Markus, sorry that I cannot help in identifying the resistance value of R10 on your JDM board. I searched my photo archive of my capacitor replacement job for my speedo but didn't see any resistors that resembled yours. Send a PM to DaleClark about the resistor on the speedo board. Maybe he could shed some light for you?

Does another forum member have their speedo apart and is willing to inspect their R10? I'd be curious to know if there are any differences between the JDM vs USDM resistor values!

Markus, best of luck to you!
George

 

Nevermind , i measured the resistor and it seems to be ok , its 20 Ohm both on my good and bad bad boards . So i think i will start replacing capacitors to fix my Knighsport speedo

 

I love this thread.

My odo is blank, presumably because of my motor swap, possibly a ground, whatever...

But it's nice to know this thread exists in the event that I find myself diving into some PCB's and soldering.

Big thanks to everyone who has and continues to contribute their experiences!

 

A litte recap of my situation since my tach still isnt working.

Both my speedo and tach went out, I replaced all damaged caps etc on the speedo and it still didnt work. I believe I burnt out the stepper motor when I was testing on it with an RC car battery(small burning smell). Because of this I bought a new cluster. I plugged it all in and only the speeo works. Small sucess!

So now, I didn't think my tach was getting signal but when I check the terminals with the car running on the tach I have +12v(actual 11v), I have ground, and I have about 4v on the signal terminal of the tach that doesn't change with revs of the motor. When my tach was going out it died slowly during a tuning session and then completely dead a week later. SO I thought the stepper was going out as well but the new one didn't work either...

So that's where i'm at till I have a little more time, any thought or ideas?

 

Is it possible to adjust the ODO reading .. i have a newer cluster with lower mileage but i want to redial it to higher mileage to match the car.

 

Yes I believe Dale Clark figured it out. Search for his thread.

 

Can't you prop up the car with a jack and put it in gear? Now where have i seen that done before?

 

Swap the mileage chips. It takes a bit of skill with a soldering iron or pay someone a few buck who is experienced and has quality soldering tools.

 

Have you checked all of your harness power and ground wires? There are several of each.

If you want to check the tach signal you'll need an actual test tach or oscilloscope.

 

which one is the mileage chip?

 

See here
https://www.rx7club.com/3rd-generati...o-mph-1015964/

 

is there a certain ground to check before tearing apart the cluster assembly and re working the board?

 

just wanted to give a huge thanks to this thread, i replaced the large 6.3V capacitor that people said was 9/10 times the problem, and cleaned the board with alcohol and a q tip, and now IT WORKS, well worth the few hours of removing the cluster and soldering in the new piece.

 

Before reinstalling your speedo, did you clean up the other contacts with alcohol around that bad capacitor (transistors and zener diodes)? Are those other solder points burned, corroded, or dirty from soot?

I'm glad to see that your effort fixed the board. Great work!
Cheers,
George

 

yes, i cleaned the area thoroughly with rubbing alcohol on a q-tip, even though alot of the diodes and transistors in the area looked like they were bad because of alot of build up of old fluid on the contacts(that im assuming leaked from the capacitor) they were indeed ok and it was only the 6.3V cap that was the issue. i checked the resistance across everything in the area and it all looked ok, the bad 6.3V capacitor was reading something like 50 megaohms(M), and the new capacitor was reading something like 400-500 kilohms(K).

 

Right on! You are correct, the electrolyte leaked from the capacitor to the other components. If left unchecked, that electrolyte would eat away at the other solder joints. Nice work on the repair and clean up. Did you go for a victory drive yet?

 

of course, its always driving weather here in Florida.

i guess i should also note, i used a product called "M-line Rosin Solvent" to clean the contacts and the board. its specifically designed to clean off flux and small electrical circuits, and its alot safer to use on plastic compared to alcohol(i work in an aerospace electronics lab and we use this religiously)

here is a link to the same type of product

http://www.qsource.com/p-22349-acl-s...FcVkhgodb2kG2w

 

Thanks for all the input in this thread. I've replaced the 2 capacitors that gave others the no number issue and soldered both sides. I think I need to replace the part i've circled in the picture. It looks pretty corroded and like it has leaked something.

The pic is not mine I just stole if from the OP.

It has c458 d 3f3 written on it. Can anyone help with the digikey part number? I cant figure out how to find it on their site.

 

Blacksi,

That component that you circled in red is not a capacitor. It's labeled TR5. If it has 3 leads then it's a special transistor; probably a Darlington Pair power transistor. Have you tried cleaning TR5's leads with alcohol and a cotton swab? For example, take a look in the upper right corner of the photo. Those pins are not corroded; they have dried solder flux on them. It will come off with alcohol and a small amount of elbow grease.

Any chance you can share a pic of your board? You may not need to replace TR5.

Cheers,
George

 

Yes I know it is a transitor. I tried but can get a pic of it now as the speedo is reattached. but it is badly corroded and there is visible brown traces of leakage around it.

 

Blacksi,

Take a few moments to read post #'s 119 and 134. Post 119 talks about the brown discoloration on the solder cups. That was 22yrs of old flux. Post 134 shows what a TRx looks like when it fails. Again, the "brown traces of leakage" you witnessed on TR5 is arguably old solder flux.

Secondly, when solder joints corrode or deteriorate, the solder turns to a grey-ish powder or may look tarnished. Solder runs and solder joints are typically made from an alloy containing silver, zinc, copper, and tin. Only steel or iron leave a reddish-brown color when it corrodes. Hence, iron oxide or ferrous oxide is commonly referred to as rust. Feel free to google electrical solder joint corrosion to learn more.

Thirdly, read post # 109. The part number for TR5 is given. I am curious to see how TR5 looks. Perhaps you could share a photo of it when the speedometer is removed for more troubleshooting/repair?

Further, after you replaced the defective capacitors, did your odometer come back to life? Or is it still not working?

Cheers,
George

 

Thanks George,

The odometer didn't come back to life which is why I began searching for more possible issues. I read people think they got them too hot also, so I was thinking for the 30cents or whatever they cost I would redo them when I order the Tr5. This was my first time soldering on a board where too much heat could be an issue. I tried to not get anything too hot but hard to tell what too hot is.

Alright thoughts on this? The pic came out weird cause it is the fish eye through a magnifying glass so it looks like its of the green item behind it but the legs are of tr5.




And here's the brown path heading away from it.




Any thoughts whether this is just corrosion or an issue?

 

That transistor is toast or at least the leads are. Try removing the solder using solder wick or a solder sucker and then clean those leads. Looks like the leads are corroded or someone has tried to repair based on the spatter.

ZD3 is a diode that looks like it may have overheated.

 

KCREPU,

Thanks for chiming in on the components!

**break, break**

Blacksi,

Thank you for taking a pic of your board. And yes, replace TR5 as it looks bad. The corrosion/build-up from the middle leg probably created a short-circuit across the right leg. It is difficult to make out however, TR5 may have blown up. Technicians jokingly refer to that as "releasing the magic smoke". The left leg looks charred. When your odometer blanked out, did you hear any popping sounds followed by the smell of smoke? Or did you see a wisp of smoke emanate from your dash?

Do you have any plans to drive your FD for a special event? If not, leave it parked and remove the speedometer from the rest of the circuit board. Take a good look at the rest of the board. Look for cold solder joints and other poor solder joints that need attention. This could look like a big task, especially for someone who lacks experience in soldering electronic components. This process is tedious but not impossible to complete. Make sure that you arm yourself with the proper tools. Typically, a 45W soldering iron is sufficient to melt electrical solder. Could you please tell us what tools you have for soldering?

Here's what I recommend:
1. Soldering iron, 45W (ensure fine tips are part of the kit)
2. Solder, 60/40 rosin-core, .032" diameter
3. Solder flux (paste or fluid)
4. Acid brushes (set of 3 is fine)
5. Cotton swabs
6. Solder wick or solder sucker (or use Item 7)
7. De-soldering Iron, 45W (use as a substitute for solder wick/sucker)
8. Isopropyl Alcohol (any percentage is fine, over 90% is preferred)

Check out a few youtube vids on soldering & de-soldering procedures. Some helpful hints: clean area with alcohol first & then after the solder joint is completed; apply heat to the solder then let it flow onto the joint; solder flux acts like a wick for solder. Solder and flux is like Mary's little lamb... "..and everywhere the flux went, the solder was sure to flow." Additionally, never re-use (re-flow) a cold solder joint. De-solder the cold joint and then apply new solder.

As for ZR3, it may not be defective. Zener diodes are more robust from the average diode. However, the green corrosion on one leg needs to be replaced. I would remove the old solder from both ends of ZR3 and apply new solder. Additionally, look at the 3 diodes from ZD5 thru ZD4. Two of these diodes look like their joints need replacement. It has a large tarnish surrounded by a small shiny ring at its base. Clean them with alcohol first and make that determination to replace the solder.

Here's some other food for thought: when you replaced the capacitors, did you observe the polarity? There is a stripe on the capacitor that indicates the negative lead. These caps contain an electrolyte (which is why these old caps leak) and the placement of the poles on the cap make a big difference in the circuit. If the polarity on the cap does not match the rest of the circuit, then damage to the cap/board may result or the cap will never operate properly.

Does this help?

Cheers,
George

 

KCrepu and George,

Thank you very much for the responses. Kc i didn't even think twice about the diode but now that you point it out I may as well put that on my list to replace.

George,

My exhaust is loud enough when it popped I wouldn't have heard it and I would of dismissed any smoke smell as exhaust slash engine blow by.

I have almost everything you listed as far as equipment. A 30watt iron, 60 40 .032 solder, and wick.

I will clean the diodes and see what they look like. I am thinking if I am ordering the transistor I may just throw them in. It seems like the box they ship things in cost more than the items, at least it was for the capacitors.

As far as the capacitors I did put them in with the Gray strip near the negative symbol on the board.

Once again thanks for all the thoughtful input, I really appreciate it!

Mark.