AN/UGM-11 (Wavetek 404) Notes from repair

Here's what I vaguely remember from troubleshooting a couple of years ago ---

The top PC board is mainly the tone generator - some LS163 4-bit counters feed adders and then address a PROM
This eventually addresses a 12-bit D/A (AD565) and AF output via a 741 op amp (?) and Q1, Q2

The bottom PC board is the baud rate generator plus message generator circuitry.

U37 gets 3.xx mc in and divides it by 128 to 384kc output (TP1 = Test Point 1)
U38 divides this by 128 to 3kc (for 75 Baud) which eventually shows up at TP3
This gets divided by 40 (U53, U55, and U54) and shows up at TP4 at the bit frequency.
This gets divided by 8 by U17 and shows up at TP13 (Why 8 instead of 7? - needs investigation)
FINALLY, this signal drives U3, a 12 bit counter that addresses the message PROMS (FOX, KWR37, KG14, etc.)
I assume the PROM outputs feed a shift register or UART but don't have any notes on this part of the circuitry yet

Some more notes from troubleshooting (2/17)

The DISTORTION switch S2 feeds a 74LS147 10-input priority encoder (U57) which outputs 4 bits.
These feed the 4 lower address bits of an IM5600 32x8 PROM (U52).
Outputs 0-3 of the PROM preload a 74LS161 counter (U55). This counter is clocked by pulses whose frequency depends on the baud rate setting (test point TP3 - 1820 Hz for 45.5 Baud and 3000 Hz for 75 Baud)
U55 counts up N ticks from the preload value to 15 and then counts 0-15 before preloading again. So the preload happens every N + 16 ticks.
IF the distortion = 0, then N should be 4 (preload = 1100), making 20 ticks total. N is changed to create the desired distortion.
The output of U55 goes on through a little more logic to clock the serial output, increment the address counters of the message PROMs, etc.
My problem.... Somehow the output of my U52 PROM had changed from 1100 to 0100. So for 45 baud, I was getting 28 clock ticks resulting in 30 ms bit times instead of 22 ms bit times (test point TP4). I said "forget distortion" and wired bit 3 high.

HIGH LEVEL (60 ma loop) notes (2/17)

There is no internal loop supply - you must supply a loop (probably 200vdc max) with a series resistor limiting the loop current to 60mA
There are two independent loops DC-1 & DC-2. Loop polarity doesn't matter because there are bridge rectifiers on the switching transistor outputs.
DC-1 is switched by Q6 (2N3440) which is driven by Q5 (2N3440) which is driven by opto-isolator U45 (TIL-111) which is driven by Q4 which is driven by Q3.
DC-2 is switched by Q10 (2N3440) which is driven by Q9 (2N3440) which is driven by opto-isolator U44 (TIL-111) which is driven by Q8 which is driven by Q7.
Q3 and Q7 are driven by a TTL-level bit stream selected by the MODE switch (space, mark, reversals, FOX, etc.)

Operational notes (2/17)

Set the OUTPUTS switch to BAUD for 45.5 and 75 baud serial - output is 7.00 unit code, not 7.42
LOW LEVEL outputs are +/-5v for TEMPEST signaling.
I don't know what the SATCOM outputs are for.
Other settings of OUTPUTS can be used for AFSK audio output - these will run at 75 Baud (green LED on)
For UCC-1 audio output, set OUTPUTS to 85 shift and turn on desired UCC-1 channels
My tones frequencies are off, so I still have a problem there to track down - the sine wave audio out looks good though.