6. Vertical Deflection Module
Now we'll start on the vertical. This board has three separate vertical amps
that drive the yokes, and they are directly controlled by the DAC's (digital to
analog converters) on the board. There are 8 resistors I'll recommend for change
on this board. Changing the caps on this board did not make any measurable
(scope/meter) change or difference on this board. But replacing certain
resistors did.
http://www.micro-ohm.com/ You'll want Part# FRN1/4 - 1 ohm 5% tolerance
On the early version boards, you'll see that resistors R720, R721, R820,
R821, R920 and R921 are mini one (1) ohm resistors. On the later version boards,
there are two of these one ohm resistors in parallel, they are the plus and
minus 15 volt supply rails for the vertical output IC's. So that would mean that
the early version boards had a one ohm resistor on each of the IC's supply, and
the later version boards have one half ohm (1/2 ohm) on each supply rail. In
other words the upgrade was a doubling up of these resistors. I only had three
problems with the design of these projectors, and the use of these Mickey-mouse
resistors is one of them. They're supposed to be fusible metal film resistors at
1/2 watt.
Your choice would be to upgrade by adding the other resistor in parallel to
the one in place, that's if you have the early version board, or do as I do on
both the early and later version boards - remove all of them and put in real
fusible resistors. You'll also want to replace R5 and R6 with the same resistors
also.
Solder each lead on the three vertical output IC's, and remember to remove
all solder flux (denatured alcohol), flux is good for soldering, but bad for the
circuits.
The above greatly improves the vertical boards stability.
While you have this board out, it’s a good time to perform the "Vertical
Squeeze Mod". This decreases the vertical size for 16:9 operation. the circuit
was probably designed more for computer presentation.
The mod requires the replacement of 3 resistors on the vertical board (R704,
R804 and R904). These resistors are 30K ohm, they should be replaced with 56K
ohm resistors, and it's best to use metal film resistors @ 1 to 5% tolerance. I
use 1% 1/4 watt from Digikey.com, Part# 56.2KXB.
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