Channel Select switch power

[+hueyjones70]

I removed the RF modulator from an 800XL and I need to restore voltage to the channel select switch. What is the best way or easiest way to do this?

[Rybags]

Voltage?  The switch just selects which channel gets the RF out.

AFAIK no XL or XE for PAL has one, and I've looked at the 800 schematic.

I'm fairly sure it just includes/excludes part of the RLC circuit with the end result of changing the offset of the final RF frequency.

[TGB1718]

As @Rybags says and as far as I know it's 800 and maybe 400 (never had one)  only and removing the modulator on one of these requires no rewiring on the channel select switch.

[Rybags]

The PAL thing was just an aside, in the US I think all machines had the channel select.  Likely as their VHF bands would have been more crowded than most places.

[manterola]

There is no voltage to restore for the channel select switch...  just get rid of the rf modulator and you are done. You can reuse the switch for other purposes IF you want.

[+hueyjones70]

I have been installing a dual OS EPROM in the OS socket and running a wire from pin 27 to the middle post of the channel select switch. The switch then changes the OS when the switch position is changed. One post of the channel switch shows 5 volts when the modulater is present. With the modulator removed there is no voltage on any post and the switch doesn't change the OS.

[+kheller2]

 

Possibly jumper pins 2 and 4 of the RF

[BillC]

2 hours ago, hueyjones70 said:

I have been installing a dual OS EPROM in the OS socket and running a wire from pin 27 to the middle post of the channel select switch. The switch then changes the OS when the switch position is changed. One post of the channel switch shows 5 volts when the modulater is present. With the modulator removed there is no voltage on any post and the switch doesn't change the OS.

According to the schematic provided pin 27 is already connected to +5V. This connection will need to be broken in order to use a 27256 for dual-OS operation.

 

Dropcheck sells a 4in1 OS adapter which does this, plus it has pullup resistors connected to pins 1 & 27 and connection points for wiring to switches. These switches would connect to ground for OS selection.

https://www.bitsofthepast.com/?product=4in1-os-adapter

[+hueyjones70]

I know that it has to be broken that is why I have it connected to the switch but when the modulator is removed, there is no voltage on any of the switch posts.

[ACML]

The channel select (with RF modulator connected) is GND --- center post --- 5VDC.  You just need to connect a 5VDC line to the correct post.  The VCC pin on most ICs is 5VDC.  Make sure you don't tie it to the GND post on the channel selector or your short your PSU.  If you have another machine with the RF modulator still installed, test which post of the channel select switch is 5VDC using a multimeter.   

[+kheller2]

Pin #2 of the RF modulator is supposed to be +5.