Re: 577 Curve tracer ringing CRT and noisy step generator
In cases where you need to measure a transistor (or other device) at
extremely low currents, electrical noise or hum pickup and inter-electrode
capacitance can become so great it completely swamps the curves you are
trying to see.
The filter solves part of this problem. The other part of the solution is to
switch the Collector Supply Polarity from NPN or PNP, which sweep the beam
at a 60Hz rate, to +DC or -DC respectively. Then you sweep the beam manually
at such a slow rate that you eliminate any capacitive coupling due to
inter-electrode coupling. The filter eliminates electrical noise or hum
pickup that might be causing you problems.
Of course, it helps to have the D1 Storage version of the 577 when you are
sweeping the beam manually, otherwise, as you sweep the DC voltage, how can
you capture the current curve that results? One solution that comes to mind
is to use a grease pencil to trace it on the screen :)
Storage is one good reason why a 577 is a better solution than a 576. The
other one is the 577 is almost 30lbs lighter than a 576 so it doesn't take
two people to pick it up onto a desk.
Dennis Tillman W7PF
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-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of
Dave Voorhis
Sent: Monday, April 22, 2019 12:34 PM
To: [email protected]
Subject: Re: [TekScopes] 577 Curve tracer ringing CRT and noisy step
generator
Thanks for the tip!
On 22 Apr 2019, at 21:23, Ed Breya via Groups.Io <edbreya@...> wrote:
The "filter on" position is useless except for very low sweep speeds
or manual scanning - not normal operation. I found the same sort of
thing when I was refurbishing the switches (Deoxit-treatment) in all my
577s, and thought it was a component failure. After attempting a "fix'"
it acted the same way. Then I looked into the manual more, and found
that this is what it does.
So, don't bother with this filter function for normal use.
Ed
-- Dennis Tillman W7PF TekScopes Moderator
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Re: Pacific Measurements or Wavetek 1038 System
Hi Dennis,
Thanks for the feedback.
Any ideas regarding the 5114 - D14 mainframe; why that number was skipped or who'd be the designers or subject matter expert(s) regarding that line of equipment?
Thanks again!
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Re: Pacific Measurements or Wavetek 1038 System
Hi,
The 5000 series mainframes were, in part, designed to be low cost products. As such they were very attractive to other manufacturers as the display portion of the product they developed. Often, Tek would have provided a way to OEM (Original Equipment Manufacturing) products like this to other companies at a substantial discount provided they were purchased in quantity. In these cases the company would or could private label them with their own logo. This is a common practice in the electronics industry.
Dennis Tillman W7PF
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-----Original Message-----
From: nonIonizing EMF
Sent: Monday, April 22, 2019 10:58 AM
Subject: [TekScopes] Pacific Measurements or Wavetek 1038 System
<SNIP> Interestingly, after acquiring the Pacific Measurements 1038 system, I
found the Tekwiki had a reference regarding using the D10 and D11
mainframes.
I noticed the D14 which I had wasn't noted as being Tektronix and found
the reference tekwiki page I found that alluded to wondering like me
and others... what happened to the 5114 - D14 and what is the story
behind?
Was this item developed by Tektronix or a team from and sold to Pacific
Measurements?
Does anyone know the story behind the development? -- Dennis Tillman W7PF TekScopes Moderator
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Re: Again a 7854 power supply beast to be repaired...
More. You can check diodes by making differential measurements across the diode. I found two bad power diodes this way. You can do this measurement while the unit is in tic mode. I found the diodes conducting in both directions!
G?ran
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Re: Again a 7854 power supply beast to be repaired...
You need a load of about 50W, possibly equally shared between positive and negative outputs. Either on the raw voltages or after the regulator board. You need to check all caps and diodes on the rectifier board, if you have not done this before. You can check diodes by making differential measurements across the diode. I found two bad power diodes this way.
G?ran
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Re: Again a 7854 power supply beast to be repaired...
Hi Max,
Well, I didn't say that the load MUST be distributed. For me reasons to do so were that I could use available 5 W and 10 W resistors and that I wasn't always sure about the maximum current an output could deliver. Your 10 W resistor will survive start attempts, but when an error has to be detected which tends to occur after several minutes then you have a problem.
I am really surprised that about 11 W was sufficient. IIRC in a 7904 the HV circuits are less easily to disconnect so maybe these formed a load also. At this moment I don't remember all the details, but I think 11 W would not even be enough to maintain the 7.5 zener voltage inside th IC. Anyway, over 50 W was my experience.
Albert
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To Albert:
I really don't know how a dummy load must be connected to raw outputs! Some
people told me to load +17V was sufficient, some others the +108, now you and
others say that the load MUST be distributed across the raw outputs! I'm
really confused now...
And yes, I've disconnected the supply to HV unit obviously... since the SMPS
block sits on my workbench, alone.
Some times ago (several months ago I suppose), a friend of mine fixed a 7904
SMPS; he told me that as a load he had connected a 20 ohm resistor on the +15
(regulated output) and nothing else and the smps worked ...
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Re: Again a 7854 power supply beast to be repaired...
To G?ran:
OK, shorted pin 13 to ground. Still same result: the SMPS refuses to starts and ticks herratically.
I've checked the signal across A and K of Q30 (the PUT): it fires up every 20 msec (I live in Italy) but there are some spurious pulses in between.
The pin 9 shows a steady +0.6V with sparse negative pulses going to approx 0 V.
To Albert:
I really don't know how a dummy load must be connected to raw outputs! Some people told me to load +17V was sufficient, some others the +108, now you and others say that the load MUST be distributed across the raw outputs! I'm really confused now...
And yes, I've disconnected the supply to HV unit obviously... since the SMPS block sits on my workbench, alone.
Some times ago (several months ago I suppose), a friend of mine fixed a 7904 SMPS; he told me that as a load he had connected a 20 ohm resistor on the +15 (regulated output) and nothing else and the smps worked ...
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Re: Again a 7854 power supply beast to be repaired...
In the archive there is another document "7k_PS_currents" describing typical loads, also scanned by Zenith. In my case the total load was 50W. I connected a number of power resistors to the various LV power supply outputs. It worked ok.
G?ran
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Re: Again a 7854 power supply beast to be repaired...
Hi Max,
From my own experiments with a 7704A SMPS I remember that it needed a much heavier load for proper operation. I tried with loads on the HV outputs and also with loads on the raw rectified outputs (LV disconnected). Other members (including G?ran) found similar results. Dennis in his recent 7104/7854 .docx file uses 70 W total, distributed over the LV outputs. So why do you think about 35 W is enough?
I guess you also disconnected the supply to the HV unit? (Some other readers might not know that the HV unit is a separate unit here, not buried deep inside the smps box.)
It has been noted that the documentation of the control IC is not very trustworthy.
[BTW your 10W resistor will be glad that the smps is not working continuously!]
Albert
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I remember you all the actual scenario:
I'm working with only boards A23 and A12 connected together.
The low voltage regulator board A22 was disconnected from the rest of power
supply, and there are no other connections (I pulled out connectors P52,P50
and P54 from A12 board to better isolate the problem).
I've put a dummy load across +17 and -17V (connector P52) , 33 ohm resistor 10
W, I think it's a reasonable load for the SMPS to start.
Max
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Re: 577 Curve tracer ringing CRT and noisy step generator
Thanks for the tip!
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On 22 Apr 2019, at 21:23, Ed Breya via Groups.Io <edbreya@...> wrote:
The "filter on" position is useless except for very low sweep speeds or manual scanning - not normal operation. I found the same sort of thing when I was refurbishing the switches (Deoxit-treatment) in all my 577s, and thought it was a component failure. After attempting a "fix'" it acted the same way. Then I looked into the manual more, and found that this is what it does.
So, don't bother with this filter function for normal use.
Ed
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Re: 577 Curve tracer ringing CRT and noisy step generator
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Re: Again a 7854 power supply beast to be repaired...
In the archive there is a document scanned by Zenith, a specification 155-0067-02, pdf. For pin 13 there shall be two conditions:
Logic "0": 0.0 - 0.05 V
Logic "1": 0.85 - 10 V
Well, if you dare you can short pin 13 to ground...
G?ran
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Re: 577 Curve tracer ringing CRT and noisy step generator
The "filter on" position is useless except for very low sweep speeds or manual scanning - not normal operation. I found the same sort of thing when I was refurbishing the switches (Deoxit-treatment) in all my 577s, and thought it was a component failure. After attempting a "fix'" it acted the same way. Then I looked into the manual more, and found that this is what it does.
So, don't bother with this filter function for normal use.
Ed
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Re: Again a 7854 power supply beast to be repaired...
Following the Goran suggestion, I've shorted to ground pin 2 (FAULT SENSE).
The behavior was the same: random burst interspersed with single pulses.
Probing with an oscilloscope the pin 13 (Current Sense) it shows a constant voltage of about +300 mV with random single peaks reaching +400 mV and sometimes some pulses of 20 ms duration with amplitude of +400 mV too.
I remember you all the actual scenario:
I'm working with only boards A23 and A12 connected together.
The low voltage regulator board A22 was disconnected from the rest of power supply, and there are no other connections (I pulled out connectors P52,P50 and P54 from A12 board to better isolate the problem).
I've put a dummy load across +17 and -17V (connector P52) , 33 ohm resistor 10 W, I think it's a reasonable load for the SMPS to start.
Max
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Pacific Measurements or Wavetek 1038 System
Hi all,
Interestingly, after acquiring the Pacific Measurements 1038 system, I found the Tekwiki had a reference regarding using the D10 and D11 mainframes.
I noticed the D14 which I had wasn't noted as being Tektronix and found the reference tekwiki page I found that alluded to wondering like me and others... what happened to the 5114 - D14 and what is the story behind?
Was this item developed by Tektronix or a team from and sold to Pacific Measurements?
Does anyone know the story behind the development?
I finally also got around to updating the wiki yesterday:
I'm still looking for more documentation regarding specifically the N10, NS20, NS201 and any other items not noted on the wiki (K13, V20, C10, etc.).
I did manage to find copies of the Instruction Manuals and/or Operation and Service Manuals for the D14, D14A, H10-13, V10-12 and will scan those with the new Brother MFC-9970CDW Color Laser All-in-One with Wireless Networking and Duplex that was given to me free a few days ago when I was up in Traverse City which has made scanning the first document I had (the Wavetek 6000 Computer for NS20) with a bunch of pages and double sided a breeze. I would also like a copy of the Wavetek 6000 Computer for NS20 application since the document doesn't list all the code if that is available.
I was thinking also adding diode information too for the detectors in at least a datasheet document if I can find.
I am also looking for any documentation related to the EDX-1 Electromyograph. If you have anything scanned or know of a reference. Please reply.
Also, feel free to reply with any question, comments and/or suggestions.
Kindest Regards
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Re: 577 Curve tracer ringing CRT and noisy step generator
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I've gotten this 7L5 worked over to where it is mechanically squared up and fits properly in the mainframe. It took a lot of blacksmithing and modifications, but it now looks good, and is apparently all functional except for still no video signal on screen - no noise floor or signal shows, just the baseline and clipper level traces are there. I've fixed and confirmed proper interconnections throughout the unit, and treated most with Deoxit, since there was evidence of corrosion here and there from damp conditions over the years.
I found a Zener broken from the damage - VR602, a 5.1V shunt regulator for U600 in the trigger circuit. I replaced it, and the triggering seems to work same as before. U600 or related circuitry may have been been damaged from over-voltage while that Zener was missing, but it does seem to be triggering and sweeping the same as before the fix, so I think the lack of video is due to something else.
I'll have to sort through it all, but just wondering if anyone has experience with this kind of trouble in the 7L5, that may lead to quicker diagnosis. It's all new to me. I do have the manual, but it is amazing how complicated this system is, and how so much stuff is jammed into the little box. It will be tricky to hunt down and access the signals needed. Any tips or shortcuts would be appreciated.
Ed
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Re: 7S12 with S-4 and S-53 troubleshooting
Hi Nenad,
I tend to disagree with your analysis. The feedback is not primarily intended to keep the base of Q36 at a constant DC level. Within limits Q36 doesn't care. The purpose is to have the bridge + and - bias voltages follow the S-4 input voltage. The only way to change Memory is a suitable AC pulse at the gate of Q36. We concluded already that the avalanche pulse alone is too slow to have effect. The same would be true when the Correction Memory "shakes" the bridge circuit voltages. Moreover, when S901 is Off then the Correction Memory is inoperable. Q960<15> is always conducting then and passing the Offset control voltage to U955 + input. Q954 is always conducting then and passing the forced-constant Corr Mem voltage to U955 - input. There are no pulses at the output of U955 and hence also not at pins 2 &B of S-4.
In the S-2 head some transistors sit in sockets and can easily be removed. Q55 provides the snap-off bias current and can safely be removed. With Q55 removed the S-52 Cert Signal Out was about +2 V and Offset had no effect.
If my analysis is correct then I am still confused about what was really going on in your S-4.
[The S-2 I used was sensitive for pressure at its front and sometimes the Vert Signal Out would also jump to +2 V because of that. In order not to be mislead by this I repeated the test now with the naked S-2 on a sampling head extender. That way I had better control over testing alternatingly with Q55 inserted and removed.]
Albert
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Re: Again a 7854 power supply beast to be repaired...
Hi, I worked on this PS in a 7904 some years ago. There are two overload conditions, over/under voltage and over current. Either shall turn the supply off. However, I think there is a third condition that will turn the regulator off which is not quite obvious. If you have arcing in the multiplier for example you will get sudden and random load changes and thus disturbances that will destroy the phase of the signal coupled to pins 10 and 11. The phase detector will go nuts and the regulator will turn off, I think.
Can you hear a hissing sound, if so it could indicate arcing?
Meanwhile, there are a couple of tests that you can do but it takes some courage. Short pin 2 (FAULT SENSE) and then pin 13 (ISENSE) to ground. If the behaviour remains the same then shut down is not triggered through these ports.
Carry on
G?ran
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Re: Searching for a Tek 7000 series scope
On 4/20/19 3:12 PM, [email protected] wrote: I think the next thing I need to find is a scope mobile cart I Have model 3 I can send you. What do you wan to pay? -- John
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G?ran Krusell