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
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.
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.
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.
Yeah, ceramic capacitors last WAY longer than 'lytics.
Please document your work (cap types, some photos).
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.
Quote from: "barcher174"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).
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. :)
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 (
http://www.thevalvepage.com/teletech/crt_rej/crt_rej.htm) and a classic way to get more life out of a tube but it's purely a temporary ordeal.
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.
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.
Quote from: "bobo68"Quote from: "barcher174"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
Yes, real life got in the way. I should have more time after next week to finish this project.
Do we have a reminder function in the forum? :D
You can find the capacitor list for the N4000A logic board here:
http://www.asterontech.com/Asterontech/NeXT_MegaPixel_Restore.htmlI will at some point add the N4000 as well.
Thanks.
Did you experience a discharge when you shorted the anode of the CRT (step 5)? There is some debate amongst e.g. compact Mac owners (SE/30, ...) if this is necessary. A modern CRT should have bleeder resistors.
I did not hear a discharge, but I did let the monitor sit for a week just in case. I would think in terms of potential charge a 17" would probably be more dangerous than the 9" in a mac, but I'm not an expert by any means. I would say it's not worth the risk to skip this step.
But there is also a risk that the discharge procudere goes wrong and you get a shock. Or you are discharging into the wrong part of the monitor and damage stuff.
It's a matter of what is more risky I guess.
Just remember: always keep one hand in the back pocket when discharging!
My N4000A was completely dark, no more high voltage. Before, it already had had a distorted picture, but since I use my TurboStation only as a server, I didn't need the monitor and so I never fixed it. But now the NeXTStation would not boot any more and I needed to see what was written on the screen.
I took the list of capacitors and checked every one of them (for capacitance and ESR). And, oh boy, 20 of them were defective! I replaced only the defective ones, eh voila, I now have a perfect picture on the screen again! Thank you so much for hinting towards problems with the capacitors!!
I also added a switch to the monitor to turn it off (cuts +12V and -12V) when not needed. This way I hope to extend the life of the picture tube (and avoid the infamous dimming).
FYI here is the list of capacitors from my N4000A with comments (sorry for the German words in there):
C: nominal value, voltage, current capacitance, ESR/Ohm, comment, new capacitance measured, ESR/Ohm of new C
C2: 22uF, 100V, 19.5uF, 10.5, replaced, 22uF, 1.33
C3: 330uF, 35V, 330uF, 5.6, replaced, 286uF, 0.1
C5: 100uF, 100V, 99uF, 0.44, ok
C6: 330uF, 35V, 286uF, >40, replaced, 335uF, 0.58
C7: 1000uF, 35V, 1139uF, 0.78, ok
C8: 1000uF, 35V, 943.7uF, 0.67, ok
C11: 22uF, 100V, 36uF, 12.7, sollte ersetzt werden
C14: 330uF, 35V, 332uF, 0.47, ok, für C36 eingebaut, 220uF, 25V, 243uF, 0.21
C15: 330uF, 35V, 335uF, 0.58, ok, für C6 eingebaut, 220uF, 25V, 254uF, 0.29
C17: 22uF, 100V, 18uF, >40, replaced, 19uF, 8.6 (kein besserer da)
C24: 330uF, 6.3V, 350uF, 0.78, ok
C31: 22uF, 50V, 16.5uF, 0.9, replaced, 25uF, 0.56
C33: 1200uF, 35V, ???, 0.24, ok
C34: 1000uF, 35V, 904uF, 0.91, ok
C35: 22uF, 50V, 14uF, 1.8, replaced, 23uF, 0.7
C36: 330uF, 35V, 309uF, 36, replaced with C14, 332uF, 0.47
C37: 22uF, 100V, 21uF, 14, should be replaced but no replacement available
C43: 1uF, 100V, 0.73uF, >40, replaced, 1.6uF, 1.6
C44: 22uF, 50V, 11uF, 7, replaced, 23uF, 0.5
C48: 100uF, 100V, 104uF, 6.4, should be replaced but no replacement available
C56: 1uF, 160V, 0.0002, ??, replaced, 1uF, 350V, 5.6
C62: 22uF, 100V, 18.2uF, 39.4, replaced, 290uF, 200V, 0.08
C68: 100uF, 35V, 64uF, 1.3, replaced, 96uF, 64V, 0.44
C69: 22uF unipolar, 25V, 0uF, ??, replaced by homemade cap, 28uF, 0.28
C70: 22uF, 50V, 9uF, 39, replaced, 24uF, 0.59
C80: 1uF, 50V, 0.41uF, 40, replaced, 1uF, 1.4 (auf Platinenunterseite gelötet, zwischen Pin8 (Masse) und 11 von IC4)
C99: 47uF, 50V, 56uF, 0.56, ok
C200: 22uF, 50V, 12uF, 6.4, replaced, 26uF, 0.38
C202: 22uF, 50V, 12uF, 5.2, replaced, 24uF, 0.38
Sound board:
alle SMD-C haben ca. 50uF und 2.3 Ohm ESR.
Grosser C hat 1798uF und 0.03 Ohm ESR.
Alles OK, nichts gewechselt.
Congrats! Glad I could help inspire the fix.
--
Brian
I recently completed a recap job on my 4000A. The image seemed to be much more stable and crisp. However, mine, too has slightly dimmed. I adjusted the white level pot to compensate, but I'd be interested in giving rejuvenation a try. There are several B&K rejuvinators on eBay. Will any of them work?