1960 to 1962 Reproduction Fuel Gauges - Failures?

**Dan D.** · February 10, 2014, 08:32 AM

Re: 1960 to 1962 Reproduction Fuel Gauges - Failures?

Rich, I cannot believe these gauges are electronic. Whats wrong with the original design? They work just fine. Are the other gauges electronic too?

Regardless, if you can tap the needle and it moves, then it sounds like a mechanical problem. Needle hanging up, but you know this. So if you load it with 15 ohms using your pot, will it always read 1/2 full?

-Dan-

**Richard M.** · February 10, 2014, 09:05 AM

Re: 1960 to 1962 Reproduction Fuel Gauges - Failures?

The repros are latest technology, yes, the temp is digital too, and ammeter is a shunt like original design, oil is mechanical like original.

Temperature (orig & repro)

orig 59 lefts, repro 60 rights
P6210105.jpg P6210107.jpg

Ammeter & Oil (repros) No internal pcs
P6210121.jpg

Nope, not a mechanical. The needle sits at left, tap lightly, and it's a slow, gradual sweep to the right then pegging. It's clearly electrical movement in the coil. Bill & I were scratching our heads Saturday trying to figure it out, on BOTH gauges. We gave up. I didn't have my oscilloscope, logic analyzer, test probes and simulation software handy to diagnose the failure.

I'll report back when I talk to Ken at K&B(Alpharetta, GA) later. He's probably preparing for another bash of bad weather in Georgia so he's probably going to be unavailable for a while.

Oh, BTW one more tidbit of information.... These repro gauges have a slight fallback. When off, the needles disappear to the left, unlike originals. When power is applied, they move slightly to the right to their start points, then to they're respective "readings". i.e. example cold engine, power off, Temp needle hidden to the left, power on, it moves to below the first "tick", then moves when temp rises normally. You can see it in my pictures.

Bill Harrison had a good idea........Bend the bottom of the needle down a bit more so it hits the bottom edge of the face, to keep the needle a bit to the right at rest.

I suspect Judges will notice this "no power needle behavior"........ eventually.

**Dan D.** · February 10, 2014, 09:30 AM

Re: 1960 to 1962 Reproduction Fuel Gauges - Failures?

Okay Rich, but I still don't understand why its not the needle hanging up. It could be a heavily dampened spring loaded movement. In your photo it looks like it's enclosed and you can't see the actual needle movement.

But one other thing comes to my little pea brain mind. Not knowing how the electronics is designed, I would hope that if something in the electronics shorted out, like a transistor, it would not put a hard 12V on the sender line. I just do not trust any of this repro stuff, especially anything electrical/electronic. If I were you I would return this thing to the sender and use the original. They are obviously no good, and even if you did get one that works - no telling how long it will continue to function after the warranty period is up. I think you are beating a dead horse again.

But to me, the highlight would have been the 90 minute ride in your C6. That would be heaven to me right now. We are freezing, blowing, and drifting here in upstate NY.

-Dan-

**Ken A.** · February 10, 2014, 09:49 AM

Re: 1960 to 1962 Reproduction Fuel Gauges - Failures?

Rich,
The gauge must be grounded to work correctly (the shiney strip o the back of the gauge) and it is short protected-unlike the od meter movements. BTW, Bill has not purchased any of the new gauges. We have sold hundreds with no complaints. The problems only occur when the customer/installer tries to set up a "test without grounding the gauge. Dan-most of the old gauges have been restored and are pretty in accurate.
Ken

**Dan D.** · February 10, 2014, 10:09 AM

Re: 1960 to 1962 Reproduction Fuel Gauges - Failures?

Good point Ken. I know the gauges have to have a ground return, but did think of it. Don't know if Rich grounded his test setup or not. But this does not explain why his failed in the car. The gauge pod is grounded when installed in the car. I will let you and Rich sort this out now. Over and Out.

-Dan-

**Richard M.** · February 10, 2014, 10:51 AM

Attached Files

KandB_Fuel_Gauge_Test.txt (1.1 KB, 25 views)

**Thomas H.** · February 10, 2014, 12:36 PM

Re: 1960 to 1962 Reproduction Fuel Gauges - Failures?

Looks like you spread your "fun" across many projects Rich!

I am surprised to see that the repop gauge appears to use an air core meter for the meter movement vs the old d'arsonval (sp?) type movement. I have used air core meters in the aircraft instruments we used to design. The meter requires a sin +/- and a cos +/- signal to work correctly. The electronics are used to generate these signals based on the input from the sender. If any one of the four signals are missing, the gauge will usually drive to one direction or the other. Or it could work fine in one quadrant and jump through the next.

When power is shut off, the pointer will move (float) in a direction based on the weight of the needle unless they have included some sort of "return to zero" circuit which would drive the needle back to a specific point, in your case, empty.

Nice looking gauges.

Tom

**Richard M.** · February 10, 2014, 02:04 PM

Re: 1960 to 1962 Reproduction Fuel Gauges - Failures?

Hi Tom, Yes K & B did a nice job on them. It's quite nice to have a reproduction available as the old ones wither away in time. As I mentioned, I chose them to restore a set for the '60 I'm on, and saved much time searching for used & "functional" originals. Most were complete dual gauge assemblies, and all I needed were the meter movements.

Rich

**Richard M.** · February 11, 2014, 09:16 AM

Re: 1960 to 1962 Reproduction Fuel Gauges - Failures?

I believe I found the problem with gauge #1. I did a little research and drew up a diagram of the digital circuit using my eye-loop to identify the components and trace the circuit etches the best I could. Coming in from the power lug, 12v goes to a 5 volt semiconductor voltage regulator, U1. It's marked 78L05L, a industry standard ID for electronic components of this type.

Spec here...
http://media.digikey.com/pdf/Data%20...s/NJM78L00.pdf

It simply takes up to 30 volts in, 12 volts in this case, and delivers a regulated 5 volts out. 5 volts is needed for the other digital circuits as their power source. There's a 8 pin device, marked 358 EZ727 which I cannot identify, and 2 other 3 pin transistors, Q1 & Q2 locations.

Anyways, the VR is dead. I get 12 volts in and only 1.39 volts out. Because the other digital devices need 5 volts, the meter won't function.

P2110002.jpg P2110003.jpg P2110004.jpg P2110005.jpg

I suspect the problem was either infant mortality of this device after working for a few months, or it lost it's ground input and the input voltage floated with no negative reference and destroyed the device. I have seen this anomaly throughout my career in electronics. When ground floats in digital devices, they can self destruct.

And.....I think I may have the answer to why ground floated. When I restored the Fuel/Temp gauge cans, I painted the backside silver after bead blasting to clean it up. The ground for the fuel gauge is dependent on the mechanical contact of the case to the cluster, then to the ground wire in the harness. Looking at this case's mount tabs, there are some scrape marks from the Palnuts when I installed it in the cluster, but it may not have been tight enough the first time installed. Because I didn't have a good ground connection, I believe it's possible that the VR floated ground, and.......... kapoof.

My fault, but I need to contact Ken so he can add some cautions to the installation instructions and possibly make some changes to the circuit to prevent device failures on future builds. I really like these gauges. It's great that we have alternatives to the hard to find old stuff.

Gauge #2, was DOA when i got it. I verified that the VR on that one works, 12 volts in, a good 5.1 volts out. Something else is wrong with that one but i don't really have time to play with that one, maybe later. I'm getting a replacement from Zip due in tomorrow, so hopefully that one will be fine. BTW, the Temp Gauge uses NO digital circuitry, so the ground float never hurt that one.

Rich
p.s. Sorry if my spellng s off lately. My "I" isn't workng too good on my keyboard. I can't catch 'em all.

**Dan D.** · February 11, 2014, 11:42 AM

Re: 1960 to 1962 Reproduction Fuel Gauges - Failures?

Hi Rich,

Glad you found the problem. But these 78L series 3 terminal regulators are extremely reliable, and I doubt very much if it failed after working for a while. I'm sure you know too that all these 78L series devices are over-current proof. If current or power is exceeded they will just shut down and not self destruct. With 1.39 volts out I would say there is a short somewhere in the circuit that is dragging the voltage down until the current is at a safe level. I don't believe the device is bad, but you would have to isolate the output pin in order to tell. I do believe that your lack of ground return is what destroyed the gauge. When you get your new gauge I would just send these two back and not void your warranty.

-Dan-

**Thomas H.** · February 11, 2014, 01:21 PM

Re: 1960 to 1962 Reproduction Fuel Gauges - Failures?

The 358 is more then likely an LM358 op amp.

As Dan said, most of the linear regulators on the market today have overcurrent protection built in. They will throttle back the output to limit the current and thus reduce the possibility of internal part damage. One thing they don't like is reverse voltage (putting + on - and vice versa). Usually though the designer will put a diode inline with the power going to the regulator to protect against reverse voltage.

But, one thing that a lot of circuit designers don't always design for are transients. In automotive electronics there is a thing called load dump that can produce power transients of upwards of 80v. If there is no protection in the power line feeding a regulated circuit, any sort of load dump or overvoltage transient can easily damage the electronics. Doesn't take much to "let the smoke out" of a part if it is not protected.

If you want to try to replace the regulator, go on Texas Instruments web site and a lot of times they will send out sample parts on request. Otherwise, they are easily bought from sources like Digikey or Mouser.

Keep in mind...., please don't think what I wrote is any sort of critique of the circuits used in the gauges Rich is working with. I have no first hand knowledge of the circuits used and am just providing some "tech talk" based solely on my experiences. From what I can tell the gauges Rich has are well made and the support being provided is tops.

Tom

**Dan D.** · February 11, 2014, 01:54 PM

Re: 1960 to 1962 Reproduction Fuel Gauges - Failures?

Yea Tom, the 358 is most likely an op amp (operational amplifier - a very common electronic device). Rich can tell us if a series diode is on the input, but I doubt very much if Rich put any reverse voltage on the gauge.

With no ground return on the gauge, because of paint on the rear surface, then the only ground return the gauge would have had would have been through the sender. With not much gas in the tank, it would be very close to ground potential. Not knowing how it is designed, this could have provided a current path through places it was not intended to. So my guess would be this is was what happened.

-Dan-

**Thomas H.** · February 11, 2014, 02:50 PM

Re: 1960 to 1962 Reproduction Fuel Gauges - Failures?

Yup, Current needs to go somewhere and through the sender is a good bet.

Hmmmm.......... In a past life, part of our product line was a fuel gauging system for general aviation aircraft. One of the requirements was that the energy provided to the resistive fuel sender needed to be limited to 25 micro joules (going by memory here.........) to maintain intrinsic safety (read, not enough energy to cause a spark big enough to ignite any fuel or vapors). I'd be interested to know what the signal conditioning interface is ahead of the op amp. It didn't take much circuit wise limit the energy to to meet the requirements, but we all had our fingers crossed during the actual qualification testing. (Where's the Kaboom, there was supposed to be an earth shattering Kaboom!)

Fun stuff.

Tom

**Richard M.** · February 11, 2014, 03:29 PM

Re: 1960 to 1962 Reproduction Fuel Gauges - Failures?

Yes, gauge #1, arrived BO'd from CC late summer IIRC, has no protection diode on the input. Ken said his new ones have it, and gauge #2 bought a while ago and recently installed has the diode. see pics. Good catch on the LM358. I used to test these things years ago. Yikes I forgot a lot of this stuff.

Gauge #2 has a protection diode(marked DEE) between 12v+ stud and C1, and U2 pin 8(green wire) of the LM358(power pin).

I read up a bit more on the VR. Yes it's ruggedized for short circuit current limit and thermal overload protection. I wanted to open the output lead on it and test it, and if truly failed, swap it out with the good one from gauge #2 but I don't want to jeopardize warranty, unless Ken asks me to do that. I'm planning to call him later today when I get time. This '60 is going to NY Thursday morning so I have some other last minute stuff to do on the punch list now.

Thanks for the info,
Rich

gauge#1
P2110016.jpg

gauge#2 diode and green wire to U2
P2110015.jpg

1960 to 1962 Reproduction Fuel Gauges - Failures?

1960 to 1962 Reproduction Fuel Gauges - Failures?

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment