Dashboard instrument cluster repairs

[casey]

Another cluster arrived for repair on Monday afternoon, 2 March. I managed to diagnose and repair and ship it back within 48 hours (it was a pre-booked job).

No surprises, the usual failed IC on the tacho PCB. no needle movement as received.

Tacho removed from cluster and set up on my tacho tester, still dead - but 5 seconds of 100 degrees from a heat gun onto the IC and the tacho sprang into life and worked perfectly. Unfortunately, that "fix" doesn't last long, so I replaced the entire OEM PCB with my replacement design PCB, which uses automotive grade components. All straightforward to install - the hairiest bit is removing the tacho needle with extreme care. Calibration done on my tester, tacho reinstalled in cluster, retested on my cluster test rig and all good.

Pic of tacho with replacement PCB installed:


Video of tacho on tester for calibration;

Pic of cluster on final, full function test:


Two more repairs booked into my diary, but DM me if you have a cluster requiring a repair.

 

[casey]

I have extended my suite of test boxes to enable me to function-test full clusters, plus tachos and CPU boards in isolation, when removed from clusters:

 

[rotors7]

I have extended my suite of test boxes to enable me to function-test full clusters, plus tachos and CPU boards in isolation, when removed from clusters:

View attachment 43558View attachment 43559View attachment 43560View attachment 43561

I'm well impressed with all that !
Awesome

 

[Jester*]

The nerd in me loves this.

 

[casey]

Another cluster turned around in 2 days and currently winging it's way back to the car owner in SWEDEN.

No tacho OR speedo operating, so I was thinking this could be an expensive and time consuming repair. In fact, the cause (which didn't take too long to diagnose) turned out to be a short circuit diode, costing pennies. It was a bit if a faff to remove it and replace with a new one from stock, as the gauge had to be removed from the CPU PCB, but straightforward enough.

 

[casey]

Teaser - 3D CAD image of Speedo daughterboard that can be used to fix "errant speedo needle" issues, when caused by a (now obsolete) failed driver chip. It has taken some time to design and test the electronics, plus a tricky physical design to fit within the space limitations and available fixing points. I've even managed to retain the use of the existing speed calibration variable resistor on the CPU board.

I have just sent off an order for 5 PCB's to be manufactured. Hopefully, they will be perfect, but I'm allowing some time to do a tweak or two when I do some testing.

 

[Jester*]

So cool

 

[RX2761]

Hey I have a faulty tach, I was about to ship it overseas and have just come across this! I'm still relatively new to using the forum, but have been signed up a while. I'll send you a message now!

 

[MILLION]

very nice!

 

[casey]

Hey I have a faulty tach, I was about to ship it overseas and have just come across this! I'm still relatively new to using the forum, but have been signed up a while. I'll send you a message now!

You have a DM

 

[casey]

First batch of "daughterboard" PCB's to replace failed IC6 driver chip on CPU/Speedo board has arrived for assembly, fit and test. I have 3 cluster repairs booked over the next week, so might be a delay in working with these.

 

[casey]

Another cluster will be winging it's way back to the owner tomorrow. This was a weird fault/repair. Customer reported intermittent tacho, sometimes stuck at zero, other times OK, initially pointing to an intermittent electronic issue, maybe a dry joint or component failure.

The tacho, when tested in the cluster on receipt was, indeed, stuck on zero. When removed from the cluster and tested on it's own, it worked perfectly. The more I thought about it, the more it seemed like a mechanical fault, requiring more "energy" to lift the needle off zero. Bingo, that was it. I have a very close look at the needle stop on the gauge face and noted a physical "gouge" in the stop pin and a corresponding faint mark on the needle.

This video shows the needle stuck at zero, but a slight nudge would get it moving. This was reproducible. You can even hear a slight click as the needle, hooked onto that gouge, breaks free.

The solution was to place a heat shrink sleeve over the damage to stop the sticking, and clean the mark on the needle. You'd never know the sleeve was there.

A very unique failure mode!

 

[casey]

Right, two more clusters arrived today for repair, so the fun continues.....

 

[RandomVillager]

There getting to that age where alot of weird little electrical issued come.

Had a Soarer 1j that would cold start idle for a bit run like shit stumble stall then once it was hot it was fine.

All the electrolytic caps were dead/leaking.

Quick recap and it was all good.

 

[casey]

I've just invested in a dedicated capacitor tester which claims can test electrolytic caps in circuit, so if no classic signs of failure (bulges or leaks) I should be able to check if a cap has deteriorated to the point it needs changing.

 

[casey]

Another cluster partially repaired and will be on its way back tomorrow. Main fault was a badly leaking capacitor. The corrosive electrolyte had damaged other, nearby components too. I'll post up a fuller report next week.

Partially repaired only, as sadly one issue could not be fixed. I diagnosed a failed odo display driver chip. Another obsolete IC that, at least for now, I cannot offer a solution

 

[casey]

Report on partial repair. The cluster had very "twitchy" needle on both the tacho and the speedo, plus a fault with the odo display.

Speedo twitch;

As both the needles were twitching at the same time, it suggested a common fault, likely a power issue. Sure enough, on examining the speedo PCB, this was what greeted me:

A classic, but slight bulge on the large cylinder, an electrolytic capacitor, and signs of leaking electrolyte having run down the PCB and causing some corrosive damage and lifted PCB silkscreening. This cap is a "smoothing" cap for the power supply, common to circuity of both speedo and tacho.

Cap removed and board cleaned up as best I could, at least removing remains of lurking electrolyte:

A new cap was soldered in and the twitching was much reduced, but still evident. Further checks revealed a diode and a capacitor, both downstream of the electrolyte leak, were suspect. Both were replaced with new and bingo, no twitchy needles any longer!

The last fault was the odo display, which was either blank, or looked like this:

That looked like a leaky LCD (Liquid being the operative word).

Replaced with known good one, but, again, either blank or this:

Well, the diagnosis of a failed LCD display was correct, but further diagnosis revealed the (obsolete) OKI LCD driver chip had a failed internal oscillator. This, is, at least for now, a fault for which I cannot offer a solution

Well at least the needles are rock solid now - this after ~30 minutes on test:

Cluster now on its way back to the customer.

I have another cluster on the bench now and it looks like a full repair will be possible on that one.

And then I can get to work on my theory of how to repair RX-8 OMP's, which are beginning to fail at an alarming rate. Mine has already been replaced once, when the car was about 15 years old. I've been searching for the cause of the failure for the past 5 years or more and now think I understand the cause and remedy.

 

[Paul-Knightsport]

I have a spare complete dash sat on the shelf at home with same symptoms, (erratic rev counter and very dim odo) , swapped out for a newer pack about 8 years ago. Glad i kept it as a broken spare, now there is a potential fix available !
Keep up the good work Casey this is just what we need with "Now Old cars " top work
Paul

 

[casey]

Thank you Paul. As a rotary enthusiast, and now retired, it's great to deploy my lifetime of electronics knowledge and skills to help keep iconic FD's on the road.

 

[casey]

Another cluster repaired and packaged up ready to ship back to it's owner.

Another unique fault. The primary issue was the odo display would be backlit, but blank for several minutes (or more) before any mileage data appeared. Strangely, if the cluster was switched off, then immediately back on, the data would appear after a much shorter delay. This pointed to maybe a failed capacitor not charging/discharging as it should. As we know, leaking/failed electrolytic capacitors are often an issue with FD clusters, so seemed a reasonable hypothesis. So, 'scope and multimeter probes in hand, together with a sketched circuit diagram I have painfully derived from the PCB tracks, the challenge was on to find the cause of the issue.

The first clue was that the reset pin on the NEC microprocessor chip (which processes speed data to calculate mileage) was being held low (zero volts, so switching it off) and when the pin went high (5 volts), the processor would spring to life and the data would then appear on the odo. By why/how was the reset pin being held low for so long? The circuit diagram revealed 7 components involved in producing the reset signal. One was an electrolytic capacitor. A 'scope trace showed this to be charging very, very slowly on power up. When charged enough, it operated a Schmitt trigger to send a clean high (5v) signal to the processor to start processing data for the display chip. So, cap changed, but no improvement! Next, what components were involved in charging the cap? A few resistors and a diode array (essentially 2 diodes in a TO-92 "transistor plastic package). Resistors rarely fail, and when they do, there are usually visual signs, so the array, DA2, was a potential problem. In circuit testing showed one of the diodes was suspect. I had a used, known good, spare in stock, so changed it out and that fixed the fault.

There is now the usual slight delay as the processor starts to operate, as seen in this video of the CPU board on my test box. The processor is held off deliberately for a short period at "ignition on" to allow the voltage to stabilise.

Here is the section of the PCB after changing C6 and DA2. Note the main solder (and critical) contacts are on the rear of the PCB. The front pads are simply plated through holes.

Note the early signs of black corrosion, caused by the large cap (C3) in the photo starting to leak it's electrolyte. The customer agreed I change this cap out and clean up the corrosion. In doing this, I noted ZD3 (a zener diode) looked pretty badly corroded!

So that was changed as a precaution. I have seen this component fail on two previous repair jobs!

That's much better, new cap and diode in place, with electrolyte corrosion cleaned.

Back side soldering of DA2 and C6....

There were a few other, minor, items to fix (blown warning lamp, broken trip button...) but all good on final test: