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 Post subject: Re: Help with scope power supply- old Hitachi
PostPosted: May Tue 17, 2022 12:44 pm 
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The main thing is to make sure the Tek scope is working properly or it is a useless diagnostic tool.

So make sure that on a low sweep rate on the Tek, the beam is moving from left to right. And that when you apply a positive voltage to the probe tip (say from a battery) the beam deflects upwards.

If the above is ok then you can believe what the Tek scope is telling you about the Hitachi.


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 Post subject: Re: Help with scope power supply- old Hitachi
PostPosted: May Tue 17, 2022 5:26 pm 
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Location: New Albany, IN 47150
I again checked - the Tek465M sweeps from right to left, the Hitachi sweeps from left to right. So perhaps the both scopes have a sweep problem!

One additional thing I now notice- the Hitachi sweep alternates between two speeds! Setting it to a low speed, the trace/dot (as said above) starts at the left and moves to the right. However, when the sweep starts again at the left edge the next sweep is about twice as fast! Then the pattern repeats- goes back to reg sweep rate followed by a faster sweep rate. The T/div setting does not affect his behavior other than at some point the sweep is too fast to distinguish. This behavior cannot be seen when using the 1Khz calibration square wave.

I'm wondering how I might easily confirm these sweep issues... can someone recommend a simple almost-fool-proof circuit I could put together for an external signal generator? Perhaps making a sawtooth waveform? Maybe using a Raspberry Pi? A sine wave or square wave would be too ambiguous. Perhaps some RC charging waveform?

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 Post subject: Re: Help with scope power supply- old Hitachi
PostPosted: May Tue 17, 2022 9:39 pm 
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You can build up a pretty simple saw generator using a 555 and a very few other components. That's probably about as goof proof as it gets. Just google "555 timer sawtooth generator circuit" without the quotes. Dozens of hits so I'm not going to re-write them here. Dirt cheap, plenty of parts available, even brand new ones.

Also google 555 ramp generator. Similar results. If you can get your hands on a function generator, you may be able to create a decent enough ramp using the triangle waveform and varying the symmetry control, but of course unless you have a scope you trust, you won't know if you've got the function generator set correctly.

Brain Twister: which came first.. the signal generator, or the way to look at it (i.e. oscilloscope).

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 Post subject: Re: Help with scope power supply- old Hitachi
PostPosted: May Tue 17, 2022 10:54 pm 
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Location: Dallas, TX
A 555 timer circuit is what I would have suggested also. One based on a "astable" circuit, that repeats the waveform. A "monostable" puts out one pulse only when it gets a trigger.
EDIT: I will say also that using a battery is a good way to diagnose the problem, but it is DC.

From your last photos of the traces on the Tektronix scope it suggests that the Hitachi is working like a delayed trigger scope with two different sweep speeds (like the Terktronix could). However I think you said it should not have that sweep mode.
This certainly is a puzzling situation. I do think the lines to the horizontal CRT plates are switched, that would look the same on the Hitachi screen as the vertical plates being switched.
Another thing that could have somehow happened is that the CRT was installed upside down!

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 Post subject: Re: Help with scope power supply- old Hitachi
PostPosted: May Wed 18, 2022 4:46 am 
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Greetings to Tim, Barry, Keith and the Forum:

Tim: I think it unlikely that the Tek CRT is upside down because I don't think the high voltage lead would reach... although anything is possible, I suppose. Keith mentioned that the CRT has left and right labels not only on the circuit board but also on the CRT itself. I don't recall seeing anything like labeling on the CRT, but I am too lazy and don't have enough bench space to take one of mine apart to look.

My best guess therefore is that the horizontal deflection plates are indeed reversed and the labeling was applied in error. According to my 465B manual, the pins are accessed through holes in the main board under the CRT. If the leads are long enough, I would reverse them and call it good, since the scope seems to work properly otherwise. It is also possible, I suppose, that the CRT was replaced with the wrong type. This would make all calibration extremely suspect. Hopefully, this is not the case.

However, I agree completely with ACORNVALVE.... if the Tektronix is not displaying properly, it is useless as a diagnostic tool. If it looks OK once the horizontal deflection plates are reversed, then consider it good to go and use it to examine the Hitachi. You can get a pretty good idea of the calibration using the scope's 1 KHz square wave calibration signal.

Set the probe and volts per division controls so as to display .1 volts per division. Set the sweep speed to .5 mSecs per cm. The resulting square wave display should be 3 cm tall and each horizontal top and bottom of the wave should occupy 1 cm horizontally. If so, the scope is working well enough to use.

If the scope passes this calibration test with the horizontal deflection plate leads reversed and the sweep can now be observed to proceed from left to right, then you can start using the Tek scope as a diagnostic tool.

The alternate sweep speeds are a feature of the Hitachi scope. I was unable to download a user manual from the internet; if anyone can find one in PDF format, I would appreciate a link. I was only able to find one where I could look at (but not download) individual pages. However, I do remember that there is a setting of the controls that will allow successive sweeps to alternate back and forth from normal to X10 magnification. I don't recall what control sets this mode, but it sounds as though it is engaged. If someone can find a user's guide that we can all download, that would be of great help.

I don't think it will be necessary to build a ramp generator. Once we get the Tek sweeping the right direction, then things should begin to look a little closer to what we should actually expect. I suspect the weird sweep waveforms in the horizontal amplifier section of the Hitachi are due to the alternating switch between normal and "Mag".

Lastly, if Keith can borrow another Tektronix scope in known good working condition, the third "vote" should decide the matter.

Regards,

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 Post subject: Re: Help with scope power supply- old Hitachi
PostPosted: May Wed 18, 2022 7:04 pm 
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Location: New Albany, IN 47150
The Hitachi manual I am using is here for download: https://www.manualslib.com/products/Hit ... 46653.html

It is not a great manual, and I don't see any mention of an alternate sweep speed setting- would be nice if someone could discuss that.

Attached see a photo showing the Tek465M Horizontal Deflection Leads where they connect to the Interface board directly beneath the CRT. The horizontal module was not very difficult to remove in order to reach these leads, but I will say that two of the three screws holding the module to the frame were missing, so that is evidence someone before me has been in there doing something... The photo shows things how I found them- note the leads appear to be in their proper place. However, I have now reversed them. So NOW the Tek465M sweeps from left-to-right! I also checked (with 9V battery) the vertical deflection to make sure that is correct.

Attachment:
tek465m_horiz-defl-leads_8028.jpg
tek465m_horiz-defl-leads_8028.jpg [ 631.35 KiB | Viewed 422 times ]


Now when I take the trace from schematic <5> page 99 at the junction of R526 and TR522 the trace looks oriented properly! Yay!

Attachment:
hitachi_v211_v212_v222_v422_page99_partial1.jpg
hitachi_v211_v212_v222_v422_page99_partial1.jpg [ 511.94 KiB | Viewed 422 times ]


Attachment:
hitachi_v211_v212_v222_v422_page99_partial1-trace-5-18.jpg
hitachi_v211_v212_v222_v422_page99_partial1-trace-5-18.jpg [ 454.3 KiB | Viewed 422 times ]


You can see it looks pretty close to what it should look like... the freq is off by just a bit. I am puzzled how to set the Hitachi sweep controls when taking this trace... I assume the schematic shows the settings for the investigating scope (Tek465M), not the DUT (Hitachi). So I have set the Tek465M as shown on the schematic, but in order to get this trace the Hitachi must be set to 0.5mSec/div. Not sure what that means.

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 Post subject: Re: Help with scope power supply- old Hitachi
PostPosted: May Thu 19, 2022 1:23 am 
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Greetings to Keith et al and the Forum:

I found it! Couldn't find it last night, but I found it just now on ElectroTanya.com. Here's the URL:

https://elektrotanya.com/hitachi_v-422_ ... ad.html#dl

This is the OPERATION Manual for the scope... NOT the service manual. It tells you what all the controls do and generally how to use the scope features. I refer you specifically to page 13: look for CH1 ALT MAG switch. If you look here, you will discover how to place the scope in a mode where every other horizontal sweep is magnified 10 times. The portion of the waveform that is of interest is placed in the center of the screen and the ALT MAG switch engaged. When in this mode, the sweeps alternate, with the first sweep normal and the second sweep displaced down 3 cm and magnified 10 times with the center of the magnified sweep remaining in the same place, so that a comparison of the waveform magnified can be done. The next sweep (3rd) is back to normal and the next (4th) is magnified and so on.

Keith, if you can locate the control referenced in the operator's guide and turn it off, it should simplify trouble-shooting by making all of the horizontal sweeps the same.

I would suggest that everyone download the user's guide and a DJVU viewer if you don't have one (necessary to view the User's Manual). The djvu viewer is a handy thing; I prefer it to pdf when looking at schematics; it is a lot more versatile and user friendly. Unfortunately, not everything is available in djvu, so you really need both.

Congratulations, by the way, on getting the 465 squared away. We should now be able to have confidence in what you are seeing with the Tek and hopefully that will let us find the problem with the Hitachi.

Regards,

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 Post subject: Re: Help with scope power supply- old Hitachi
PostPosted: May Thu 19, 2022 1:44 am 
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Location: Dallas, TX
The setting for the Hitachi used for the schematic scope traces are given on the first page of the schematics in the manual.
The horizontal time control should be set to 0.5 ms./div.
By the way, it is typical for the horizontal ramp to deflect the beam past the right side of the screen.

If you get the ALT MAG Switch squared away (bad switch, loose wire, etc.), and now the Tek scope is straightened out, what is/are the problem(s) with the Hitachi? Will that just leave the trigger problem?
I've kind of lost track.

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 Post subject: Re: Help with scope power supply- old Hitachi
PostPosted: May Thu 19, 2022 2:01 am 
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Location: New Albany, IN 47150
@Notimetolooz- Thanks Tim for clarifying that for me. I had been looking on page 11 at the Initial Starting Procedure settings and somehow missed seeing those settings on page 51 at the start of the schematics. EDIT: the continuing issue is that the Hitachi won't trigger.

@Jthorusen- Jim thanks for finding the operator guide, I did not know one existed and had not thought to look for one. I don't have much time to play tonight but I did go ahead and download that user manual - my Linux system's default document viewer can read djvu files natively. Reading the description and playing with the CH1 Alt Mag switch and the Position Pull x10 control shows me that both those controls are still in need of cleaning, as there is intermittent and weird interaction between them, but I was able to manipulate them enough to finally get the horizontal sweeps all the same. Yay! Progress!

It may take me a few days, but I will continue to pursue this... I will attempt to clean these switches and take some more traces when I get time...

I still don't know if it is "normal" for this Hitachi sweep to change direction from 2mS to 1mS (with 1KHz calibration signal input).

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 Post subject: Re: Help with scope power supply- old Hitachi
PostPosted: May Thu 19, 2022 4:13 pm 
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By the way, I've worked with many scopes and this is the first one I know of that I've heard of that had a ALT MAG switch!

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 Post subject: Re: Help with scope power supply- old Hitachi
PostPosted: May Thu 19, 2022 9:49 pm 
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Notimetolooz wrote:
By the way, I've worked with many scopes and this is the first one I know of that I've heard of that had a ALT MAG switch!


I'm guessing it's a poor man's delaying sweep.

Regards,

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 Post subject: Re: Help with scope power supply- old Hitachi
PostPosted: May Sat 21, 2022 1:51 am 
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Location: New Albany, IN 47150
I am very happy to tell you that the Hitachi now triggers! Yay!

Of course it still needs work- lots of adjusting to do, but at least it is now triggering seemingly properly. What did the trick? Well, not sure... but I spent several attempts spraying DeOxit into the four controls which have push-pull features and the Alt Mag switch. Suddenly, it is working. Those controls would be impossible to simply buy and replace, and I am not up to disassembling them... I actually want to use this as a tool, not a life-long project!

I will be spending time calibrating/adjusting what I can with the limited tools I have, and then I will use it to do the same for the Tek465M.

This has been a very long thread, and several of you have really hung in there with me. I so very much appreciate it! I learned so much from you guys! But I also learned that I need to be more observant, more cautious, more thorough, and more thoughtful (not rushing into assumptions or being hasty). And I hope that others following this thread have enjoyed it as well. I am just returning to this hobby after having been away for almost ten years, so I had a lot to remember and dots to connect.

The entire side-step created by the Tek465M having its Horizontal deflection reversed was puzzling and caused a lot of confusion... that's the way it goes when one is using old unknowns. Still don't know what the deal with that is... but that is for another day. I know I will need to spend time replacing the power electrolytics in the Tek465M at some point ... But at least now the Hitachi is working. Yay!

Keith

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 Post subject: Re: Help with scope power supply- old Hitachi
PostPosted: May Sat 21, 2022 6:46 am 
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Greetings to Keith and the Forum:

Congratulations on hanging in there and getting it working! It just goes to support what Barry says about exercising the controls a gazillion times. :D

I'm glad it is working for you and hopefully you will now have two scopes that you can use to diagnose difficulties in other equipment.

One thing you said bothers me a bit:
Quote:
I know I will need to spend time replacing the power electrolytics in the Tek465M at some point


I have three Tek 465's.... and all of them are running just fine with the original power supply filters. I would not borrow trouble.... it will be difficult if not impossible to find capacitors of the same quality as Tektronix used originally. Therefore, I would not replace them unless the scope starts to exhibit problems like noisy traces, poor triggering or other weirdness.

You can then use your Hitachi to look at the Tek's power supply rails to see if there is hum or noise present. If the supply rails are clean, leave the electrolytics alone... they are working fine. Just my $.02 worth; others may differ.

Thanks for sticking with us and reporting your success.... too many people never check back in and leave us all hanging.

Of course, you know that no good deed goes unpunished. You have now become the resident expert on Hitachi scopes and anyone else who has a problem with one will be told to "ask Keith... he knows all about them". :D

Regards,

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 Post subject: Re: Help with scope power supply- old Hitachi
PostPosted: May Sat 21, 2022 5:11 pm 
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Location: New Albany, IN 47150
Hi Jim- Well... I haven't actually played with the Tek465M long enough to know very much about its condition, and I don't relish the idea of replacing caps on the it, but there is 0.44VAC p-p (428KHz) on the +32V rail... so one of these days I think I am going to need to look into that...

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Last edited by keithostertag on May Sat 21, 2022 7:31 pm, edited 1 time in total.

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 Post subject: Re: Help with scope power supply- old Hitachi
PostPosted: May Sat 21, 2022 7:08 pm 
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Having replaced filter caps in 3 out of 4 Tek 465M scopes, I can tell you that it basically requires complete disassembly.
The filter caps are on the main board at the bottom of the case. All the sub-assemblies and the CRT are on top.

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