[sdiy] [OT] My Scope Saga

Richie Burnett rburnett at richieburnett.co.uk
Thu Mar 21 23:51:58 CET 2019


Adam, Oscilloscope HV problems are a nightmare because if the HV is wrong it 
messes up the calibration for the horizontal and vertical deflection too :-(

For example, if the HV is too low the electrons pass through the deflection 
plates slower than intended and the resulting trace on the CRT screen is 
larger than it should be.  Also usually dimmer and probably out of focus 
too.

-Richie,


-----Original Message----- 
From: Tim Ressel
Sent: Thursday, March 21, 2019 6:42 PM
To: synth-diy at synth-diy.org
Subject: Re: [sdiy] [OT] My Scope Saga



My replacement power supply came in this morning. I am no longer 
scope-negative!


On 3/17/2019 5:25 PM, Adam Inglis wrote:



On 18 Mar 2019, at 9:56 AM, Brian Willoughby <brianw at audiobanshee.com> 
wrote:


I think it’s kinda funny, because sometimes I repair vintage synths for 
local musicians, but I have to look to someone else to get my ‘scope 
repaired.




I’ve recently finished repairing a 50 year old CRO. There were a variety of 
(mostly power related problems) but the area that really stumped me was the 
high voltage circuit for the CRT itself. I had no experience with this type 
of circuit and no way of testing the high voltages. I made a divide-by-10 
test probe, took a voltage measurement at virtually every point on the 
schematic and muddled through, ended up virtually rebuilding the entire HT 
circuits either side of the coils, and eventually got those electrons 
hitting the screen in a coherent way. Took a couple of years between all the 
other jobs….

Adam

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