help with energy concepts 30820 oscilloscope

Thread Starter

neospam

Joined Jan 13, 2020
94
Compensation is only for 10x or greater probes. Metal screwdrivers can change the capacitance. There are plastic "alignment tools".

In a lot of switching power supplies are either full (120V) or 1/2 wave rectified (240 V) to start wit 3xx volts DC.
The two diode drops at the full-wave bridge cause major issues when trouble-shooting.
how do you get around testing a circuit with a full wave bridge?
 

AlbertHall

Joined Jun 4, 2014
9,310
how do you get around testing a circuit with a full wave bridge?
You can measure DC voltages (with care) and you can test components with no power applied.
You could power the supply via an isolation transformer then you can connect a 'scope - not cheap though.
You could use a 'scope with fully isolated inputs - expensive.
 

Thread Starter

neospam

Joined Jan 13, 2020
94
CAL OUT has a little hole in it. That is for the oscilloscope probe clip. You don't need the ground wire.

other notes:
CH2 red knob is in CAL (or where it's supposed to be)
CH1 red knob is in UNCAL or variable mode within the range.
You have the horizontal in x3 in time mode as well. Push the red control in.

You asked for project questions, but lets get operation down first. See if you can read freqency from the scope.

Then set your signal generator for 60 Hz, 1 V p-p. Now try to read AC on your DVM. You should read 0.707 VAC.
So you are saying, turn off all red lights so the uncal light are not lighted? On all v/div and time/div? The see if I can read a frequency?

I believe my function generator only makes DC? I do not have a manual for it. Have a ECI 40600 - its a Iwatsu.
 

Thread Starter

neospam

Joined Jan 13, 2020
94
You can measure DC voltages (with care) and you can test components with no power applied.
You could power the supply via an isolation transformer then you can connect a 'scope - not cheap though.
You could use a 'scope with fully isolated inputs - expensive.
yea, I been looking at buying or making some sort of isolation transformer. Can you just make a simpler one with light bulbs until I hit the lotto? Like to have one with variable voltage and current.
 

AlbertHall

Joined Jun 4, 2014
9,310
yea, I been looking at buying or making some sort of isolation transformer. Can you just make a simpler one with light bulbs until I hit the lotto? Like to have one with variable voltage and current.
The light bulb idea is only to stop loud bangs and smoke. It won't make it safe for connecting a 'scope ground lead, or for your fingers. This one of the things that makes repairing SMPS difficult.
 

AlbertHall

Joined Jun 4, 2014
9,310
Not difficult just advanced.
Differential probes make this easy.......and safe.
I will stick with difficult and I spent quite a few years repairing the things.
I forgot the differential probes. You can also do this with a two channel 'scope if if one channel has an invert switch. Just be sure to keep the ground clips out of the way or better insulated.
 

tautech

Joined Oct 8, 2019
59
I will stick with difficult and I spent quite a few years repairing the things.
Me too and as you know that's evolved into a business selling test equipment in NZ.
I forgot the differential probes. You can also do this with a two channel 'scope if if one channel has an invert switch.
Or a DSO with Maths formulas.
Just be sure to keep the ground clips out of the way or better insulated.
Hence my previous comments about doing this safely.
We give all manner of advice on forums to those that have limited understanding of dealing with potentially lethal voltages where once upon a time it was considered acceptable to float a scope to gain measurements. Today not so and none of us want a electrocution on our conscience so best advice is to get the right tool for the job.
How might we know when different measurement techniques be required, well it's extremely simple; when there's a voltage differential between the scopes BNC (mains ground) and where we want/need to connect the probes reference lead.
 

AlbertHall

Joined Jun 4, 2014
9,310
once upon a time it was considered acceptable to float a scope to gain measurements.
I took over supervising a line repairing SMPS and all the scopes had the earth wire disconnected. I don't know how they got round the PAT testing. I got them all connected again and tried to get the company to buy an isolating transformer but it was a cheapskate company (now gone bust) and I couldn't presuade them it was necessary.
 

tautech

Joined Oct 8, 2019
59
I took over supervising a line repairing SMPS and all the scopes had the earth wire disconnected. I don't know how they got round the PAT testing. I got them all connected again and tried to get the company to buy an isolating transformer but it was a cheapskate company (now gone bust) and I couldn't presuade them it was necessary.
Today with companies required to meet health and safety requirements there's no way floating scopes would be allowed and now it's something that's universally frowned upon. Any technician that's required to do so should move to a company that values their safety and not only their bottom line.
 

Thread Starter

neospam

Joined Jan 13, 2020
94
CAL OUT has a little hole in it. That is for the oscilloscope probe clip. You don't need the ground wire.

other notes:
CH2 red knob is in CAL (or where it's supposed to be)
CH1 red knob is in UNCAL or variable mode within the range.
You have the horizontal in x3 in time mode as well. Push the red control in.

You asked for project questions, but lets get operation down first. See if you can read freqency from the scope.

Then set your signal generator for 60 Hz, 1 V p-p. Now try to read AC on your DVM. You should read 0.707 VAC.
I was able to get a reading. See pict. Can anything be measured now, or being probs might be off w/o proper calibration.
 

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neospam

Joined Jan 13, 2020
94
You need the correct impedance on the input and output of the filter to see the proper response.
Taking a look at the circuit. The Q420 transistor I cannot get to easy. In the schematic, there are 4 resistors groped together, in the schematic 2 of them are R459 & R460. At one leg of those (not sure what side) I am getting 2.634V on both of those. those are from cap to IC CMOS NAND GATE 4011, believe its CD4011BE. I grounded pin 6 as in the test for volt for Cal OUT. I got 0v. It's like there is no power.

Note - the other two resistors, not sure where they go are at 5v ish.. you cannot see them in the schematic, but they are right next to each other.
The C450 cap I cannot find, it might be up front by controls.

Not sure I understand the schematic right. The power source looks to be +5 going into a transistor. If I am getting 2.6v at those resistors could it still be the transistor? Is there a way to test the 4011 IC? There is 0v out for Cal OUT.
 

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AlbertHall

Joined Jun 4, 2014
9,310
You can use the 'scope to test the calibrator. Connect the probe to pin 3 of IC402 (no need to connect the ground clip). You should see a 5V square wave at about 1kHz.
If that is OK then move the probe to Q402 and see if you still get the 5V square wave.
 
The DTA114ES is a digital transistor: https://www.datasheetq.com/DTA114ES-doc-ROHM Since your voltage are about 1/2 the supply, the circuit is probably oscillating.

My guess is between Q420 and the output.

Everyone else covered me pretty good.

ground clip use:

Battery powered. Generally, you need a connection to ground.
High frequencies where you need to keep leads short.

isolation Transformer: it's more like an isolation transformer and a metered variac. If you build yourself, use two fuses. Line and wiper. The wiper MUST be fused. Wiper is front panel mounted. You can re-create the neutral-ground bond on the secondary side.

My variac, has the isolation xformer separate because takes up too much space. I used an analog voltmeter and ammeter with a front panel 3-prong plug and binding posts.

I only has a 3A variac, so my switch is full on @ 10A, off and variable at 3A. Made like 50 years ago when I was a 10 YO kid.

The schematic of the PR57 is around somewhere. See

The PR570 is it's bigger brother.
 
Today with companies required to meet health and safety requirements there's no way floating scopes would be allowed and now it's something that's universally frowned upon. Any technician that's required to do so should move to a company that values their safety and not only their bottom line.
I heard this story about a University Physics lab where they had made variacs. I thiink they color-coded the variacs for what side of room they were supposed to be used on. The difference between the sides is that they had the ot and neutral reversed.

Then my other story is about an all yellow wired valve controller that used ground instead of neutral. It controlled a diffusion pump (DP) heater and the foreline valve. On a power failure, the DP should be switched off and the foreline valve shut. A power fail with the gate valve open was still disasterous. About 2-days would be lost cleaning the pump. The experiment would have been bust too.

Boss said, it's worked for 20+ years, it does not need to be fixed.

The manual-valve systems were retro-fitted so the foreline was air operated. There was an Liquid Nitrogen refrigerator for the cold trap.

What should have happened is that the decision to shut the foreline and turn off the diffusion pump be made based on the temperature of the cold trap when power returned. Time would have worked too. A <5 minute interruption of power would be OK.
 

Thread Starter

neospam

Joined Jan 13, 2020
94
You can use the 'scope to test the calibrator. Connect the probe to pin 3 of IC402 (no need to connect the ground clip). You should see a 5V square wave at about 1kHz.
If that is OK then move the probe to Q402 and see if you still get the 5V square wave.
update -

Well, Da......... where the Cal OUT plugged into the circuit board, I was testing the ground lug.... :) When I was probing pin 3 I noticed my scope was flashing like it was getting a signal, so I scoped the other plug-in prong and magic happen..

Well, making progress. Still not sure its working right or I am not using it right. When I setup the CAL like it say in basic operation, they are saying 5mv/div and 1ms/div I do not get the same picture as shown in the manual. They have several smaller sq waves. I do not get that unless I increase my mV, to 20 or so. I was able to adjust the prob wave flat in the pict. Look at pictures and labels. The very first pict with sq waves, its showing 3 division, I accidentally had the tv-v on. It did not do anything when I moved it back to AC. Those 3 div in 1x mean anything?

Still need to solder the one CAL wire.

Most of the analog dials and switches show a lot of static on the screen. Sometimes I have to wiggle them. Can I use break cleaner or should I use something else?
 

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Thread Starter

neospam

Joined Jan 13, 2020
94
Yes, that's what you should see using a X10 probe.
need to thank you for your help & keep it simple...

Might try and solder the wire that is off. Not sure I can without removing the CB, will give it a try, much easier..

So what do you think? Is there some more testing I should/could do?

Need to learn the multiplication of what I am seeing. I suppose can feed some dc low voltage into the scope and compare what a dvm says.
 
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