multiple issues with multiple monitors

[shess]

So I'm trying to troubleshoot a few monitors and am having various issues.  I wouldn't consider myself a noob when it comes to monitors, I've done capkits, flybacks, and tube swaps successfully so I'm not afraid of testing/replacing anything.  I tried to be as methodical as possible so here's what I've got.

1.  WG 19K7901 with tube1
2.  WG 4900 with tube2 (don't know the exact model, had to use Bob Roberts monitor ID page)
3.  WG 13K7886

With monitor 1 the picture is clear and the colors are normal but it is shrunk to the middle third of the screen.  Playing with all the size/pos pots changed nothing.  I haven't replaced any capacitors yet, but more on that in a sec.

Monitor 2 has a deep blue/purple tint to it and none of the RGB pots on the neckboard change anything.  This board looks like it was recapped.

Monitor 3 looks fine for the most part except it's kind of dim.  When I up the gain pot or fiddle with the RGB pots, I can get it a little brighter, but then the colors smear pretty bad.  This has not been re-capped from what I can see.  Will a cap kit likely fix this?

Now back to 1 and 2.  I swapped chassis to see if I could eliminate any problems.  When I put the 4900 on the first tube, the picture is still shrunk and now the picture is only tinted blue.  Again, none of the size/pos pots change the picture.  I'm thinking bad tube?  Other issue is that none (except green) of the color pots on the neck board change the picture at all, it's as if they don't exist.  I checked the solder joints on the neckboard and everything looks fine.  Looking at the main chassis I only see a bad joint on a tiny ceramic capacitor, but I doubt this will affect the neckboard.  So any suggestions on this chassis?  Also does the tube sound bad?  I don't really know what to look for on the yoke or tube itself to see if anything is bad.  How do I know if the yoke impedance is compatible with this chassis?

I put the chassis from monitor 1 (7901) on the second tube to see if anything else could be eliminated.  This time the picture is still purple/blue but the picture is now full size.  Again, none of the rgb pots on the neckboard affect the picture.  Another bad tube?

I didn't think tubes went bad all that often, but I don't see what else could be the problem.  Any ideas on any of the three monitors?  Sorry for the essay, but there was a lot of troubleshooting going on.


Thanks,
Scott

[Ken Layton]

Rule-of-thumb:

Capkit first, check for bad solder joints.

Another observation:

You are swapping chassis between two totally different monitors, a k7000 and a k4900 series which use totally different yokes. What are you trying to do destroy your chassis and burn down your house?

[shess]

Yes I am trying to burn it down.   I didn't think it was an issue because they're both 19" WG standard res monitors and the neckboards physically fit on both tubes.  But if we pretend that the yoke impedance is the same is there anything else I can check besides a cap kit?  The 4900 already had a capkit done and it was putting out all blue on both tubes.  And both tubes exhibited the same problems with either chassis, shrunken on one and purple on the other.

Scott

[shess]

My mistake, you're right.  I found a website where the guy did a chassis swap on a 4900 and a 7000 and the impedance was completely different.  I should check the tubes again and make sure they match up properly with their chassis.  Who knows if something got swapped before I got these monitors.  http://home.earthlink.net/~arcadeparts/index.html


Scott

[Ken Layton]

K7000 has a low impedance yoke. The 4900 series uses a high impedance yoke.

[shess]

Updates:

Found some troubleshooting flowcharts for these monitors.

1. WG 7000 - tested IC3 and the voltage is correct, going to try replacing C50. I noticed some of the caps have a white paste around the base, is this a leak or some kind of glue to keep the cap secured to the board?

2.  WG 4000 - after reflowing the solder at the input connectors I now have red and blue working.  I swapped the red and green lines on the neckboard and I'm able to get green now.  I checked the transistor on the neckboard and the voltages were comparable to the others.  I guess I need to check the other transistors on the PCB for green and other broken traces?  Any other place to look for a break in the signal path?

Scott

[Ken Layton]

That's normal hard glue Wells-Gardner uses for securing parts to the board. If you're going to change just one cap, why don't you do a whole capkit? Otherwise you could be just wasting your time.

Keep in mind that the 4900 series is well known for many bad solder joints all over all the boards. Also remember that the color driver transistors on the neckboard can test fine but actually be bad. The sure cure is to install a brand new transistor of the correct type. They don't cost much.

[shess]

Thanks for the advice.  I'll probably end up doing the part replacements then check for more broken traces.

Scott

[shess]

So with the k7000 I noticed a couple resistors missing, R80 and R83 which could be affecting the size issue.  And the cap kit I have didn't include some of the other caps so I'll need to order those separately.

With the k4900 I swapped the transistors on the main PCB from blue to green and now green works so those need to get replaced.  Looking in the manual it says I need 2SA562-Y-TM and 2SC1815GR .. I looked on the actual transistors and what I see is A562 and C2458.  I tried looking up all those parts in mouser, jameco and came back with nothing.  Is there an equivalent part I can use for those?

[shess]

Anyone know which transistors I can substitute on the K4900 board?  None of the part numbers are showing up in Jameco/Mouser.  Thanks!

[Ken Layton]

I believe Mouser and Jameco do NOT stock Japanese transistors (2SA, 2SB, 2SC, 2SD series). I think they only handle USA type 2N series.

Go to MCM Electronics instead.

Nowadays, most people drop the "2S" prefix off the Japanese number anyway.

[shess]

Monitor 1 is fixed!

Looks like 2 resistors  (R80 and R83) were removed.  So I pulled them off my other k7000 chassis and now the problem is fixed.  I'll still replace the other capacitors to clear up the picture a bit, but I think it's good now.