Tek 310 and Looking for Advice


stan mcintosh <mcintosh@...>
 

Last week, I got the last of the finishing touches complete on the power supply section. All voltages from the rectifiers, dropping resistors, and caps are within 3% of spec. The Black Beauties and old electrolytics are also gone. However, this is a good news/bad news situation.

The good news is that I now feel confident that the selenium rectifiers, Black Beauties, and old electrolytics are not causing trouble. The bad news is that the voltages are still pretty far off, in the same manner as before I started. the -150 is now around -140, +100 is about +60, and +300 is around +260.

What do the sages advise? Should I disconnect and load-test the regulated supplies to see if they are possibly just being overloaded by a faulty circuit? If so, what current would the sages recommend? Or, should I go through disconnecting and reconnecting circuits until I find the one that is throwing the system off-balance? What do the sages say?

I know that this is not a high-performance scope, but it has character, and I would like to make it part of my bench.

Thanks.

stan


Morris Odell <morriso@...>
 

Stan,

The bad news is that the voltages are still
pretty far off, in the same manner as before I started. the
-150 is now around -140, +100 is about +60, and +300 is around +260.

What do the sages advise?
Check or try replacing the 5651 voltage reference tube. There should be
exactly 87 volts across it when it's lit. They can drift, causing the
-150 and therefore all the other supplies to go out of spec. I've found
this fault in a couple of old Teks, including my 310A.

Morris


stan mcintosh <mcintosh@...>
 

Check or try replacing the 5651 voltage reference tube.
Thanks, but the new tube checks fine. I accidentally cracked the old one while removing a few weeks ago, so replacement was mandatory. Was happy to find a sleeve of 5 5651WA's in le boxe du junque.

Again, thanks.

stan


Stan & Patricia Griffiths <w7ni@...>
 

HI Stan,

I still think the problem you see now is in the power supplies themselves.

The first question I have for you is this:

Are the power supplies "regulating"? That is, do the voltages remain the
same as the line voltage is varied from 105 to 125 VAC? If you don't have a
metered variable line voltage source, now is the time to get one.

Second question:

How much "ripple" is on each supply? Is is about the amount stated in the
manual calibration procedure? (10 millivolts)

Third question:

As you try to set the -150 volt power supply on -150, can you vary it at all
with the adjustment control or is it just at -140 all the time?

Fourth question:

Have you checked the output from the 5651 reference tube? It should be
about 85 volts. Measure this between pins 1 and 7 on V613.

Since all of the power supplies are referenced to the -150, it has to be
accurate for the rest of the supplies to be accurate. Also, the -150
depends on a working +300 to work properly, which means you have a problem
in either the -150 or the +300 or both.

Stan
w7ni@easystreet.com

----- Original Message -----
From: "stan mcintosh" <mcintosh@triad.rr.com>
Cc: <TekScopes@yahoogroups.com>
Sent: Sunday, November 02, 2003 6:22 PM
Subject: [TekScopes] Tek 310 and Looking for Advice


Last week, I got the last of the finishing touches complete on the power
supply section. All voltages from the rectifiers, dropping resistors, and
caps are within 3% of spec. The Black Beauties and old electrolytics are
also gone. However, this is a good news/bad news situation.

The good news is that I now feel confident that the selenium rectifiers,
Black Beauties, and old electrolytics are not causing trouble. The bad news
is that the voltages are still pretty far off, in the same manner as before
I started. the -150 is now around -140, +100 is about +60, and +300 is
around +260.

What do the sages advise? Should I disconnect and load-test the regulated
supplies to see if they are possibly just being overloaded by a faulty
circuit? If so, what current would the sages recommend? Or, should I go
through disconnecting and reconnecting circuits until I find the one that is
throwing the system off-balance? What do the sages say?

I know that this is not a high-performance scope, but it has character,
and I would like to make it part of my bench.

Thanks.

stan


stan mcintosh <mcintosh@...>
 

Thanks for the advice. It helped rule some items in and some out. I hope
we're getting closer.

From Morris and Stan, respectively...

Check or try replacing the 5651 voltage reference tube. There >>should be
exactly 87 volts across it when it's lit.

Have you checked the output from the 5651 reference tube? It should be
about 85 volts. Measure this between pins 1 and 7 on V613.
The NOS 5651 that I put in 1-2 weeks ago had a 77 volt drop! The next one
had a 106 volt drop, and it *was* lit. The next two had voltage drops of
83.5 volts. I have one more in a box, but I decided that an 83.5 volt drop
tube would work for checking out a few of the other items.

From Stan (as are the rest of the quotes):

I still think the problem you see now is in the power supplies themselves.
Oh, I'm hoping it's restricted to the supplies. I'd rather chase a gremlin
through a small section rather than the whole scope.

Are the power supplies "regulating"? That is, do the voltages remain the
same as the line voltage is varied from 105 to 125 VAC? If you don't have
a
metered variable line voltage source, now is the time to get one.
Here is where we see some differentiation. From 105-125VAC input: the +100
V regulates right at 59V, the -150 regulates at -139, and the +300 swings
from 270 to 290. I don't have a metered line voltage source, but I do have
a voltmeter for making such measurements when using a Variac input.

How much "ripple" is on each supply? Is is about the amount stated in the
manual calibration procedure? (10 millivolts)
The ripple values in the +300, +100, and -150 are 3 mV, 1 mV, and 3 mV,
respectively.

As you try to set the -150 volt power supply on -150, can you vary it at
all
with the adjustment control or is it just at -140 all the time?
The adjustment does affect the -150 output voltage.

I'm going to have a cold one and pore over the power supply schematic,
again. However, I'm hoping that you'll effortlessly say, "Ah-Ha! You
obviously failed to check ..."

Again, thanks for all of the help. If this scope didn't have so much
character, and if I didn't really want it to be part of my bench, I'd go
back to working on my superhet.

Sincerely,
stan


Stan & Patricia Griffiths <w7ni@...>
 

OK Stan,

I have inserted some more comments below:

----- Original Message -----
From: "stan mcintosh" <mcintosh@triad.rr.com>
To: "Stan & Patricia Griffiths" <w7ni@easystreet.com>; "TekScopes"
<TekScopes@yahoogroups.com>; <morriso@vifm.org>
Sent: Tuesday, November 04, 2003 6:11 PM
Subject: Re: [TekScopes] Tek 310 and Looking for Advice


I have one more in a box, but I decided that an 83.5 volt drop
tube would work for checking out a few of the other items.
***That's probably close enough to make it work . . . I have a bunch of
5651's if we need one that's closer.

Are the power supplies "regulating"? That is, do the voltages remain
the
same as the line voltage is varied from 105 to 125 VAC? If you don't
have
a
metered variable line voltage source, now is the time to get one.
Here is where we see some differentiation. From 105-125VAC input: the
+100
V regulates right at 59V, the -150 regulates at -139, and the +300 swings
from 270 to 290. I don't have a metered line voltage source, but I do
have
a voltmeter for making such measurements when using a Variac input.
***A Variac with an outboard meter attached is good enough. You can vary
the line voltage and you know about how much it is. That's all you need.

How much "ripple" is on each supply? Is is about the amount stated in
the
manual calibration procedure? (10 millivolts)
The ripple values in the +300, +100, and -150 are 3 mV, 1 mV, and 3 mV,
respectively.
***Wow! That's pretty low ripple but the lower the better. It seems a
little strange to me that you could have such low ripple on the +300 supply
and it still varies from 270 to 290 when you vary the line voltage from 105
to 125 VAC . . .

As you try to set the -150 volt power supply on -150, can you vary it at
all
with the adjustment control or is it just at -140 all the time?
The adjustment does affect the -150 output voltage.
***But apparently you can't bring it up (or down) to -150. The next thing I
would check are the precision resistors on both ends of the -150 adjustment
pot. This would be R609 (56.5K) and R611 (68K). These need to be close to
those values. You should also check R669 (1meg) and R670 (490K) in the +300
supply for 1% accuracy and they need to be right on.

Bear in mind that the -150 and +300 supplies depend on each other and they
must both work for either one of them to work. Concentrate your efforts on
these two supplies and make them both work before you look anywhere else for
other problems. The +100 will not work unless both the -150 and +300 are
working but the +100 does not need to work for the -150 or +300 to work.

I'm going to have a cold one and pore over the power supply schematic,
again. However, I'm hoping that you'll effortlessly say, "Ah-Ha! You
obviously failed to check ..."

Again, thanks for all of the help. If this scope didn't have so much
character, and if I didn't really want it to be part of my bench, I'd go
back to working on my superhet.

Sincerely,
stan
***Well, Stan, the 310 and 310A are both gems in my opinion and well worth
the trouble to make them work.

Stan
w7ni@easystreet.com


Craig Sawyers <c.sawyers@...>
 

The ripple values in the +300, +100, and -150 are 3 mV, 1 mV, and 3 mV,
respectively.
***Wow! That's pretty low ripple but the lower the better.
I've been fooled by this too - the numbers that Tek quote on the schematic
are peak-peak values, whereas what is measured on a meter is the rms value.
Perhaps that expains the difference?

Craig


stan mcintosh <mcintosh@...>
 

With respect to ripple measurements, all I can say is oops. I was measuring with a true RMS meter, but my results were thus off by a factor of 2.8. So, the +300 and -150 are within the 10 mV spec, but just barely. The +100... well, seeing as it's under 60 volts, I'm not sure it counts.

I'll check the resistors. I'm starting to really suspect that one has drifted, or something has drifted, based on my 5651 results. All of the tubes I tried were NOS, warfare-grade tubes. I'm wondering if the circuit is off and the tube is not being fed properly.

As another thought, I may break out the +300V supply to -150, and feed from an outboard source. Well, this depends on whether the resistor hunt turns up anything. A 300V source indepenent of the -150 should help bless or curse the -150, right?

Thanks for the suggestions, Stan G.; I'm going to work my way through them. I'm grateful for this group. Without it, this scope wouldn't have had a chance.

Sincerely,
stan