component testing with keysight dsox1102g scope

Question

hello would like to learn how to measure components on my elenco am radio kit.

am new to electronics, trying to figure things out.

read about lissajous patterns, just need some direction as to how to set up my connections, see if components are functioning as necessary.

my 9 volt battery gets hot, no audio output,so i think i have short somewhere?

thanks

john

Jan Cumps · Answer

The soldering is good. I see that most of the transistors are NPN. There's 2 PNPs that I can see (Q5, Q7). You have different part numbers for those?

Electrolytic capacitors look correct (I can't see the symbol under C13 but when viewing the schematic, it looks that it's correct too).

The diode is correct too.

I don't see anything obvious.

What is the resistance if you take out the battery and measure over the two solder points of the battery housing?

Maybe double-check if this is repaired correctly:

Jan Cumps · Answer

Looking at the potentiometer, it seems that it has been inserted from the wrong side (inserted from above instead of pushed in from the underside)..

The movable switch part looks forced (blue), and the right connector of the switch is above the PCB instead of below, on the solder pad (red).

Jan Cumps · Answer

I think that the second pin of the switch is soldered to the wrong hole:

johnwater · Answer

shabazi believe you are right.

one of the wiper pins is physically touching the base of switch,vom shows low resistance, almost like a short.

i am going to take whole switch off and realign and report back .

thanks

john

michaelkellett · Answer

Which kit do you have, can you post a schematic ? MK

jw0752 · Answer

Hi john, You may find that trouble shooting this short will be easier with a simple analog ohmmeter or multimeter than with a scope. It is a matter of removing the battery and looking into the circuit with the meter and eliminating components by desoldering or temporarily cutting traces until you have isolated the source of the short. John

fmilburn · Answer

Found a link to the instructions: https://www.elenco.com/wp-content/uploads/2011/05/AM-550CK_REV-A.pdf

Jan Cumps · Answer

shabaz · Answer

Also, this bit looked strange:

Is something missing where the red arrow is pointing at a rectangular slot? To me it looks like the switch (marked with blue arrow) isn't connecting, because nothing is connected to that rectangular slot, so power cannot be enabled into the circuit.

It doesn't explain how the battery could be getting hot though! That's the opposite to what would be expected..

Maybe a second photo is needed of the PCB, I just can't tell from that angle.

Jan Cumps · Answer

The unsoldered contact can't create a shortcut. But this may be the cause:

johnwater · Answer

Thanks Jan i see your drawing. lots of questions re this switch. I will de solder, take it off ,take some pics, then desolder and check. With my vom one of the pins was bent toward the housing of the switch, should be separate and part,so i have created a short. gonna straighten things out and repost some images. john

Jan Cumps · Answer

Taking off the switch is not easy, once the pins are soldered. It may be easier to try and desolder only that one that's mounted in the wrong hole, and place it in the correct hole.

If you can't get it out, clip it as close to the PCB as you can, then use some wire to bridge the gap.

It will impact the strength of the construction though. The 2 switch contacts also play a role to keep the potentiometer from twisting in place ...

johnwater · Answer

thanks jan

yes i can post pics of back and front.took battery Outland ic also.

have looked on front and back by solders, but my untrained eye fails to pick up anything obvious.

if u see something, let me know.

john

Jan Cumps · Answer

While reworking, you may want to redo C14 as per instructions.

fmilburn · Answer

J1 is the jumper wire on page 8 of the instructions - it looks like you installed it

johnwater · Answer

i took the knob off of pot so we can see underside better.the nut and washer fit on top side of board, there are 5 lugs to solder on bottom of pc board.

looking at 3 of the lugs i will re-solder those to fill holes better,

everything is soldered from the bottom ,not on top of board.

how would i check to see if this pot is shorting out somewhere?

john

johnwater · Answer

took switch off, looked at connection points. still not sure that what is circled in blue is correct slot. i think these boards are made generic for other radios as wetland that slot seems to be way off to the side. took pics of top and bottom of board. definitely had a part of pot on /off blade touching the base of pots i unbent it and straightened it out. gonna desolder everything and get back to u all. slot i circled in red appears to need to stay open, it just would be too outside the pot pins, may be for some other project. thanks for all the help.better eyes than mine found a problem. johnpot

shabaz · Answer

Hi John, The switch terminal cannot go in the nearer slot, because that area of copper connects to ground, you can follow it to the negative terminals of capacitors for example, and if the switch is connected to ground, that's a short to ground. I agree it's confusing, but that nearer slot is likely for a different potentiometer/switch, where perhaps the shell has a locating peg that could be soldered there.

fmilburn · Answer

Hi John, I agree with Michael that to get assistance it would be helpful to post the schematic. Also agree with John that a multimeter will probably be the most useful tool for trouble shooting. As for using your oscilloscope for component testing there is information on using the DSOX1102G DSOX1102G to generate Bode plots for capacitors and inductors in the comments below this post . There is information on using an oscilloscope to determine ESR of a capacitor here . If you do a search, you will find a number of videos on component testing but I find the videos by w2aew well done. For example, this one which describes an oscilloscope "curve tracer" and use for resistors, standard diodes, LEDs, Zeners, BJT transistors, etc. Frank

Jan Cumps · Answer

... also, does the documentation say when you should plece the wire J1?

component testing with keysight dsox1102g scope

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