOR!!!

I found the bad part. C010177. This is a large can, left rear, near CPU card. Off to Best for a replacement. Another 800 saved!

Thanks

[SignGuy81]

Glad you got it working. I directed the person from this post http://atariage.com/forums/topic/276641-atari-800-only-getting-black-and-white/ to check this one out in case theirs is the same problem.