Author Topic: LG OS-5100RB problem  (Read 2732 times)

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Offline CX8JD

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LG OS-5100RB problem
« on: April 23, 2014, 04:00:59 pm »
I have a problem with an oscilloscope LG OS-5100RB. LA image disappears and I was able to determine that there is a problem with the CRT DRIVE BOARD, specifically in the high-voltage module. I tried to get a replacement but this model is no longer manufactured oscilloscope few years ago.
Any of you have any idea how to replace the damaged component or where I can buy a device that has an HV-MODULE that can replace?
Attached are some photos and the circuit with the defective part.  :-//



Offline zinda

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  • Posts: 1
Re: LG OS-5100RB problem
« Reply #1 on: March 29, 2015, 01:03:02 pm »
HI dear

First of all I feel  HT black box is not the thing to be worn out so quickly. please let try again if you have time, then review small parts behind that bit by bit. I am sure you can have the solution.

Further if you have the catalog the complete circuit of this board and relevant boards, please share with me, also the picture of board from both sides, but in good resolution. I think I can help you as I can.
I have some similar model of EZ scope. may be the voltages and parts components value I can check here and tell you t verify. This can be a good combination if you agree.

I would be looking forward to hear you, if you may like my suggestion.


Offline LA9QV

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Re: LG OS-5100RB problem
« Reply #2 on: June 20, 2018, 04:40:05 pm »
I also have a problem with the response of the "volts/DIV" encoders on my OS-5100RB scope.
Have tried cleaning them with contact spray to no avail. There are other controls also which do not respond correctly, but jump up and down randomly instead of increasing and decreasing with movement. Therefore I would like to get a manual for this instrument, which is working fine apart from this

Offline ulyanoff

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  • Posts: 22
  • Country: ua
Re: LG OS-5100RB problem
« Reply #3 on: January 02, 2020, 09:07:04 pm »
Hi ! I also ask for help with the service manual for the OS-5100RA model, anyone can help with any documentation .

Offline hugarefe

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  • Country: uy
Re: LG OS-5100RB problem
« Reply #4 on: February 25, 2020, 09:31:17 pm »
Hello. Y will try to relate my experience with an OS-5100RA with the same crt drive board.
The first symptom was F741 burning aparently without reason at intervals, at the begin
 of weeks, after days, and finally hours. Simultaneously and sporadically with this fault,
the crt filament no turn on, in spite of having a good oscillation level on collector
of Q746 (2SD613F). Dont try to measuring the filamet voltage with a tester, because
if the transistor is working, you will have 1.47KV with respect to ground. After verifying
the crt´s socket, inclusive changing it, I noticed that diconecting the crt´s socket,
and measuring the conduction of the filament winding from the H-V Module, it measured
open. So that taked out the H-V Module, and after cuting the black plastic cover in
the line of the two points that feed the filament, I found that the two wires are soldered
 to a  printed circuit at the top of the module and was VERY bad soldered.
To removing the pink sealant used as insulation, I used a hot air blower at
aproximately 180° centigrades, (356 fahrenheit) and a screwdriver. To isolating this again I used hot glue and a layer of PTFE of 0.5mm thicknes, (0.019685 inch) covering the cutted parts.
As the voltage at this point is 1.47KV, you can use maylar instead of PTFE.
After this, the filament always turned on with Q746 working ,but keeped burning
 F741 sometimes. After some days F741 blowed and Q746 shorted. After checking
 the H-V Module´s conection to the colector of Q746 have found the same fail as the
filament.  After applying the same procedure as with the filament, the conections
was fixed. BUT after trying several transistors to replacing the 2SD613F without success, found the datasheet where says that the "F" means hfe from 160 to 320. After comparing with other of my oscilloscopes, an Tek 7623,  noticed that the transistors used in the HV tranformers in oscilloscopes must work in the lineal region,and therefore the base bias and coupling are low. This means that on the colector you must have a sinusoidal waveform. In my case, Y found an old good quality TIP31 (Motorola) that worked OK. About the schematics Y have found that is very similar to LG Goldstar OS-3020, in particular the file "LG Goldstar OS-3020 Schematics PT2.pdf" page 5. I hope this information can help you.

Hello. I found two photos that I took when I did the first repair of the H-V Module.
« Last Edit: June 13, 2020, 10:03:20 pm by hugarefe »

Offline tongbajiel

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  • Country: id
Re: LG OS-5100RB problem
« Reply #5 on: July 27, 2020, 08:45:19 pm »
Hello CX8JD
Can you share or send me OS-5100RB schematic please..
i have same item and its no display problem..
maybe same as your problem to...

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