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Old 11-22-2020, 09:31 AM
DavGoodlin's Avatar
DavGoodlin DavGoodlin is offline
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Join Date: Aug 2011
Location: near Strasburg PA
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Convergence rectifier question

It was impossible to bring in some dynamic adjustments on a Zenith 21" so I figured there was something I forgot about these. This has not affected static convergence, center screen is all OK.

One reason that I suspected the convergence rectifier pack was it looks to be selenium. Then one tested open, so I put in three 1N4005s, which are silicon rectifiers. There were also two paper caps, one a bumble bee and the other a white tube-stuffed one.

Replaced two 100 ohm 1W resistors in series with these rectifiers, and a (blue-horz top) pot connected to the third. Then also, there was an 82 ohm 1 watt I replaced.

Since I replaced these three diodes with silicons, the negative voltage to ground as shown Sams is higher at resistors. The red vert lines are impossible to pull in on both sides. The 100 ohm I put in both run hot.

I noticed that later sets like Z-models used 220 ohm resistors in place of both 100 ohm 1 watts. Zenith schematic also shows a current of 25 ma. Maybe I answered my own question.

Pretty sure RCA, Magnavox and others used similar circuits, and surprisingly I never went into the weeds on convergence boards of all things. I'm aging into being a perfectionist or just started doing what was expected of a tech 50 years ago.

Has anyone else had this issue?
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Last edited by DavGoodlin; 11-22-2020 at 09:36 AM.
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