What's this please? (Component Advice)

[PointyOintment]

Several months ago I found a low temperature gauge at the local government surplus store, and bought it, thinking it might be useful for cryo experiments. I disassembled it and looked at the circuit: it seems to be a Wheatstone bridge for use with RTDs (several RTDs, with a rotary switch to choose which one to read). However, there are resistors in it with strange color codes that have yellow at both ends. I didn't know what to make of these and didn't find anything helpful online. Any ideas?

The first picture is a crude schematic I drew when I disassembled it. I omitted the transformer, bridge rectifier, and smoothing cap. There was only the one PCB in the thing, which was mounted to the back of the panel meter's movement.







BTW, it's been quite an ordeal trying to post this. I tried to post these as attachments but it failed to post and sent me to the new topic posting form instead… Next I tried to post them externally hosted and it told me my attachments were too big! Then I tried to post again (having reloaded the posting form from scratch and pasted my post back in rather than using Lazarus) and it told me my last post was less than 60 seconds ago, even though it wasn't (because it failed). Then I waited more than 60 seconds, and clicked post again, only to be told that this post had already been submitted. This time I've deleted cookies, logged back in, and waited half an hour before trying again. Hopefully it works.

[PA0PBZ]

The yellow band is temperature coefficient: https://www.eeweb.com/toolbox/6-band-resistor-calculator
 

[hipi66]

This is a voltage to current transmitter. Input is 0-10V from pot wiper on A5. Output is 4-20mA on C1.
What's the purpose of 19C1 and 19C2 caps?

[salbayeng]

@pointyointment:
So from PaoPbz 's link that makes the resistors 470ohms , 5% tolerance with 25ppm tempco. (For comparison 1% metal film are typically 50ppm)
I think these are metal film , even though they look like carbon resistors.
Odd to have 25ppm with 5% tolerance , I'm guessing there must have been calibration somewhere else : VR2.
R7 seems unnecessary?

[salbayeng]

What's the purpose of 19C1 and 19C2 caps?

Hi HiPi,
They are just for noise rejection.
Simple capacitors are quite effective noise filters on current mode signals.
The adjustment pot is probably in a noisy location.
Normally you would use a single capacitor to gnd 19C2.
The other one, 19c1, will couple power supply noise into the 4-20mA signal, it's not the way I would do it.
The capacitor should be as close as possible to the PLC inputs,
the way the schematic is drawn the gnd side of 19C2 , it seems to have multiple links on X31 , this is not particularly good practice as it gives scope for the installer to use a long loopy gnd return and hence pickup noise on that.
**edit changed to 19C2 in last sentence**

[hipi66]

Thanks salbayeng.
That's what I thought also but wasn't sure about that 19C1.

 

[salbayeng]

In the rare case where you had an analog or digital signal swinging from 0 to 24v AND you had a distant load across 0 to 24v that switched on and off, then you might argue the split capacitor scheme would be useful. But for av current mode signal, the best place for a capacitor is across the terminals at the receiver.
Looking at the schematic, and assuming a 250 resistor inside the PLC, and the capacitors totalling 1\$\micro\$F, this forms a low pass filter at ~600Hz.  but, as drawn, it also forms a high-pass filter to couple power supply noise in above ~600Hz.
So above 600Hz, noise from your signal will be removed, but replaced with power supply noise.

If I were putting in split capacitors i would put them across the 3 pot wires (at the input to the 4-20 converter) , maybe that's what the designer said, and draftsmen mis-heard him??

[vodka]

A few years ago , i found a "thing" that it was stored a box on my garage . I think that the " thing" is a kind the inductance sensor  but  it only has one wire, when i tested  with the multimeter , it hasn't continuity neither resistance.

Do somebody know  what it's ?

https://drive.google.com/drive/folders/0BzVlJNeWPQJzUDR6LVNQRkdMcVU?usp=sharing

Thanks for you help.

[Fortran]

It's a capacitor for magneto ignitions.
Outboards, lawnmowers.. That sort of thing.
The casing is the second wire.

[vodka]

It's a capacitor for magneto ignitions.
Outboards, lawnmowers.. That sort of thing.
The casing is the second wire.

Thanks

[Cubdriver]

That's a condenser for an old automotive breaker point ignition.

https://goo.gl/images/xRMbwy

-Pat

[vodka]

That's a condenser for an old automotive breaker point ignition.

https://goo.gl/images/xRMbwy

-Pat

I am sure that the capacitor is the SEAT PANDA 40

https://www.elmuseodelrecambio.es/prod-4295-seat-condensador-seat-panda-todos-modelos-delco-femsa.php

Thanks

[HwAoRrDk]

An acquaintance discovered this mystery box under the dashboard of his Porsche 911, but has no idea what it's for.



Any thoughts?

I'm thinking it's quite old, as the blue cap is labelled in 'MFD', which I believe hasn't been common practice for a long time now.

[PA0PBZ]

Looks like a filter for speakers, one input and outputs for high (tweeters) and low.

[gamalot]

Looks like a filter for speakers, one input and outputs for high (tweeters) and low.

Yes, I think it is a 2 way frequency divider.

[Cubdriver]

As others have said, it looks like an audio crossover network.  The electrolytic cap appears to be a non-polarized one; note that it has crimps at both ends.

-Pat

[HwAoRrDk]

Ah, that makes sense, what with the 'hi' and 'low' terminals. Thanks everyone.

[SeanB]

In+ In- are the input from the amplifier. Low+ Low- are for the low frequencies ( the larger speaker) and Hi+ and Hi- are for the tweeter.

There should be another for the other side of the car.

[pas7680]

i'm looking for help to identify this please, it appears to be a tos232 or very similar package but i've been unable to reference the value. All help appreciated.

it's marked BR (which is underscored) and has a small N in the bottom corner

[salbayeng]

Hi Do you what size package it is?
SOT-23 is about an 0805 resistor
SOT-323 is a bit smaller
SOT-523 is smaller again

Is the part likely to be of European // Asian, // or American origin ( for transistors this means the first characters will likely be "B" // "2S" // "2N")

Is the part loose, or installed in something?

With a DMM on diode test , does it look like a PNP or NPN?

there's a few hits here:
http://www.s-manuals.com/smd/br
page 35 https://www.sos.sk/pdf/SMD_Catalog.pdf

[pas7680]

As best as i can measure it is: 2.9x1.7x1.1mm

it comes from a NEC pc engine cdrom component number tr305 - can't find a service manual though.

it's a very early cd rom drive, which shares a lot in common with early sony drives.

[salbayeng]

OK The package size is either SOT-23   or  SC-59 , both are nearly identical in size ,  see page 5 of the datasheet I've attached (for a completely differnt transistor, it just happened to have a good drawing in it ).

The 2SC2412  is probably your transistor
(a) it is SC-59 size
(b) It's from a Japanese OEM manufacturer, hence will most likely be a 2SA or 2SC part.
(c) this part seems to be usually marked with "BQ" ,"BR", or "BS" , "BR" is the medium gain variety (hFE = 180-390)
(d) it's quite a common general purpose transistor.
Here is the datasheet :
http://www.s-manuals.com/pdf/datasheet/2/s/2sc1740s%2C_2sc2412k%2C_2sc4081%2C_2sc4617%2C_2sc5658_rohm.pdf

[pas7680]

thank you for all your help, i'll get one a give it a go.

[salbayeng]

As you are in the UK, you may find it easier to use a "pro-european" series transistor.
You can get these from RS , Farnell and probably a whole bunch of retail outlets.

The BC850C is probably closest to the 2SC2412

It is part of the BC846 series ,  the table on the first page shows the variations:
http://docs-asia.electrocomponents.com/webdocs/0b21/0900766b80b219a8.pdf

The trailing letter "C" is the gain group this is hFE ~ 300 which is the same as gain group "R" of the 2SC2412
The BC849 and BC850 are the low noise variants ,  you would use these if the transistor is in an audio section.

Given your CD drive most likely runs off 12v, you could probably use the BC849 (30v variant) .

What does the transistor do in your device?
If it works a solenoid or something digital, and has failed due overload, you might be better off with a "higher current" transistor (MMBT2222, BC817-25 etc)  http://www.mouser.com/ds/2/308/BC817-16LT1-D-104560.pdf

[pas7680]

i was able to order the 2SC2412 from Rs so will give them a go, my electronics knowledge is basic i don't really know what it does but traces back to the dc in jack. I don't think it failed but was ripped off the board when clumps of glue were being removed. I'll give the first part a go, if that doesn't work i'll try the other - either way the board was only a parts board to begin with so no problem if i can't get it working.

Either way thanks for all your help.