MWLyon
 
 
 

Design Work Completed

>Prototyping
 
>Schematic Capture
 
>PCB Layout
 
>Initial Fabrication

2000
iMac Sync-Lock Modification
 
Sync-Lock your iMac - 800X600 at 96Hz


When sync-locking a computer display to 24 frame interlaced video (24 frames per second, 48 fields per second), the optimal computer vertical refresh rate would be 48Hz.

Unfortunately, the display control panel on the computer seldom allows an appropriate resolution (i.e. 800x600) to be chosen at or near that value.

In the case of the iMac, it's 800x600 resolution is at 95Hz.

This is perfect for sync-locking the iMac at 96Hz.

The LOX2000 sync-lock with it's frame rate doubler enabled inputs 24 frame interlaced video (24 frames per second, 48 fields per second) and sync-locks the iMac to twice that or 96Hz (96 frames per second, progressive scan).

The LOX2000 is the only sync-lock unit to our knowledge that works with the iMac at it's native rate of 800x600 at 96Hz.

Reliable and easy to install, the LOX2000 is the first choice for sync-locking the iMac.

Click here for more specific information on the LOX2000.

 

iMac Lineage

We have installed the LOX2000 in three versions of the iMac as of 2001.

The original unit that was converted was seen during the holidays in 1998.

This unit had a blue case and on the I/O panel was a small metal cutout secured by two screws.

This version iMac had a 14.318180 MHz crystal as it's video timebase.

Although we have successfully modified some of these units, some others have not produced positive results.

We suggest modifying a later version iMac.

The second version was seen about 6 months later and was identical in appearance to the first with the exception that the I/O panel was solid and had no cutout.

This version also had a 14.318180 MHz crystal as it's video timebase.

The third version we have modified is similar in external appearance but is totally new and improved internally.

This version iMac has a 29.498 MHz oscillator as it's video timebase.

 

 
Version 1
Version 2
Version 3 (DV iMac)
 

Version 1 and 2 Modification

1. Remove the iMac chassis from the monitor.

2. Remove screws holding the motherboard.

3. Flip the motherboard over.

4. Mount the LOX2000 PCB in the desired location.

5. Place wire from LOX2000 J1 Pin 1 to connector pin with the Red wire as shown.(+5V)

6. Place wire from LOX2000 J1 Pin 2 to connector pin with the Blk wire as shown.(Gnd)

7. Place wire from LOX2000 J1 Pin 5 to connector pin 10 as shown.(Feedback V Dr In)

8. Place wire from LOX2000 J1 Pin 6 to connector pin 3 as shown.(Gnd)

9. Remove crystal Y3.

10. Solder one lead of .01uF cap to indicated Y3 pad.

11. Place wire from LOX2000 J1 Pin 3 to .01uF cap at Y3 pad.(Clk Out)

12. Place wire from LOX2000 J1 Pin 4 to Gnd side of C140 22uF SMT cap near Y3 pad.


(Version 1 only)
 

13. Place wire from LOX2000 J1 Pin 7 to the BNC connector pin.(Ext Sync In)

14. Place wire from LOX2000 J1 Pin 8 to the BNC connector Gnd lug.

15. Place wire from LOX2000 J1 Pin 9 to the Red LED lead.(Sig LED)

16. Place wire from LOX2000 J1 Pin 11 to the Grn LED lead.(Lock LED)

17. Place wire from LOX2000 J1 Pin 10 to the LED Gnd lead.

18. Place wire from LOX2000 J1 Pin 13 to LOX2000 J1 Pin 14.(96 Hz)

19. Re-assemble unit.

 

Operating the iMac (Version 1 or 2) with the LOX2000

1. Two 8 pin personality EEPROMs are available for use with the LOX2000 iMac sync-lock. One EEPROM is labeled "002Y" and the other is labeled "002N". The letter "Y" on the first EEPROM means Yes as in "Yes the iMac will store the optimal sync-lock frequency in EEPROM and will retrieve it from EEPROM when no external reference is present". This means that upon removal of reference the iMac will remain at it’s last phase and frequency. The "N" on the second EEPROM means No as in "No the iMac will not store the optimal sync-lock frequency and will always retrieve the original sync-lock frequency from EEPROM when no external reference is present". This means that upon removal of reference the iMac will immediately return to it’s fixed startup frequency and will lose it’s phase reference. Please see the LOX2000 section on "Automatic Frequency Store".
2. With no external reference applied to the BNC connector, the Red/Grn LED will be off. Upon application of video Black or V Dr. to the BNC the Red LED will illuminate to indicate the presence of signal. As the LOX2000 mod phases the iMac closer to the reference signal the LED flickers Red-Grn rapidly, indicating a fine-tuning of the reference vs. iMac phase. When both the Red and Grn LEDS are on steadily, the unit is phased(and if the "002Y" EEPROM is installed, the sync-lock frequency is stored). If the Red LED blinks, it indicates that the combination of applied reference frequency and selected iMac resolution are out of range.

 

Version 3 Modification

This is an example of the third version of iMac that we have converted.
This is the DV iMac.
 

1. Place the iMac on it's top and expose the plastic shell covering the expanded metal
EMI shield.

2. Remove the plastic shell.

3. Remove the expanded metal EMI shield.

4. Locate the 29.498MHz oscillator.

5. Remove it using the utmost care! A specialized de-soldering tool is the best bet if you have access to one.

6. Install one lead of the .01uF cap to the exposed oscillator solder pad as indicated. Place wire from LOX2000 J1 Pin 3 to .01uF cap at oscillator pad.

7. Locate the motherboard power plug.

8. Place wire from LOX2000 J1 Pin 1 to connector pin with the Red wire as shown.(+5V)
9. Place wire from LOX2000 J1 Pin 2 to connector pin with the Blk wire as shown.(Gnd)

10. Locate the VGA connector.

11. Place wire from LOX2000 J1 Pin 5 to motherboard plate-thru as shown.(Feedback V Dr In)

12. Mount the Red/Grn LED near the I/O access area as shown so that it shines through the translucent case when illuminated.
13. Place wire from LOX2000 J1 Pin 9 to the Red LED lead.(Sig LED)
14. Place wire from LOX2000 J1 Pin 11 to the Grn LED lead.(Lock LED)
15. Place wire from LOX2000 J1 Pin 10 to the LED Gnd lead.

16. Place double-sided tape in the location where you will mount the LOX2000.

17. Insure that a jumper wire from LOX2000 J1 Pin 13 to LOX2000 J1 Pin 14 is in place.(96 Hz)
18. Place wire from LOX2000 J1 Pin 7 to the BNC connector pin.(Ext Sync In)
19. Place wire from LOX2000 J1 Pin 8 to the BNC connector gnd pin.
20. Solder all wires to the LOX2000 and mount it using the double-sided tape.

19. Shown here is the BNC for external sync input.

20. Choose a spot to mount the BNC.

21. Cut a hole in the metal shield, mount the BNC, and re-attach the shield to the iMac.

22. Re-install the plastic shell.

23. Fire up the iMac, select 800X600 in the monitor control panel, apply 24.00FPS video black to the BNC connector and voila!

 

Frame Rate Tables

The following tables reflect the frame rates achievable with the LOX2000/iMac combination.

1. The Resolution and Rate columns reflect the choices offered by the iMac Monitor Control Panel.

2. The Doubler column indicating "ON" refers to the jumper wire from J1 Pin 13 to J1 Pin 14, selecting 96Hz.

3. The 23.98FPS through 30.00FPS columns refer to the frame rate of the normal rate interlaced video black signal applied to the BNC connector.

4. The rows below the 23.98FPS through 30.00FPS columns refer to the iMac's progressive scan vertical refresh rate produced by the combination of selected Resolution, Rate, and Doubler values. The --------- symbol means that no sync-lock is possible with that selection combination.

5. iMac Family Number: M4984 (iMac Version 2)
Normal rate interlaced video black signal


Resolution Rate Doubler 23.98FPS 24.00FPS 24.02FPS 25.00FPS 29.97FPS 30.00FPS
640x480 117Hz OFF ---------- ---------- ---------- ---------- ---------- ----------
  117Hz ON ---------- ---------- ---------- ---------- 119.88Hz 120.00Hz
 
Resolution Rate Doubler 23.98FPS 24.00FPS 24.02FPS 25.00FPS 29.97FPS 30.00FPS
800x600 95Hz OFF ---------- ---------- ---------- ---------- ---------- ----------
  95Hz ON 95.92Hz 96.00Hz 96.08Hz ---------- ---------- ----------
 
Resolution Rate Doubler 23.98FPS 24.00FPS 24.02FPS 25.00FPS 29.97FPS 30.00FPS
1024x768 75Hz OFF ---------- ---------- ---------- ---------- ---------- ----------
  75Hz ON ---------- ---------- ---------- ---------- ---------- ----------