Re: 475 questions


ciclista41@...
 

Hi Eric!

Thanks for your suggestions. Just like your advice to ask a million questions, I appreciate as much input as I can get. I look forward to sharing in the satisfaction you obviously enjoy from having restored one of these scopes!

Bruce

On Wed, May 27, 2020 at 05:41 AM, Eric wrote:


I have some things to add given that I was in a similar position
recently but with a 485.

Go glacerly slow. There are some parts in these wonderful instruments
that you will not be able to replace if they get zapped. And you can zap
things with static / probing

Spend LOTS of time with the schematic especially in the theory of
operation section. Tek wrote some of the best technical manuals out there

Practice your soldering skill NOT on the 475 get a few soldering
projects and build them up soldering is 30% knowledge and 70% feel / Art
you just have to do it.. A Lot

DO NOT use a cheap iron. Minimum recommendation here is a Hakko 888D or
equivalent from a different vender. The last thing you want to do is
over heat a trace and de-laminate it from the board. Due to poor
temperature regulation or long dwell time.

It took me 8 months to fully restore my first 485, but mine was hacked
up pretty good by the previous owner. Lots of pots were replaced with
fixed resisters.

If you going to Calibrate/align the scope you will need to know some
high voltage probing -4000 Vdc will blow your meter input with out the
proper tools.

Proceed with caution and ask a million questions. It is better to ask
then to lose a hybrid that you cant replace.

Good luck I look forward to hearing about your success


Eric

On 5/27/2020 4:14 AM, David C. Partridge wrote:
I found that by searching "neon bulb oscilloscope", I found this:
https://en.wikipedia.org/wiki/Pearson%E2%80%93Anson_effect
So the bulbs are used as an oscillator
I don't believe so. IIRC the neons in the 475 are in the EHT supply
circuit and are effectively over-voltage spark gaps.

To add to this discussion - replace nothing until you know it is causing a
fault especially if you have limited soldering skills.

David



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