Recreation of VGA module PCB for Loewe TVs with Q2500M chassis.
Project based on work done by Oelii from circuit-board.de/forum
Schematic recreated from the scratch in KiCad. PCB based on Oelii's layout and verified with Desing/Electrical Rules Checker tools.
Components footprints replaced with KiCad standard ones.
Unverified, obtained from post by djcalle on circuit-board.de/forum:
- Q23, Q24, Q25 can accept VGA cards.
- Q25 and Q24 use the same VGA card (only 2 differences: cable length and 150R termination on RGB lines.)
- Q25 seems to be inconsistent with VGA card compatibility.
- Q24 seems consistent with vga card compatibility.
- Q23 uses its own different card.
For widescreen TVs EDID EEPROM option can be installed and flashed, helping to automatically add 848x480@60Hz (CVT) default widescreen resolution.
Original schematic from Loewe Q2500-M chassis service manual
Recreated schematic and PCB
| Reference | Value | Footprint | Qty |
|---|---|---|---|
| C811,C817,C826,C828,C829 | 100n | 0805 | 5 |
| C813,C814,C821,C827 | 10p | 0805 | 4 |
| C816 | 10u | 0805 | 1 |
| C818 | 22n | 0805 | 1 |
| C822 | 100p | 0805 | 1 |
| L816,L826 | 1210(3225) | 4.7uH | 2 |
| R814,R819,R821,R823,R828,R829 | 100R | 0805 | 6 |
| R817 | 10k | 0805 | 1 |
| R818 | 1k | 0805 | 1 |
| R827 | 47k | 0805 | 1 |
| R836,R837,R838 | 150R | 0805 | 3 |
| I811 | 74HCT86 | SO-14 | 1 |
| W801 | VGA DSUB-15 Edge pin offset 8.35mm Mounting holes offset 10.89mm |
1 | |
| W831 | JST XH 2.54 12 Pin | 1 | |
| U2 | AT24C02 (EDID option) | SOIC-8 | 1 |
| R1,R2 | 2K2 (EDID option) | 0805 | 2 |
Send "gerbers" folder content packed to zip archive.
AT24C02 EEPROM and R1,R2 are EDID option, useful for connection widescreen models to PC/VGA.
L816 and L826 SMD 1210(3225) inductors value are unknown; 4.7uH in Q2300 VGA module schematic; can be replaced with 0R resistor.
W831 connector originally is Molex 22-23-2121. Probably can be replaced with XH 2.54 12 pin connectors / cables, note pins step 2.5/254 mm.
Pay attention on cable connectors type: same direction or reverse direction.
12 pin 50 cm cable are required for Q25 chassis, 30 cm cable for Q24 chassis. For Q23 chassis, two 10 pin cables are required.
Double-check ground and VCC connection on VGA module PCB and TV chassis before soldering 12-pin W831 connector and power on.
Extended Display Identification Data (EDID) ROM sends display info to PC over VGA I2C DDC (Display Data Channel), such as supported / default resolutions, supported frequency ranges, physical dimensions and display name.
Standard VGA resolutions 640x400@70Hz and 640x480@60Hz marked as supported.
Added custom default resolution 848x480@60Hz.
Added modeline generated with CVT formulas.
Display reported as "Loewe CRT".
Generated edid.bin can be in-system programmed to AT24C02 EEPROM with CH341 (I2C) programmer, 8 pin chip clip and NeoProgrammer V2.2.0.10: "IC/I2C/Generic/_24C02 [3.3V]" or "Detect", "File/Open" .bin, "Write IC" (Erase, Blank Check, Write, Verify).
EDID 1.3 display description ROM image in raw .hex format generated with generate_edid.py script.
Generate edid.hex:
python generate_edid.py > edid.hex
Convert raw .hex to .bin:
type edid.hex | xxd -r -p > edid.bin
To view generated display description:
edid-decode edid.bin
Conservative / more compatible custom modeline included by default:
Modeline "848x480_60" 31.75 848 864 944 1024 480 483 493 517 -hsync +vsync
Alternative modeline generated with cvt utility can be selected in generate_edid.py:
cvt 848 480 60
Modeline "848x480_60" 31.50 848 872 952 1056 480 483 493 500 -hsync +vsync
Q2400 chassis:
Q2500 chassis:
Mods information provided by @neonname.
Combined VGA adapter board output and TV input termination/load resistance for RGB lines should be ~75 Ohm.
TV Signal Board schematic:
PCB components side:
Q2400 signal board already have 75 Ohm termination resistors on RGB lines.
150 Ohm RGB termination resistors on adapter board should be removed.
TV Signal Board schematic:
PCB components side:
PCB solder side:
PCB missing W1011 VGA connector and RGB input resistors, RGB input connected to ground with 0R load resistors.
Suggested changes, needs to check on real board:
- Replaсe R2641, R2643, R2646 (0R) with 27R, add missing R1016, R1017, R1018 47R resistors (like Q2500-M) (probably incorrect termination)
- Or replaсe R2641, R2643, R2646 (0R) with 150R; add missing R1016, R1017, R1018 (0R) (like Q2500-H). Note: R2512, R2513, R2514.
TV Signal Board schematic:
PCB components side:
PCB solder side:
Recommended changes:
- Replaсe R2641, R2643, R2646 (68R) with 150R; R1016, R1017, R1018 (10R) with 0R; R2512, R2513, R2514 (0R) with 47R; remove C1016, C1017, C1018.
TV Signal Board schematic:
PCB components side:
PCB solder side:
Suggested changes, needs to check on real board:
- Replaсe R2641, R2643, R2646 (47R) with 150R; R1016, R1017, R1018 (27R) with 0R; remove C1016, C1017, C1018. Note: R2512, R2513, R2514.