Hi guys,
First post here jumping in at the deep end its about my PPG wave 2.3, which after about 4 months nap switched on and no sound was being produced. Not a huge amount of PPG 2.3 fault finding info online, so I’m very much hoping we can share some here.
(Service Manual)
I’m not an electrical engineer or synth tech just confident with a soldering iron, DMM etc and like to understand more.
Of course I may well be sending these boards to the very excellent Virtual Music folks, however what with Covid and Brexit deliveries are so slowed up I worry.
So if it’s a case of a wonky OP Amp or logic IC I’d like to make an effort to fix it. PPG Waves are apparently notoriously tricky to troubleshoot especially the Proz board, however I am confident this part of the synth is operational ( I see all 8 voice signals emitted from the voice board DACs)
Symptoms
- No Sound on any output (headphones, balanced ch1, ch2 or the individual voice outs)
- Resonance turned fully up no difference
- Waveform audio sinks at VCF inputs
Basic Checks Made OK:
- Power supply rails and regulators -12V / + 12v
- Reload the presets / sounds
- Reseat boards
- Ribbon cables
- Test (replacement) DA IC (Panel IO)
- CPU reads analog panel ok (LCD panel show pot values)
- Test (replacement) CV AD558 DACs (RES, VCF, VCA)
- Battery
- Audio signal to voice DACs
The good news I traced audio from the sound generators out of the voice DAC’s.
This audio/voice signal however gets “sunk” at the VCF input(s). I note the freq CV ~0.6v max at the VCF.
On the schematic there is a provision for a VCF pedal input (backed by a TL084) I measured the output of pin 1, which was 10.75v, which maybe suspicious (This circuit is on the schematics, but I can’t read if some of the R’s in the Op amp network say 22k or 2.2k). Since this IC is soldered to the board I tried piggybacking, with a known working TL084 and I note that this lowered the voltage at pin 1 ~ 4.6v ( a sometimes are very faint but scratchy sound output…The IC gets hot after ~20secs so I power it down). Could this op amp be a suspect?
Any thoughts of guidance would be greatly appreciated.
Wilson
(Measurements below ;))
IO BOARD
IC29 (RES DAC)
1 (0) - 2v
2 (1)- 1.8v
3 (2)- 2.32v
4 (3)- 1.75v
5 (4)- 1.77v
6 (5)- 2v
7 (6)- 1.73v
8 (7)- 1.89v
9 (CE) - 4v
10 (CS) - 0v
11 (VCC) - 11.77v
12 (GND) - 0v
13 (GND) - 0v
14 (OUT) - 0v(RES pot low) - 3.51v(RES pot high)
15 (OUT SENSE) - 0v(RES pot low)-0.61v(RES pot high)
16 (OUT SEL) - 0v(RES pot low) - 5.1v(RES pot high)
IC30 (VCF DAC)
1 (0) - 2v
2 (1)- 1.8v
3 (2)- 2.32v
4 (3)- 1.75v
5 (4)- 1.77v
6 (5)- 2vv
7 (6)- 1.73v
8 (7)- 1.89v
9 (CE) - 1.92v
10 (CS) - 0v
11 (VCC) - 11.77v
12 (GND) - 0v
13 (GND) - 0v
14 (OUT) - 2.86v(freq pot low) - 0v(freq pot high)
15 (OUT SENSE) - 0.5v(freq pot low) - 0v(freq pot high)
16 (OUT SEL) - 4.3v(freq pot low) - 0v(freq pot high)
IC 31 (VCA DAC)
1 (0) - 2v
2 (1)- 1.8v
3 (2)- 2.32v
4 (3)- 1.75v
5 (4)- 1.77v
6 (5)- 2vv
7 (6)- 1.73v
8 (7)- 1.89v
9 (CE) - 1.92v
10 (CS) - 0v
11 (VCC) - 11.77v
12 (GND) - 0v
13 (GND) - 0v
14 (OUT) - (keys pressed env full) ~1.8vDC (ripple 1.55v AC)
15 (OUT SENSE) - no key pressed 0v (1 key pressed env full) 10.3v
16 (OUT SEL) - (keys pressed env full) ~1.86DC (ripple 1.9v AC)
IC 32 (Verified ok with drop in replacement… )
VOICE BOARD
IC 51 VCF (A)
1 (in) - 0.175v —> AC 1-1.3 (note before R100 … after R100 AC 0v)
2 (Q) - 0.273 (res pot lower) to 1.55v (res pot upper)
3 (out) - 5.77v —> AC 0v
4 - (-1v ~ -0.5v ramp)
5 - (-1v ~ -0.5v ramp)
6 - 9.71v
7 - 9.71v
8 - 0.21v
9 - (-11v)
10 - 0.2v - 0.6v slow ramp
11 - 0.2v - 0.6v slow ramp
12 - 9.7v
13 - 0.645v(freq pot lower no env) to 0.433v (freq pot upper no env)
14 - 9.74v
15 - 0.172v
16 - 10.75v
IC56 VCA (A)
1 - 0v
2 (out) - 0v(AC/DC)
3 (cv) - 1.71v (key on/off and loudness pot low/high)
4 - 0v
5 - 0v
6 (in) - 0v(AC/DC)
7 - (-10.94v)
8 - 1.96v
9 (in2) - 0v
10 - 0v
11 - 0v
12 (cv2) - 1.71v
13 (out2) - 0v
14(+) - 0v
There is audio signal out of the DAC that gets as far as the R100 (82k) resistor array and is gone at input of the VCF
MOTHER BOARD
A last check at IC9 TL074 providing the EXT VCF CV at pin 1 is at 10.75v (8v on EXT VCF the jack tip), which routes to the voice board R99.