Bill
1) (C) dates have no real bearing on date of manufacture they can be
years apart or even decades apart.
2) Unless you know or have access to the repair history for your unit,
anything is possible as relates to actual board versions in your unit.
If it was repaired at some point in the past by an "Authorized Service
Center" it can have a "later" board installed as part of the repair, by
the early 80's there was already little incentive for these centers to
repair to the component level, swap a board instead, takes less time and
generates more revenue. If it was repaired by some "entrepreneur" using
boards from? an "organ donor - parts scope" the board in question can be either or later than the board it left the factory with.
3) Coming to life after an hour can be a function of some electrolytic
capacitor forming up after time
4) Replacing caps can usually never hurt unless someone gets sloppy with
a soldering iron, after all this scope is getting close to 50 years old.
5) Does the beam finder work at all?
6) Are all the LV power Supply voltages in spec ?
7) Why do you suspect HV diodes?
-DC
manuals@...
On 6/11/2018 1:50 AM, william_b_noble wrote:
I decided to dig into an early 453. Interestingly it does not match the schematics for the 453 or the 453A - some boards seem closer to the A, some to the earlier one - for example the Z axis board is clearly dated (C) 1965, but its layout matches the board found in the A manual (unless I'm just loosing my mind). This scope sat around for several years after I got it and never plugged it in - when I did plug it in there was initially no light on the CRT (except the scale illuminator) - as I messed with it for about an hour trying to make sure what was wrong, it fired up and showed a spot and vertical deflection, I could center it, but there was no trace. then it stopped. The HV circuit is one of those that will stop oscillating if there is an overload, so it's hard to troubleshoot, and harder without an HV probe. But it's clear that something is overloading the circuit. If I disconnect the cathode and grid bias circuits, it makes HV and powers the CRT filament just fine. I've tried all sorts of things, one at a time, and disconnecting the .015uf 3Kv capacitors by itself doesn't work, disconnecting the diode that drives the grid string does let it work, and the list goes on. I've come to the conclusion without a good way to verify it that it is most likely that at least one of those 3KV ceramic caps is leaky, and if one is bad, the others are probably not far behind, so I've ordered some. The HV diodes are also suspect, though they both seem to act like diodes at 115V (with a 10 W lightbulb as the load), I ordered some microwave oven diodes just to be on the safe side. I don't think my 1M CRT Grid Bias control is bad like was found upthread, when the power supply works, I can adjust the grid bias. But now, if the supply oscillates the current can rise to about 2.9 amps (it's fused at 2 amps) with all the loads connected. The transformer isn't potted, so I think it's probably not the issue.
anyone care to offer some advise on something I could have missed? I'd like to get this scope working just to say that I did it - I have a couple of newer ones to look at next, I figured this one first, it's all discretes, how hard could that be >>>
--
Dave
Manuals@...
www.ArtekManuals.com
