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Poorly 485


Ondrej Pavelka
 

Hi folks,

I acquired abandoned abused lonely 485 for equivalent of $40. I couldn't leave her there.

When the time base is 10uS or shorter it works but it's rather blurred, very far from nice sharp trace. At settings shorter then 10uS I can even run delayed B sweep and all behaves rather well.

Ventilator is not turning
6 pots are missing knobs
Vertical amps look both OK

I will start by checking the PSU and clean and lubricate all the switches and pots but I don't think this will resolve the problems with times above the 10uS.

What do you think is causing the defunct ranges above 10uS?

Thanks


 

On Sun, Nov 29, 2020 at 12:31 AM, Ondrej Pavelka wrote:


What do you think is causing the defunct ranges above 10uS?
The first suspect would be a bad contact in a timing switch associated specifically with times above 10 us/div (SM, dwg page 10, "Timing Switches"). At time base settings longer than 10 us/div, switch A26 is (supposed to be) engaged. So have a look at the functioning of the switch and associated components, like R877 (dwg 7) and don't forget the associated contact of relay K879, also on dwg 7.

Raymond