红灯记 发表于 2020-2-27 19:24
# m% U6 h! W: q% V, b/ o$ P这个帖子不一定有多人看，但是错了一定要更正补上，否则会把对此有兴趣的人的认识带偏，我个人丢丑是小事, Q! ?( K; J5 ]- \1 h6 T
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https://www.eevblog.com/forum/testgear/tektronix-2465b-oscilloscope-teardown/750/' G5 w) w! P" C
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Mark, first....I want to publicly thank you for the prior assistance you've given me in getting this 2465 fully functional. It is greatly appreciated.
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2nd, I saw your post in the other thread concerning lowering the voltage to the EAROM and I did wonder if perhaps it would help with mine. So I did some checking but I found a discrepancy in what you did vs what is currently in place and perhaps your memory of what you did 20 years ago is a little fuzzy.: P$ [+ \$ }& z" B9 e4 S8 l1 }
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I looked up A5 Board VR2003 and it's currently a 7.5 V Zener. You indicated that you lowered the voltage by 2 volts by installing a 9.1 V Zener. Isn't that actually RAISING the voltage by approx 2 volts? But you are correct. That line (OEA35) does supply the EAROM's on the both the A5 Board and the Buffer Board.1 H1 ^5 g5 }3 `& E; _
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+ G3 H4 t/ }: U. w/ @! l# {4 Y' RYou are most welcome! I enjoy working on this old equipment and I'm usually looking for excuses to pop the lid off and get out the service manuals. It's not something I get to do with more modern equipment I use on a daily basis for work.
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! z6 v7 K% I) o* N4 o/ pOn VR2003, note that it and CR2004 are used as a dropper from the +42V rail to supply the EAROM. So, the end result to the EAROM is 42V - 9.1V - 0.7V = 32.2V. The spec on the ER1400 says 35V +/- 8%, so the minimum happens to also be 32.2V.! V5 k; K' y7 F% n0 r3 h/ Z/ f
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I just verified the voltage on my EAROM (between pins 1 & 2) as 32.3V. With the original 7.5V zener, this would be higher by 1.6V ( = 33.9V).
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, g' Z1 g9 k* h9 LMy EAROM had intermittent checksum errors and I was able to get it working by lowering the operating voltage 2V (replaced VR2003 with a 9.1V zener). It's been working fine with that modification for at least 20 years now.. ~9 X2 _) b5 ~! l l- D3 p
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你有沒有A26板?% [. a9 ]& i; ]! [" z% p
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发表于 2020-2-26 12:09:28
