CurtPalme.com Home Theater Forum

[seanoise]

hello.
anybody knows for what these variable inductances on the hdm board are good for?
what can i adjust with them?

[Tim in Phoenix]

Hello


Those are width coils. The Marquee features a two-band horizontal sweep system with two sets of windings on each scan yoke. Below 59khz the windings are operated in series, as lower frequencies demand less current. At about 59khz the relays on the HDM switch the windings to parallel for more current, this enables the use of most of the tube face anywhere from 15khz to 130khz and, in the Ultra models, all the way to 150khz. For each yoke then, a width coil is provided for low-band and high-band width matching, six width coils in all. To match widths, one wants to null out all zone convergence then select a low-band frequency from Internal Frequencies, 31khz is fine. Turning the ferrite slug into the coil reduces width for that color, turning it out widens.

You can turn all the low-band coils out to the tip of the sleeve then turn in the ferrite slug for a color that is too wide. Same for high-band coils in part two of the process.

Once low-band widths are matched half-way up the raster, select an internal frequency such as 63khz and repeat. The low-band coils are L411 (red), L401 (green), and L421 (blue). The high-band coils are L410 (red), L400 (green), and L420 (blue).

They are arrayed, from front to rear, Red low, Red high; Green low, Green high; Blue low, Blue high.

A plastic hex tool size 0.10 inch is needed, never use anything metal. Stay away from the windings on the coil as they carry pulses over 1000 volts. One also wants to match raster heights, this is done in the service menu. The reason for matching raster widths and heights is to put the smallest load on the convergence amplifiers.


Jeez, I beat Nashou to a Marquee thread, maybe the first time ever!
.

[Nashou66]

[JustGreg]