Wobbly Scope Screen - Hitachi 1050 - Page 1
Forum section: electronics / repair

author: dan3460
author_rank: Frequent Contributor
timestamp: September 22, 2015, 07:55:16 pm
content: I'm a newbie to this forum, but I collect antique radios and I have been messing with electronics since a kid 50 years ago. Looking for some help on try to find this problem. A little history of the scope. Got it from ebay for $30 including the shipping. The high 56V winding of the transformer was open. I left that transformer to supply all the other voltages and bought a 56V transformer that I put on this thing. I have tested all the voltages out of the power board and they are pretty close and well within the specs from the manual.I have followed to schematics and scoped almost every point where they show a waveform and all are very close, within 4% of what is shown. When the input selector is set to GND and time/div set to 1ms the line wobbles up and down, it doesn't change with the volts/div knob. It is the same for both channels. It is the same with ADD setting too. As I said, I checked voltages and waveforms for both input amps, the channel selector and the vertical controller board. All seem fine.I have the suspicion that it could be power supply related, does anyone have other ideas before I go and start changing all the caps?

author: KJDS
author_rank: Super Contributor
timestamp: September 22, 2015, 08:23:57 pm
content: I read the title and thought, "Ah! I've seen that before, when the scope has been too close to a transformer from another piece of equipment." I then read your description and found you'd added another transformer. I suspect it's direct coupling into the deflection coils.

author: tautech
author_rank: Super Contributor
timestamp: September 22, 2015, 08:30:44 pm
content: Quote from: KJDS on September 22, 2015, 08:23:57 pm+1That is, if all PSU voltages measure very little ripple.But not deflection coils, electrostatic deflection, right?

author: OldSchoolTechCorner
author_rank: Frequent Contributor
timestamp: September 22, 2015, 08:39:15 pm
content: If your using a second transformer, yes I do know it's AC, but you have to make sure you wired the second transformer in phase of the first transformer windings, or will cause issues as you describe. Also did you check for ripple on the PSU rails?

author: OldSchoolTechCorner
author_rank: Frequent Contributor
timestamp: September 22, 2015, 08:42:28 pm
content: Quote from: KJDS on September 22, 2015, 08:23:57 pmPlus 1

author: dan3460
author_rank: Frequent Contributor
timestamp: September 22, 2015, 08:49:30 pm
content: whoosh, this was quick. Thanks guys for the answers. I thought about that the additional transformer may be bugging the deflection coils but I should see the same wobble of the point when put in x-y mode. That is steady. The point is not crisp, but I saw that when I was doing tests before putting the extra transformer.OldSchoolTechCorner, did not think about that. Is easy to test, I have connectors to the new transformer I juts have to switch the connectors around. I will do it this evening.

author: dan3460
author_rank: Frequent Contributor
timestamp: September 23, 2015, 01:00:51 am
content: I switched the connections and tested all the possibilities, it did not chain.So, I'm starting by changing all the lytics in the power supply and any cap or resistor that looks doggy.

author: OldSchoolTechCorner
author_rank: Frequent Contributor
timestamp: September 23, 2015, 01:45:33 am
content: Could be capacitors when high ESR. Also check ground connections to

author: oldway
author_rank: Super Contributor
timestamp: September 23, 2015, 07:37:51 am
content: Remove the new 56V transformer and install it far from the scope.See if this help.

author: dan3460
author_rank: Frequent Contributor
timestamp: September 23, 2015, 12:09:29 pm
content: Indeed oldway, I mounted the transformer in a bracket so it is easy to pull. I order a few caps that I was missing but when I put the scope back together I will put the transformer outside the box and see what happens.