Aron bs-601 scope issue

[The_Todd]

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.

[eccerr0r]

Re: Aron bs-601 scope issue

The Aron BS-601 is a dual trace 20MHz single timebase oscilloscope.

Need to back up a moment, so you're saying the signal is "flat" or is it just a line?

Also there's a vertical position knob, do these move the trace up and down? Both of them?

As an aside though not quite needed yet: do you have a working oscilloscope to debug with?

[The_Todd]

Re: Aron bs-601 scope issue

The Aron BS-601 is a dual trace 20MHz single timebase oscilloscope.

Need to back up a moment, so you're saying the signal is "flat" or is it just a line?

Also there's a vertical position knob, do these move the trace up and down? Both of them?

As an aside though not quite needed yet: do you have a working oscilloscope to debug with?

Helo there,

mostly flat, if iput it on the lowest voltage division i can get a smalll imagae of thr signal, but where it should take up the screem from top to bottom it ont even go up to the first line. The position knob works a bit, again only moves up and down a little bit.

Also should mention that both sides are the same, ive done thoughough testimg on the calibration pots with makes minimal diferences and yes i do have a fully working scope to test with

[The_Todd]

Re: Aron bs-601 scope issue

I should also mention all the horizontal controls work fine

[The_Todd]

Re: Aron bs-601 scope issue

Could i ask as its doing my head in, what is the relation btween Q18 and Q20 (and Q17 Q19) im asumings ones basicly a mosfet controling the full voltage output but whats the other for? Feedback of some sort or perhaps pulling the voltage down...?

[eccerr0r]

Re: Aron bs-601 scope issue

So the trace stays near the bottom of the screen and you can't get it to go to the top?

Yeah looks like some sort of complementary drive for slew rate, looks like one of the halves is not working, you're probably looking in the right place.

[The_Todd]

Re: Aron bs-601 scope issue

So the trace stays near the bottom of the screen and you can't get it to go to the top?

Yeah looks like some sort of complementary drive for slew rate, looks like one of the halves is not working, you're probably looking in the right place.

Oh no, stuck in the middle, its doesnt gk uo nor down very far but tbey are about equal, botb up and down outputs are about 12v they should be about 60v

[eccerr0r]

Re: Aron bs-601 scope issue

Okay, THAT's a big piece of information. If it stays towards the center, power supply is working, and both deflection outputs stay at 12V, I'd then look at the bias voltages across that voltage divider tree there - D10 R80 R89 D11 D14 ... are those voltages correct?

Also what does the scope do in XY mode, does it also not want to deflect vertically?

[R_J]

Re: Aron bs-601 scope issue

Does the VERT POSITION control move the trace up and down?

[redwire]

Re: Aron bs-601 scope issue

OP cross-posted here also: https://www.eevblog.com/forum/repair...cal-amp-issue/

[eccerr0r]

Re: Aron bs-601 scope issue

Ah... I was wondering where that 60 volt number came from, looked like it came out of someone's brown gas generator. It is the most logical number however as it is in the middle of the 120V and 12V, but it doesn't necessarily have to be there for the scope to work. As long as the voltages are about equal, the trace will be in the middle. Just need the voltages to differ and somewhat be closer to the 120V mark to make a larger deflection.

[The_Todd]

Re: Aron bs-601 scope issue

Does the VERT POSITION control move the trace up and down?

Funny you ask that, it actually doesnt move it, it only stretches of shrinks the signal slightly. doesnt move it at all

[R_J]

Re: Aron bs-601 scope issue

It looks like you should have -8 volts going to the center of the vert. position control, That shouuld change the bias on q29 and q30 moving the trace up or down. You say you have all the voltages but where did you check them? they may be at P3 but do they get to get to where they should. There are a number of coils in the voltage lines, make sure the voltage is on both sides of them and one is not open.

[eccerr0r]

Re: Aron bs-601 scope issue

There are two vert position knobs and the impression is that neither apparently work, so I'd imagine the fault is in some common stage after those controls, hence suggesting something wrong with the power/bias of the final amplifier... but wondering what other controls have effect on the trace just to make sure.

BTW, once you determine both channels behave identically, test with just one channel, that would be a PITA if one has to deal with the chop/alt signal... heh.

Looks like Q15 is identified wrong in the schematic, looks like it should be 2SA836 PNP in the BOM but it's written as 2SC458 NPN there... The (lack of) symmetry is bothering me...

[The_Todd]

Re: Aron bs-601 scope issue

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

[The_Todd]

Re: Aron bs-601 scope issue

and thanks for your help guys, ill Be gettjng back into it later this arvo

[petehall347]

Re: Aron bs-601 scope issue

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

pull out red knob to calibrate

[R_J]

Re: Aron bs-601 scope issue

Even with no input signal you should be able to move the trace "position" from the center of the display up or down close to the top or bottom of the screen.
If both inputs act the same, that should eliminate the front ends/inputs

[The_Todd]

Re: Aron bs-601 scope issue

pull out red knob to calibrate

already tried makes litter difference, same for both sides.

[R_J]

Re: Aron bs-601 scope issue

The fact that you get a waveform at all is a good sign. too bad you don't have a scope to trace the signal
Check some of the voltages on the vertical board and see if something is missing or a voltage that does'nt look right, I see a few voltages listed on the schematic so check them first