Yamaha TG77 User manual

Yamaha TG77 LCD Replacement Guide
produced by: glitchscience.com 2011©
2022©
1
Yamaha TG77
Replacement Display
Install Guide
glitchscience.com
Replacement TG77 LCDs can be purchased via E-bay glitchscience items on E-bay

Yamaha TG77 LCD Replacement Guide
produced by: glitchscience.com 2011©
2022©
2
Yamaha TG77 LCD Replacement Guide
Table of Contents
Required Tools and Additional Info .......................................................................................... p. 3
Installation .............................................................................................................................. p.4 - 19
Opening the Case................................................................................................................ p. 4-5
Replacing Contrast Resistor and Potentiometer ……........................................................... p. 6-8
Installing LCD Power Connector.......................................................................................... p. 9-13
Front Panel Removal ........................................................................................................... p. 14-16
LCD Panel Removal / LCD Installation.................................................................................. p. 17-18
Finishing the Installation ..................................................................................................... p. 19
Read this entire document before beginning the installation process. Take your
time, take notes, and take photos, if the need arises. We recommend that you do
not attempt this installation if you do not have the proper equipment and or skills
to do so.

Yamaha TG77 LCD Replacement Guide
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Tools needed for installation:
Phillips Head Screwdrivers
Soldering equipment
Desoldering equipment
Solder
Soldering and Desoldering Info
This guide does not cover how to solder or desolder electronic components.
If you do not have any experience and or are not confident in your ability to solder and
desolder we recommend that you do not attempt this installation. If you would like to attempt
this installation but have no experience we recommend that you get some practice before
proceeding with this project. There are many tutorial videos that can be found on YouTube and
plenty of tutorials all over the internet. Watch some videos, do some reading, and practice on
some old electronics you are willing to sacrifice or kits specifically made for practicing soldering
and desoldering.
In terms of desoldering equipment, I recommend using a good quality solder sucker. A good
quality solder sucker will simplify the process of desoldering components. Below are some
affiliate links to a couple that can be purchased via Amazon:
Edsyn Deluxe Soldapullt DS017LS
Engineer SS-02 Solder Sucker
Having done quite a bit of desoldering work over the years, I have settled on using an Edsyn
Deluxe Soldapullt DS017LS, this is the best solder sucker I have used to date. I have not used
the Engineer SS-02 but linked it because it is a quality solder sucker that has been
recommended by trusted sources. There are now clones of both of these desoldering pumps at
cheaper prices than the originals, I cannot vouch for the quality of these clones but they may
function just as well as the originals.
Many places carry soldering equipment online. Check out the following Amazon affiliate link
Soldering Equipment on Amazon.com
or just do a Google search to find what you need.
**************************************************
ELECTRICAL SHOCK HAZARD!
UNPLUG the TG77 before working on the inside,
the voltages inside have the potential to be very dangerous!

Yamaha TG77 LCD Replacement Guide
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Fig. 0 - Top Case Screw Locations Circled in Red
Step 0:
You will need to open the TG77.
First, be sure to unplug the TG77.
Now, to remove the top of the case you will need to remove the screws
from the top, sides, and back of the case. Remove the 2 screws from
the top front, the locations are shown above in Fig.0. Remove two
screws from both sides, the locations are shown in Fig. 1 on page 5.
Remove three screws from the back of the case, the locations are
shown in Fig. 2 on page 5. Now remove the top case cover and set it
aside.
*TIP - Be sure to make note of which screws go where as you go along, this way
you are able to correctly put it all back together once you are finished.

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Fig. 1 - Side Case Screw Locations Circled in Red
Fig. 2 - Back of the Case Screw Locations Circled in Red

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Fig. 3 - Contrast resistor labeled R476 and contrast potentiometer labeled
VR301 CONTRAST VOL. Both located in the Upper Right Corner
Step 1:
Both the contrast resistor labeled R476 and the contrast potentiometer
labeled VR301 CONTRAST VOL. need to be removed and replaced.
These parts are both located in the upper right corner as shown in the
photo above, Fig. 3. In order to desolder these parts the circuit board
needs to be removed and flipped over. The circuit board is held in place
by 7 screws on the inside as shown in Fig. 4 on page 5 and another 6
screws on the back as shown in Fig. 5.

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Fig. 4 - Inside Circuit Board Screw Locations Circled in Red
Fig. 5 - Backside Circuit Board Screw Location Circled in Red

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Fig. 6 - R476 replaced with provided 3.3K Ohm resistor
VR301 CONTRAST VOL. replaced with provided 10K potentiometer
Step 2:
Desolder R476 from the circuit board and solder the provided 3.3K Ohm
resistor in its place. Desolder VR301 CONTRAST VOL. from the circuit
board and solder the provided 10K potentiometer in its place. Reinstall
the circuit board into the TG77 and screw the circuit board back into
place.

Yamaha TG77 LCD Replacement Guide
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Fig. 7 - Location of CN605 which needs to be removed
Step 3:
In order to power the backlight of the new replacement LCD the wired
connector labeled CN605 located on the power supply circuit board
needs to be desoldered and replaced with the white 2-pin connector
part that is provided with the replacement LCD.
In order to desolder CN605, the power supply circuit board needs to be
removed and flipped over to work on. To remove the power supply
circuit board, first remove the metal box that covers the inverter. This is
shown in Fig. 8 on page 10. The metal covering is held in by 2 screws on
the side of the case as shown in Fig. 9 on page 10.

Yamaha TG77 LCD Replacement Guide
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Fig. 8 - Metal Box Covering the Inverter Circuit Board
Fig. 9 - Metal Box Screw Locations Circled in Red

Yamaha TG77 LCD Replacement Guide
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Fig. 10 - Metal Box Covering Removed from the Inverter
Step 4:
Once the metal box is removed, you will find a small inverter circuit board
with two wired connections. Unplug both of these connections and remove
the inverter circuit board, it is held in place by two screws. The inverter
circuit board is no longer needed for the replacement LCD.
The 2-pin connector that was unplugged from the inverter is connected to
the power supply board and labeled CN605. As stated, CN605 needs to be
desoldered from the power supply board.
Remove the power supply circuit board, which is held in place by 6 screws,
the locations are shown in Fig. 11 on page 12. In order to flip the power
supply board over you will need to also detach the black plastic power
switch button; note how it is oriented so you can correctly reinstall it once
finished. Flip the power supply circuit board over, desolder and remove
CN605, the 2-pin wired connector.

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Fig. 11 - Locations of Screws on Power Supply Board Circled in Red
Fig. 12 - CN605 2-pin Wired Connector needs to be Desoldered and Removed

Yamaha TG77 LCD Replacement Guide
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Fig. 13 - Included 2-pin Connector soldered into CN605 Position
Step 5:
Once the CN605 2-pin wired connector is desoldered and removed, the
included white 2-pin connector needs to be soldered in its place as
shown in Fig. 13 above. Be sure to correctly orient the connector as
shown, with the slots facing the edge of the board.
Once the 2-pin connector is properly soldered into place, reinstall the
power supply circuit board and screw it back into place, also reattach
the power switch button.

Yamaha TG77 LCD Replacement Guide
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Fig. 14 - Knob Locations on Front Panel Shown in Red
Step 6:
Remove the front panel.
In order to remove the front panel you will need to remove the Data
Entry knob and the Volume knob. The volume knob consists of two
knobs, a top portion and a bottom portion. The top portion can be
easily pulled off from the front. The bottom portion needs to be pushed
from the back in order to be pulled off from the front. The Data Entry
knob can also be easily pulled off from the front.
There are 8 screws that hold the front panel in place. Remove the 3
screws from the top, the locations are shown in Fig. 15 on page 15.
Remove a screw from each side, the locations are shown in Fig. 16 on
page 15. Remove the 3 screws on the inside, the locations are shown in
Fig. 17 and 18 on page 16. Now the front panel can be removed.

Yamaha TG77 LCD Replacement Guide
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Fig. 15 - Top Front Panel Screw Locations Circled in Red
Fig. 16 - Side Front Panel Screw Location Circled in Red

Yamaha TG77 LCD Replacement Guide
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Fig. 17 - Inside Front Panel Screw Location Circled in Red 2of 3 Screws Shown
Fig. 18 - Inside Front Panel Screw Location Circled in Red Remaining Screw Shown

Yamaha TG77 LCD Replacement Guide
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Fig. 19 - Screw Locations on LCD Front Panel shown in Red
Step 7:
Remove the LCD front panel.
There are 4 screws that hold the LCD front panel in place as shown in the
photo above Fig. 19. In addition, you need to unplug the ribbon cable,
shown in Fig. 20 on page 18. When you remove the LCD, be sure to take
note of how both the ribbon cable and LCD power cable are threaded
through the case openings so you can later properly thread the wiring of the
new replacement LCD.
Once the LCD front panel is removed from the case, you will find the LCD is
attached to it with 4 screws as shown in Fig. 21 on page 18. Remove the
original LCD from the front panel; make note of the orientation of the LCD.
Install the replacement LCD in its place, be sure it is oriented correctly and
properly aligned. Correctly thread the LCD power wire and ribbon cable
through the case openings and plug them in. The power wire will plug into
CN605 the 2-pin white connector you installed earlier and shown in Fig. 13
on page 13.

Yamaha TG77 LCD Replacement Guide
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Fig. 20 - LCD Ribbon Cable Connection shown in Red
Fig. 21 - LCD Screw Locations shown in Red

Yamaha TG77 LCD Replacement Guide
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Fig. 22 –Blue replacement LCD installed in the TG77
Step 8:
Finishing up the installation.
Now that the new LCD is installed, before screwing the case back
together it would be a good idea to test that your installation of the
LCD is working. Adjust the LCD contrast knob on the back of the TG77
as needed. Once you have verified your LCD installation works, screw
everything back together and you are finished.

Yamaha TG77 LCD Replacement Guide
produced by: glitchscience.com 2011©
2022©
20
This guide is not to be distributed or redistributed without explicit permission from the owner of the document.
contact: glitchscience[at]gmail[dot]com with inquiries
Replacement TG77 LCDs can be purchased via E-bay glitchscience items on E-bay