红灯记 发表于 2020-2-27 19:24) w" A$ l9 x1 U- {4 o) d$ ]) k( Q) v
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) k. t$ G4 ~# u) v0 ]
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, n9 H/ r7 i' h4 z6 R# jhttps://www.eevblog.com/forum/testgear/tektronix-2465b-oscilloscope-teardown/750/0 M' F& @) I X. j( b$ X9 m
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3 i% V) C; _! T. {) t7 j7 o! tMark, 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.
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. g2 T* y; l t; c6 L- YI 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.
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You 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.1 `; ^( _/ x$ x" k! ?7 `" b' p: \
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On 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.
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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).5 d& y* ]5 {* K# ]+ [, N* f- J; j; E
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My 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.
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$ m) Q) ]& z0 n; P% d* |! o你有沒有A26板?
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发表于 2020-2-26 12:09:28
