[SOLVED] ID component from photo, circuit diagram / PCB layout (24v dc) voltmeter power suppy

[Roger_T]

Hi there, I’ve been given a lcd volt / amp meter to repair. See attached photos. The circuit board has burnt the track beyond repair. I have etched a new board and would like some help / advice.

There is a small (8.5mm * 12.5mm) component which I cannot identify. It originally had 6 legs although 1 was removed at time of fitting. The original supplier / manufacturer seems to have sanded the part numbers off!

This unit is fitted on a sailing yacht to monitor battery voltage and current. The current can be measured both when charging and discharging.

The supply voltage is 24v dc nominal and the measured voltage is 24v nominal. The battery charger can output 50a max and the current is sensed via a shunt.

The lcd display is similar to the one in the data sheet, I have powered it with 5 to 12v dc and it seems happy.

From the circuit diagram the supply power feeds a voltage control chip LM317t and outputs 5.2v

The measured voltage is the same as supply and is fed to the IN-lo and IN-hi terminals via relay1 through a voltage divider, one volt displayed = one mv.

When in amps mode the voltage is read direct from the shunt, again one amp = one mv.

What seems odd is the voltage at the lcd supply pins has increased to 9.58 v dc, so I’m guessing the 4093 and BC549 transistors increase voltage then feed it through the signal diodes.

Now it all seems to work OK except the display seems to fluctuate too much with a steady input. Can anyone identify the mystery component? And what is it and what does it do?

Also can anyone tell me what the 4093BE IC does along with the transistors and signal diodes.

I kind of understand the Schmitt triggers but if anyone can explain the flow through it and the transistors that would be great.

It seems very complicated when if the lcd requires 9,58 volts why not increase output from the LM317t?

Is it possible the mystery component is an Opto isolator? The reason I ask is the display vss is isolated from 0v. The 9.58 volts is accross vss and vdd.

The image of the pcb from solder side is an identical unit fitted and working.

All replies greatly appreciated Roger T.

 

[srizbf]

the mystery component looks like a microtransformer for generating (-V) supply for LCD.

first info:

1,2 ,3 --- transformer py. pin no 2 is center tap.

4, 5 --- o/p wndg.

confirm that by making a continiuity measurement on the pins 1,2 and 3.
next 4 and 5.

 

[andre_luis]

Now it all seems to work OK except the display seems to fluctuate too much with a steady input. Can anyone identify the mystery component? And what is it and what does it do?

It is quite difficult infer some conclusion based solely on the PCB layout design.
This view do not allow us to see the whole circuit.
In such cases the standard action is you draw the schematic, connection by connection.
The size of the board is not too big.

 

[Roger_T]

Hi there, very many thanks for looking and taking time to reply.

I've uploaded a pin diagram to show pin layout & size.

--srizbf I've tested the part and pins 1,2 & 3 are all connected to each other in any combination.
Pins 4, 5 & 6 are also connected to each other in any combination.
The resistance accross any two pins is approx 0.8 to 1.2 ohms

--andre_teprom, I have uploaded a circuit diagram although the text is small. You can find the values on the PCB layout image.

Many thanks again.

Regards Roger_T

 

[andre_luis]

--andre_teprom, I have uploaded a circuit diagram although the text is small.

I was expecting a schematic drawing of the circuit used for testing this part.

 

[KlausST]

Hi,

look for MURATA 76602 pulse transformer or similar.

Klaus

 

[Roger_T]

Hi there again, I have now learnt a lot more about the pcb thanks to you guys.

--andre_teprom, As advised I have split the circuit into three parts. The two that I'm interested in are uploaded as power_supply 1 & 2.

--KlausT, many thanks you are absolutely right. The part is indeed a Murata pulse transformer.

The Murata transformer is actually fitted to the track side of the pcb along with the LM317t.


So, I have redrawn the PCB layout to make it easier to understand. I now have some more questions !

1/ What purpose is R1 (47r) in Power_supply_1? The supply voltage of 24 vdc is well within the LM317t limits.

2/ What is the reason for the TI CD4093BE and the BC549C's? are they just to increase voltage from 5.2 to 9.58?
Can anyone explain the flow through the various connections? (Power_Supply-2).

3/ Should I mark this tread as answered and start a new one with the new questions?

Once again many thanks for helping.

Regards Roger_T


View attachment Power_Supply-2.png