Monday, December 11, 2017

Aftermarket Stepper Motors for Icom IC-756 Auto-tuner

This may be old news, but just in case, here it is... I just repaired the auto-tuner in my IC-756 (not a pro version). One of the motors failed. I found a procedure online for repairing the motor, but also decided to try an aftermarket replacement motor. The OEM part number from Icom was MP28GA, and their new # for their replacements is MP24ZA. This happens to be the same replacement part used in some Yaesu auto-tuners, their part # is M2190023. The Icom part costs about $35 + shipping, the aftermarket part is $4.95 + shipping. Looks to be the same part, except that the aftermarket part has a brass output shaft vs. plastic on the OEM. 

This looks to be the same motor used in several Icom HF rigs as well as Yaesu. I bought the aftermarket motor from https://www.adafruit.com , and it is their item #918 and cost $4.95 each. The plug is slightly different, but I was able to slice off a piece of the plastic clip from the socket on the tuner PC board and it snapped right on, but you could simply replace the connector from the original tuner motor...the wiring colors match perfectly. 

There's a great Youtube tutorial on how to repair the original stepper at:

http://youtu.be/UdY6RhNOCWg

 
 Comparison of back side of stepper motors...

 Comparison of front side of motors...

 
 Tuner is under this board...

 Board remove, exposing metal cover on tuner...

 Metal cover removed, stepper motors seen in lower RH side of pic. Remove screws from tuner, lift it up, loosen screws on motor coupling, and replace the motor. Very easy!
 

UPDATE, 2/2/2019:


I got a message from Jim Durham, and wanted to add it in before I lost it. This is a link to a stapper with a 1/64 gearbox ratio, and seems to tune a bit more smoothly than the units I use. Mine are still working fine, but this looks like it might be a better choice. Here's the link:

https://www.amazon.com/Diymore-28BYJ-48-Valve-Stepper-Motor/dp/B01J3KV3B2/ref=sr_1_1?ie=UTF8&qid=1518217311&sr=8-1&keywords=stepper+motor+12+volt+4+phase




Dave WB4IUY
http://www.WB4IUY.net





Display Transplant into an Icom IC-756 (non-pro)


 Before...

 After!!

 The display has a more brilliant color than this, my phone cam just doesn't do it justice!



This blog is about replacing the LCD display in a Icom IC-756 classic. The displays in these radios haven't been supported by Icom in several years. This is an attempt to archive info & notes from myself and others about different displays used. I'll probably add to / edit this blog as I continue to test & install more displays.

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Winstar WG320240D-TMI-TZ# display: When installing this model, I had tried to drive the display contrast input (display pin 13) from the 756 contrast output (DV0, radio pin 1). It works, but over the period of an hour or so, one has to go into the radio menu and readjust the contrast setting. It seemed to be a thermal drift of some sort in that circuit. After working with the mfg, I discovered a few things:

1- The display generates it's own -25vdc and outputs it to pin display 12. The -30vdc from the radio pin 2 should not be connected to the display. The display is temperature compensated and it varies the -25vdc output at display pin 12 accordingly.

2- When driving display pin 13 from the radio, it ignores the display's temp compensation, thus causing the contrast "drift" or instability. Installing a linear potentiometer of 15k, high side to pin 12, low side to pin 14, and wiper to pin 13 allows the display contrast input to reference the temperature compensated internal -25vdc supply of the display, and I've found the contrast to be perfectly stable. Keep the pot as close to the display as possible, leads short...

3- I prefer to have the contrast adjustment where it can be easily reached, as contrast is somewhat subjective and based partially on the viewing angle. An internal pot is fine, but I like to be able to adjust it easily. I found the lower LH side of the cabinet (just below the handle) to be a good, easy-to-reach location for this. When mounting the pot somewhere that requires a few inches of wire to make the connection, install a 100pf capacitor across the high and low connections to the pot. The -25vdc output of the display acts like a nice antenna to radiate processor noise to the rest of your rig, and I found 100pf seems to be adequate to resolve the issue.

 
 100pf cap across high and low terminals of the remote contrast pot I installed in this radio...


4- Source a +12vdc switched point to build the 5vdc regulator for the LED back light. I use the point from the 4-pin rear panel  accessory port. Use a 7805 regulator and heat sink to chassis, and a 33 ohm 1/2 watt resistor in series with the output to the back light, to limit the backlight current. Open coil L103 along side of the HV compartment to shut the CCFL HV supply off when using displays with LED back lights.










5- If you plan to buy a Winstar display, try to locate the WG320240D-TML-TZ# instead of the WG320240D-TMI-TZ#, it is more easily viewed from above the radio.

6-  APlus Displays: AG320240D-TTI-TZ# seems to be the same as the Winstar display

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Stanley GMF32024ABTW1X: The Stanley display found by Rick K4PQ is by far the easiest to install electrically (no back light mods required and seems to be temp compensated in some other way) . This has been the easiest display to install to date, but availability seems to now be an issue...

1- Contrast setting is very stable, the current requirement at display pin 13 is only a few MA (contributing to stability).  Connect the -30vdc supply from the radio to display pin 12 via 2k 1/2 watt resistor. Be sure to turn the trimmer down on the sub-logic board to about the 9 O'Clock position.


2- The back light is directly driven from the radio CCFL HV supply with no mods. This is not a polarized connection and polarity is not important. No back light supply mods needed!

3- This display has the best viewing angle of any of the displays I've tested / installed. It is viewed from above the radio easily, best of all the displays I've tested in this blog.

Can anyone find another source of the Stanley display GMF32024ABTW1X ??
 
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I'm waiting on a East Rising ERM320240SBS-1 to test now. It also looks like the New Haven NHD-320240WG-BxTGH-VZ#-3VR will work, but much more expensive.

*** Update*** Another person bought a New Haven NHD-320240WG-ATMI-TZ# display, and it was MUCH too wide. Avoid that model. Try to choose displays that have a max board width of around 142mm wide and 96mm tall (although board height isn't as critical)

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Folks have physically installed these various displays in the metal sub-chassis a number of ways from building brackets, re-drilling holes, etc. I prefer the Hot glue method recommended by Rick K4PQ...quick, easy, and very solid.

I use the Dremel tool to remove the little folded edge from the sub-chassis for best fitment...


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When disassembling the face of the radio from the sub-chassis, I've found cutting small cardboard tabs and inserting under the clips around the perimeter makes removal much easier.



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Using the original display as a donor, cut the plug for the ribbon cable and a piece of the board away, and stick it to the new board with thick double-side tape as a sort of "break-out" board to help with assembly. The numbers are backwards on the cut-away board from the actual ribbon cable and socket on the radio main board...makes no sense, but the cross reference chart takes this into consideration. Mark the ribbon cable TOP surfaces and make sure to not get the cable reversed during re-assembly.




Cross ref for the Winstar Display



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When removing the front panel from the sub-chassis, slip the rubber cover off of the main VFO knob, loosen the set screw found below it, and remove the long silver screw from the VFO brake.




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When removing the sub-logic board, be sure to unsolder the S-Meter connections to allow the boards to separate.

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Another model successfully fitted and installed was purchased from aliexpress.com as Yuxian model #
LG3202404BMDWH6N . It was fitted and worked fine. It's board dimensions measure 139mm wide x 106mm tall. 

The board pinout labels seem to be reversed fro the latch and shift pulse. The corrected pinout conversion from the cut board outlined above (cut piece from oem display) to the radio is:


Cut board = New display
1 = 9
2 = 10
3 = 11
4 = 12
5 = 1
6 = 4
7 = 3 (latch)
8 = 2 (shift)
9 = 13
10 = Frame ground, internally jumpered to pin 7
11 = 7
12 = 6
13 = 8 via 2k resistor (note below**)
14 = 5

It looks like 15 & 16 on the new display goes to the back light.

** If the display has internal temperature comp, I've found that leaving the connection open between pin 13 on the cut board and the -Vout (pin 8 on your new display) yields much better contrast stability as the display warms up.


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List of displays used:

- Stanley GMF32024ABTW1X (easiest fit to date)
- Yuxian LG3202404BMDWH6N (from aliexpress.com)
- Winstar WG320240D-TML-TZ#
- Winstar WG320240D-TMI-TZ#
- APlus Displays: AG320240D-TTI-TZ#- East Rising ERM320240SBS-1
- New Haven NHD-320240WG-BxTGH-VZ#-3VR (dimensional issues on some)
- New Haven NHD-320240WG-ATMI-TZ# (too big)




Dave WB4IUY
http://www.WB4IUY.net