Need help with Meguro MO-1252 Oscilloscope - Page 1
Forum section: electronics / repair

author: chill4
author_rank: Newbie
timestamp: January 26, 2021, 03:46:34 pm
content: I recently acquired a free Meguro MO-1252 35MHz oscilloscope. It’s been several decades since I used an oscilloscope and that was an early digital one I used more for data acquisition than signal analysis, so my skills weren’t much more than novice then. The scope seems to function and responds to volts and time per division when I apply an AC signal and play with the basic controls. Triggering controls function as best I can tell. The problem I don’t seem able to remedy is the trace is limited to the right side of the screen, about one division right of center. When I use the horizontal position control to move it left, it hits a wall and the trace partially compresses against it. I can move it to the right completely off the screen. It’s like the position control is misaligned with the CRT.I did find a link on the forum to a manual that looks to be applicable to this scope. Apparently, this is a highly cloned scope, represented in the manual as a Hung Chang OS-635. I am a mechanical guy, not a sparky (no offense. I’ve work around EE’s my whole career and am jealous they understand my mechanical stuff better than I understand theirs), so I struggle with much of the manual, but with some guidance I might be able to make sense of some of it. I figured it might be wise to ask for help before I start turning things inside the box.Any thoughts on what I should try first?

author: BreakingOhmsLaw
author_rank: Frequent Contributor
timestamp: January 26, 2021, 05:12:34 pm
content: This is most likely a power supply issue. Deflection voltage won't go negative (negative rail missing).Check all voltages from the power supply. Do you have the service manual?

author: chill4
author_rank: Newbie
timestamp: January 27, 2021, 03:14:40 pm
content: I have a partial operation & maintenance manual that I think is applicable to this scope. It has a section on power supply unit adjustment which identifies voltage adjustment locations and values. Looks like next step is to find and verify voltages on that board. It might be a bit before I get back to it. Thanks much for your response. Assuming I can find my way around it to troubleshoot, should I expect to find a non-responsive circuit that is the culprit? Sounds like it would be dead, not just out of adjustment.

author: CaptDon
author_rank: Super Contributor
timestamp: January 27, 2021, 05:57:33 pm
content: If you get full vertical deflection but no horizontal then the power supply is probably o.k. Some scope C.R.T.'s have the deflection plate connections part way up the neck of the tube and if one horizontal lead comes off you get exactly the problem you describe.

author: floobydust
author_rank: Super Contributor
timestamp: January 27, 2021, 07:34:40 pm
content: Many threads here about this scope. Meguro MO-1252 apparently is Japanese and then copied by the Koreans Hung Chuang and many other brand names.https://www.eevblog.com/forum/testgear/need-help-on-identifying-a-mystery-korean-oscilloscope/https://www.eevblog.com/forum/repair/old-meguro-mo-1251-scope/(changed to 1252)Note: 1252A is 25MHz, different from 1252 35MHz; link to OS-635 schematichttps://www.eevblog.com/forum/repair/meguro-mo-1252a-25mhz-analog-oscilloscope-nothing-on-crt/msg1530890/#msg1530890

author: jdragoset
author_rank: Frequent Contributor
timestamp: January 27, 2021, 10:07:13 pm
content: Working on one Tek 2215, deflection output amplifier had series connected collector resistors where one open-circuited resistor caused the same response, good deflection from center to one side only.After checking deflection plate pin/socket connections, check for balanced change between deflection amplifier oututs.

author: chill4
author_rank: Newbie
timestamp: January 28, 2021, 07:40:00 pm
content: Ok, I'll check the connections. If that's not it, I'm probably over my head but it's fun trying. Looking to retire this year so will have more time to get in trouble. Thanks for the guidance. I'll update as I progress.

author: floobydust
author_rank: Super Contributor
timestamp: January 28, 2021, 10:34:29 pm
content: Definitely just check the power supply DC voltages are OK. The 160VDC is used for the deflection circuit and is regulated, the pass-transistor isn't rated for much more (150V) same as the deflection transistors so if it goes high things can get damaged.