GT2101 — Motor & PCB Signal Map
A consolidated probe map for the Gale GT2101’s logic and motor-drive boards, compiled from bench measurements and archived notes.
This table records typical signal behaviour across the control stack and motor assembly — forming a foundation for reverse engineering, repair, and historical documentation.
Diagnostic Tips
- “Drops to 0 when Start/Stop pressed” = momentary, edge-triggered control line.
- Clock lines (1.048 MHz / 10 Hz / 1 Hz) drive timing and display multiplexing.
- Tach = motor feedback. Speed Ref = user-set frequency from the main dial.
Top PCB
| Pin |
Name / Function |
Notes |
| 1 |
Positive Supply |
+ V rail |
| 2 |
Drops to 0 when Start/Stop pressed |
Edge control |
| 3 |
Display-generation frequency (tach ↔ desired) |
Higher when showing desired speed and not running |
| 4 |
1 Hz / 10 Hz display-refresh clock |
Motor/desired display timing |
| 5 |
LED signal |
7-segment display driver |
| 6 |
1 Hz / 10 Hz display-refresh clock (duplicate) |
Redundant feed |
| 7 |
Speed Reference (10 Hz – 999 Hz) |
Main pot setpoint |
| 8 |
Ground |
0 V reference |
2nd PCB
| Pin |
Name / Function |
Notes |
| 1 |
Positive Supply |
+ V rail |
| 2 |
1.048 MHz Clock |
Master timebase |
| 5 |
Pulse High when Start/Stop pressed |
Edge command |
| 6 |
Drops to 0 when Start/Stop pressed |
Complement control |
| 7 |
Return for 33⅓ Select Switch |
|
| 8 |
Display Frequency (tach / desired multiplex) |
Matches Top Pin 3 |
| 9 |
Inverted Tach Signal |
Phase-inverted feedback |
| 10 |
1 Hz / 10 Hz Display Clock |
Multiplex timing |
| 11 |
Fixed 33⅓ × 40 = 1332 Hz |
Reference for locked speed |
| 12 |
Negative Supply |
– V rail |
| 13 |
1 Hz / 10 Hz Display Clock (duplicate) |
Redundant feed |
| 14 |
Ground |
0 V reference |
3rd PCB (Middle)
| Pin |
Name / Function |
Idle V |
Active V |
Notes |
| 1 |
Positive Supply |
– |
– |
|
| 4 |
Pulse High when Start/Stop pressed |
0 |
10 |
Command edge |
| 5 |
Pot Signal × 4 (40 Hz – 3996 Hz) |
0 |
10 |
Derived setpoint |
| 6 |
Unknown |
– |
– |
To be confirmed |
| 7 |
Speed Signal |
– |
– |
Control to motor drive |
| 8 |
Negative Supply |
– |
– |
– V rail |
| 9 |
Ground |
0 |
– |
Reference |
4th PCB (Near Bottom)
| Pin |
Name / Function |
Idle V |
Active V |
Notes |
| 1 |
Positive Supply |
– |
– |
+ V rail |
| 2 |
1.048 MHz Clock Signal |
0 |
10 |
Timebase |
| 3 |
Return from 33⅓ Select Switch |
– |
– |
|
| 4 |
Inverted Tachometer Signal |
0 |
10 |
Feedback (inverted) |
| 5 |
Tachometer Signal |
0 |
–10 |
Feedback (non-inverted) |
| 6 |
Unknown |
– |
– |
|
| 7 |
Negative Supply |
– |
– |
– V rail |
| 8 |
Ground |
– |
– |
0 V |
| 9 |
Speed Reference (10 Hz – 999 Hz) |
0 |
10 |
User setpoint |
Bottom PCB (Power Section)
| Pin |
Name / Function |
Idle V |
Active V |
Notes |
| 1 |
33⅓ Indicator (selected / not) |
9.18 |
0 |
Mode lamp logic |
| 2 |
Positive Supply |
11.9 |
– |
+ rail |
| 3 |
Return from 33⅓ Select (Freq = Pin 4 or 7) |
0 |
10 |
Mode return |
| 4 |
Frequency Set by Pot (0.1 – 99.9 × 40 → 4–3996 Hz) |
0 |
10 |
Main setpoint |
| 5 |
Tach Signal |
0 |
–10 |
Motor feedback |
| 6 |
Speed Signal |
0 |
5 |
Drive control |
| 7 |
Fixed 33⅓ × 40 = 1332 Hz |
0 |
10 |
Reference |
| 8 |
Negative Supply |
–10.9 |
– |
– rail |
| 9 |
Ground |
0 |
– |
0 V reference |
Motor DIN Connector (Brushless DC Motor)
| Pin |
Function |
Notes |
| – |
Run / Stop |
Start/Stop control |
| – |
V Speed |
Control voltage input |
| – |
PG OUT |
Pulse Generator (tach) output |
| – |
AGND |
Analogue ground |
| – |
PGND |
Power ground |
| – |
Vin |
Motor supply voltage |
Troubleshooting Cues
- No start or frozen display → Check the 1.048 MHz clock (2nd / 4th PCB Pin 2) and ± supply rails (+11.9 V / –10.9 V).
- Speed hunting → Compare Speed Ref (Top 7, 4th 9) vs Tach (Bottom 5, 4th 4 & 5). A large phase error indicates comparator or trace fault.
- 33⅓ lamp stuck → Inspect Bottom Pin 1 and select returns (Pins 3 & 7).
- Display incorrect but speed OK → Check multiplex clocks (Top 4/6, 2nd 10/13) and display-frequency line (Top 3, 2nd 8).
Contributions from bench measurements and archival records.
If you verify unknown pins or capture oscilloscope traces, please add them here to extend the archive.
