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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: Sun Jan 03, 2016 8:22 pm    Post subject: Reply with quote

You can find the capacitor list for the N4000A logic board here:

http://www.asterontech.com/Asterontech/NeXT_MegaPixel_Restore.html

I will at some point add the N4000 as well.
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bobo68



Joined: 03 Jun 2015
Posts: 194
Location: Germany

PostPosted: Tue Jan 12, 2016 10:28 am    Post subject: Reply with quote

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.
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barcher174



Joined: 07 Dec 2012
Posts: 560

PostPosted: Tue Jan 12, 2016 10:41 am    Post subject: Reply with quote

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.
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bobo68



Joined: 03 Jun 2015
Posts: 194
Location: Germany

PostPosted: Tue Jan 12, 2016 12:21 pm    Post subject: Reply with quote

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!
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cpu



Joined: 24 Apr 2011
Posts: 1
Location: Germany

PostPosted: Mon Mar 21, 2016 5:57 am    Post subject: N4000A with new life! Reply with quote

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.
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barcher174



Joined: 07 Dec 2012
Posts: 560

PostPosted: Mon Mar 21, 2016 10:43 am    Post subject: Reply with quote

Congrats! Glad I could help inspire the fix.

--
Brian
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SlateBlue



Joined: 23 Aug 2015
Posts: 75

PostPosted: Wed Apr 12, 2017 7:22 am    Post subject: Reply with quote

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?
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