Leader LBO 505 x-y mode - X channel not covering full width of the screen - Page 1
Forum section: electronics / repair

author: Newbutlearning
author_rank: Contributor
timestamp: August 20, 2022, 02:20:44 pm
content: {{{{This did get solved but in an unconventional way. See the final few posts for details}}}}Hello everyone!This is my first post so I'm sorry if I don't understand all the social norms here.I need some help. Here's my dilemma, I have a Leader LBO 505 that seems to be in great condition and works for all I can tell. I'm mostly interested in the x-y mode as I'm using this oscilloscope as a movie prop and need it to display in this mode. However, I got it working in x-y mode but the X channel doesn't extend beyond a small portion of the screen. The Y channel goes all the way up but not the X. I've provided pictures to better show you what I mean since I'm not very good at this stuff.(Quick note, it might not look like a Leader LBO 505 but that's because I took the front off because, as I said, this is going to be a movie prop. I still have it and won't be throwing it away.)This is as big as I can get the x-y mode to display without warping.This is what it does when I try to make the display bigger.This is an example showing the Y channel being able to go to the top of the screenThis is what happens if I try to get the X channel to stretch out like the Y channel.This last image is just showing the beam can extend to the edge of the screen and isn't stuck.All of this is to say, does anyone know if this is a setting I need to adjust, or is this oscilloscope broken? Happy to take more pictures and the like if requested.Cheers.

author: Martian Tech
author_rank: Regular Contributor
timestamp: August 20, 2022, 04:14:08 pm
content: 1. When you "try to make the display bigger" are you increasing the input signal level or adjusting the VOLTS/CM control? Can't tell from the photos.2. What is the frequency of the signal you are feeding to the X input? Horizontal amplifier bandwidth on this scope is only 200KHz while vertical amp is 15MHz...

author: floobydust
author_rank: Super Contributor
timestamp: August 20, 2022, 06:13:13 pm
content: I would first see if it simply works as a scope, to rule out a problem with the Horizontal Deflection. Display a sine-wave and see if it's centered and wide then.I doubt it's ready for the trip to outer space. Don't burn the CRT phosphor having no X, Y signal and a really bright dot at idle.

author: Newbutlearning
author_rank: Contributor
timestamp: August 20, 2022, 06:15:03 pm
content: Yeah, I'm sorry about the faceplate being off. I can try and put it back on so you can get a better look if needed.Quote from: Martian Tech on August 20, 2022, 04:14:08 pmI tried both. At some point, adjusting either would hard-stop as shown.Here's a video of me adjusting the Volts control and you can better see the "clamping" I'm talking about.and here's the face plate:Quote from: Martian Tech on August 20, 2022, 04:14:08 pmThat is harder to say. What I'm sending is an audio signal from my computer. it looks like it's only sending ~100hz-~500hz but I can boost the audio signal and the frequency doesn't seem to change.I'm sorry I know so little, but that's a big reason I'm coming to you all. I know I'm not using this device for its intended purpose but this seems like an issue regardless of what the user is trying to display.

author: Newbutlearning
author_rank: Contributor
timestamp: August 20, 2022, 06:26:08 pm
content: Quote from: floobydust on August 20, 2022, 06:13:13 pmYou are very right. I'm trying to be careful with this thing so I don't damage it or myself. (I don't like breaking things even if I'm using them for films or outside their intended purpose.)Here's an example of running a 1kh sine wave into the scope.(I'll put the face back on so any future videos or pics can be better understood.)

author: floobydust
author_rank: Super Contributor
timestamp: August 20, 2022, 07:26:23 pm
content: It seems to work OK, then I would confirm the soundcard output is symmetrical (swap X, Y) or L/R. No way to get more H-defl with low V/DIV settings?Then I would look at the special X-Y calibration trimpots, X-Y GAIN VR VR809 and VR801 X-Y POS CENTER (they interact) that would be next, to see how they behave.Leader LBO-505Service Manual and Operation manual.

author: mag_therm
author_rank: Frequent Contributor
timestamp: August 20, 2022, 07:29:31 pm
content: Refer 505 manual.On my hand held it is hard to read.But fig 22 shows set up for Y:X with 10 mV per division on both channels X, YSpecs sayHorizontal input is 200 mV per cm division.Maybe you should follow fig 22 instead of using X input?Anyway, horiz time base should be switched out.

author: Newbutlearning
author_rank: Contributor
timestamp: August 21, 2022, 02:54:35 am
content: So first off everyone has been very kind with the help so thank you!Second, I've been messing around with this thing, trying the different things you all have mentioned, and I found that when I turn on the magnifier it does zoom in but it sends the image way off to the right side of the screen. Nothing I do brings it back to the center. Could there be something wrong with the centering dials?

author: Martian Tech
author_rank: Regular Contributor
timestamp: August 21, 2022, 03:04:49 am
content: In that last video, there appears to be a DC offset on Channel 2. It looks like the input coupling is set to DC, not AC...

author: Newbutlearning
author_rank: Contributor
timestamp: August 21, 2022, 03:21:59 am
content: Quote from: Martian Tech on August 21, 2022, 03:04:49 amJust tried flipping the switches to AC and all their positions and only the ground changes anything (flat lines it).

author: Martian Tech
author_rank: Regular Contributor
timestamp: August 21, 2022, 05:24:43 am
content: OK, now I'm thinking maybe VR808 (on main PC board) is misadjusted, as the offset only appears on MAGx10I would try setting to CH-1 mode with Horizontal mode set to EXT. Center the H-POS knob. Then connect the signal that's currently going to CH-2 to EXT H instead. That will bypass the Q801/Q802 circuit. (Just another way of getting X-Y mode, but you lose the amplitude adjustment provided by CH-2). Or just ground the EXT H input - that should give you a vertical line (or dot, if there's no input signal on CH-1). If it still doesn't center on MAGx10 then VR808 probably needs adjusting... If it does center OK then there's something wonky in the Q801/Q802/VR801/VR809 circuitry (we can rule out the CH-2 amplifier because it is shown to work OK in dual-trace mode when being used as a vertical amplifier)...

author: floobydust
author_rank: Super Contributor
timestamp: August 22, 2022, 01:32:17 am
content: The scope first needs calibration and running it in X-Y with 10X mag is just asking for this to be obvious.All the offsets pile up. You can do a basic check by seeing if the H-POS, V-POS controls are near center when looking at a normal sine wave. If a position control is near one end, then do the cal.OP why use 10X mag, get your sound source to put out more or lower the V/DIV setting.

author: Martian Tech
author_rank: Regular Contributor
timestamp: August 22, 2022, 02:54:11 am
content: Hmmm... Doing a proper calibration requires equipment that the OP may not have. My understanding of the goal of this effort is to do the minimum possible so the OP can use the scope in X-Y mode as a movie prop. If using X10 as a workaround achieves this goal, then there is nothing wrong with taking that route. If using the EXT H input instead of CH-2 produces the desired results, then that's a valid workaround as well. More work will probably be required to make it work as a proper oscilloscope, but most movie projects work on a tight schedule so it may not be justified at this time...

author: Newbutlearning
author_rank: Contributor
timestamp: August 23, 2022, 04:30:26 pm
content: Quote from: floobydust on August 22, 2022, 01:32:17 amI'm not married to using 10x mag, but it did get me closer to my end goal of filling the screen with my image as Martian mentioned. And I actually have the sound source backed off from sending as much as it can (it would hurt my ears if I tried to listen to it) and the second picture in my original post shows what happens when it sends any more than what I have it sending. It "clips" the image into a square. That was actually the purpose of the image collection on the first post; to help illustrate that the oscilloscope won't let the image get any bigger for some reason.Quote from: Martian Tech on August 21, 2022, 05:24:43 amI have two questions with this: first, with this oscilloscope, how do I connect to the EXT H input? it seems to be a different port than the CH-1/2 ports (those are BNC), so is there a name for the connector so I can find an adaptor for the rca cable I'm using? or am I missing something?Second question: Is there an easy way to find VR808? I'm not sure what that is. I'm comfortable with taking things apart and figuring things out, I'm just not very good with the technical verbiage and the like. (Also, I'm very aware there are possible capacitors and the like inside this device that could really hurt/kill me if I'm not careful so I'm very cautious with pocking around inside this thing.)

author: floobydust
author_rank: Super Contributor
timestamp: August 23, 2022, 07:32:37 pm
content: With a basic sine wave displayed, check the H-POS and V-POS knobs are not way off center, indicating there is an offset issue.Given the scope's age, it likely needs tweaking or there is a weak transistor that is causing your problems.Inside the scope has trimpots for adjustment, on the PC boards. They are small controls that you use a small slotted screwdriver to rotate, and nearby they are labelled i.e. "VR801" etc.You can use an well insulated screwdriver, put electrician's tape around the shaft etc. to lessen the chance the oscilloscope god attacks you...How is the Horiz. centering and width? These trimpots affect it:VR809 X-Y GAIN (seems low)VR801 X-Y CENTERVR808 10X MAG CENTER (seems way off according to your vid)VR808 Ext. H input DC BAL but I'm not sure how much signal it needs there.I can't find pics of the PC boards or input jacks.

author: Newbutlearning
author_rank: Contributor
timestamp: August 23, 2022, 11:41:26 pm
content: This is great, floobydust! I'll give all of those a look. Thanks for the really clear explanation! I'll report back once I've given those a try.

author: Newbutlearning
author_rank: Contributor
timestamp: August 24, 2022, 12:59:59 am
content: I am back and all I can say is.......Thank you to all who helped me figure this out. Not that many will care, but when this film is finally shot in December, I'll link the finished film here so you can enjoy the fruits of your labor!Also, since you said you couldn't find a photo of the board anywhere I took one while I had it open. I also took a photo of the bottom panel of the oscilloscope that helps indicate where the holes are.Cheers to all of you!

author: Martian Tech
author_rank: Regular Contributor
timestamp: August 24, 2022, 03:08:05 pm
content: Bravo!

author: Newbutlearning
author_rank: Contributor
timestamp: February 14, 2024, 07:52:58 pm
content: To all who helped me get this thing working, I am so grateful to you. We made the film. There's no way we would have been able to without you all being so helpful and patient. I wanted to make good on my word and post the film now that it's finished and also a few frames of the modified oscilloscope in action.Enjoy!The Trailer:The film: (WILL ADD WHEN RELEASED)Keep being wonderful folks!Cheers,T