Electronic circuitry wizard needed.

[JRLesan]

I have an old truck which I converted from 6V to 12V nearly 50 years ago. A good friend and electronics wizard put together a regulator for me which reduced the 12V (approximate) voltage to 6V (actually 7.2V no load) with a current output high enough to power the heater motor, wiper motor and gauges simultaneously. I still get 7.2V output with no load but as soon as a load is put on the device output drops to ZERO or slightly above; thus the title. I can send pictures to anyone interested. NOT interested in experimenting with ballast resistors or buying some Chinese *** that won't last another 5 years let alone 50.

[lancem]

Clear some privet message space and I'll send you my email to send pics to.

[JRLesan]

Box cleared; am heading out to shop to remove device...

[Rizzo]

Shooting from the hip.....
Most voltage regulators are short circuit proof.
If one of the loads on the output has an issue (short circuit?), then I would expect the output of your 6 volt regulator to go to zero volts (there abouts).

I'd start lifting the load wires on the output of the regulator one at a time to see where the problem is. It may not be your regulator but some other issue.

[MaryB]

Drop me some pics via PM. I sent 40 years repairing electronics as a career.

Modern DC to DC converters from a name brand will last quite awhile... but like all electronics they will fail with time.

[45_Colt]

Mr. 45,
If you'd bother to read my original post, I said REGULATOR, not big ass resistor. My device is a transistorized regulator which was working fine until recently.

I read your post, a voltage variation of 17% is hardly being regulated.

As far as a transistorized 'regulator', a 2N3055, some resistors and a zener should cover it. But is wide open to self destruction should a short circuit occur, or just plain old fatigue from in-rush currents.

45_Colt

[rbuck351]

If you don't like resistors or regulators you could use two 6v batteries and a series parallel switch. This would give you 6v to run everything but the starter and 12v to the starter. This would last 50 years and then some as they were made for semi trucks using 24v starters and 12v for the cab and will handle loads far above what you could have on your truck.

This is not a cheap fix but would last longer than you or your truck.

[JRLesan]

Not a 'voltage variation' at all; 6 volt auto systems were designed at 7 volts or slightly over as were 12 volt systems designed at 13 1/2 volts or slightly over. Can't charge a 12 volt battery with 12 volts and a 12 volt wet cell in good shape is actually around 12-3/4 volts.

[popper]

Yup, probably a short someplace. A decent regulator will have protection and shut down.

[MaryB]

From the description he gave me I suspect it has current monitoring and the shunt resistor may have changed value enough to make it think to much current is being drawn. That resistor usually runs hot and they eventually break down.

[JRLesan]

There is no resistor (unless a transistor can act as a resistor) in the circuitry. two transistors in parallel beyond a 10 pin regulator, a 3rd transistor and a cap between two regulator terminals which, I'm guessing, is to 'smooth' out input. I can pencil a rough circuit diagram but symbols would be incorrect. Device will light a small lightbulb but will immediately shut down if a load is applied. The device worked fine, powering a 6 volt heater motor, windshield wiper, and dash gauges for a number of years without problems. I parked the truck in a barn around the year 2000 and only recently brought it out and got it running again. I know my friend gave me a parts list and we went down to his lab on a Sunday afternoon in MAY81 and he put it all together without incident and without instructions; just knew how to design circuitry. I have part numbers and have replaced the three transistors which I had extras os left over from the original build. Any additional help appreciated...

[n9tkf]

Is the capacitor electrolytic? These can dry out over time and cause problems. Do you know the part numbers of the 10 pin regulator and transistors? Might help to figure out the problem.

[JRLesan]

Capacitor is ceramic about the size of a pea and marked: Z5U 2200P 1KV
Two transistors 2N3055
One transistor 2N3054
One regulator ECG923 - Only part I did not have on hand so not yet replaced.

[45_Colt]

One regulator ECG923 - Only part I did not have on hand so not yet replaced.

Odds are it is the ECG equivalent of the LM723 regulator chip. DigiKey has them in stock, be sure to be seated when you check the price.

45_Colt

[n9tkf]

Odds are it is the ECG equivalent of the LM723 regulator chip. DigiKey has them in stock, be sure to be seated when you check the price.

45_ColtIt is a LM723 equivalent in a metal can configuration since OP states it has only 10 pins.

[JRLesan]

Are y'all saying that odds are the ECG923 has failed? That would explain why replacing the three transistors had no positive effect.

[n9tkf]

Are y'all saying that odds are the ECG923 has failed? That would explain why replacing the three transistors had no positive effect.Could be a possibility. A few more questions. Is the output close to 7 volts?

What is connected to pin 1 and 10? This is the internal current limit circuitry. Pinouts attached.https://uploads.tapatalk-cdn.com/20230227/a9c1cc6842d35cc0a8390180d6109a0e.jpg

[popper]

ECG923 Jap replacement for LM 723. Power resistors usually go open, not shorted, which will shut the regulator down. It will be a very low resistance (0.1ohm) so hard to measure. Output cap is for spike protection, they seldom go bad. 2n3035's die from spikes. Also make sure the wiring is clean, sitting a long time they get conductive dirty. Assume this is run from alternator vs generator? Generators sitting a long time have to be 'poled' to get them to work.

[MaryB]

The 10 pin regulator has current sensing as other have mentioned so either it is bad or whatever it is using to sense the current draw is bad.

Sounds like the standard pass transistor power supply circuit used in millions of 12 volt power supplies...

Data sheet for the 10 pin VR IC

https://www.ti.com/lit/ds/symlink/lm723.pdf

[JRLesan]

Pin 1 goes to ceramic cap and then on to the two 3055 transistors in parallel. Pin 10 is unused. Now, I may have that reversed as I can't tell from the data sheet which is ten and which is one; suffice to say they are next to one another and one is used and one is not.

[JRLesan]

Forgot: the output is 7.5 volts more or less but have not been able to measure with a load as it open circuits as soon as any load beyond a light bulb is connected...

[BamaNapper]

If the output is only running smaller loads, could a simple buck converter be installed in place of the custom piece? The output from them could be a little noisy if you were powering a radio, but I don't remember seeing one in the list.

This one's about $20 and is rated at 10 amps out. At that price you could put two of them under the hood and split the load if necessary. There are also heavier models out there for just a couple more dollars.

https://www.amazon.com/gp/product/B08BXFC6MD/ref=ox_sc_act_title_1?smid=A2B1LC74DVEKDL&psc=1

[BamaNapper]

If I had to guess on your failed unit without seeing a schematic, I'd assume the pass transistors are shot. They are the workhorses of the regulator, and if their collector opens you tend to read the regulator voltage through the base-emitter or a bias resistor without a load attached. But that path is only good for a very small current and any load at all will drop it to zero. The fact you're reading 7V without a load has me assuming the regulation part of the circuit is working.

I just got done rebuilding my ham radio power supply after a lightning strike killed it. I had symptoms of no output, then wrong output, then good output no load, then good up to maybe 10% of normal load, then good up to 30% before finding the last failed component. Depending on the complexity of the design there can be a fair number of causes for what you're describing.

[JRLesan]

Is the pair of 'pass transistors' the 2N3055's? The 2N3054 is mounted on it's own heat sink if that tells anything while the pair of 2N3055's are mounted on one large sink that was (apparently) designed to hold them.

[BamaNapper]

I would love to see the schematic of your regulator, sounds fun. A 2N3055 is capable of passing 4 amps. I have to assume they are being used as pass transistors. They would be turned on just enough to pass the needed current to the output to keep the voltage at about 7V. The fact they are on a large heat sink supports this thought.

If I've done this right, a simple schematic is below. It's from a small power supply I have on the bench. As you can see, the 2N3055 is a common pass transistor. In this schematic, 28 volts is passed through the two 2N3055's and regulated down to 13.6 volts on the output. Since this is such a common circuit I assume you have something similar. It would be nothing more than a guess what the 2N3054 is for. It may be connected to the regulator chip and used to drive the pass transistors, similar to the TIP41 in the picture. Or it may be used to generate an internal fixed voltage used by the circuit. No way to know from here. Hope some of this helps. If you were across town I'd stop by with a handful of 3055's. They're super common, and cheap. I see they're about $1 apiece on ebay. Anyone who messes with electronics probably has more than a couple sitting in their junk parts box.

311097

[MaryB]

Pin 1 goes to ceramic cap and then on to the two 3055 transistors in parallel. Pin 10 is unused. Now, I may have that reversed as I can't tell from the data sheet which is ten and which is one; suffice to say they are next to one another and one is used and one is not.

10 is right under the tab on the body...

IS there a big resistor off one pin of the 2N3055? If so that is the current sense resistor and is typically 1 ohm or less...

[MaryB]

I would love to see the schematic of your regulator, sounds fun. A 2N3055 is capable of passing 4 amps. I have to assume they are being used as pass transistors. They would be turned on just enough to pass the needed current to the output to keep the voltage at about 7V. The fact they are on a large heat sink supports this thought.

If I've done this right, a simple schematic is below. It's from a small power supply I have on the bench. As you can see, the 2N3055 is a common pass transistor. In this schematic, 28 volts is passed through the two 2N3055's and regulated down to 13.6 volts on the output. Since this is such a common circuit I assume you have something similar. It would be nothing more than a guess what the 2N3054 is for. It may be connected to the regulator chip and used to drive the pass transistors, similar to the TIP41 in the picture. Or it may be used to generate an internal fixed voltage used by the circuit. No way to know from here. Hope some of this helps. If you were across town I'd stop by with a handful of 3055's. They're super common, and cheap. I see they're about $1 apiece on ebay. Anyone who messes with electronics probably has more than a couple sitting in their junk parts box.

311097

I looked in my parts bin... 10 of them LOL think I got them on sale 10 years ago 10/$1...

[45_Colt]

Wow, a 2N3055 is capable of passing 15 amps. Two in parallel, 30 amps. But good design practice is no more then half that. Which means this P/S should be good for 15 amps, probably even 20 with transient in-rush currents.

If pin 10 and/or pin 1 is open, as the OP stated, then there is no current limiting in the circuit.

Since the two 2N3055's and the 2N3054 have been replaced. Doesn't leave much else but the LM723.

Note that the 2N3054 is being driven by the LM723, which then drives the two 2N3055 transistors. And, the outputs of the two 2N3055s should go through a 'ballast' resistor before being tied together. But then again, maybe each 2N3055 is a separate output for different devices.

A sketch of the circuit is required for further diagnostics. Which is easily done via a DVM.

45_Colt

[JRLesan]

I do not know what a DVM is other than a vet which is not what you're talking about. I can draw an unsophisticated diagram but not sure how to post. I can also take a picture of my unit but again, I do not know how to post.
As far as replacing the transistors, I found extras left over from the original build in 1981 which I had saved all these years. Don't really know if they were any good or not but they did not make the unit function; if anything it's worse as before it would power a headlamp bulb and now just a dash light bulb. Help is appreciated.

[45_Colt]

I do not know what a DVM is other than a vet which is not what you're talking about. I can draw an unsophisticated diagram but not sure how to post. I can also take a picture of my unit but again, I do not know how to post.
As far as replacing the transistors, I found extras left over from the original build in 1981 which I had saved all these years. Don't really know if they were any good or not but they did not make the unit function; if anything it's worse as before it would power a headlamp bulb and now just a dash light bulb. Help is appreciated.

Your best bet is to find someone local that can fix it. Or, find someone to ship the unit to to do the same.

Continuing to shotgun it is a possibility. But that could prove to be futile.

I don't see any other options then the two choices outlined above.

45_Colt

[BamaNapper]

I posted earlier the option of a buck converter. It has 4 wires on it, but the two black ones are tied together inside. The black wires would connect to the vehicle ground, anywhere convenient. The red wire would connect to the battery, or where ever the 1981 regulator gets it's power. The yellow wire is the 6 volt output. Job done. It's good for 10 amps so it should be a good replacement for what you have.

Buck converters are a great way to convert from one DC voltage to another. They use a high frequency circuit to build the voltage you want to output, instead of just throttling down the voltage coming in. Your current arrangement takes 12 volts from the battery, outputs 6, and drops the other 6 volts across those pass transistors. Every bit of current has to take that route. So at 10 amps through, and 6 volts across the transistors, they act like a 60 watt heater. Heat kills electronics. The buck converter method is probably 95% efficient and only generates maybe 3 watts of heat. You could run it all day and it should be no more than slightly warm.

Of course while a buck converter would be simpler, fixing broke stuff is more fun.

[JRLesan]

Once the new parts are here I'll try replacing everything at once and see what happens. If a nogo, I'll get the Buck Converter from Amazon.
I have converted the blower motor to 12 Volt in the meantime so wiper and gauges are the only 6 volt parts left.
I have looked for someone local to no avail; it's not a matter of paying someone. I just can't find anyone to even call back let alone fix the device.
Fixing broke stuff gets old quickly; I have too much of it already...