红灯记 发表于 2020-2-27 19:24
$ a! }6 o" H4 F. p8 ~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
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" V$ Z% B& g% }0 E) T5 T/ Bhttps://www.eevblog.com/forum/testgear/tektronix-2465b-oscilloscope-teardown/750/; n" O2 K' `2 T5 ?8 K
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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. 5 c% P/ L* v2 I
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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.( T H( p, R! q; k: n4 D& D
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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./ O5 x* ?4 V4 Z! |5 `
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' F- d; ~; M& s7 yYou 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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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).
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7 o% v& J, J# W& K8 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.; s" k0 ?$ U; o; ]
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你有沒有A26板?0 \4 k, s5 l) F& j& L& I
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发表于 2020-2-26 12:09:28
