G3 All In One Wonky Display

[bsteckler]

Hello everyone,
I've got a G3 All In One that I did a recap on not too long ago (just the AB and neckboard, the PSU didn't seem to need it), I also replaced the flyback.

The machine was fine for about a month until lately I booted it up and saw this:


Something obviously came loose, either on the AB or video connector. Any ideas what I should check first, or anything to narrow down the problem?

 

[CircuitBored]

Wow! That is quite a look!

To me it looks like your colour masks are all out of alignment. Is it possible that the machine was knocked or dropped? It's quite likely an issue with the deflection coils around the neck of the tube but it's hard to tell where it originates from. It could be mechanical or electrical.

The machine was fine for about a month until lately I booted it up and saw this:

Does this mean that you ran the machine every day for a month or left it powered down for a month?

Firstly, you should revisit every part of the machine that you worked on and inspect the work that you did. Reseat any connectors that you touched. When recapping, did you make sure to replace the capacitors with equivalent specs? Voltages and capacitances are easy to get right but you need to be aware of tolerance, ESR, and temperature ratings too. Were all the caps replaced with those of the same type? i.e. electrolytics replaced with electrolytics? CRT analog boards are extremely sensitive and a single mis-specced cap can throw the whole thing out of whack.

Is it possible that there is a significant source of interference nearby? Radio equipment, large magnets, motors, etc?

Degauss your tube.

Lastly, although you have clearly already worked on this CRT without dying, I would be remiss if I didn't state the not-so-obvious:

CRTs and capacitors can hold a lethal charge for hours or even days after being unpowered. Safely discharge these components before working on or near them. If you do not know how to do this, do not try to do it.

Lastly, get that thing up off the carpet!

 

[bsteckler]

I certainly didn't leave it on, but I'd say I powered it up 5-6 times afterwards, then let it sit for maybe three weeks cause I didn't have the time to work on it. I made sure to check the voltage and capacitance on each cap, and replaced it with a like electrolytic.

It's on the floor cause I don't have much room for it elsewhere, it got knocked slightly but not dropped or hit hard. While this was my first time working on CRT components, I made sure to discharge the CRT and follow all safely precautions when doing so. I'm very much aware of what these can do to the uninitiated.

There's nothing like a strong magnet, etc nearby, and this doesn't appear to have any sort of degaussing option, either on hardware or software

 

[joshc]

Start with the simple stuff, open it back up, check for loose connections. Going back over your work is important, there could be a weak solder joint.

 

[ried]

Do these use the same CRTs as the iMacs?

 

[AwkwardPotato]

A damaged shadow mask or yoke are unlikely to be the culprits here; the former would generally cause purity issues, as for the latter, the geometry/width/height all seem to be about what they should be. Go over your work like the others have said in case of any loose connections or bad solder joints. If you're comfortable with the idea and there's enough room inside the machine for you to work, you might try tapping the neck of the CRT (preferably with something non-conductive like a wooden dowel) with the machine turned on to see if this is caused by a short inside the tube, taking care not to break the glass or get zapped.

 

[techknight]

You are missing a voltage to the video amplifier/driver stage. Need to find out which fusible resistor burned open and check for a diode that shorted.

 

[ried]

I have this EXACT issue and it is intermittent. I'm losing my mind. Most of the time, my G3 AIO boots and has the same display issue as @bsteckler's machine



Coincidentally, when this monitor smearing occurs, sound isn't working, either - no boot chime, nothing. Something is not connected and it's causing both the smearing and cutting the sound.

I have:

1. Un-plugged and re-plugged everything on the logic board (personality card, etc).
2. Replaced the logic board.
3. Replaced the personality card.

No change under any of these circumstances. But I can let the machine sit (i.e. overnight), fire it up first thing in the morning and it chimes and boots normally, with beautiful display and working sound. But then after running for 5-10 mins, display smears and sound is lost (simultaneously). I suspect heat from the machine running may be exacerbating the issue / breaking a connection somewhere? Just a guess.

Doesn't seem to be the logic board, or the personality card... So what could it be? It affects both the display and the sound at the same time?

Coincidentally, Steve from Mac84 had this display issue when he picked up his first G3 AIO from an eWaste facility a couple of years ago. In his case, it seemingly went away by plugging the RGB connector back into its spot on the personality card. No such luck in my case, and I've tried two different personality cards with the same result.

Help me 68kMLA, you're my only hope.

 

[AwkwardPotato]

As someone who doesn't own an AIO: do the speakers on these plug into a header on the motherboard like the G3 desktop/tower, or do they connect somewhere else (as in, somewhere on the analog board perhaps)? Personally I'd start by powering it on and once it starts acting up, pull out the motherboard tray and start spraying parts on the personality card with a can of freeze spray (a.k.a. compressed air can turned upside down) to try and eek out any thermally intermittent parts. Not gonna help if the problem is on the analog board though.

Dag nabbit, not doing great with reading comprehension today. Question about the speaker still stands. Any chance you could get a photo of both sides of the analog board for clues as to how its laid out? Can't seem to find good ones online.

 

[AwkwardPotato]

Glanced over the G3 AIO service manual and what I've gathered is that the speaker cables connect to the personality card through the system's main wiring harness.

Looking through some low-res photos of the Wings personality card online, it looks like the audio side of it consists of the main Crystal audio IC, a TDA- series audio processor, and a handful of op-amps/power amps, at least a couple of which will likely be driving the speakers. I wonder if you could power on the G3, wait for it to act up, and then measure each of the TDA chip/amps positive and negative supplies until you find something amiss (datasheets should be available online for all of them, but not for the Crystal chip)?

Chances are the positive supplies to some/all of the audio op-amps will be derived from the system's +12V rail. Thinking about the video amp that techknight mentioned: while I don't have an AIO, I know for certain that the video amp in the early iMac G3 (similar analog board for the same type of CRT, designed by the same OEM) takes one +12V supply for the bias voltage. Wonder if there's a link there and that supply is dropping out for some reason...

 

[ried]

So the suspicion is that it's a power delivery issue, either at the power supply or (more likely) somewhere along the +12V rail? We should be able to exclude the logic board and personality card; swapping those out didn't change anything. So it must be somewhere else...

 

[mg.man]

This is just wild speculation (I don't have a AIO), but doesn't it use the same 'board as the beige desktop / minitower? If so, could it be the VRM module playing up?

 

[Torbar]

So the suspicion is that it's a power delivery issue, either at the power supply or (more likely) somewhere along the +12V rail? We should be able to exclude the logic board and personality card; swapping those out didn't change anything. So it must be somewhere else...

Did you replace the flyback too with the one from Technotronic Dimensions?

edit:
Do you have a PRAM battery in your board?

I talked with bsteckler(OP) through PM's yesterday/today and they said one of the things they did was use a new PRAM battery. Have had it on for 20-30 minutes with no issue.

I had this issue yesterday after replacing my flyback, but one of the things I did at the same time was remove the PRAM battery. So maybe something wonky is going on with it with the personality card?

 

[ried]

Did not replace the flyback. That would require soldering that I am not (yet) prepared to handle. Also, the flyback would be one thing, but my issue also results in the loss of sound - which would seem unrelated to the flyback.

Just put in a new PRAM battery. No change.

I have used two personality cards: Wings and Whisper. No change in either case. The personality card does not seem to the the culprit, nor the logic board.

 

[Torbar]

Forgot to mention. I lost sound in mine as well. (I assumed I just didn’t hook something up until I saw your comment)

 

[ried]

Whatever's on the other end of that IDE cable connecting the personality card to the front panel / speakers seems to be the likely culprit... I know that cable carries two signals for the display, too (H sync, V sync) as well as sound.

I'll have to remove the case again and poke around.

 

[AwkwardPotato]

Will be interested to hear how the cabling in the chassis is laid out. If the rest of the system still seems to function, just without sound or clear video, I think the VRM module on the motherboard can also be ruled out. Flyback transformer should have no bearing on the sound either. I also wonder if perhaps there's some circuitry on the front panel control board that could be intermittently shorted and killing the +12V (maybe the amps for the speakers are on it rather than the personality card?).

Would also be greatly appreciated if you could get a couple photos of the solder/back side of both the analog board+power supply while you're in there.

 

[Torbar]

This seems to be a semi common issue, so I wanted to get all my notes in one place

bsteckler:
Replaced flyback with the one from Technotronic Dimmensions(same part number, but different revision), recapped analog board. Fine for about a month, then had this issue. Replaced PRAM battery, issue is resolved.
Has left machine powered on for 30+ minutes, issue has not returned, so its safe to say it's been resolved.


ried:
Stock flyback, intermittent issue. When the video is messed up, no sound either

If they leave it overnight, it works fine for about 5-10 minutes, and then same issue happens.

Tried 2 logicboards and 2 personality cards, fresh pram battery

Steve/Mac84:
Same issue on his trash picked molar mac, reseated RGB connector on personality card, resolved.
verified with steve, no pram battery


Me:
When I got the molar mac, sound/video worked fine, but the CRT would click/make a spark noise and flash. Bought a new flyback from TD.
Swapped it, now have the same issue as above(with no sound). I did remove the PRAM battery at the same time, but I just tested it with a meter and the voltage is pretty much zero, so I don't think thats it.
Verified voltages coming off of the back of the flyback(-120v, 30v, 40v)
reseated personality card, and connectors on personality card, same issue.
Next up I'm going to reseat all the connectors on the analog board/neckboard. But not sure when I can get to that.
I saw some talk above about the 12v rail, I double checked on the molex connector on mine and it is showing 12v(and 5 is showing 5)

linear on twitter:

https://twitter.com/i/web/status/1586114244541435904

Before flyback replacement, no video at all.
After flyback, same issue



At this time, I'm suspecting it's a connection issue with the RGB cable going between the personality card, and the neckboard.

 

[3lectr1cPPC]

We got another one! https://68kmla.org/bb/index.php?threads/molar-mac-free-to-a-good-home.39017/

 

[Torbar]

I just reseated my RGB cable to the neckboard, same deal.

@Unknown_K any luck with the one you picked up with this issue?