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Worth it to try replacing the caps in a monitor?
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barcher174



Joined: 07 Dec 2012
Posts: 560

PostPosted: Fri Nov 13, 2015 11:55 am    Post subject: Worth it to try replacing the caps in a monitor? Reply with quote

I have a megapixel that has a distorted screen. It starts up looking like it has a sync issue, then seems to stabilize after it warms up. Still it has what I would call ghosting or streaking next to text. I've tried adjusting the pots on the back but can't get rid of it. Has anyone recapped a megapixel monitor? I'm inclined to think they are the problem due to the warm up behavior. Should I just do the electrolytic? What about the ceramic or mylar? I only want to do the discharge procedure once....

Thanks,
Brian
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nekonoko



Joined: 31 Oct 2007
Posts: 27
Location: Pleasanton, CA

PostPosted: Fri Nov 13, 2015 2:31 pm    Post subject: Reply with quote

I haven't recapped a megapixel display, but I have recapped an arcade monitor with similar symptoms to what you describe and it cleaned it up beautifully. I'd say it's certainly worth a shot.

Usually you would only need to worry about electrolytics, ceramic and mylar don't normally fail.
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barcher174



Joined: 07 Dec 2012
Posts: 560

PostPosted: Fri Nov 13, 2015 3:31 pm    Post subject: Reply with quote

OK, sounds good. I only ask about the other capacitor types because of the voltages and heat inside. I may do the ceramics next to the pots just because they are cheap, but I'll ignore the mylars.
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mpatoray



Joined: 06 Jul 2015
Posts: 2

PostPosted: Tue Nov 17, 2015 5:30 pm    Post subject: Reply with quote

I would really not worry about the ceramic capacitors, they rarely fail. As for the electrolytic capacitors replace with good quality Panasonic or Nichicon I would get either 105 or 125 degree high temp capacitors, and for the horizontal section use high frequency capacitors and in the power supply area use low ESR caps.
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pentium



Joined: 23 Jun 2006
Posts: 1148
Location: Kamloops, BC

PostPosted: Wed Nov 18, 2015 9:28 am    Post subject: Reply with quote

Yeah, ceramic capacitors last WAY longer than 'lytics.
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bobo68



Joined: 03 Jun 2015
Posts: 194
Location: Germany

PostPosted: Sun Nov 22, 2015 2:23 pm    Post subject: Reply with quote

Please document your work (cap types, some photos).
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barcher174



Joined: 07 Dec 2012
Posts: 560

PostPosted: Mon Nov 23, 2015 1:31 am    Post subject: Reply with quote

Caps fixed it. I'll get a list together of the ones I used. Wasn't too bad to do. Took me about 3 1/2 hours start to finish.
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bobo68



Joined: 03 Jun 2015
Posts: 194
Location: Germany

PostPosted: Mon Nov 23, 2015 3:05 am    Post subject: Reply with quote

barcher174 wrote:
Caps fixed it. I'll get a list together of the ones I used. Wasn't too bad to do. Took me about 3 1/2 hours start to finish.


Thank you. Problems also fixed, I guess (so the caps were the cause).
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barcher174



Joined: 07 Dec 2012
Posts: 560

PostPosted: Mon Nov 23, 2015 9:59 pm    Post subject: Reply with quote

I tried doing the original MegaPixel model with a dark screen tonight. The caps didn't have much effect except to slightly stabilize the image. I went one step further and used a CRT rejuvenator I picked up on eBay and now the image is what I would consider passable. I need to read up more on rejuvenation. It's possible I didn't do it totally correctly. At the moment it's all magic to me. Smile
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pentium



Joined: 23 Jun 2006
Posts: 1148
Location: Kamloops, BC

PostPosted: Wed Nov 25, 2015 8:22 pm    Post subject: Reply with quote

The dim screens are the result of worn cathodes which is no surprise given how NeXT's completely lacked any form of power management so in some cases the monitors baked away for days or weeks on end in some cases.
A recap might restore our-of-spec voltages in the brightness or high voltage circuits though.

CRT rejuvination is always fun and a classic way to get more life out of a tube but it's purely a temporary ordeal.
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barcher174



Joined: 07 Dec 2012
Posts: 560

PostPosted: Wed Nov 25, 2015 10:22 pm    Post subject: Reply with quote

At the end of the day they have a usable life and will all eventually fail. I had not seen any reference to these tubes being restored using a rejuvenator before and decided to take a risk. I got the idea watching Arcade machine restorations on youtube. I bought a Sencore CR70 for less than the price of a monitor + shipping. I was able to use the clean/restore option which is supposedly less harmful to the life of the tube than a full rejuvenation. The Toshiba tube is fully supported and documented in the Sencore user manual along with a pre-made adapter for the pins. From my shallow understanding this clears carbon deposits on the guns. I have some more caps on order to do the soundboard on the original megapixel. I will take some photos when I go in to do those caps. At the end of the day I don't put much time on the CRTs anymore but I have a pre-release MegaPixel (no FCC ID or serial number) which I felt was worth restoring to full operation.
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nekonoko



Joined: 31 Oct 2007
Posts: 27
Location: Pleasanton, CA

PostPosted: Thu Nov 26, 2015 5:09 am    Post subject: Reply with quote

The prototype would even be worth finding a replacement tube for if it came down to it. Some old Usenet posts seem to indicate it isn't overly exotic so NOS parts should be out there still.
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bobo68



Joined: 03 Jun 2015
Posts: 194
Location: Germany

PostPosted: Sat Dec 12, 2015 10:38 am    Post subject: Reply with quote

bobo68 wrote:
barcher174 wrote:
Caps fixed it. I'll get a list together of the ones I used. Wasn't too bad to do. Took me about 3 1/2 hours start to finish.


Thank you. Problems also fixed, I guess (so the caps were the cause).


Can we have the list of caps as you said?

TIA, bobo68
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barcher174



Joined: 07 Dec 2012
Posts: 560

PostPosted: Sun Dec 13, 2015 8:35 pm    Post subject: Reply with quote

Yes, real life got in the way. I should have more time after next week to finish this project.
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bobo68



Joined: 03 Jun 2015
Posts: 194
Location: Germany

PostPosted: Mon Dec 14, 2015 3:32 pm    Post subject: Reply with quote

Do we have a reminder function in the forum? Very Happy
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