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https://www.eevblog.com/forum/testgear/tektronix-2465b-oscilloscope-teardown/750/1 q* ^+ x# ^5 N0 t( U
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" r: o& T W5 [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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% ~' X6 {& D8 ?7 y: [; g2nd, 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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, X! P7 C! C7 Q/ L+ `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./ R; P8 `9 D4 o6 A8 j
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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.4 I, f8 [0 d: S! Z) i6 K
$ M8 x) j% A: N# r5 R+ `. _( lOn 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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8 t7 R8 H4 r3 kI 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).$ n5 A# N8 q, m8 q9 f
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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.$ x" s3 y8 q* S) R+ m! o
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你有沒有A26板?, U5 \0 `& L2 Z( F, K
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