I finally got my R-7 working again. I fried the PROM, U201, on the digital control board nearly two months ago when I accidentally created a solder bridge between the 5 & 10-volt P/S lines while trying to change the use of the Aux. Program switch [S6] so it selects the P/S outputs for a meter output jack I added on the rear panel.
This PROM is apparently obsolete, particularly with the required programming so I had to design something that converts the digital inputs from the band switch to the necessary BCD values for the DR-7 & translator boards. Since this PROM is the core of the entire digital control board I ended up replacing the board to avoid the need for an additional board to house the replacement parts for the PROM. The radio works on all bands again [TR-7 boards don't work on the lowest three ranges] & appears more stable than before although I can't be sure that the improvement is totally because of the new board; it may also be due to the various board connections being reseated. I used a perf board & wire wrap termination but any wiring style should work fine. Also, I used 1N5817G Schottky steering diodes to reduce internal voltage losses although 1N914/1N4148 should work just as well. If you want a copy of this circuit &/or the truth table let me know off list via e-mail & I'll send it. [Also, if you want to use the Aux. Program switch to select P/S voltages this switch has shorting/overlapping [make before break] contacts so it must be replaced with a non-shorting type.] 73s. Dave _______________________________________________ Drakelist mailing list [email protected] http://mailman.zerobeat.net/mailman/listinfo/drakelist
