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 Post subject: Tek 475 CRT anode lead won’t come apart
PostPosted: Feb Sat 16, 2019 8:53 am 
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Joined: Oct Thu 26, 2017 5:04 am
Posts: 52
I need to remove the CRT from one of the Tektronix 475 scopes I’m repairing. The problem is, I can’t get the anode lead to come apart. Does anyone have any tips on how to do this?


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 Post subject: Re: Tek 475 CRT anode lead won’t come apart
PostPosted: Feb Sat 16, 2019 4:51 pm 
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Joined: May Thu 14, 2015 4:15 pm
Posts: 1375
Location: Dallas, TX
There were a few scope CRTs that had the anode lead as part of the tube. I don't know if that is the case here. Does the other end of the anode wire unplug?

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 Post subject: Re: Tek 475 CRT anode lead won’t come apart
PostPosted: Feb Sat 16, 2019 4:59 pm 
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Joined: Jan Thu 24, 2019 1:22 pm
Posts: 47
Location: Centennial, Colorado 80122
The CRT anode lead has a compression connector to the HV power supply and its normally tight, but over time has likely got stuck. I would try soaking it in something like alcohol, but take care not to let it drip into the unit.


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 Post subject: Re: Tek 475 CRT anode lead won’t come apart
PostPosted: Feb Mon 18, 2019 2:40 am 
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Joined: Oct Thu 26, 2017 5:04 am
Posts: 52
Success! I decided I just needed to get a better grip on the connector so I put on a dishwashing glove. The connector popped right out! Amazing how easily the CRT slides out of the chassis.

Unfortunately, this didn’t solve my problem. This particular unit had several screws rattling around in the chassis. I got two out but couldn’t find the third. Thought it might be in the CRT housing, but no luck. Turns out it was in the housing containing the high voltage multiplier and transformer. I’m surprised it got in there since it was barely smaller than the opening where the HV anode lead comes out.

I wonder if that screw is what caused the blown fuse I see on the 15V unregulated HV supply? I understand that other likely culprits are the 47uF decoupling tantalum capacitor and HV oscillator transistor. Time to take some resistance measurements...


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 Post subject: Re: Tek 475 CRT anode lead won’t come apart
PostPosted: Feb Wed 20, 2019 12:19 am 
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Joined: Oct Thu 26, 2017 5:04 am
Posts: 52
Culprit found—the decoupling capacitor for the horizontal amplifier had shorted out. Amazing that after replacing only one bad component the whole scope roars back to life.


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