Broken vertical vpp oscilloscope for sale

[ripsdevala]

Hi all, just wondering if this thing is easy to fix, there is someone sell his scope with broken vertical scale, horizontal is ok

Model LG OS9020A
Price $23
Is this worthed?


Manual and scheme
https://www.google.co.id/url?sa=t&so...7K8vSIFtnzxbqw

[rickb]

Can you provide some more info? Is the screen photo an indication of the fault? Will the seller provide a better description? The rounded square wave on the screen coming from the calibrator output could be nothing more than a misadjusted probe. What does the other ch. show? I spent about 15 years repairing and calibrating test equip.

Rick

p.s. Is the frame above the scope photo supposed to be a video?

[ripsdevala]

Thanks for the reply Rick, let me ask him more detail about it

[ripsdevala]

Please take a look, the wave cannot go to the center display, at 02.05 he will show you the vertical adjustment button is not working on ch1 and 02.42 on ch2, he says all other function is work.
https://youtu.be/EneY24xscb0

Any opinion will be apreciated.

Best,
Rips

[rickb]

ripsdevala

Has he made ANY attempt to "repair" or make any adjustments? If so, forget about it.

Have you repaired any electronic equipment using standard trouble shooting methods? What is your experience level? This would be a relatively simple repair if the scope were sitting in front of me. On the other side of the world, not so simple.With experience, a lot of the trouble shooting can be done from the front panel by changing switches and controls, and noticing the effect.

Did this scope fail during his use, or did he buy it in this condition thinking he could fix it?

Believe it or not, I have fixed many scope problems by cleaning the switches and controls with a good spray contact cleaner. At one point late in the video, the scope shows an intermittent problem while he is turning a control or switch, when the amplitude of the signal drops to zero in a way that looks like a dirty/intermittent switch. Since this symptom affects both channels, the problem may be in the dual trace switching circuit.

Question to ask him.

Will it show 2 traces offset from each other in chop or alternate mode with or without a signal?

The question you have to ask yourself, is whether you can afford to lose the $23 plus shipping if you decide to buy it and are unable to repair it (sell it to someone near you?). As Clint Eastwood said in Dirty Harry, "Do l feel lucky ..."?

I need a reply to all of this before going further.

Rick

[ripsdevala]

He buy it from unhonest seller that says all function of the unit is working and know it after the first use.
Once he open the box just to see if there any faulty, but unfortunetly he found a repair attemp with soldering and wire jumper on the pcb.
Im an IT support for many years and have standart electro fixing and troubleshoot, like bad component replacement, ,make a jumper wire from burned silk cable, loose wiring, etc.

Maybe I should find another scope, thanks for the all the sugestion and answer Rick, very helpfull.
☆☆☆☆☆

[rickb]

I suspect it is a relatively simple problem, but a working scope would almost certainly be needed to trace the signals. The first step would be to restore the wiring to be that of the schematic. Can you bargain the with him? Is $15 worth the risk if he would accept that?

Rick

[ripsdevala]

I think that so, $15 would be ok, let me do some merchant skills

[Hyena]

If I were you I would buy it.

I bougt 2 channel TESLA BM 556 (for less than 20€) with similar problem. Horizontal scale was fine but vertical was broken. When I connected calibrating square 6Vpp wave I was not able even to get it on screen. After few days of probing circuits (I have 1 channel chinese DIY osciloscope for 18$) I realized that problem was in contact on two transistors Now it works like it have to without any intervention to the PCBs...