Evening Members! I first want to thank Dale Clark for the generous donation of 2 instrument clusters and associated spares. This affords me the opportunity to continue my investigation into the mysteries of the Speedometer!

This thread is focused on the flex print circuitry that is on the backside of the instrument cluster. This flex print seldom has any issues but I would like to document its components for posterity. The donor flex print came from a USDM 1993 model.

First, the components soldered to this flex print are as follows:

NOTE: N/I means the component is not installed on the flex print.

Transistors:
Q1 (T1): D1922 / 2SD1922 (1)
Q2 (T2): N/I
Q3 (T3): A1013-O / 2SA1013-O / Mfr P/N: KSA1013OBU / Mouser P/N: 512-KSA1013OBU
Q4 (T4): D1922 / 2SD1922 (1)

(1) For purchase, refer to FD Speedometer-Odometer Circuit Board - Odometer Components Thread, Post #41: https://www.rx7club.com/3rd-generati.../#post12217991

Resistors: All resistors have tollerance of +/-5% unless noted
R1: 1.2kΩ, Mfr P/N: CF14JT1K20, DigiKey P/N: CF14JT1K20CT-ND
R2: 300Ω, Mfr P/N: CF14JT300R, DigiKey P/N: CF14JT300RCT-ND
R3: 3kΩ, Mfr P/N: CFR-25JB-52-3K, DigiKey P/N: 3.0KQBK-ND
R4: 5.1Ω, Mfr P/N: PR01000105108JR500, DigiKey P/N: PPC5.1W-1CT-ND
R5: N/I
R6: N/I
R7: 6.8kΩ, Mfr P/N: CFM14JT6K80, DigiKey P/N: S6.8KQCT-ND
R8: 62Ω, 2W, Metal Oxide (blue color), Mfr P/N: ERG-2SJ620, DigiKey P/N: P62W-2BK-ND
R9: 6.8kΩ, Mfr P/N: CFM14JT6K80, DigiKey P/N: S6.8KQCT-ND
R10: N/I

Diodes: All but D8 are the same part number.
D1: M1 22, Mfr P/N: M100A-E3/54, DigiKey P/N: M100A-E3/54-ND (2)
D2: N/I
D3: N/I
D4: M1 22
D5: M1 22
D6: M1 22
D7: M1 22
D8: 8 (Zener Diode, only partial P/N)
D9: See R1

(2) This is a proposed part number based upon observation and internet searches. More research would be required!

Jumper: All but J4 are solid & thin wire.
J1: Wire
J2: N/I
J3: Wire
J4: M1 22 (Diode serves as “one-way” jumper) (2)
J5: Wire
J6: N/I
J7: N/I
J8: Wire

Next, photos of the flex print. Note the location of each “Series” connector that corresponds to C1-01.



Connector C1-01 4 Series in red box.




Connector C1-01 3 Series in red box.




Connectors C1-01 1 Series (bottom) and C1-01 2 Series (top).




Hidden side of the flex print with C1-01 1 & 2 Series Connectors. 1 Series on the bottom, 2 Series on the top.




Hidden side of the flex print with C1-01 3 Series Connector and other visible components.




Hidden side of the flex print with C1-01 3 Series (far left) and C1-01 4 Series (center).

Cheers,
George

 

Cool! I didn't even realize there were components on the reverse side!

Glad to help with the project!

Dale

 

Thanks again for the help, Dale!

For the Forum,

Here are some better shots of the flex print connectors. I identify them as C1-01 1 Series, 2 Series, 3 Series, 4 Series, and Speedometer, or in short: C1-01-1, C1-01-2, C1-01-3, C1-01-4. Please note all connectors (minus the speedo connector) have a triangle in the center. This triangle is an index mark and signifies the top of the connector. Furthermore, each connector is labeled with its corresponding pin according to the Wiring Diagram Manual (WDM).

Cheers,
George


C1-01-1



C1-01-2



C1-01-3



C1-01-4



Speedometer Connector

 

I am pleased to announce the next breakthrough with the Flex Print! I spent the past few days sketching out a wiring diagram of the flex print, using a physical example as a guide. Please note, this flex print was taken from a 1993 Instrument Cluster with Manual Transmission. Heed the following notes about this schematic:

1. This schematic represents an electrical and physical layout of the flex print. It will look more complex when compared to the schematic in the Wiring Diagram Manual (WDM). Unlike the WDM, this schematic maps out the 15-pin Speedometer connector.

2. A dot (.) indicates a connected intersection. An unconnected intersection would look like a cross (+). Refer to the WDM, Section Z-GI-9, Pg Z-9 for an example.

3. All transistors on this schematic are noted as “Q”, according to the electrical standard. However, the non-standard designation of “T” is printed on the flex print.

4. All light bulbs are drawn with its filament as the Positive (+) leg and the outer shell as the Negative (-) or Ground (GND) leg. Typically, the Ground leg of a bulb was drawn at a 45* angle.

5. Some Illumination Bulbs were simplified for this schematic.

6. Wire traces to Jumper locations J5 and J6 were simplified for this schematic.

7. The notation of (NI) adjacent to a designator indicates a component is “Not Installed.” For example, D9 (NI) indicates Diode #9 was not installed on the flex print.

8. Some components were not physically installed on the sample flex print. However, solder points for these components remain. These components were drawn on this schematic with placeholders. This means a component was partially drawn with “missing” legs. This applies to:

---D9 not installed. If D9 was installed then remove R1 from the circuit. It is either R1 or D9 that connects to C1-01-4 Pin 4L.

---Q2, R5, and R6 not used. These components are drawn but are electrically disconnected.

---Components listed as (NI) are: D2, D3, D9, J2, J6, J7, Q2 (T2), R5, R6, and R10.

9. Transistor Q3 and its associated circuitry applies to Manual Transmission cars only. This helps display the “CRUISE” light in the tachometer.

10. Interesting findings about 15-Pin Speedometer Board Connector:

----Pin 3 – Speedo receives input from Water Thermoswitch. Applies to Automatic Transmissions only.

----Pin 4 – Not used.

----Pin 5 – Speedo receives input from ECU Pin 1M, Vehicle Speed Sensor and/or from Cruise Control Unit Pin E, Vehicle Speed Sensor via C1-01-3 Pin 3E. This is important to note when an odometer blanks out because this would cause speed surges when the cruise control is set at a specific speed.

NOTE: ECU/Cruise Control Vehicle Speed Sensor signals are separate from the signal generated by the actual Vehicle Speed Sensor, located at the transmission.

----Pin 8 – Speedo sends Buzzer signal for Over-rev and Low Coolant Alarms to Body CPU’s (CPU #2) buzzer.

Cheers,
George

 

Below is the schematic for the Instrument Cluster's Flex Print. Members should be able to download it without issue. It is scaled to print on a standard 8.5x11" sheet of paper. If Members wish to have a higher resolution version then PM me.

NOTE: Refer to Post #17 for an updated version of the schematic.

Cheers,
George

 

Below is a list of Input/Output pins to all the flex print connectors.

Cheers,
George


Connector Pin List:
C1-01-1
1A – ABS CPU
1B – ABS Light
1C – Air Bag Light
1D – Water Temp Signal
1E – Ground (GND)
1F – To Alternator
1G – Illumination (-)
1H – Illumination (+)

C1-01-2
2A – Check Engine Light (CEL)
2B – Fuel Level Sender
2C – Fuel Level Low Light
2D – Ignition +12V
2E – Illumination (-)
2F – Oil Pressure Sender
2G – Illumination (+)
2H – Right Turn Switch
2I – Rear Defrost Switch
2J – Left Turn Switch

C1-01-3
3A – Vehicle Speed Sensor “A”
3B – To CPU #2 Buzzer
3C – Vehicle Speed Sensor “B”
3D – Water Level Sensor
3E – Vehicle Speed Sensor from ECU & Cruise Control Unit
3F – TAM
3G – Not Used (N/U)
3H – Not Used (N/U)
3I – Not Used (N/U)
3J – Oil Level Sensor
3K – Not Used (N/U)
3L – To Cruise Control Unit (MT Only)

C1-01-4
4A – Water Thermoswitch (AT Only)
4B – Illumination (+)
4C – Mileage Switch
4D – Illumination (-)
4E – +12V
4F – To CPU #2 Seat Belt Light
4G – Combination Switch (High Beam)
4H – Ground (GND)
4I – To Alternator Voltage Regulator
4J – Emergency Brake Switch & Brake Fluid Level Sensor
4K – Ground (GND)
4L – Starter Cut Relay (MT) / Park-Neutral Switch (AT)

Speedometer Connector (CON1)
01 – +12V
02 – Mileage Switch
03 – Water Thermoswitch (AT)
04 – Not Used (N/U)
05 – Vehicle Speed Sensor from ECU & Cruise Control Unit
06 – Vehicle Speed Sensor “B”
07 – Vehicle Speed Sensor “A”
08 – To CPU #2 Buzzer
09 – Water Level Sensor
10 – TAM
11 – Tachometer Signal
12 – Tachometer +12V
13 – Water Level Low Lamp
14 – Tachometer GND & GND
15 – Ignition +12V

 

This post provides an update to the Zener Diode, D8. I removed this diode from the flex print then used a magnifying lens to read the part number stamped on it. It reads "B1" and on the opposite side, "3". I presume this means the part number is B13. A google search for Zener Diode B13, uncovered this potential replacement for D8.

If anyone attempts to desolder D8 or solder in a replacement then I offer a word of caution. The heat from the soldering iron will melt the plastic surrounding the copper trace. These components have a lot of solder on them so I would guess that damage to the flex print is inevitable.

Thanks in advance for reviewing this new data.

Cheers,
George

Here are some close up shots of the diode:


Front side of diode with "B1" stenciled on it.



Back side of diode with "3" stenciled on it.



Here is some information on the Zener Diode (see the attached datasheet for more details):


The yellow highlights row is the proposed D8 replacement.

 

This post reflects the proposed replacement for D8 based upon the findings from Post 7, above.

NOTE: N/I means the component is not installed on the flex print. N/I components depends upon the configuration of the Instrument Cluster, i.e. Manual Trans and Cruise Control installed.

Transistors:
Q1 (T1): D1922 / 2SD1922 (1)
Q2 (T2): N/I
Q3 (T3): A1013-O / 2SA1013-O / Mfr P/N: KSA1013OBU / Mouser P/N: 512-KSA1013OBU
Q4 (T4): D1922 / 2SD1922 (1)

(1) For purchase, refer to FD Speedometer-Odometer Circuit Board - Odometer Components Thread, Post #41: https://www.rx7club.com/3rd-generati.../#post12217991

Resistors: All resistors have tollerance of +/-5% unless noted
R1: 1.2kΩ, Mfr P/N: CF14JT1K20, DigiKey P/N: CF14JT1K20CT-ND
R2: 300Ω, Mfr P/N: CF14JT300R, DigiKey P/N: CF14JT300RCT-ND
R3: 3kΩ, Mfr P/N: CFR-25JB-52-3K, DigiKey P/N: 3.0KQBK-ND
R4: 5.1Ω, Mfr P/N: PR01000105108JR500, DigiKey P/N: PPC5.1W-1CT-ND
R5: N/I
R6: N/I
R7: 6.8kΩ, Mfr P/N: CFM14JT6K80, DigiKey P/N: S6.8KQCT-ND
R8: 62Ω, 2W, Metal Oxide (blue color), Mfr P/N: ERG-2SJ620, DigiKey P/N: P62W-2BK-ND
R9: 6.8kΩ, Mfr P/N: CFM14JT6K80, DigiKey P/N: S6.8KQCT-ND
R10: N/I

Diodes: All but D8 are the same part number.
D1: M1 22, Mfr P/N: M100A-E3/54, DigiKey P/N: M100A-E3/54-ND (2)
D2: N/I
D3: N/I
D4: M1 22 (See D1)
D5: M1 22 (See D1)
D6: M1 22 (See D1)
D7: M1 22 (See D1)
D8: B13, Zener Diode, Mfr P/N: BZX79B13, Mouser P/N: 821-BZX79B13 or DigiKey P/N: 1727-6122-1-ND
D9: See R1

(2) This is a proposed part number based upon observation and internet searches. More research would be required!

Jumper: All but J4 are solid & thin wire.
J1: Wire
J2: N/I
J3: Wire
J4: M1 22 (Diode serves as “one-way” jumper) (See D1)
J5: Wire
J6: N/I
J7: N/I
J8: Wire

Cheers,
George

 

For the pins that go to the buzzers, are you saying the Speedo connector circuit is what actually feeds the buzzer the signal? Where are the buzzers physically located?

 

TwinCharged,

There are 5 warning alarms that the Body CPU Buzzer sounds according to the Body Electrical Troubleshooting Manual (BEM). Refer to BEM Pg C2-12, Warning Alarms table, for a description of each alarm. This table also provides a troubleshooting flowchart for each alarm.

The Speedo board provides an output to the Buzzer, which is located in the Body CPU (CPU#2). That output affects 2 warning alarms. The first is the Over-rev Alarm and the second is the Low Coolant Level Alarm. The Low Coolant Alarm flowchart begins on BEM Pg C2-34 and the Over-revolution Alarm flowchart begins on BEM Pg C2-35.

Did I answer your question?

Cheers,
George

 

 

Here is a photo to provide a physical example of Not Installed components on the flex print. Refer to Note 8 from Post #4. It stated:

"Some components were not physically installed on the sample flex print. However, solder points for these components remain. These components were drawn on this schematic with placeholders. This means a component was partially drawn with “missing” legs."


Bare solder eyelets within the red highlighted box are reserved for Q2 (T2), R5, and R6. The same is true for Jumper locations J7 and J6, directly above the box.



Red highlight boxes show placeholders for Not Installed components Q2 (T2), R5, R6, J7 and J6. Note the missing legs on Q2, R5, and R6.


Does this eliminate any confusion when comparing the photo to the schematic?

Cheers,
George

 

To successfully work on the flex circuit board you have to use the right procedures and have the right equipment to avoid overheating and melting or delaminating the flex board. The first thing you need is a digitally controlled soldering/desoldering station they are around $300-$500


The other thing you need is 63/37 solder, which: 1. has the lowest melting point (183 °C ) of all the tin-lead alloys; and 2. the melting point is truly a point — not a range.

As for the technique. You need to pre-bake the flex circuit card at 121 °C for about one hour before soldering. This is to drive out the moisture that has absorbed into the flex card. An added plus is all the components are now preheated and it will take less time to get them up to soldering temperature. Use lots of flux for soldering and desoldering, that speeds up the heat transfer and helps lower the soldering iron temperature required. I have never worked on an RX-7 flexcard, but soldering/desoldering temperatures should be between 260°C and 370°C for a double sided polyimide flex circuit. Polyimide continuous use to temperatures is around 232 °C and for short excursions, as high as 400 °C, however the adhesive that attaches the copper traces may soften at higher temperatures. My best recommendation is to do what I do, take it to an electronics technician with experience working on polyimide flex circuit and let her do it.

 

mdp,

Thanks for the great info! I would like to have a sweet soldering station like the one pictured in your post. Would you like to cross-post this to my General Soldering Tips thread here: https://www.rx7club.com/3rd-gen-gene...dvice-1121639/? I think others would benefit from your knowledge!

Cheers,
George

 

Done!

 

These photos show a good labeling scheme to each Flex Print connector. This was used to digitally add the connector labels in Post #3. An Ultra-Fine Point Sharpie marker was used to mark up each pin. Marking up the Speedometer Connector was a big help in tracing out the schematic!

Cheers,
George


Connector C1-01-1



Connector C1-01-2



Connector C1-01-3



Connector C1-01-4



Speedometer Connector (Con1).

 

I did more research on the Flex Print and Speedometer Connector (CON1) labels and found an error! The error concerns Pin 13 on CON1. The proper label on the schematic now reads, "Water Lvl Low Lamp". This signal is an output from the Speedo Board via Pin 13 and goes to the Negative terminal of the Water Level Low Lamp. The Speedo Board receives a Water Level Sensor input via Pin 9 on CON1. After it is processed, the output (ground) is sent to the lamp housing to complete the circuit for the lamp to illuminate when the coolant falls below the sensor.

Here is the updated schematic of the Instrument Cluster Flex Print. It can be downloaded. Please disregard any previous versions of this schematic.


Corrected Flex Print Schematic for CON1, Pin 13

 

This is the updated list of Pins for the Speedometer Connector (CON1)

Speedometer Connector (CON1)
01 – +12V
02 – Mileage Switch
03 – Water Thermoswitch (AT)
04 – Not Used (N/U)
05 – Vehicle Speed Sensor from ECU & Cruise Control Unit
06 – Vehicle Speed Sensor “B”
07 – Vehicle Speed Sensor “A”
08 – To CPU #2 Buzzer
09 – Water Level Sensor
10 – TAM
11 – Tachometer Signal
12 – Tachometer +12V
13 – Water Level Low Lamp
14 – Tachometer GND & GND
15 – Ignition +12V

NOTE: Post 6 was also updated to reflect the change to Pin 13.

 

Hi,

Awesome work thank you very much for sharing it!
By any chance do you know the connector type used to connect to the ECU?

I'm working on a test stand for FD clusters and I'd like to build a clean harness for it.

Thank you,

nick

 

Nick,

Thanks for the compliments.

Are you looking for a connector to the ECU, to the Speedo board, or to the instrument cluster? Unfortunately, I do not have any information on connectors to either of these components. I am curious to see progress on your test rig.

I do have an old thread that identifies a few websites for automotive connectors. You might be able to find the proper connectors in those websites. If you do find the proper connectors then please share them. I'd be happy to add them to a list of parts for the Speedo board and instrument cluster.

 

I'm looking up those connectors myself on a few sites, no luck so far. They're weird since they contact rather than "connect", as in they aren't male or female, they just butt up against the flex print. TE Connectivity does most of the FD, maybe someone can send a picture to them and see if they can identify it. (I'm at work right now and have also removed those connectors from mine...SPEEDHUT!)

 

Did you completely removing the flex print? Im in the middle of installing speed hut gauges. I have a power FC for ecu, I just want to retain the turn signals and charge lamp.

 

Great thread and very useful topic.
I am trying to power up the cluster in my lab so anyone have done this ? I give +12v to 4E ,2D and gnd to 1E ,4H,4K and the light up the battery the cooland led but no odometer if i apply and gnd to pgnd of odometer pcb then lcd light up but very dim.I dont want to pull out my cluster from my fd to check the repaired one.