Re: Batteries in 7S14 plug-in
You need to read the the wiki article, and message #112514 to get the background info and update. Then look at #96664 for the best implementation that I have seen, in my opinion.
Ed
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Let's try this one more time. Sorry for the bandwidth...
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Sorry, here is the image [image: voltages] On Thu, Dec 4, 2014 at 1:42 PM, Kevin Crossett <kcrossett@...> wrote: That's what I figured. I will look in my junk box for an old power supply
or some other electronics gizmo for the 100 v cap. Assuming I find one in
the next day or so, I am now trying to determine the positive side of the
cap...
I found this image on the internet of someone with a similar problem as
me. He laid out what he thought were the solder points for the 4439 cap. Is
he right, and if so, how can I determne which one is positive?
On Thu, Dec 4, 2014 at 1:29 PM, raymonddf@... [TekScopes] <
TekScopes@...> wrote:
Kevin,
Don't try a 470 uF 35V cap. unless you're looking forward to an early
firecracker party a few seconds or minutes after switching on...
Raymond
[Non-text portions of this message have been removed]
[Non-text portions of this message have been removed]
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Re: Batteries in 7S14 plug-in
The photovoltaic MOSFET approach would work of course. Current is more than enough but regulation is compulsary at >13 V open circuit. The sampler diodes in reverse bias hardly allow any current through.
Raymond
Another possibility on the photovoltaic approach is Vishay's LH1262 photovoltaic MOSFET drivers. It has two photovoltaic generators in a DIP or SOIC package. You can get a minimum of 2.6uA each (3.4uA to 6.9uA typ, depending on drive current), with an open circuit voltage of about 13.5V.
Regulation would still be needed, obviously, probably by loading the output and controlling the drive current as in the referenced artcicle. Or maybe that's enough current for an ultra-low power regulator.
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That's what I figured. I will look in my junk box for an old power supply or some other electronics gizmo for the 100 v cap. Assuming I find one in the next day or so, I am now trying to determine the positive side of the cap... I found this image on the internet of someone with a similar problem as me. He laid out what he thought were the solder points for the 4439 cap. Is he right, and if so, how can I determne which one is positive? On Thu, Dec 4, 2014 at 1:29 PM, raymonddf@... [TekScopes] < TekScopes@...> wrote:
Kevin,
Don't try a 470 uF 35V cap. unless you're looking forward to an early
firecracker party a few seconds or minutes after switching on...
Raymond
[Non-text portions of this message have been removed]
[Non-text portions of this message have been removed]
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Re: Batteries in 7S14 plug-in
Another possibility on the photovoltaic approach is Vishay's LH1262 photovoltaic MOSFET drivers. It has two photovoltaic generators in a DIP or SOIC package. You can get a minimum of 2.6uA each (3.4uA to 6.9uA typ, depending on drive current), with an open circuit voltage of about 13.5V.
Regulation would still be needed, obviously, probably by loading the output and controlling the drive current as in the referenced artcicle. Or maybe that's enough current for an ultra-low power regulator.
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Kevin,
Don't try a 470 uF 35V cap. unless you're looking forward to an early firecracker party a few seconds or minutes after switching on...
Raymond
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Kevin,
All PC Power supplies contain at least one large electrolytic cap. with several 100 Volts of working voltage and at least several 100's uF capacitance. That will do the job. It doesn't matter if you have to put wires of a few cm's length on the cap or on the board to be able to solder the short connections.
Just make sure you connect the polarities correctly.
Since your "new" temporary cap hasn't been used for a while and it may not be of high quality, it may not like the voltage applied suddenly.
Common countermeasures, like a series resistor in a temporary fuse-like role, wouldn't be completely straightforward because of the unknown power supply / load situation. OTOH, I don't think the 100 V suffers from large load or even overload so I'd put in a low-wattage resistor of say 100 Ohm, 0.25 Watt in series with the new, temporary C. The resistor will burn up if the new C has a real problem. Even with 100 Ohm in series, I think your 100 V AC will become significantly lower if C4439 is the problem.
After a while, it may be safer to remove (short) the temporary resistor.
Raymond
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Thanks for the offer Tom. I can, of course, go to mouser, but I'm not too keen on paying shipping for such a small part, especially if I will have to go back to that well for additional parts. I will go in my attic and look at some old computer boards. Maybe I can find something on one of the boards that will work. On Thu, Dec 4, 2014 at 12:01 PM, 'Tom Miller' tmiller11147@... [TekScopes] <TekScopes@...> wrote:
Hi Kevin,
Raymond is absolutely correct, I did use the wrong schematic. The cap I
suspect is bad is C-4439.
And I agree with his comment about what to try.
If you really can't find a cap easily, let me know and I can send you one.
Tom
----- Original Message -----
From: raymonddf@... [TekScopes]
To: TekScopes@...
Sent: Thursday, December 04, 2014 11:00 AM
Subject: [TekScopes] Re: Tek 465B woes
Hi Kevin,
1. I think that Tom made a mistake here. C1512 is the correct ref. for a
465. In a 465B, it's C4439.
In my 465B manual, it's at the top of the Power Supply schematics (page
12), right where the fold is in the middle of the schematics on the paper
page.
Physical location is shown in Figure 8-7 "A4 interface Circuit Board,
behind Tab 7. Location F8/9.
2. Any cap with at least 100 V working voltage and a few 100's uF would do
and make a big difference if C4439 is low-cap. Just solder it on as a
temporary measure. Easy to do from the bottom of the 'scope and see what
happens.
Raymond
[Non-text portions of this message have been removed]
[Non-text portions of this message have been removed]
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Eureka. I found it. Thanks Raymond. It must get confusing helping so many people out with different scope problems. I did in fact find C4439 in the service manual. Now I have to find a 100 v cap. I guess its a trip to mouser.com. Radio shack has only 470 ohm rated at 35 v. I don't suppose that rating is adequate for the test... On Thu, Dec 4, 2014 at 11:00 AM, raymonddf@... [TekScopes] < TekScopes@...> wrote:
Hi Kevin,
1. I think that Tom made a mistake here. C1512 is the correct ref. for a
465. In a 465B, it's C4439.
In my 465B manual, it's at the top of the Power Supply schematics (page
12), right where the fold is in the middle of the schematics on the paper
page.
Physical location is shown in Figure 8-7 "A4 interface Circuit Board,
behind Tab 7. Location F8/9.
2. Any cap with at least 100 V working voltage and a few 100's uF would do
and make a big difference if C4439 is low-cap. Just solder it on as a
temporary measure. Easy to do from the bottom of the 'scope and see what
happens.
Raymond
[Non-text portions of this message have been removed]
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Re: Batteries in 7S14 plug-in
The difference of 0.1 volts is insignificant as far as risk to the sampling gate
diodes but as Raymond points out, zinc-air batteries are a poor choice because
of their short life once activated.
I would consider either using silver oxide batteries or the photovoltaic option.
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On Thu, 4 Dec 2014 08:46:32 -0800, you wrote: I wish I could direct this question to the engineer who designed the
sampling bridge in the 7S14 plug-in. The original design made use of
Mercury batteries in the sampling gate back-bias (BT1 and BT2). The mercury
cells which are no longer available had a voltage of 1.35 volts. I need to
know how critical this voltage is??? Can these cells be replaced with
Zinc-Air which have a voltage of 1.25 volts? 1.25 volts should be
sufficient to back-bias the sampling diodes, but will the sampling pulse
amplitude be too much and over-drive the sampling gate? Does anyone still
have contact with the original engineers to get a definitive answer?
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Re: Batteries in 7S14 plug-in
I wouldn't consider zinc-air batteries a good choice for this purpose. Zinc-air batteries have a relatively long shelf life unopened but once opened (activated), they discharge rather quickly, even without load, since the zinc-air reaction just proceeds.
Several good options are available:
I have replaced the batteries with a DIY photovoltaic solution, using LEDs (4 sets total). This solution is easy to build and works well.
There's been a lot of traffic on this forum re. the replacement of these bias batteries, some of it less than a month ago.
Have a look at Ed Breya's very useful article here:
7S14 repair - TekWiki
7S14 repair - TekWiki The following document was authored by Ed Breya and originally posted on the TekScopes Yahoo forum. Contents 1 Background 2 Design and construction 3 Findings and recommendations Background
View on w140.com
Preview by Yahoo
Raymond
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Hi Kevin,
Raymond is absolutely correct, I did use the wrong schematic. The cap I suspect is bad is C-4439.
And I agree with his comment about what to try.
If you really can't find a cap easily, let me know and I can send you one.
Tom
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----- Original Message -----
From: raymonddf@... [TekScopes]
To: TekScopes@...
Sent: Thursday, December 04, 2014 11:00 AM
Subject: [TekScopes] Re: Tek 465B woes
Hi Kevin,
1. I think that Tom made a mistake here. C1512 is the correct ref. for a 465. In a 465B, it's C4439.
In my 465B manual, it's at the top of the Power Supply schematics (page 12), right where the fold is in the middle of the schematics on the paper page.
Physical location is shown in Figure 8-7 "A4 interface Circuit Board, behind Tab 7. Location F8/9.
2. Any cap with at least 100 V working voltage and a few 100's uF would do and make a big difference if C4439 is low-cap. Just solder it on as a temporary measure. Easy to do from the bottom of the 'scope and see what happens.
Raymond
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Batteries in 7S14 plug-in
I wish I could direct this question to the engineer who designed the
sampling bridge in the 7S14 plug-in. The original design made use of
Mercury batteries in the sampling gate back-bias (BT1 and BT2). The mercury
cells which are no longer available had a voltage of 1.35 volts. I need to
know how critical this voltage is??? Can these cells be replaced with
Zinc-Air which have a voltage of 1.25 volts? 1.25 volts should be
sufficient to back-bias the sampling diodes, but will the sampling pulse
amplitude be too much and over-drive the sampling gate? Does anyone still
have contact with the original engineers to get a definitive answer?
|
Connect a BNC Tee to the lowest, most central connector. 2 fingers around that and your thumb against the bottom of the mainframe while operating the release with your other hand should be enough pressure and also give you a better feel for what's going on. This is especially helpful for big plug-ins like the 7D20. [Non-text portions of this message have been removed]
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Hi Kevin,
1. I think that Tom made a mistake here. C1512 is the correct ref. for a 465. In a 465B, it's C4439.
In my 465B manual, it's at the top of the Power Supply schematics (page 12), right where the fold is in the middle of the schematics on the paper page.
Physical location is shown in Figure 8-7 "A4 interface Circuit Board, behind Tab 7. Location F8/9.
2. Any cap with at least 100 V working voltage and a few 100's uF would do and make a big difference if C4439 is low-cap. Just solder it on as a temporary measure. Easy to do from the bottom of the 'scope and see what happens.
Raymond
|
I don't have the scope in front of me at the moment. This image has a partial serial number included. Its ?067605 so it should be in the range of the service manual that came with the scope. On Thu, Dec 4, 2014 at 10:51 AM, Mark Wendt mark.wendt.ctr@... [TekScopes] <TekScopes@...> wrote: On 12/04/2014 10:40 AM, Kevin Crossett kcrossett@... [TekScopes]
wrote:
Thanks Tom and Raymond for the advice. Two questions from a novice
troubleshooter.
1. I don't have access to a 550 uF, 100 volt electrolytic cap. Tom, when
you say "tacking a radial leaded cap across C1512" to you mean soldering it
on the pads and then checking the AC measurement again. Also, I can't find
C-1512 on the board or in the service manual. The manual is for 465B scopes
with B06000 and up. According to the service manual, all caps on the
horizontal amp are in the 4XXX range. What's the serial # of your scope?
2. Since I don't have a cap anywhere near the 100 volts, is there another
way to check the cap to see if it is faulty?
Easiest way is to remove one leg from the circuit and make a direct
measurement of it, both capacitance if your DMM does it, and also ohm it
out. An ESR meter would be handy to have also.
Mark
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On 12/04/2014 10:40 AM, Kevin Crossett kcrossett@... [TekScopes] wrote: Thanks Tom and Raymond for the advice. Two questions from a novice
troubleshooter.
1. I don't have access to a 550 uF, 100 volt electrolytic cap. Tom, when
you say "tacking a radial leaded cap across C1512" to you mean soldering it
on the pads and then checking the AC measurement again. Also, I can't find
C-1512 on the board or in the service manual. The manual is for 465B scopes
with B06000 and up. According to the service manual, all caps on the
horizontal amp are in the 4XXX range. What's the serial # of your scope?
2. Since I don't have a cap anywhere near the 100 volts, is there another
way to check the cap to see if it is faulty?
Easiest way is to remove one leg from the circuit and make a direct measurement of it, both capacitance if your DMM does it, and also ohm it out. An ESR meter would be handy to have also. Mark
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-------- Original message --------
From: "strijw426@... [TekScopes]" <TekScopes@...>
Date: 02/12/2014 13:00 (GMT+01:00)
To: TekScopes@...
Subject: Re: [TekScopes] Zenith 36" problem!
Does changing the brightness also change the focus of the picture? If so the CRT may be conducting too much due to improper bias of the control and screen grids.
Vertical fold-over can also be an indication of power supply problems. So is inadequate horizontal deflection. The first place to look is in the LV power supply. Look for any high wattage resistors that may have fractured solder underneath on the PC board where they are connected. The same can happen on power regulation transistors and ICs. This is a common problem with both tube type and solid state power supplies. The unit could also have electrolytic capacitors that have dried out enough to cause problems too. Many sets produce from the late 1960s onward have special parts that are safety related items and must be replaced with specific part types in order to maintain compliance with fire and other safety issues.
Some sets also had HV regulation circuits that would kick the set out of horizontal frequency lock to keep the HV from rising too high (and consequently cause X-rays from the CRT and HV components). That makes the set unwatchable of course. You did not describe that type problem though.
I would start with the LV power supply. There are still sources for schematics on TV sets, so find the one appropriate for your set first. Working on one without the schematic is a stab in the dark. The schematic will tell you what voltages to expect and what waveforms to expect in each circuit if you get a good manufacturer's schematic or a Sam's schematic.
Joe
KC5LY
[Non-text portions of this message have been removed]
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Thanks Tom and Raymond for the advice. Two questions from a novice
troubleshooter.
1. I don't have access to a 550 uF, 100 volt electrolytic cap. Tom, when
you say "tacking a radial leaded cap across C1512" to you mean soldering it
on the pads and then checking the AC measurement again. Also, I can't find
C-1512 on the board or in the service manual. The manual is for 465B scopes
with B06000 and up. According to the service manual, all caps on the
horizontal amp are in the 4XXX range.
2. Since I don't have a cap anywhere near the 100 volts, is there another
way to check the cap to see if it is faulty?
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David Hess
Gary Robert Bosworth