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Yes, Jaap option 12 is installed. I think you are right about that high valve. Do you think the VR board or the Log board alignment can reduce that valve? Thank you so much for taking the time to review the data.

Ken

The one who's going to charge the most is the one who's going to move the most while being the most insulated from the ground. If we analyze the different protagonists present:
A rack presenting the products for sale, which doesn't move at all. It can only be charged by someone or something touching it.
A cart that moves with 4 wheels that turn around an axis with 4 ball bearings. There is very little friction, so there will be very little charge from the cart.
A man who pushes the cart and/or abandons it from time to time. Depending on the type of shoe used, it's usually the man who charges more often, and who also has a higher capacitance (around 80 to 120 pF) than the cart. This means it can accumulate larger charges.

Women in high heels often charge even more than men. They often wear nylon clothing, which helps to explain the rapid accumulation of charges, but above all, for an equivalent quantity of charges, if wearing heels reduces the capacity in relation to the ground by a factor of 2, then the resulting charge voltage is multiplied by two!
Now, I don't think the accumulated energy is capable of lighting up a neon light. And even if it could, the discharge time is so short (10 to 20 ns) that it seems impossible to have time to see anything.

If we take the most violent discharge that a human can achieve, the energy accumulated at 20 kV in 100 pF represents 0.02 joules. The smallest neon light requires 0.3 mA at 90 V to light up, which represents 0.027 joules. So I remain extremely dubious as to whether we can achieve the desired result.

F1EKU

Where do you live?? Have 1L5,10,20.? Have 1s2.? I'm about 3 miles south of Lake Michigan.

Hello Ken,
Looking at your pictures I assume you have the extra filter board (100kHz, 10kHz and 1kHz). Its on the left side of the analyzer, left to the tube. Is that correct?

And comparing your values to mine I notice that you have one value at 3.0. Could that be a too high value to correct by the normalisation process? I don't know that, just a guess. But perhaps that particular filter (don't know which one) has a too amplitude responce?

Its all a whild guess from me. I think there is nothing written about these specific values.

Jaap

I have three different style covers that fit on the 2400 series instruments. The one with the high sides and indented center I suspect is specifically for the 2467 series but will fit on all 2400 series.
Then there is a lower profile cover that is flat on face with clips to attach on the sides.
Then same idea except it has the black latch on sides. I think the black latch ones were for early model 2445 and 2465 scopes.
Send me PM if interested
Electronixtoolbox@...

Please check your email. I have one.
Sam
W3OHM

Barry,

I meant 43xx numbers.

Check the base voltages at Q4356 and Q4366. That will tell what the emitter voltage should be. See if the thermal balance is correct. That could alter the voltages.

Mark

On Tue, May 21, 2024 at 11:22 AM, Albert Otten wrote:

AUTO PP is not the best way to obtain a free running sweep (and not intended
to be so) since some noise as tigger signal is already treated as "adequate".
I tried a 7B80 in a similar way and at all position of LEVEL I get a
flickering, rather dim trace because of "false" triggering.

Well, *that's* a great data point! Maybe I should RTFM for the 7B70 and study what it says about operation in more detail; coming from the 475 world, AUTO PP is a bit unfamiliar, but I assumed it would be a sensible default as the uppermost setting. Since my other 7B70 and 7B85 don't behave this way, I further assumed this 7B70 was misbehaving.

AUTO should work well to get a free running trace when LEVEL is set outside
the range of the trigger signal. With just noise as trigger signal that range
is very small, so for merely a very small range of LEVEL settings you get
false triggering and a flickering, dimmer trace. For other settings you get
the brighter free running trace.

The range is very small for AUTO to trigger on noise (or whatever it is), and larger for AUTO PP (say 8:00 to 10:00 for AUTO PP, whereas AUTO has to be right on 8:30). It's annoying as the trace sometimes is so dim that it's invisible when I expect it to be free running. For the other timebase plugins, I can very rarely see a blip of the trigger light if I rotate it slowly, but it won't stay on like this one does. If I need to adjust my expectations, that's probably easier than adjusting the plugin :).

thanks,
Adam

Adam,

AUTO PP is not the best way to obtain a free running sweep (and not intended to be so) since some noise as tigger signal is already treated as "adequate". I tried a 7B80 in a similar way and at all position of LEVEL I get a flickering, rather dim trace because of "false" triggering.
AUTO should work well to get a free running trace when LEVEL is set outside the range of the trigger signal. With just noise as trigger signal that range is very small, so for merely a very small range of LEVEL settings you get false triggering and a flickering, dimmer trace. For other settings you get the brighter free running trace.
I understand that (in your case) 9 o'clock position for AUTO but not for AUTO PP.

Albert

Mark,

You list some 23xx resistors. I presume those were supposed to be 43xx, correct?

I have tried swapping at least one pair of the horizontal output transistors and didn't notice any difference. I may need to try swapping others further back up the line and see if I find anything.

I'm still puzzled about the higher-than-expected voltages at the collectors of the output pairs of transistors as well as the difference in the voltage and waveform level at the collector of Q4351. That voltage and waveform is that way for all three of my 7704As. I could understand a typo on the voltage (-5.8) but having the center voltage on the waveform the same thing seems quite odd.

Thanks,
Barry - N4BUQ

Like with my other post, will consider trades for a 3D printer. Need one for an upcoming school project.

I will also consider trades for a 3D printer. I will need one for an upcoming school project.

The covers are on eBay, but they have been selling for over $100.
They used to sell for around $40, suddenly the price went up to over $100 in unison.


Are you talking about the plastic strip that sticks on right above the BNCs?
I've never seen one missing. Next time I discard a cracked rear cover I'll try to save one for you.
Just PM me so I have your info.

--Victor

Barry,

Since the problem tracks boards, swap the four horizontal outputs to see if it tracks. If not, start with other pairs. On mine, resistors: R4340, R4342, R2358, R2366, R4370 and R4396 are 2W. Resistor R2348 is now 5W.

Mark

Hi Ozan,

Hi Barry,
If you remove Q4304 does horizontal shrink to normal beam-finder size?

That produces the same horizontal results as pressing the beam finder button.

Do you see -15V in beam finder mode, and ~ -14.3V (0.7V above) in normal mode
at base of Q4304?

Other possibilities:
- R4303 is open circuit, not turning off Q4304 in beam finder mode

R4303 checks good (100 ohms).

- R4304 went down in value or there is a short connecting mid point of
R4307/R4309 to -15V

From the junction of R4307/R4309, there's just the 100 ohms of R4304.

- R4301 went high in value and what you see normally is already compressed.

R4301 checks good.

- Bad solder/trace somewhere from connector N6 to base of Q4304

Would need to check closer for this but I'm pretty sure that's all good. I've checked voltages in/around that circuit as well as compared them to the other two scopes and don't see anything very much different between them.

Is it possible that the higher voltage at the collectors of Q4371/Q4356 and Q4395/Q4366 causes the trace width to be too "wide" which would cause the compression to have a lesser effect? As a follow-on question, is that voltage primarily set by the current from +100V -> R4371 -> R4370?

Ozan

Thanks again,
Barry - N4BUQ

On Mon, May 20, 2024 at 03:29 PM, n4buq wrote:

That part of the circuit was the first place I started looking. I think I
already tried it, but I just now went out to the shop and tried swapping Q4304
from the working scopes and the results don't change.

Thanks Ozan,
Barry - N4BUQ

I was expecting a dirty beam finder switch but since it followed the board
probably Q4304 has a C-E short.
Ozan

On Mon, May 20, 2024 at 11:19 AM, n4buq wrote:

I decided to try swapping the horizontal amplifier boards between two of

the

7704As and the problem followed the board. I expected it would but just
wanted to make sure it wasn't something else.

Thanks,
Barry - N4BUQ

I have three 7704As. In my latest one, when I press the Beam Finder, the
vertical part looks okay; however, the horizontal part doesn't compress

very

much at all and I don't know why. Looking at the traces at various

points

from

the input to output, they shift their baseline in very much the same way

as

the

other two scopes; however, the amplitude of the trace doesn't change very

much

- hence, the lack of reduction in the horizontal.

Two things I've noticed:

1) The voltage at the collectors of Q4373 and Q4356 is shown as being

+39V

(similarly, very close to the same for the right plate output transistors

Q4395

and Q4366); however, those collectors are measuring almost 10V higher in

this

scope. The base voltage is correct for both transistors, the 100V is

very

close, all the resistors check good (or, since they're in-circuit, at

least

the

same value in the other scopes). The reason I mention this is because I
presume that if this value is too high, then the circuit can't reduce the

sweep

properly but that might not be true.

2) The trace shown at the collector of Q4351 is centered at -5.8V;

however,

that

trace is "centered" at around 0V for all three scopes. The base voltage

is

correct and, since the voltage at the collector of Q4325 is shown, I

calculated

the value for the emitter voltage of Q4351 and it measures very close to

that

value. Also, the trace shown at the collector of Q4361 is shown centered

at

-11.2V but on my scopes, that's centered at about -8.2V. That might not

be

too

relevant but thought I'd mention.

Anyone know what might be going on with this? If the trace compressed
horizontally, I likely wouldn't have checked this circuit as closely but

since

it doesn't compress, then I keep looking for causes and looking for some
causes.

Thanks,
Barry - N4BUQ

Does anyone know where I can find a cover for a 2445? I finally got mine going a few days ago and would like something to protect the front. Also, does anyone know of a source for rear decals showing what the rear BNC connectors are? Or am I going to have to make a label?

As a professional user of coaxial cables I would not use LMR-240 for instrumentation - the solid inner conductor makes it too stiff. It also requires four rather expensive Times Microwave proprietary tools for prep and installation.
--
Dale H. Cook, GR/HP/Tek Collector, Roanoke/Lynchburg, VA

I started poking at this 7B70 again, now that the 7704A seems to be working reasonably well. I finally realized that it's triggering on false events, so I don't get a proper free-running trace.

With the mainframe set to RIGHT (empty) vertical, and 7B70 in B horizontal slot, trigger set to INT/AC coupled/AUTO PP or AUTO, setting the trigger pot to about 9:00 will cause the trace to flicker as it triggers on nothing. Probing around, I see a square pulse on base of Q309, and collector of Q181/Q182, but no waveforms earlier in the amplifier (e.g., base of Q170). The pulses are ~70 ms apart and 100 mV amplitude.

This is a low serial 7B70, so does not have the 6.8 pF cap across CR182/CR181. Adding a 10 pF cap there just moves the problem to another setting of the trigger pot. I immediately suspected the +15V supply to Q309 and VR304, but see nothing in it that lines up with the pulses; IIRC there's a 25 kHz or so waveform that I assume is the switching supply.

What would cause a ~14 Hz false trigger?

thanks,
Adam

Never heard of LMR240, mfg? Spec sheet?

Type of BNC connector and crimp tool contemplated?

Jon

I'm wondering if there's a logic probe available for the TDS 794D. In the manual it lists the P6408 for all of the scopes in that family, but the TDS 794D. Does anyone know for sure?