pmr@drutx.UUCP (Rastocny) (08/16/84)
<will this bug ever go away?> While cleaning the video heads of my Fisher 730 VHS last week, I noticed a couple of things about its design that I thought I'd pass along to you technical types who like to dabble. Fisher carefully grounded all metal parts and circuit ground to the chassis, but in doing so they built in about a half dozen ground loops. After lifting all ground straps and connecting a VOM to chassis ground, I removed three unneeded ground wires and rerouted all grounded components to a true single point ground configuration at the power supply with larger (#14 stranded) wire. At this time, I also noticed a high contact resistance where the center ground contact touches the rotating video head (see illustration). This resistance measured between about 4 and 250 ohms, depending on the position of the head. I carefully polished the surface of the video head at the ground contact point with #400 sandpaper and lightly sanded the graphite-composition contact (v in the illustration) to remove any oxide buildup. Ground resistance improved to less than one ohm at any position of the head. Center Ground Contact ----------------------------------------- | | v ------- ----- --- | | - --------------- --------------- Chassis | Rotary Video Head | Ground --------------- --------------- | | ----- Observed results: No noticeable record/playback improvement in SP, but markedly improved resolution in both LP and SLP. These mods may not apply to every VCR on the market, but it is something that can be easily checked out and changed. I'm not sure that the new #14 ground wires bought me anything, but on the other hand it didn't hurt anything either. Anyone else discover built-in bugs like this from the factory in their units? Phil Rastocny ihnp4!drutx!pmr