红灯记 发表于 2020-2-27 19:24. h& |9 r" Q+ C$ c! M! l- ?
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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8 B4 K2 ~- g9 F0 K5 Xhttps://www.eevblog.com/forum/testgear/tektronix-2465b-oscilloscope-teardown/750/$ X$ h9 Y( w- ?# h) U# y {
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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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$ N& X# w1 ]& b0 v" q2nd, 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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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.- C3 c# A) m$ Y
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6 k" d! h( y: f' C* ^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.) I) Z0 \0 b3 M `
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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. G& f: {" e. v: T! h0 \- _- N
$ z- q- O0 V9 o# s2 h2 lI 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)./ P6 d9 H5 y( W/ [
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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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, f; l, K( ?: p5 ^' x你有沒有A26板?! R4 T+ d0 u! v' G8 v5 X5 V
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发表于 2020-2-26 12:09:28
