What the PROM does is it "monitors" the N-Code fed to the Translator board from the DR7 for two purposes. The first is to disable the action of the Up or Down button when your reach the edge of a band switch segment. This keeps you within the limits of the high pass and low pass filter sections of the band switch. The second is to keep your from transmitting outside of a ham band. It is pretty clever really. The address lines of the PROM follow the N-Code and the contents of the PROM memory at any given address will either enable or disable the buttons as needed and also operate Q9001 to inhibit transmit in 500 KHz segments that do not contain a ham band.
The radio will work perfectly well with the PROM removed entirely but you would need to be mindful of the filter edges. Worst case, you could smoke a low pass section by transmitting above it's cutoff frequency or transmit unwanted harmonics.
A known failure mode of these PROMS is one of the address lines going shorted which disrupts the N-Codes. This may be from careless handling causing ESD damage as the PROM inputs are tied directly to the male Molex pins on the bottom of the board.
PROMs are available if you need one.
73
-Jim
NU0C
On Fri, 24 Mar 2023 15:11:39 -0700
"kmg53 via groups.io" <kmg53@...> wrote:
(Belated) Thanks, Nick. I have time again to work on it. I also have the TR-7 service manual which explains what the chip is doing, but I was unclear about why the two legs were broken. I'll be looking up that chip diagram to see how it does what it does.
--
Ken KA4MIE
Jim Shorney