Gauges stopped working

[XXL]

Both fuel and temp gauges stopped working.  I just noticed it this morning when I thought I was almost out of gas... until I remembered... I filled it to the brim yesterday.  That's when I noticed the temp gauge not working either.  I haven't pulled out my schematic yet, but did quickly buzz all the fuses under the hood.  They're all good.  Any pointers that might put me in the right direction before I go in blindly?

 

 

[Charlie69]

The gauge voltage regulator is most likely the problem.

Surrounded by yellow

 

http://community.ratsun.net/topic/30636-521-special-kinda-voltage-regulator/?do=findComment&comment=458046

 

http://community.ratsun.net/topic/54598-bad-gauge-cluster-voltage-regulator-easy-2-fix/page-2

[XXL]

I've got the gauge panel out on my bench.  What should I be looking for on that regulator (voltages, etc.).  And... if mine is bad, is this something I can source?  

 

Edit:  This looks like a basic resistance stuck in a metal box.  I'm seeing about 64 ohms across the ground leg (GND) and the pin I've labeled #1 below.   I see no continuity between #1 and #2, and a bouncy 180 or so ohms between GND and #2.

 

 

 

And here are the guts.  #2 is same as labeled on the first pic.  #2b is just a direct trace to it (it is the darker round pin on the first pic just above #1). 

 

 

 

It's an incredibly simple device, but I'm not really sure what the objective is.   It looks to be a 'circuit breaker' of some sort (????).  When ????? happens, that poorly wound coil (the white wire) causes that arm to bend up and break the contact at #2b (???).  But why?  And that's not really a regulator.  It's more like a circuit breaker of sorts.

[TENDRIL]

i believe Dguy210 makes an upgraded plug in option

[DanielC]

It is a circuit breaker.   It is turned on, and it heat up.  Then it turns off.  The gauges react slower than the "voltage regulator" turns on and off.

So the voltage averages to about 8 volts.

[XXL]

It is a circuit breaker.   It is turned on, and it heat up.  Then it turns off.  The gauges react slower than the "voltage regulator" turns on and off.

So the voltage averages to about 8 volts.

 

 

Yeah, it appears that the Japanese had never heard of actual voltage regulation in 1968  :confused:   How about just a simple resistive circuit to bring the voltage down to 8 volts?  Or, how about a simple IC regulator like an LDO voltage regulator transistor? ... well... I get that they didn't have those 50 years ago.  Hmmm.  If only my local Rat Shack didn't shut down with the bankruptcy... I could probably whip up a replacement part in about 5 minutes.

[XXL]

Here's one at Mouser for $1.86.  About 2 minutes of soldering some wire leads with .187 male spades, and it's done.  Now... to find one in this podunk town so I don't have to wait for UPS to deliver such a tiny part.

 

edit:  Oh... that's what TENDRIL posted a few messages up that another board member has already done.

[MikeRL411]

The original design is a relay driven  "chopper" that heats up the bimetal strip in the can! The meter coil opens the through connection and then cool down and re-connects.  It generates a square wave of asymetric configuration.  The thermal lag of the bimetal strip that drives the meter needle averages out the almost square wave output of the "Voltage Wave" plug in and results in an averaged 6.7 volt application to the fuel and head temperature gauges.  If you don't want to spend the rest of you life pounding the top of the instrument gauge housing to "free up" the frozen or pitted relay contacts [it does work]  there is an "How to" on an electronic Voltage Regulator replacement that will eliminate this furure concern.  Happy usage of the "search" function!  It is really in there!

[XXL]

The original design is a relay driven  "chopper" that heats up the bimetal strip in the can! The meter coil opens the through connection and then cool down and re-connects.  It generates a square wave of asymetric configuration.  The thermal lag of the bimetal strip that drives the meter needle averages out the almost square wave output of the "Voltage Wave" plug in and results in an averaged 6.7 volt application to the fuel and head temperature gauges.  If you don't want to spend the rest of you life pounding the top of the instrument gauge housing to "free up" the frozen or pitted relay contacts [it does work]  there is an "How to" on an electronic Voltage Regulator replacement that will eliminate this furure concern.  Happy usage of the "search" function!  It is really in there!

 

Yep, I understood what it was doing.  I was explaining to someone here that it's like flipping the light switch on and off over and over to "reduce" the amount of light in the room.  Such a horrific design.  Square waves are not your friend.

 

I'm going to pick up an LM7809 tomorrow and get it back up and running.  Easy peasy, assuming I can find one in my podunk town.  There's an awesome electronics store I used to frequent in my youth about 20 miles from here, so I'll hit them up if needed.  

 

In the mean time, while I had everything torn apart, I gave the needles a fresh coat of safety orange and cleaned the lens, then put it all back together.  Tomorrow, I'll also try to hunt down some bulbs.  The ones that are in there are so old, inside the glass are little dinosaurs holding flames.

[DanielC]

This is the multipin connector on a 521 dash cluster, and the function of each pin.

 

This is the 521 cluster voltage regulator.

 

If you connect positive 12 volts to the Ignition power in, and connect negative 12 volts to the ground pin, you power up the instrument cluster.

 

If you then ground the fuel sender pin, or the temp sender pin, that will cause that gauge to go to full scale, full tank, or red zone hot.

One of the gauges reads in the middle with a 35 ohm resistor, the other reads in the midde witha 40 ohm resistor.

 

[DanielC]

I disagree that it is a horrible design.  Remember when these trucks were new, most electronic devices used vacuum tubes for amplification.   If you get good connections outside of the combo meter, the gauges are very reliable.  It is a simple system, that works.

[MikeRL411]

I disagree that it is a horrible design.  Remember when these trucks were new, most electronic devices used vacuum tubes for amplification.   If you get good connections outside of the combo meter, the gauges are very reliable.  It is a simple system, that works.

 

Agreed!  Bimetal strips will always open when hot enough!  The dash meters are also bimetal strip driven with a linkage to the needle, so they also "even out" the not quite square wave input from the VR and sensor.  Thermal lag is a very nice phenomenom!

[zed1]

http://www.tannerelectronics.com/

Awesome place.

Keith

[XXL]

http://www.tannerelectronics.com/

Awesome place.

Keith

 

Yep, that's the place I alluded to above.  I used to spend a lot of time there 25 years ago... first met Jim and son at Saturday "trade days" downtown under the bridges.  Last time I was at their store before moving out of the area 20 years ago, they were on Beltline... looks like they've moved a few exits down now.

[XXL]

I disagree that it is a horrible design.

 

We may have to agree to disagree on that one.  To soften my assessment, I'll just call it a "hack."  I have no issues with the functionality of bimetal strips.  They have their place (included on everyone's wall thermostat), but to "regulate" voltage by flicking the circuit on and off is not one of them.

 

The proper design of the system would have been to use 12v to power the gauges.  Problem solved.  However, since they didn't do that, and I get that they were in vacuum tube era... why not just do a simple voltage divider with a ballast resistor?  It'd have been more reliable, and would have eliminated the square wave issue altogether.  It is, of course, exactly what they do under the hood with the ignition coil.

 

/2 cents

[DanielC]

The reason for a gauge voltage regulator is that "12 volt" voltage varies.   Datsun alternator voltage regulators actually put out more voltage when they are cold.   Lead acid batteries can use a higher charge current when freshly discharged, and need a higher charge voltage when cold.

Additionally, the 12 volts voltage varies depending on what accessories are turned on.  On a 521, everything that operates with switched ignition power goes through the ignition switch.  Heater fan, wipers, turn signals, reverse lights, radio, power for the combo meter, ignition coil power, alternator field power.

 

Power for the accessories goes from the battery, to the fuse box, but not fused, to the ignition switch, back to the fuse box, through accessory fuses, including a fuse that supplies power to the combo meter, and back to the combo meter.

 

The 12 volt charging voltage varies.  After going through.all the wire, and connectors, the voltage supplied to the combo meter varies even more as different things are turned on and off.

To keep the gauges reading consistent, a second voltage regulator is needed at the combo meter.

 

Datsun electrical system design was generally pretty good.  You probably have seen many posts about using a matchbox distributor, instead of a aftermarket electronic setup.  Many posts on using a Nissan ignition coil, not some yellow or red painted and finned ignition coil designed to look shiny in a blister pack, at an auto parts store.

 

The 521 truck was used world wide.  45 years ago, semiconductors were not as reliable as now, or even available.

 

A simple resistor voltage divider circuit will drop the voltage.  But the output of the voltage divider varies just as much percentage wise as the input voltage, and that is with constant load.  And the electrical load is not constant.

[XXL]

The 521 truck was used world wide.  45 years ago, semiconductors were not as reliable as now, or even available.

 

A simple resistor voltage divider circuit will drop the voltage.  But the output of the voltage divider varies just as much percentage wise as the input voltage, and that is with constant load.  And the electrical load is not constant.

 

Lot's of great info in your post.  The above quoted is the only thing relevant to the topic, or to my comments about the circuit design.  

 

I'm engineer... or I was (though I spent most of my time developing high available computer storage systems, and I have a stack of design patents related to the field).  Now I'm just old and tired.  I understand all of your comments... and it's a poor design.  I also understand that 1968 isn't 2015.  I didn't berate "all things Datsun," just the decision to use such a clumsy design to "regulate" voltage.  The original decision problem appears to have been in their gauge design, which necessitated the "regulator."  They could have done it another way, but just like every other car manufacturer (and manufacturer of [insert anything here]), they stuck to a design for cost savings/because they had already committed to it/because someone's brother-in-law was in charge/whatever.  GM used an ignition switch for 10+ years that turns out to have been a bad design.  A dozen car companies used Takata airbags that turned out to have been a bad design... and on, and on.  It's just business decisions companies make. 

 

In the case of our old Datsuns, we can all either live with the bad design (as I had unwittingly been doing until mine failed and I looked into the problem), or we can update it (what I'm hoping to do this afternoon... with parts they didn't have access to then).

 

/another 2 cents... which has pretty much emptied my pockets on the topic

[Charlie69]

Please post what you are doing.  I am always interested in different ways to fix problems.

[thisismatt]

There are a lot of little solid state regulators on Amazon for really cheap, direct from China :D  Some even have readouts, etc.

[thisismatt]

Like these:

 

http://www.amazon.com/gp/product/B00BYTEHQO?psc=1&redirect=true&ref_=oh_aui_search_detailpage

[XXL]

Please post what you are doing.  I am always interested in different ways to fix problems.

 

 

Will do.  I'm going to a semi-local electronics place later this morning to grab a VR transistor to build what, as it turns out, aintnobiscuit already worked out.  I'm not going to try to reinvent the wheel.  I'll grab an LM7809 like he used.  

 

However, someone mentioned the gauges want 8.6V.  The LM7809 is 9V and the LM7808 is 8V.  While I doubt their is an issue, to tweak the circuit down to exactly 8.6Vo, I can use an LM337, which is a variable VR transistor that can be adjusted with a couple of resistors. 

[XXL]

Like these:

 

http://www.amazon.com/gp/product/B00BYTEHQO?psc=1&redirect=true&ref_=oh_aui_search_detailpage

 

Yeah, those are neat little gadgets...  especially for the ability for a user to just dial in Vi and Vo values.  And it's cheap enough.  It's a little  overkill for this circuit because you only need to set the Vi and Vo once, and then you're done with most of the circuitry on this board.  

 

This is all that's really needed...

 

 

You apply Vi to pin #1 (12v straight from the existing connector on the cluster), and it puts out a regulated Vo on pin #3 (in the case of the 7809, that's a very consistent 9v).  Pin #2 goes to ground (the original regulator's mounting screw on the back of the cluster can be used).

 

And as I prod around more, it looks like there are a couple of people who've already done this.  Here's one that a board member looks to be selling...

 

[Charlie69]

That was one of the links in my post above.  I guess you did not look at the links!  LOL

[XXL]

That was one of the links in my post above.  I guess you did not look at the links!  LOL

 

 

Sorry, I missed them below the pic when I was reading on my phone (read as "too small"), and didn't re-read before replying when I was sitting at my 30" computer monitor (read as "almost time to get a bigger one!" damned eyes).

[Charlie69]

No apologies needed I do the same thing.  I have a couple of these pictured and I am going to install one with my 520 cluster.  You do not need the ground terminal connected.  When you screw it to the printed circuit it is grounded.