Author Topic: Aron BS-601 Oscilloscope vertical amp issue (FIXED) (Read 7316 times)

The_Todd · « **on:** January 27, 2019, 04:47:33 am »

Hello guys,

im trying to fix a Aron BS-601 scope but the issue im having is the vertial part is not worki ng properly, whatever signal you put in ans whatecer setting you use the trace is always very thin and flat.

the problem is the the vertical amp, its only pumpi g out about 12v to the scope with of couse needs to be much more. ive attached the circuit that im refring to, the circuit has all the corect voltages going ito it and q19 nd q20 also have the 120v sitting behind it.
however about 12v is geting to the outputs

The exact way this circuit works is a bit beyond my capa bilities but if i coukf get any help it wold be appreciated.

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Armadillo · « **Reply #1 on:** January 27, 2019, 04:51:48 am »

Could it be a simple severe case of contact tarnished. Have you tried cleaning the contacts?
Watch the video;

The_Todd · « **Reply #2 on:** January 27, 2019, 04:53:25 am »

Yup tried that. And the signal is dull overall. No matter how much i fiddle with the switches

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tautech · « **Reply #3 on:** January 27, 2019, 10:39:09 am »

With zero signal and V position centered each plate should see ~60V.
The 120V is supplied to the final output amps via a current limiting resistor so down stream from that check for componentry failed short that might effect both plates.
Things like C38.

The_Todd · « **Reply #4 on:** January 27, 2019, 12:45:36 pm »

Quote from: tautech on January 27, 2019, 10:39:09 am

With zero signal and V position centered each plate should see ~60V.
The 120V is supplied to the final output amps via a current limiting resistor so down stream from that check for componentry failed short that might effect both plates.
Things like C38.

Oh that makes sense il check
it tkmmorrow

Cheers

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tautech · « **Reply #5 on:** January 27, 2019, 09:10:27 pm »

You might also spend a little time studying this, it can be very helpful in pointing you in the right direction:
http://www.sphere.bc.ca/test/tek-parts/troubleshooting-scopes.pdf

Armadillo · « **Reply #6 on:** January 27, 2019, 10:10:58 pm »

Hi, I see that you can probe around powered on, so you know well the safety aspect.

Aside from the multimeter, what other kinds of testing instruments or component testers do you have?

The_Todd · « **Reply #7 on:** January 27, 2019, 11:11:41 pm »

I have all the Main tool, incuding a working scope and microscpe.

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The_Todd · « **Reply #8 on:** January 28, 2019, 12:57:42 am »

Here is a pic of the signal the best i can get it, thisis a .5v test signal

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Armadillo · « **Reply #9 on:** January 28, 2019, 03:14:01 am »

You have a handful of equipment there.

The test signal, what was the volt/div you used and was the probe set to Divide by 10 setting?

If you set the volt/div to lowest 10mv/div any change?

If you switch your probe to Divide by 1 any change?

The_Todd · « **Reply #10 on:** January 28, 2019, 03:27:55 am »

Quote from: Armadillo on January 28, 2019, 03:14:01 am

You have a handful of equipment there.

The test signal, what was the volt/div you used and was the probe set to Divide by 10 setting?

If you set the volt/div to lowest 10mv/div any change?

If you switch your probe to Divide by 1 any change?

yeah just few thing

the probe is on 1x

and no mater what there is little difference. it will go anywhere from a dead straight line to a small signal
about 1cm in hight. and that it. ive tried every setting and different probes and bot sides are the same.

tautech · « **Reply #11 on:** January 28, 2019, 03:57:29 am »

By any chance are the red knobs on the V/div not clicked home in the Cal position ?

Armadillo · « **Reply #12 on:** January 28, 2019, 04:19:35 am »

We have tried the easy ones, now the harder part [your choice, up to you if you want to do it, considering the age of this scope];

Please be careful, observe safety.

Use a working scope, set to AC, probe Divide by 10, Volt/Div as appropriate;

The scope under repair, set to 10mv/div, apply test signal into the input.

Probe with respect to GND, [if you are save the traces, please post it up]

Collector Q5, then Collector Q6,
Collector Q9, then Collector Q10
Emitter Q13, then Emitter Q14

Volt meter measure Voltage at Cathode of D10 and then Anode D14 with respect to GND.
[You sure you have checked the 5V, 12V and 20V?]

The above just merely divide the areas of search.

I suspect one of the common biases is OUT.

The_Todd · « **Reply #13 on:** January 28, 2019, 04:27:11 am »

Quote from: Armadillo on January 28, 2019, 04:19:35 am

We have tried the easy ones, now the harder part [your choice, up to you if you want to do it, considering the age of this scope];

Please be careful, observe safety.

Use a working scope, set to AC, probe Divide by 10, Volt/Div as appropriate;

The scope under repair, set to 10mv/div, apply test signal into the input.

Probe with respect to GND, [if you are save the traces, please post it up]

Collector Q5, then Collector Q6,
Collector Q9, then Collector Q10
Emitter Q13, then Emitter Q14

Volt meter measure Voltage at Cathode of D10 and then Anode D14 with respect to GND.
[You sure you have checked the 5V, 12V and 20V?]

The above just merely divide the areas of search.

I suspect one of the common biases is OUT.

Oh this is detailed thank you, my other scope is analog too, so ill try and try and get photos.

with the ground isolation, i haven't got an isolation transformer, so should it be ok without it
or should I detach the ground odd the faulty scope of the scope used for testing? (and yes, all equipment
i use is going thought a safety switch designed for testing equipment)

thank you again,for you help.

Armadillo · « **Reply #14 on:** January 28, 2019, 04:35:41 am »

Your scope is powered by isolation transformer already.

I only assumed here the isolation transformer is working fine, otherwise use a isolation transformer to be safer.

Just don't, NEVER probe beyond the isolation points like probe the mains....

Armadillo · « **Reply #15 on:** January 28, 2019, 05:07:41 am »

Don't know if your schematic is updated, the old one has 2 Q4 there;

Anyway, see attached.

You start with mid point pairs. if no signal despite lowest V/div, you forget downstream points, always move upstream.
Conversely if there are signal, then move downstream mid points and repeat same procedure. Divide by 2, Divide by 2.... got the idea.?

That will cut measurement points down a lot.

Hope you understand this short English.

The_Todd · « **Reply #16 on:** January 28, 2019, 05:29:06 am »

Quote from: Armadillo on January 28, 2019, 04:19:35 am

We have tried the easy ones, now the harder part [your choice, up to you if you want to do it, considering the age of this scope];

Please be careful, observe safety.

Use a working scope, set to AC, probe Divide by 10, Volt/Div as appropriate;

The scope under repair, set to 10mv/div, apply test signal into the input.

Probe with respect to GND, [if you are save the traces, please post it up]

Collector Q5, then Collector Q6,
Collector Q9, then Collector Q10
Emitter Q13, then Emitter Q14

Volt meter measure Voltage at Cathode of D10 and then Anode D14 with respect to GND.
[You sure you have checked the 5V, 12V and 20V?]

The above just merely divide the areas of search.

I suspect one of the common biases is OUT.

Ok let’s star with Q5 collector