Repair an oscilloscope - Page 1
Forum section: electronics / repair

author: Jasonbit
author_rank: Regular Contributor
timestamp: July 26, 2018, 11:55:28 am
content: Hello folks,I have this oscilloscope (https://snag.gy/QngL2s.jpg). I need repair this equipment because the pottenciometer (which regulate the timer horizontal division) has broken. I have already been wacthing and I need open the all case, disconnect some wires to dessolding pottenciometer and put a new pottenciometer. Do you suggest any advice to do this work? I think the process is a little basic. Only I need is a very attention and beware to don't forget any wire.Which model is it this oscilloscope (https://snag.gy/QngL2s.jpg)?hasn't any label!Thanks

author: alsetalokin4017
author_rank: Super Contributor
timestamp: July 26, 2018, 01:21:45 pm
content: Are you talking about replacing the time/div switch, or the horizontal position adjustment? Can you indicate on the photo exactly which part needs to be replaced?Also, look carefully at the back of the scope, there may be some manufacturer data there.

author: Jasonbit
author_rank: Regular Contributor
timestamp: July 26, 2018, 05:12:46 pm
content: Sorry, my fault. On this photo (https://snag.gy/O6odVb.jpg) I indicated which component I need repair/substitute! I was see inside the oscilloscope and to substitute this potentiometer (I think this is a simple potentiometer) I will need desolder!I rechecked and I don't see anything which identify the instrument. On the back have this label's:https://snag.gy/6oUgEz.jpgOn above hasn't anything. Maybe inside, in pcb have any markings!

author: MaxFrister
author_rank: Regular Contributor
timestamp: July 26, 2018, 06:15:24 pm
content: Sorry, I can't help you identify the oscilloscope.Can you say why you need to change the potentiometer?It is common in old oscilloscopes with controls that have not been used for a while to get dirty and electrically noisy. Often all that is required is to spray it with a contact cleaner and work the switch or knob back and forth for a few minutes. After cleaning I then spray a tiny amount of potentiometer cleaner into it (similar to contact cleaner but also has a lubricant).If you do still need to change it the hardest part will be determining what the replacement part is. The parameters include size, shaft length, shaft kind, resistance, taper,....

author: borghese
author_rank: Regular Contributor
timestamp: July 26, 2018, 07:56:50 pm
content: Perhaps you could post some better photos to identify the model

author: dml
author_rank: Regular Contributor
timestamp: July 28, 2018, 08:22:49 pm
content: The scope in that pic has exactly the same style, knobs, switches and layout as an old LG 20MHz scope "OS 5020".However it seem to be some blank spaces where the 5020 had function generator gang switches. And one knob missing, with one moved.Looks like either a different/earlier model in the range, or maybe an OEM using a licensed design.https://www.scribd.com/document/134639836/LG-OS-5020G-Oscilloscope-Service-Manual

author: Jasonbit
author_rank: Regular Contributor
timestamp: July 30, 2018, 11:51:43 am
content: On this link I uploaded photos about oscilloscope (https://drive.google.com/drive/folders/1EXiVCObPpYAUrqavmgsCgRv3ErF2K-r4?usp=sharing).I will read and try confirm if this manualhttps://www.scribd.com/document/134639836/LG-OS-5020G-Oscilloscope-Service-Manual(share by dml) was the manual I need!Thanks

author: dml
author_rank: Regular Contributor
timestamp: July 30, 2018, 05:11:47 pm
content: I took a couple of quick snaps of the LG, which I was using recently as a backup (it has seen happier days, kept in storage so long).As you can see - the shell at least looksreallysimilar. But a different model - function gen absent and a couple of things moved.I think we're probably looking at an OEM design sold by more than one company under different names. Chances are the service manual is a match in enough areas to be useful.Unfortunately I don't have time to go dismantling the LG just now to compare the insides. If I do that, I'll post pics.D.

author: Jasonbit
author_rank: Regular Contributor
timestamp: August 06, 2018, 11:21:44 pm
content: Hello,Thanks to your great help.Today I opened the oscilloscope and I can saw which all potentiometer are soldiers on boards, more a less in this zone:https://snag.gy/FTdLfD.jpgBefore I try open more equipment and unsolder the potenciometer I think it is best try to find the potenciometer equivalent yo this model. Please see my new galleryOscilloscope Detailson this link:https://drive.google.com/drive/folders/13xtHBkd8qPcPcygl0kGaZ-d47O2UbqkE?usp=sharingWhere do you suggest try yo find another similar model? Or first of all the best decision it is try to paste witch super gule all the pieces?Thanks

author: james_s
author_rank: Super Contributor
timestamp: August 06, 2018, 11:54:37 pm
content: Are you sure it's a potentiometer and not a rotary switch? Finding an exact replacement could be very difficult, you might have to repair what you have or find a damaged scope to take one out of.

author: Jwillis
author_rank: Super Contributor
timestamp: August 07, 2018, 12:07:31 am
content: I think dml is correct in the possible identification of the make and model.Yours seems to be missing part the front plastic cover.If you can identify the Potentiometer or encoder you can use a standard equivalent and wire it to the board.I've had to do this to many rebuilds because it was impossible to find an exact match.

author: Jasonbit
author_rank: Regular Contributor
timestamp: August 07, 2018, 12:18:14 am
content: Quote from: james_s on August 06, 2018, 11:54:37 pmGood Point. Maybe the potentiometer it is good, and maybe is, and the problem is rotary switch (package plastic). Tomorrow I will test oscilloscope and try to rotate with a tool or my own hands the rotary switch.Yes, I am thinking the same. To find the exactly component on older and damaged scope. maybe on ebay. Which the best place to find this equipament and buy this scope is it ebay? Or do you suggest another place?Thanks

author: james_s
author_rank: Super Contributor
timestamp: August 07, 2018, 03:20:06 am
content: Generally ebay is the easiest place to find this sort of thing, other options will depend heavily on the local market. If you still have any hamfests or I think you call them car boot sales there anymore those would be reasonable places to look. You could also post in the buy/sell/trade section of this forum, someone may have a damaged scope of the same or similar model and be willing to send you just the part(s) you need.

author: stevengendron
author_rank: Contributor
timestamp: August 08, 2018, 04:19:44 pm
content: If the rotary switch is defective, maybe the contacts inside are just corroded. Especially if you haven't used it for a long period of time.Before replacing the switch, you could try to fill it with contact cleaner and rotate the switch back and forward a couple of time to clean the contacts.If the switch is sealed, you might want to drill a tiny hole on it before to fill it.

author: Jasonbit
author_rank: Regular Contributor
timestamp: September 03, 2018, 05:53:54 pm
content: Hello everyone,I tried paste the pieces but I didn't succeed!After some movements the parts are released again.I will search on ebay or another similar website (including here in forum) per pieces or older oscilloscope similar to this.Thanks to all for your support and advices!

author: james_s
author_rank: Super Contributor
timestamp: September 03, 2018, 06:02:53 pm
content: What type of adhesive did you use? There is no one-size-fits-all glue, you need to use something appropriate for the specific material(s) being glued. Some materials are much harder to glue than others. For plastics if there is a solvent that softens it then a glue containing that solvent is usually going to provide the best bond.