Re: 7D20 with unknown options or mods
Richard,
I can consult my micro fiche file for factory modifications. It's a bit tedious and slow to paw through the film, but I'll have a look.
Clark
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Re: Help Troubleshooting 466, No +15VDC
Our favorite way was to use a HP 2100 power supply 5VDC at 50Amps. Finds¡¯um every time
Regards,
Stephen Hanselman
Datagate Systems, LLC
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On Sep 9, 2020, at 07:00, Martin <musaeum@...> wrote:
?Hello Sparky,
my preferred method for instant finding of shorts in these caps is with my IR-Cam.
You may supply the +15V rail with a current limited supply, or shortly apply mains power - the component will instantly reveal itself.
IR-cams are getting more and more accessible, perhaps you can borrow one?
cheers
Martin
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Re: Tek 4654M; No Trace, No +5V, No +95V; Help
Harrison,
When my U550 failed, I got one from Sphere. I don't think they were listed on his site but, at least at that time, had some pulls from working scopes. You might check there if you still suspect it is in that module.
Thanks,
Barry - N4BUQ
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----- Original Message ----- From: "Harrison" <buma7@...>
To: [email protected]
Sent: Wednesday, September 9, 2020 3:47:17 PM
Subject: Re: [TekScopes] Tek 4654M; No Trace, No +5V, No +95V; Help
I am afraid that I have been jumping around too much and now, even with good
shop notes, am not sure what elements/modules I think are good and which
might be bad. Looking at the troubleshooting diagrams every thing still
points to the HV power supply. Currently there doesn't seem to be any out
there so it is a case of building a complete unit or repairing what is
there. I am coming close to declaring this unit a parts machine and closing
the book on it but I hate to do so. A repair might be right around the
corner or I am missing the obvious and the fix is staring me in the face.
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Cleaning Leads of IC Chips (Tektronix Related)
I am preparing to remove the Dallas DS1742W-150 NVRAM chip with dead lithium cell from my scope. My plan is to add a low-profile socket, then to cut-out the dead cell and extend the connections to a separately located replacement. Is there a favorite way of cleaning up IC leads (other than with vacuum devices) so as to improve the connection reliability of the reinstalled chip. I have heard Chinese resellers sometimes use a hot peanut oil bath for this purpose.
Bruce, KG6OJI
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Re: Tek 4654M; No Trace, No +5V, No +95V; Help
I am afraid that I have been jumping around too much and now, even with good shop notes, am not sure what elements/modules I think are good and which might be bad. Looking at the troubleshooting diagrams every thing still points to the HV power supply. Currently there doesn't seem to be any out there so it is a case of building a complete unit or repairing what is there. I am coming close to declaring this unit a parts machine and closing the book on it but I hate to do so. A repair might be right around the corner or I am missing the obvious and the fix is staring me in the face.
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Re: Help Troubleshooting 466, No +15VDC
Hello Sparky,
my preferred method for instant finding of shorts in these caps is with my IR-Cam.
You may supply the +15V rail with a current limited supply, or shortly apply mains power - the component will instantly reveal itself.
IR-cams are getting more and more accessible, perhaps you can borrow one?
cheers
Martin
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Re: 7D20 with unknown options or mods
Ok,
But there was an option on the 7D20 that made it work with
the 7854 digital storage scope. Perhaps that is the option
you seek?
-Chuck Harris
Clark Foley wrote:
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Chuck,
The 7D20T did not require anything extra from the 7D20. Any production 7D20 will function in the T package without modification. You could add the rear access cable for the GPIB that had a companion mod for the R7603. The mainframe for the 7D20T has the necessary 7k interface, rear GPIB wiring and power in a TM5003 skin (the notorious modular package system (MPS)).
Regards,
Clark Foley
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Re: Help troubleshooting a 2710 SA
From my experience with these, certain PCB revisions have an issue in the EHT section; on one I've repaired, there had been creepage and flashover in the high resistance potential divider chain which caused a cascade of power supply faults. Have a look at the back left corner of the power supply board to seeif there is any sign of burning (under the perspex cover)
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'Osculation' ???? (Sorry, couldn't resist it !!!) Tim On Wed, 9 Sep 2020 at 00:52, fauffing via groups.io <fauffing= [email protected]> wrote: I believe I've narrowed the issue to the probe tip, as you've suggested.
Seems hitting it with a shot of cold air will calm the oscillation for a
short period of time. The probe tip seems to be an amplifier microcircuit
in the P6249 with 4 capacitors. The microcircuit had some red/rust color
material on the traces, and I am leaning to corrosion as a potential
contributor to the problem. Capacitors or microchip degradation may also be
contributors. The tip is very well contained within the housing, and easily
destroyed in attempting removal. There is a small, maybe 1/8" hole in the
housing covered by a piece of tape. The traces of the circuit can be
accessed at this point, with the remainder of the microcircuit well
contained in the housing. It does not seem to be easily repairable. I have
not been able to make further progress, and am not willing to sacrifice my
remaining two probes, as even with the osculation, they are usable at
higher frequencies.
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Re: 7D20 with unknown options or mods
Chuck,
The 7D20T did not require anything extra from the 7D20. Any production 7D20 will function in the T package without modification. You could add the rear access cable for the GPIB that had a companion mod for the R7603. The mainframe for the 7D20T has the necessary 7k interface, rear GPIB wiring and power in a TM5003 skin (the notorious modular package system (MPS)).
Regards,
Clark Foley
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Re: Strange Tek2440 issue
Ok, here's where I'm at.
ALL of the electrolytics, except the two big ones in the back, have been replaced. I tested them and they were all good with very low ESR so I'll toss them in a box for now.
Q870 and Q879 have been replaced. Had to order these.
All resistors in the 5V Regulator have been checked and are all well within spec.
The few small caps (.001uf) were also checked and are right on.
Problem still exists.
Before I was toying around with the idea of hanging an external 5V supply on it. I did try that last week and it did NOT do it and according to the meter on the supply, it wasn't really drawing much current from it - less than 100ma.
Tomorrow I'll go thru the supply again and take more measurements, there were a few points I was looking at and couldn't remember if I checked them and if so what they were. So tomorrow I'll check them and take pictures and better notes.
That's it for tonite.
Vince.
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On 09/02/2020 02:50 PM, Siggi wrote: On Wed, Sep 2, 2020 at 2:07 PM Vince Vielhaber <vev@...> wrote:
I had actually done that last nite, but didn't have the parts layout
handy to see which probe was on which pin (I had them on the diodes>.
Here they are with voltage measurements:
Uh, this makes no sense to me.
The base of Q870 should be pulled toward +15V unreg through R864(? hard to
read on the schematic), and the two op amps shunt it towards ground when
they detect too high voltage or too high current, respectively. Whichever
of pins 1/7 is lower is the op-amp in control of the output.
... time passes ...
Yeah, still doesn't make sense to me. I'm going to guess that either the
op-amps are (pins 1/7 are) reversed on the schematic, or that your channel
designations are.
Even so, it still doesn't make sense, as the voltage-control op-amp starts
dialing more voltage (Channel 2 normal at 5.54V rises to 16.94V), while the
current limit op-amp goes on the limit (Channel 1 normal at 16.76V dips to
6.16V). What doesn't make sense here is that the current control op-amp is
dialing a voltage that exceeds the voltage control's usual/normal voltage.
I haven't done the maths, but as there's a bias on the current limit
op-amp's feedback input, it might be that it's simply kicking in because
the output voltage has sagged.
I think you need to look further afield, how's the +8V rail doing,
the +-15V rails, raw and regulated? How is the -5V rail doing? Any other
rails you can find...
If you can't find a bad rail, start looking at the biasing for Q870 & Q879,
have the resistors drifted? If R864(?) or R478 have drifted significantly
upward, that'd explain why the transistors can't meet the current demand.
If the biasing is OK, you need to look at the transistors themselves. If
their gain is down, that'd also explain things. You can measure the base
current to Q879 indirectly by the voltage drop over its base resistor. Even
looking at what's happening on Q870's emitter under collapse - is that
transistor going to saturation, indicating that Q879 is dozing off on the
job?
Good luck!
--
K8ZW
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I am having issues with a 2445 Oscilloscope that is not showing the A horizontal sweep. The ¡°B¡± sweep appears when the B delayed time base is used. The readout shows some dots on the bottom line of text on the CRT. And the A sweep appears to have a starting dot which is offset to the left of the CRT.
I had wondered if the 2445 has issues with the horizontal output hybrid (as the ¡°A¡± sweep is offset to the left) or the Z-axis hybrid (as there are dots on the CRT). As the ¡°B¡± sweep and readout appears however this seems to imply that the horizontal output hybrid may be working? I am not sure is there could be a failure mode of the horizontal output hybrid which results in the ¡°A¡± sweep not appearing.
I have swapped the ¡°A¡± and ¡°B¡± sweep hybrids which did not resolve the issue.
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I believe I've narrowed the issue to the probe tip, as you've suggested. Seems hitting it with a shot of cold air will calm the oscillation for a short period of time. The probe tip seems to be an amplifier microcircuit in the P6249 with 4 capacitors. The microcircuit had some red/rust color material on the traces, and I am leaning to corrosion as a potential contributor to the problem. Capacitors or microchip degradation may also be contributors. The tip is very well contained within the housing, and easily destroyed in attempting removal. There is a small, maybe 1/8" hole in the housing covered by a piece of tape. The traces of the circuit can be accessed at this point, with the remainder of the microcircuit well contained in the housing. It does not seem to be easily repairable. I have not been able to make further progress, and am not willing to sacrifice my remaining two probes, as even with the osculation, they are usable at higher frequencies.
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Re: Tek TDS694C advice pls
On Tue, Sep 8, 2020 at 11:25 PM, Bruce Griffiths wrote:
Wrong, when calculating the impedance of a parallel R +C the 90 degree phase
shift should be taken into account.
The input impedance is actually closer to 550 ohms.
You're of course absolutely correct about the numbers in my example, Bruce. My approximation is only valid if R >> 1/(2 * pi * f * C), in which case R as a parallel R may be ignored. In my example it obviously isn't. My "calculation" gave a wrong result, as you indicate. My example would yield about 550 Ohm, as you say, and a phase angle of - 56 degrees. Thanks for waking me up! The main point that I was making, i.e. it's not so much the R but the C-dominated Z that makes the P6249 the better choice at high frequencies, remains valid of course. Raymond
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Re: Tek TDS694C advice pls
Wrong, when calculating the impedance of a parallel R +C the 90 degree phase shift should be taken into account.
The input impedance is actually closer to 550 ohms.
Bruce
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On 09 September 2020 at 07:56 Raymond Domp Frank <hewpatek@...> wrote:
On Tue, Sep 8, 2020 at 09:21 PM, Ray wrote:
On second read I checked the specs of the P6249.??So it is active (Fet) and
has higher input resistance (20 kohm) then the P6158 (1 kohm)So the P6249 will
do less loading of the measured circuit.
At higher frequencies the P6249 is a lighter load than the P6158, not because of its 20 kOhm parallel resistance vs. the P6158's 1 kOhm, but because its input capacity is significantly lower (< 1 pF) vs. the P6158's (1.5 pF).
Because of the much lower input capacitance of the P6249, its impedance decreases much slower than that of the P6058 with increasing frequency.
Be aware that at 160 MHz, the input Z of the P6249's input capacitance (if 1 pF) is around 1 kOhm, the same as the P6158's input-R. Input-R is unimportant at higher frequencies, as always with parallel capacitances. The input-Z of the P6158 at 160 MHz is about 670 Ohm, parallelled with 1 kOhm, so 400 Ohm.
Raymond
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Re: Tek TDS694C advice pls
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Thank you Raymond, learned something new today.RaySent from my T-Mobile 4G LTE device------ Original message------From: Raymond Domp FrankDate: Tue, Sep 8, 2020 14:56To: [email protected];Cc: Subject:Re: [TekScopes] Tek TDS694C advice plsOn Tue, Sep 8, 2020 at 09:21 PM, Ray wrote:
On second read I checked the specs of the P6249.??So it is active (Fet) and
has higher input resistance (20 kohm) then the P6158 (1 kohm)So the P6249 will
do less loading of the measured circuit.
At higher frequencies the P6249 is a lighter load than the P6158, not because of its 20 kOhm parallel resistance vs. the P6158's 1 kOhm, but because its input capacity is significantly lower (< 1 pF) vs. the P6158's (1.5 pF). Because of the much lower input capacitance of the P6249, its impedance decreases much slower than that of the P6058 with increasing frequency. Be aware that at 160 MHz, the input Z of the P6249's input capacitance (if 1 pF) is around 1 kOhm, the same as the P6158's input-R. Input-R is unimportant at higher frequencies, as always with parallel capacitances. The input-Z of the P6158 at 160 MHz is about 670 Ohm, parallelled with 1 kOhm, so 400 Ohm. Raymond
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Re: Tek TDS694C advice pls
On Tue, Sep 8, 2020 at 09:21 PM, Ray wrote:
On second read I checked the specs of the P6249.??So it is active (Fet) and
has higher input resistance (20 kohm) then the P6158 (1 kohm)So the P6249 will
do less loading of the measured circuit.
At higher frequencies the P6249 is a lighter load than the P6158, not because of its 20 kOhm parallel resistance vs. the P6158's 1 kOhm, but because its input capacity is significantly lower (< 1 pF) vs. the P6158's (1.5 pF). Because of the much lower input capacitance of the P6249, its impedance decreases much slower than that of the P6058 with increasing frequency. Be aware that at 160 MHz, the input Z of the P6249's input capacitance (if 1 pF) is around 1 kOhm, the same as the P6158's input-R. Input-R is unimportant at higher frequencies, as always with parallel capacitances. The input-Z of the P6158 at 160 MHz is about 670 Ohm, parallelled with 1 kOhm, so 400 Ohm. Raymond
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Re: Tek TDS694C advice pls
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On second read I checked the specs of the P6249.??So it is active (Fet) and has higher input resistance (20 kohm) then the P6158 (1 kohm)So the P6249 will do less loading of the measured circuit.RaySent from my T-Mobile 4G LTE device------ Original message------From: fauffing via groups.ioDate: Tue, Sep 8, 2020 07:19To: [email protected];Cc: Subject:Re: [TekScopes] Tek TDS694C advice plsHave you used the P6158 probes with this scope, and if you have, what are the drawbacks of the P6158 compared to the P6249? Thanks, - Frank
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Re: Help Troubleshooting 466, No +15VDC
There are a number of tricks.? One is to put a current limited supply on the +15.? Adjust the supply to +15 volts and the current limit to roughly between 50 ma to 100 ma.? Look for the lowest voltage across each capacitor.? Suspect the ones with the lowest voltage drop.? Bear in mind that in a parallel string fed from one end, the bad one and all the ones in the string after that would have the same voltage.
Another would be to take a current trace probe (HP made one), feed the line with a pulse train, and then see where all the current is going.
The third method is the LED test.? In a dark room, look to see what capacitor lights up like a dim LED, the dull red glow may be something you could observe.? Ditto if you had an infrared camera.? If there are any filter resistors (Tektronix frequently used a 10 ohm series resistor for isolation), check for damage.
Oh, and disconnecting boards to try to isolate to a particular board isn't a bad idea.
Harvey
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On 9/7/2020 3:18 PM, Sparky wrote: This 466 worked great for years, then suddenly I smelled something burning, and the fan stopped. All low voltages good on interface board, *except* for +15VDC. Reads about 4VDC, (and about 4 ohms to ground with power off....). If I leave power on past about 15 sec, I can smell something burning again, so I only power up long enough the check the voltages.
I'm thinking tantalum cap, but wondering a good way to isolate the offender? Assume the the +15VDC goes all over the scope, to other boards, so would be a bear to lift all tant caps one at a time. Thinking of breaking the trace somewhere near the PS source. Any other tips or likely suspects?
Thanks in advance!
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ebrucehunter
Martin
David C. Partridge
Raymond Domp Frank