开云体育

So now it seems to be just fine. Last night I fired it up and it still had the problem. Then I took it out and poked around in the circuitry looking for anything suspicious, jiggling stuff around some more, and pondering how to measure some of the resistors.

Then I put it back in to make some measurements, and the trace was nearly the right width. I also learned that the "SWP CAL" pot has nothing to do with setting the width, only the actual sweep ramp velocity. I initially assumed it was a gain control, but no. The specs just say that the width should be at least 10.2 divisions, so that must be the minimum that it gets to considering tolerances and drift - there's no 1X gain adjustment or comparator setting. So the trace was just about 10 divs wide, and stayed good for quite some time. I could adjust the sweep cal and set it right on to match the calibrator signal, so close enough to call it done.

This morning I fired it up again, and the width was about 10.5 divs when cold, then warmed up to where it is now 10.2 divs and holding. So, it's a mystery exactly what caused it, but I think the combination of poking around in there, working the controls more, and running time has restored it to normal. So, I'll have to call this one a done deal - I'm sure it will be just fine until I need to use it.

Ed

There is a file in the files section called Tek 465 Power Supply Capacitor Replacement Guide.pdf that might help you find what you need. Since the yahoo boobs went to neo, I am unable to open the file, so good luck.

In any event, the capacitor has three negative terminals in a circle. the positive terminal is within the circle.

- -
+

-

Watch your fingers when making measurements in this area or it can bite you.

Also, when and if you go to change this cap, the capacitor can and the three contacts are a part of the circuit. Also, you dont want to pull the track and the plated through holes out when removing the bad cap. Come back for some more advice when you get to that point.


Regards,
tom

Thanks Mike. I think I'm thinking too hard about this. That makes obvious
sense.

Cheers
Kevin
KN4M

On Thu, Dec 4, 2014 at 2:35 PM, n2lym n2lym@... [TekScopes] <
TekScopes@...> wrote:

Use you dmm on the existing capacitor to verify the correct polarity
BEFORE attaching added capacitor.

Mike N2LYM

On Thu, Dec 04, 2014 at 01:42 PM, Kevin Crossett kcrossett@...
[TekScopes] 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]

Use you dmm on the existing capacitor to verify the correct polarity
BEFORE attaching added capacitor.

Mike N2LYM

Hello everyone!

I'm searching for two parts for my sampling scope (Tek 11801):

1) 2x knob for sampling plugin (part# 366-0673-00 (KNOB:O.096 ID X 0.24
OD X 0.299H)
2) 1x empty plugin slot cover (part# ???)

I would be pleased if someone could help me!

Best, Simon

Makes sense. I'll report back my findings as soon as I locate a cap and
solder it on.

Thanks for bringing the image issue to my attention. My apologies to the
group.

You may find the positive side for your temp. C. by switching the 'scope on and measuring DC voltage across C4439. The plus side of the cap. goes where the more positive voltage on C4439 is seen (100V)


Raymond


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?

Hey Kevin,

I don't think the Yahoo forums like photos in messages. You can create a new photo album and upload to that.


Siggi

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

Let's try this one more time. Sorry for the bandwidth...

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]

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.

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]

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.

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

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

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]

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]

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.