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Hi all,
So I have these 2 465 scopes on the bench, both of which I’m struggling with at the moment.
I will here focus on the first one for the time being.
This scope has been entirely recapped, and all the low voltages are absolutely fine, as well as the HV -2450V.
The beam finder is working, but I only have a very feint vertical trace that is also about 1cm wide. The intensity control has no effect on it. I can see the focus control does something, but it’s almost un perceivable.
This vertical trace can be moved left and right, but not up or down.
I have checked for disconnected deflection plates, but all 4 of them are well in place.
The scale illumination is also working.
However, the pilot light indicating the scope is ON, does not show any sign of life.
Also, after measuring the voltages across the bulb, there is nothing.
Also, I have checked almost all the transistors on the A9 board, and all seem fine.
I don’t really know where to go from here, and I’d could really use some help.
Thank you.
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Stephen,
Are these 465's or 465B's? There is no power on "pilot light" on a 465, instead, the 465 has a "Low Line" indicator. If that lamp is illuminated, then there is an issue with your line voltage.
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Michael Lynch
Dardanelle, AR
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I would also check the HV multiplier as well.
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Michael Lynch
Dardanelle, AR
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On Tue, May 31, 2022 at 04:19 PM, Michael W. Lynch wrote:
Stephen,
Are these 465's or 465B's? There is no power on "pilot light" on a 465,
instead, the 465 has a "Low Line" indicator. If that lamp is illuminated,
then there is an issue with your line voltage.
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Michael Lynch
Dardanelle, AR
Hi Michael, Both are standard 465, not B’s. My 465B is working fine. This one in particular is the one I got the HV replacement for a few years back. As it turns out, the HV voltage is well present and it seems to be within specs. It actually reads -2350V, which is a bit low, but considering the VOM I used to check it has a 3% margin of error at these ranges, I’m assuming it’s ok. Yes, I just realized that about the pilot “Low Line” indicator. Thanks for pointing it out. Best Regards, Stephen
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On Tue, May 31, 2022 at 04:21 PM, Michael W. Lynch wrote:
I would also check the HV multiplier as well.
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Michael Lynch
Dardanelle, AR
I have. And as I said, all things considered, it “seems” ok. Albeit a bit low, I suppose….
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Did I mention that the Beam Finder is working and extremely bright, and that the intensity control has absolutely not effet on that vertical trace whatsoever? The wide and dim vertical trace runs the entire length of the display, and can be move left and right.
Also, when I engage the Beam Finder, I can hear cracking from the HV Multiplier.
I’m not sure this is supposed to happen.
Regards,
Stephen
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The HV Multiplier does not create the -2450, that voltage comes from the HV Transformer. The HV Multiplier creates the 14kV Post Deflection Acceleration potential. If the HV Multiplier has "failed open" it might allow the -2450 to remain unaffected. If there is any "crackling" noises, it could be a loose CRT anode connector or and extremely dirty CRT causing arcing. Is the area under the HV Guard cover on the interface board "very dirty? If the Intensity cannot be controlled, then you could have issues with the Z-axis circuitry or the DC Restorer,
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Michael Lynch
Dardanelle, AR
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You do not mention if there is any vertical deflection in response to an input signal. What happens if you apply a signal to either input channel?
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Michael Lynch
Dardanelle, AR
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On Tue, May 31, 2022 at 04:50 PM, Michael W. Lynch wrote: Interleaved. The HV Multiplier does not create the -2450, that voltage comes from the HV
Transformer. The HV Multiplier creates the 14kV Post Deflection Acceleration
potential. Ohh. I see… If the HV Multiplier has "failed open" it might allow the -2450 to remain unaffected. But in the case of a shorted or opened HV multiplier, would I have the Beam Finder working, or even something showing on the CRT? If there is any "crackling" noises, it could be a loose
CRT anode connector or and extremely dirty CRT causing arcing. Is the area
under the HV Guard cover on the interface board "very dirty? I cleaned it quite extensively as best I could without removing the CRT itself. The crackling noise does not come from the back of the CRT. I can actually see (and hear) the small arcing beneath the board, circled in red in the picture: /g/TekScopes/photo/275495/3437708?p=Created%2C%2C%2C50%2C2%2C0%2C0You’ll also notice a solid wire hanging upright loose with nothing attached to it. It apparently had something soldered to it at some point (I can see the remnants of a wire). But I can’t figure out what it was. It is a ground wire. If the Intensity cannot be controlled, then you could have issues with the Z-axis
circuitry or the DC Restorer, DC restorer? All the transistors in the Z-Axis circuitry check ok. I haven’t checked anything else there. Best Regards, Stephen
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Michael Lynch
Dardanelle, AR
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On Tue, May 31, 2022 at 04:54 PM, Michael W. Lynch wrote:
You do not mention if there is any vertical deflection in response to an input
signal. What happens if you apply a signal to either input channel?
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Michael Lynch
Dardanelle, AR
I haven’t tried inputting any signals yet. Will do though. Best Regards, Stephen
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On Tue, May 31, 2022 at 10:23 AM, Stephen wrote:
If the HV Multiplier has "failed open" it might allow the -2450 to
remain unaffected.
But in the case of a shorted or opened HV multiplier, would I have the Beam
Finder working, or even something showing on the CRT?
If there is any "crackling" noises, it could be a loose
CRT anode connector or and extremely dirty CRT causing arcing. Is the area
under the HV Guard cover on the interface board "very dirty?
I cleaned it quite extensively as best I could without removing the CRT
itself.
The crackling noise does not come from the back of the CRT. I can actually see
(and hear) the small arcing beneath the board, circled in red in the picture:
/g/TekScopes/photo/275495/3437708?p=Created%2C%2C%2C50%2C2%2C0%2C0
You’ll also notice a solid wire hanging upright loose with nothing attached
to it. It apparently had something soldered to it at some point (I can see the
remnants of a wire). But I can’t figure out what it was. It is a ground
wire.
If the Intensity cannot be controlled, then you could have issues with the
Z-axis
circuitry or the DC Restorer,
DC restorer?
All the transistors in the Z-Axis circuitry check ok. I haven’t checked
anything else there.
Stephen, The crackling noise does not come from the back of the CRT. I can actually see
(and hear) the small arcing beneath the board, circled in red in the picture:
That is the ground connection for the HV Multiplier. That is part of your issue. That is normally soldered to connect HV Multiplier ground to the PCB ground trace. Without that ground, the HV multiplier will not work correctly. Fix that first, then see what happens. But in the case of a shorted or opened HV multiplier, would I have the Beam Finder working, or even something showing on the CRT?
If the HV Multiplier is OPEN, the CRT and beam finder will show activity. If SHORTED, this will take out the -2450 and you get nothing. With the previous issue of the "bad ground" mentioned above, your HV multiplier is acting as if it is OPEN. That "Extra" wire, I have no idea, perhaps a test point for some previous repair? . Do you have a Service manual? In the Circuit Description there is a section that describes the DC Restorer. Review this section for a better understanding. The DC Restorer is diode based, not transistor based, so you are not testing the parts that typically fail. -- Michael Lynch Dardanelle, AR
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On Tue, May 31, 2022 at 05:41 PM, Michael W. Lynch wrote: Interleaved. Stephen,
The crackling noise does not come from the back of the CRT. I can actually see
(and hear) the small arcing beneath the board, circled in red in the picture:
That is the ground connection for the HV Multiplier. That is
part of your issue. That is normally soldered to connect HV Multiplier ground
to the PCB ground trace. Without that ground, the HV multiplier will not work
correctly. Fix that first, then see what happens. Michael, That solder joint circled in red in the picture, under which the arcing could be seen, was not grounded. You said that this is the HV ground. And sure enough, I checked the other 465, and that joint is grounded. The loose wire is a ground connection, and is the correct length to be soldered to that point. It’s probably where it must’ve been in the first place. I reattached it. There is no more crackling noise when the Beam Finder is pushed. However, it’s now not working anymore. There is no trace whatsoever either. All the voltages are still perfect, except for the HV. It’s now down to -750V. I guess that means the HV multiplier is indeed dead…???? Best Regards, Stephen
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Stephen,
Yes, the HV multiplier is dead (i.e "shorted"). I did not recognize that "wire" sticking up vertically as a jumper. Should have know that was the end of the jumper.
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Michael Lynch
Dardanelle, AR
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Michael,
I was hoping to avoid it, but I guess I’m gonna have to make use of one of those HV enclosures after all. I’m already dreading taking apart those boards…
Best Regards,
Stephen
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Stephen,
Getting the vertical board out to access the HV Multiplier is really not that bad. I have had several 465's apart in the past few months to replace the probe coding lamps. Take pictures of the coax connections and the other connections and you will be fine. You can do this without removing the Interface board, just loosen the various screws that secure the board and flex it up just enough to clear those two studs that protrude from the HV multiplier. You may also cut the HV lead off flush with the side of the multiplier case, so avoiding problems getting that HV conductor and connector out from under the CRT. Cutting it off will still allow ample material remaining to use on your newly constructed Multiplier. Some of the screws are a bit fiddly to get out and in, but nothing that you can't handle. Feel free to PM me with questions or comments.
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Michael Lynch
Dardanelle, AR
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Thanks Michael,
I will email you as needed, and will update the post as well.
Thank you very much for everything.
Best Regards,
Stephen
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Michael,
I assembled the HV multiplier replacement. I’m sending you an email offline regarding some small details.
Best Regards,
Stephen
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I can’t find anywhere the value of the output resistor that is inside the HV multiplier. I’d like to use the correct value if possible before potting it…
I believe it’s a 510kΩ, but I’m nor sure. Someone on the EEV Blog apparently used a 47kΩ. Which one is correct? Is that value important?
Does anyone know? Thank you.
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These are the specs for the part# 152-0552-00
3x mutiplier 5kV-15kV
Series resistor: 510 .0 k
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Michael W. Lynch