Sequential prophet 5 - R603 +15 V Adjustment; R301 Dac Gain; R302 Adc Gain

4-2 R603 +1SV ADJUSTMENT
R603 (see SD711) balances the *15V and -15V supplies. Its setting should not be changed unless U601
or U605 have been replaced. To do so will unbalance all VCAs which are trimmed for CV rejection as
well as offset all oscillator and filter CVs. Positive and negative supply readings under load should be
15.0 +/- 0.5V. Readings outside of this range may indicate a malfunction.
To check the supply, remove cabinet screws as discussed in para. 1-2. Slide top panel assembly
forward only. Do not raise to "service position". The supply voltages are marked on PCB 6 (see PA610).
If required, note -15-V reading (e.g. -15.375) and trim R603 so +15-V reading matches (e.g. +15.375).
4-3 R301 DAC CAIN
The overall gain for the DAC affects the voltage scaling on all sample and holds (S/Hs). Scaling affects,
most importantly, ail of the oscillator V/OCTs. Therefore if all the oscillators are sharp or flat in V/OCT.
R301 (see SD312) can be adjusted. Conversely, if all V/OCT are fine and you trim R301. then you'll
make all V/OCTs sharp or flat.
Start in BASIC TRIM SETUP. TABLE 4-0. To set DAC GAIN:
1. With DVM. probe U370-7. UNISON CV S/H. i
2. Switch off S221, UNISON.
3. U370-7 should measure a small "offset" voltage. Note the offset and its polarity (e.g. +0.003V).
4. Switch on S221. UNISON.
5. Key B4.
6. Trim R301 to read exactly 5.000V +/- the offset voltage read in step 3 (e.g. 5.003V).
7. To recover offset voltage for checking trim, switch off S221, UNISON.
4-4 R302 ADC CAIN
R302 (see SD312) determines the range of control panel pots which are quantized by the ADC.
ADC gain can be set by ear by adjusting for an exact five-octave range of either OSC FREQ knob.
Start in BASIC TRIM SETUP. TABLE 4-0. By ear:
1. With R203, OSC A FREQ, set to 0. key C5.
2. Turn R203 to 10 and key CO.
3. If required, repeat steps 1 and 2 and trim R302 so the two keystrokes sound the same pitch.
With instruments:
1. With DVM. probe U353-1, OSC A INIT FREQ CV S/H.
2. With R203, OSC A FREQ, set to 0, U353-1 should measure in the 5-V range (e.g. +5.252V).
3. Turn R203 to 10.
4. R302 trims in 83-mV increments. Trim to the voltage measured in step 2 minus exactly 5.000V
(e.g. 5.252 - 5.000 = 0.252V).
4-3