G3 All In One Wonky Display

[ried]

Definitely appears to be a specific, recurring issue with these. Someone has to have figured it out at some point...

 

[AwkwardPotato]

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.

Apologies if I missed something again but I haven't seen where bsteckler reported that a new PRAM battery resolved this.

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)

Since you have +12V at the molex connectors, if you feel comfortable doing so, you may be able to rule out power to the video amp IC by taking the shield off the CRT neck board (if there is one) and measuring voltages on the IC. The chip in question will probably be the only one with a heatsink on the neck board, and the datasheet/pinout should be available online. In my (limited) experience there should be at least one positive supply of around 10-20V and a second one around 50-100V.

Caution would need to be taken when measuring things on the neck board, however, as the G2 and focus voltages are also present elsewhere on it (usually on the order of several hundred volts, and a couple thousand volts, respectively).

 

[Unknown_K]

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

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

I stripped it and reflowed the solder joints on the PS. I think maybe one of the power cabled got crimped when somebody was putting the MB tray back in but not sure. To be honest the thing is so large that I moved it to the garage on a dolly and its been there since (doing other projects and just lazy). I did find a SCSI ZIP and larger HD for it so when it gets fixed it will be complete.

 

[ried]

I stripped it and reflowed the solder joints on the PS. I think maybe one of the power cabled got crimped when somebody was putting the MB tray back in but not sure. To be honest the thing is so large that I moved it to the garage on a dolly and its been there since (doing other projects and just lazy). I did find a SCSI ZIP and larger HD for it so when it gets fixed it will be complete.

So you didn't resolve the smeared display issue before storing it? The search for a solution goes on.

 

[Unknown_K]

The display was very dim when it worked.

 

[Torbar]

Apologies if I missed something again but I haven't seen where bsteckler reported that a new PRAM battery resolved this.


Since you have +12V at the molex connectors, if you feel comfortable doing so, you may be able to rule out power to the video amp IC by taking the shield off the CRT neck board (if there is one) and measuring voltages on the IC. The chip in question will probably be the only one with a heatsink on the neck board, and the datasheet/pinout should be available online. In my (limited) experience there should be at least one positive supply of around 10-20V and a second one around 50-100V.

Caution would need to be taken when measuring things on the neck board, however, as the G2 and focus voltages are also present elsewhere on it (usually on the order of several hundred volts, and a couple thousand volts, respectively).

video amp IC is mc13282ep

https://www.datasheets360.com/pdf/-8350414490174498621

Should I check
Pin 9, 17 (power supply voltage)
And then
2,4,6,8,10,12?(Video amplifer inputs)?


G2 and Focus are the 2 wires coming off the flyback I assume?

 

[Torbar]

neckboard photo
P301 is RGB connector(black one). P305 and P302(white ones) go to the analog board

 

[AwkwardPotato]

Should I check
Pin 9, 17 (power supply voltage)
And then
2,4,6,8,10,12?(Video amplifer inputs)?

Checking 9 & 17 would be a good idea. Probably not much to gather taking DC measurements of the inputs.

G2 and Focus are the 2 wires coming off the flyback I assume?

Yep!

The MC13282 appears to just be the video pre-amp. On the AIO neck board, it actually seems that the video amp that drives the CRT cathodes is implemented discretely rather than being a single IC (basically the whole bottom half of the board including Q303, Q307, Q311). If P302 and P305 have their pins labeled on the back side of the board, it might be easier to verify that the amp is getting what it needs by measuring voltages on them (e.g. on the tray-load iMac, there are pins on its equivalent of P302 specifically labeled 6.3V, 12V, 79V, and 127V).

 

[Torbar]

Checking 9 & 17 would be a good idea. Probably not much to gather taking DC measurements of the inputs.

Yep!

The MC13282 appears to just be the video pre-amp. On the AIO neck board, it actually seems that the video amp that drives the CRT cathodes is implemented discretely rather than being a single IC (basically the whole bottom half of the board including Q303, Q307, Q311). If P302 and P305 have their pins labeled on the back side of the board, it might be easier to verify that the amp is getting what it needs by measuring voltages on them (e.g. on the tray-load iMac, there are pins on its equivalent of P302 specifically labeled 6.3V, 12V, 79V, and 127V).

I'll hopefully have a chance to check either tomorrow night or this weekend.

Would an issue with the G2 or Focus wiring potentially cause this? I had to splice+solder them from the neckboard to the new flyback

 

[AwkwardPotato]

G2/focus shouldn't be an issue. As long as they aren't arcing out at the splices I'd say you're good there.

 

[ried]

My AIO's internal display is smeared and dim every day now. So it went from working properly, to working for the first several minutes of operation, to not working over the last few weeks.

 

[Torbar]

So a bit of an update

I went to test the voltages from the back of the neckboard, and I turned the machine on, and display was fine!(except needing a focus ajustment). Had it running for about 10 minutes, and then it started having the issues again. (No sound, but I have the motherboard out of the case so I'm assuming somethings just not hooked up right for that.)

Anyway, I went to check the voltages after the issue with connector P302, and they all were accurate, except for the 160v was showing 127v, which seems a bit low.

I'm letting it sit unplugged again overnight, will see if it shows correct again for a while, and if it is showing correctly, seeing if the voltage is closer to the 160v. And if that's the case, will be at least a hint

 

[Torbar]

let it sit for like an hour. Screen is normal again. Same voltage from that last pin still. About 127v. So that’s not the issue.
Maybe reflowing all the connectors might help?

Edit: lasted about 10 minutes before funkyness again

 

[ried]

You're definitely honing in on the exact same issue I'm having. Behavior is just about identical.

 

[mg.man]

Maybe reflowing all the connectors might help?

Can't hurt. These two look suspicious...

 

[ried]

Pure speculation on my part, but is the neck of the CRT putting any weight or stress on that particular part of the neckboard? Such that if the unit is shipped or moved it breaks a nearby connection? If so, makes sense that the central area of the neckboard is one to watch.

 

[Torbar]

redid all the joints that go to the CRT tube, and the connectors. both analog board and neckboard. no difference. in fact, as soon as i turned it on it was the messed up display.
One theory I have(for mine at least), and potentially ried's) is heat.

When I was messing with it yesterday, just got home, so the house was like 58-60 degrees F

Today, it was like 67.

Turned the heat down in the house since i'm heading out in a bit, , also I put the metal sheielding on around the CRT, which I noticed had a metal thing on it that goes against a heatsink on the PSU. so i'm guessing the shielding is acting as a heatsink as well. that area is warm to the touch

I really know im gonna jinx it, but the machines been on for about 15 minutes and the display looks good still. Leaving in about another half hour so will keep it on, and update this post

For @ried , current advice I can give to you with this is, reseat all the cables you can. Including the RGB cable that goes to the neckboard(if you're comfortable with working in a CRT). Also, maybe put a fan against the mac for a while to cool it down, and see if you have any luck with the display being normal?


edit: its been running the graphing calculator demo for about a half hour and its still happy. Probably have about 10-15 mins before I have to head out. No sound still, but i'm not 100% sure if that's the same problem

 

[Torbar]

video still going strong. will test some more tomorrow
still no audio though. both headphones and internal speakers.

tried without AIO ribbon connected, same thing


reseated personality card, same issue

I checked with mac84, he has a g3 AIO board on his bench, headphones plugged into personality card, and it chimes.

so there also seems to be an issue with my personality card? will have to do some more digging with that

 

[ried]

For @ried , current advice I can give to you with this is, reseat all the cables you can. Including the RGB cable that goes to the neckboard(if you're comfortable with working in a CRT). Also, maybe put a fan against the mac for a while to cool it down, and see if you have any luck with the display being normal?

I disassembled it, took off the neckboard and cleaned everything with compressed air and alcohol swabs. Did a real, solid cleaning job on the entire inside of the machine. Re-installed the neckboard and ensured it was fully seated against the CRT, and that all cables between the neckboard and the analog board were seated firmly, plus the RGB cable and the two red lines coming from the flyback. Plugged in the machine and started it up. No chime, so I figured it was in the same condition as before, but held down Cmd+Opt+P+R and zapped the PRAM, subsequently heard the boot chime and the display turned on as normal.

I don't know how long it'll last, but will report back.

 

[ried]

Didn't last. Let it sit while putting the case back on and tried firing it up again. Back to smeared / dim display and no sound.

I checked with mac84, he has a g3 AIO board on his bench, headphones plugged into personality card, and it chimes.

so there also seems to be an issue with my personality card? will have to do some more digging with that

I just tried headphones plugged into the personality card and can hear a faint chime, too. When switching to the headphone jacks on the front of the machine, same faint boot chime and sound when i.e. adjusting the volume. It's faint and quite buzzy (electric noise during boot sequence), but there is sound on all 3 headphone jacks on the machine (1 rear, 2 front) - but still no sound out through the internal speakers.

Display is still smeared / dim.