PowerMac G3 All-in-One, iMac G3 - Same Symptoms

[notcrazy_iminsane]

So today a friend of mine came in with a big and beige PowerMac. It powers on and works, but the screen and picture tend to pop and go out. Are these models prone to flyback failures like the G3 iMacs? I'm hoping I won't have to handle another fried flyback. I'm still trying to find any shorts in my G3 iMac Rev C with the same issue, though much louder and frequent pops. The iMac is already disassembled and ready to be tested, even if removing the flyback has proven difficult. Chances are its working parts will be sold off and the case repurposed into a cat bed.

I haven't had a PowerMac like this one to work on. Is it going to be a simple fix or a headache flyback problem?

 

[TheWhiteFalcon]

I don't know if they're prone like the early iMacs, but it's definitely an known issue. Probably needs an analog board recap.

 

[uniserver]

i found that if leave them on for a few hours, that noise stops.   seem they do that due to moisture and dust build up.

if you can blast them out with the air compressor that would help.

 

[notcrazy_iminsane]

If it's just a dusting, that'll make things so much smoother. I disassembled it just in case I need to get to the analogue board. The entire enclosure was caked in heavy amounts of dust. I'll try to give it a good dusting tomorrow!

 

[notcrazy_iminsane]

I gave the CRT, Analogue, and Power Board a good dusting, hooked it all up, and powered it back on. The screen still pops, though not as violently or loudly. This one is a head scratcher for me.

 

[uniserver]

did you let it sit on for a couple hours?

 

[notcrazy_iminsane]

That I have not. I was wary since the loud pops the iMac could make scared me too much. I'm just a little too jumpy for that! :O I'll leave it on in the back of the office and try to keep an ear out for any popping. I'll report back once I get home!

 

[uniserver]

yeah if its still doing it after a couple hours, then it might be the flyback doing something that it shouldnt.

 

[notcrazy_iminsane]

After about 30 minutes in, it began popping more consistently and frequently. About two minutes between each pop. What is the process for testing a flyback?

 

[uniserver]

let it run for a couple hours.. it should go away.

 

[uniserver]

put it in a room with Air conditioning, or a dehumidifier. 

 

[Schmoburger]

From my experience the PowerMac 5500's had flyback issues also... basically it was just a matter of whether the logic board would last long enough for the flyback to fail. lol. So it's quite likely the G3 AIO can suffer similar issues.

 

[techknight]

the flyback is bad. 

no ifs ands or buts about it. I had changed a couple out in G3 AIOs way back in the day for this exact issue. the flybacks were made by goldstar and hungwa or some shit like that. I had a cross-reference. But this was back in high school and that information is long long gone. 

But its not the flyback itself, its the Focus/G2 block that is molded part of it. What happens is dirt gets in there, moisture, etc.. These pots are super high impedance so the substrate has to be manufactured accordingly, This breaks down and the high voltage arcs over into the focus/G2 parts of the electron gun on the CRT. and thats the arcing you hear. 

Another problem is the high voltage itself could be a bit excessive if the hold-down capacitors in the horiz output stage go bad. A good HV probe should indicate if there is a problem in this area. the HV should never ever exceed 23KV in a CRT that small. 

In rare cases on something that is ir-replaceable, older TVs the G2/Focus block was separate from the flyback, and went in-line with the HV. Sometimes if you can locate a replacement block, you can cut the leads off the flyback and wire it to the system itself. 

 

[uniserver]

wow that is hard-core mike.   thanks for that info.

 

[notcrazy_iminsane]

Guess this one may face a CRT to LCD transplant at some point in the future. It looks like it was upgraded quite a bit, so I don't want to lose that. I just don't like fidgeting with flybacks and their near by components that require more work than "replace that cap".

 

[Schmoburger]

Mmmmm at this point in time, a machine has to be fairly special to warrant me bothering with a flyback replacement. If one were to fail on either of my iMacs for instance, I dare say at this stage I would simply just replace the whole A-board with a known good unit. If I had something rareish like  a Lisa or something then obviously that would change things a little.

But yes, an LCD swap sounds like a better long term option if you arent a stickler for authenticity.

 

[notcrazy_iminsane]

It's by no means a Lisa or 128k level of special to me, so I'll more than likely go for the LCD transplant route. Make the machine so much lighter, easier to move, and a tad more practical for work! Now to figure out how to put an LCD in there..