Well, while we were shifting cabs around a couple of cabs some weeks ago, I thought up a devious plan:
How about I'd offer Ckong to work on his Gravitar ? That would give me at least a couple of weeks to
drool over,
play with work on the machine !
There was a gentleman's deal between Ckong and me. An exchange of goods for working hours, a deal we're both happy with.
Anyway, of course Erik's Gravitar was working when we bought it. It was also working when we put it up in my kitchen. In first looks the monitor is nice, but there are some (small) issues that _can_ be improved.
First there was a bit of a shock: Of course I had to remove the monitor from the cab, and (esp. because it's not MY cab) I read the manual to check how to do it. Had to unlock something on the back, but that was already loose. Then I had to remove the monitor just like on a Centipede: open CP, remove glass and bezel, remove bolts and get out the monitor. Only this time I didn't have to remove the bolts because they weren't there ! Turned out we were _very_ lucky to transport the machine on the back !
Another good lesson learned, CHECK that everything is fixed before transporting a cab. No offense to Oli, I'm sure he was in the assumption that it was fixed.
The tinted bezel glass is always good as it always "hides" minor flaws. After some cleaning of the front the monitor looks like this:
It has some slight burn in of Gravitar so it's probably the original monitor still. Also there are some tiny burn-marks at weird spots (not the center), but all this is hardly noticeable at all when playing the game.
The issue's I noticed after some thorough testing (yes this included playing the game, but purely for analysis of course) are:
1) the convergence is not perfect. It looks like the center is OK, but we can get better edges with some metal strips.....problem is I'm out of them....will need to find a source for them ASAP.
2) the brightness seemed to not be entirely stable. I tried gently tapping on the neckboard and indeed I could see (at least the red) go dimmer and brighter at times. The conclusion is pretty easy: bad driver and bias pots. Plus maybe some poor solderings, as I've experienced those on another WG6100 before.
3) The image is a bit "jittery". This is very likely also caused by bad pots. But this time they're not on the monitor but on the PCB. In the vector area there are about 8 pots to regulate the image. If pots go bad in that area, it will influence the picture in horizontal and/or vertical way.
To solve problem 2) I bought some pots today (had to resort to my trusty electronics store in the area because RS didn't even have this size pots !?!?!)
The one's I got are Euro sized but they fit great with a tiny bit of bending the outer legs.
About bad pots. We all know the effect of a bad pot on a radio: crackling. You will here a crackling sound. Sometimes when you turn the volume up or down you will notice it even more. Exactly the same happens when pots get older on monitors, but the effect is different of course.
With the pots on the neck-board, they will have an effect on the brightness of the colors. So if you move the pots slightly (or _gently_ tap them) you will see the brightness of one or more color change. It's like the crackling sound, but this time it's visible not audible. This shouldn't happen of course.
Of course you could try to use some contact spray on the pots but I'm strongly against it. IF it works, it's only temporary. The issue is that the pot has probably been on one setting for it's entire life. This causes the bad spot to be _exactly_ at the "correct" setting of that pot. You won't fix that with any spray. Replacing the pots is the only good solution.
Now, I needed 500 Ohms and 15K pots. But 15K is not in the E-series we use over here. Lukely those were the bias pots and one side of the pot goes to ground, so it wasn't that important. I bought 25k (or is it 20k?) instead. Note that it's not ALWAYS possible to do this, but it was in this case...
When replacing the pots, I carefully measured each one of them, to be able to "copy" the settings to the new pots. This saved me from having to completely re-adjust the colors, and it worked out great !
Here's the new (left) and old pots:
Even though I double-checked everything I'm always still anxious when powering it up again, but to my relief the normal picture came up. I adjusted the red a bit, because it was a bit too weak compared to the blue and green. I tried _gently_ tapping the neckboard again (I use the "rubbery" back of my screwdrivers for this) and this time the color stayed fixed. So, issue 2) is solved !
I also had to resolder a wire on the neckboard: I had taken the neckboard from the tube 3 or 4 times, and one wire simply broke off. This shows that age is doing bad things on these old machines
Any way, stripped the wire and resoldered. I of course checked all the other wires but they were still OK.
The broken wire (already newly stripped):
I ordered the pots for the PCB from RS plus also caps for the monitor. This time I decided to go with high quality Panasonic caps, 105 degree versions. Erik said the game deserved the best, so it gets the best.
Have to wait for those parts to arrive now. So let's see if I can get my high-score up a bit.....(I'm at 2nd spot now, but I doubt I will ever reach the first spot !).
Here's the monitor, it's been running happily for about an hour now...it's good to be able to test it like that on the back side
Erik will also order an LV2000 to replace the Low Voltage section of the WG. There already have been some modifications made, but I'd like to go save with one of the LV2000's.
