Date   

Re: 519 -- broken rate generator; stuck at a very high frequency?

Chuck Harris <cfharris@...>
 

Hi Sean,

I know nothing about the 519, but I do know that tektronix
had a habit of making all sorts of configurations available
on similar scopes. The folks that would buy a 519 often
had divergent interests.

Look carefully for binding posts that should have a strap
connecting them. They could be on the front panel, or the
back.

There also could be other forms of strapping inside of the
scope. It should show up in the schematics.

-Chuck Harris

sdturne@q.com wrote:

Well, no dice there either. The transistor seems fine. I'm officially stumped. The contacts for the multiplier switch are working fine, establishes by the fact that the multivibrator is both running nominally (which also implies the two 6DJ8s are fine) and controllable by the multiplier switch and the cycles/sec pot. There's really not much else to this circuit...nothing could really go wrong with the charge line right? It's just a coil of coax.

Sean

On Sun, Oct 18, 2020 at 03:34 PM, @0culus wrote:


Couldn't find anything amiss...all the passives appear to be fine. I scoped
the multivibrator as shown in the schematic, and it is works fine. It responds
to the controls as it should. I reckon the problem is most likely the
avalanche transistor. Luckily, I also have a 577D1 now...

Sean





qex@groups.io

Reginald Beardsley
 

Generally I do not cross post, but it seems to me appropriate in this case. These are the lists where the people I admire hang out.

Some time ago I created the group, but only informed a single person that I had done so.  However, enough people found it and joined that I decided I should take it live.

This is intended to be a forum primarily for discussing QEX articles as that should save authors from repeating the same answers to multiple correspondents. 

However, I should also like it to serve as a forum for serious work on a variety of topics from modulation systems similar to FT8 to teaching how to design an HF amplifier or oscillator from scratch as opposed to simply copying older designs.  Experts conversing with experts and also taking the time to instruct novices. I am hoping for a substantial educational content.

The group is unmoderated.  Unless someone gets seriously outside the bounds of polite social behavior I have no intent of exercising any control unless compelled to do so.

It is also my hope that in conjunction with QEX becoming a print option for ARRL members it will help stimulate readership and advertising revenue to support QEX. I have requested that option and my ARRL membership hangs in the balance. I will continue to subscribe to QEX in print independent of whether I continue as an ARRL member.

It is my hope that this will help QEX develop the technical stature that QST once enjoyed. I have no interest in contests and trophies. I'd like to believe I am not alone in my passion for the technology of radio.

Have Fun!
Reg


Re: 519 -- broken rate generator; stuck at a very high frequency?

Sean Turner
 

Well, no dice there either. The transistor seems fine. I'm officially stumped. The contacts for the multiplier switch are working fine, establishes by the fact that the multivibrator is both running nominally (which also implies the two 6DJ8s are fine) and controllable by the multiplier switch and the cycles/sec pot. There's really not much else to this circuit...nothing could really go wrong with the charge line right? It's just a coil of coax.

Sean

On Sun, Oct 18, 2020 at 03:34 PM, @0culus wrote:


Couldn't find anything amiss...all the passives appear to be fine. I scoped
the multivibrator as shown in the schematic, and it is works fine. It responds
to the controls as it should. I reckon the problem is most likely the
avalanche transistor. Luckily, I also have a 577D1 now...

Sean


Re: 519 -- broken rate generator; stuck at a very high frequency?

Sean Turner
 

Couldn't find anything amiss...all the passives appear to be fine. I scoped the multivibrator as shown in the schematic, and it is works fine. It responds to the controls as it should. I reckon the problem is most likely the avalanche transistor. Luckily, I also have a 577D1 now...

Sean


Re: 'Tektronix Short Destroyer'

ditter2
 

I suspect this belonged to R. Michael Johnson, who managed TM5000 engineering when I started at Tek. My cube was directly across from his. He may have worked in portables engineering previously, as a label indicates.
There were many versions of “short destroyer” throughout the engineering and production areas at Tek. In the early days of multi-layer circuit boards, registration of the individual layers was not always perfect. Occasionally you would see a board where a ground plane layer is slightly mis-registered to where one or two pads are shorted to ground. The short destroyer could be used to attempt to burn out the short. Most employed a capacitor bank to store a charge to quickly vaporize the short. Applying low voltage at high current continuously tended to burn the board, whereas a quick zap with higher voltage would quickly vaporize the short without burning the board.

Steve


Re: 519 -- broken rate generator; stuck at a very high frequency?

Sean Turner
 

OK, I got the scope on it's side. That wasn't as hard as I feared, because the 519 is very much bottom heavy. Looking at the part of the rate generator circuit that is on the bottom side, I can see nothing obvious, so I'm going to do some measurements of the passives and see if anything sticks out.

Sean


Re: OT Hameg HM103 blanking

petertech99h
 

Jean-Paul,
Is the 68pf 2Kv cap a ceramic disk cap? Sounds like it is.  I can't remember the last I had a leaky disk cap!
If there is evidence of dirt, oil, old flux right around the cap, I would clean it instead.
If it is cracked or chipped then replace for sure!

Pete

On Sunday, October 18, 2020, 11:53:45 a.m. EDT, Jean-Paul <jonpaul@ix.netcom.com> wrote:

Hello again all!

Ray thanks for the PM,


I Have just posted schematic markup and trace image in album "HM103 Hameg"

I now suspect the 68 pF coupling cap C705 is leaky and has damaged the NPN transistor.

But am traveling and Limited in tools and parts to disassemble main board and replace the 68 pF 2kV caps.

Open to your kind advise!

Jon


Re: Is my Tek 468 beyond repair?

John
 

On Sun, Oct 18, 2020 at 05:10 PM, Roger Evans wrote:

Q760 and Q772 are PNP common emitter amplifiers, they have very close to unity
current gain and they conduct because their base is positive with respect to
the emitter so the BE junction is forward biassed. In XY mode (see page 3-26
of the manual) the sweeps are disabled, the BE junction should be reverse
biassed, there is almost no collector current and they just look like a high
impedance from the output side.
Thank you for that explanation. Much appreciated.

In analogue XY mode the X input comes via Q582/Q583 and the manual shows the
DC switching signals (+5V and -8V) to turn on this input (and disable the
sweep). So you need to check that the +5V, -8V switching signals are present
and that Q582, Q583 are OK.
Will check these out as well although I can confirm the presence of -8V at the input to R689, but also at the junction of CR679 and R679. There is also +15V at R380. I will do some more investigation and confirm the +5V input tomorrow.

You're looking at a configuration called common base (can be common base, common emitter, common collector). Common collector is an emitter follower, common emitter is what most people think of as a transistor amplifier.
Harvey, thank you also for such a detailed explanation.

I had read through the Detailed Circuit Description section in the Theory of Operation chapter of the manual. Details of X_Y operation are throughout the chapter and I picked up bits and pieces but your description fills in the blanks which is very helpful.

Note that the horizontal amplifier is playing with a current input, not really voltage.
Noted. I grasped the fact that there must be a variance in current between the two halves of the circuit when I found different voltage readings at the emitters of Q760 and Q772 but I wasn't quite sure what that meant.

Had you looked at Q781 and Q782? the trigger view offset voltage goes through a diode or so (as does the trigger view offset enable) and that contributes to the offset of the horizontal amplifier.
Yes I did swap them around to see whether the problem would shift to the opposite side. It did not. I also substituted the two ICs (U690 and U789) and checked that signals at the gates were as indicated. All looked good. However, I completely omitted to investigate the right hand side of Q781/Q782 including the inputs and diodes you mention. I will check that out and re-read your comments tomorrow morning when when my mind is fresh when hopefully this will all fall into place.


Re: Early 577 service manual needed.

 

The 22 ohm resistors are not for current sensing. They are just to connect the Kelvin sensing terminals to the device terminals when a non-Kelvin adapter is used.

--
Bob Haas


577D1 Phantom base current

DW
 

I have a 577 that has developed a interesting problem

It seems to be exclusive with transistors when the base terminal is used, when I am testing components such as diodes where only the base and collector are used there is no issue.

I included pictures that describe the problem or you can check the Tekscopes photos and look for 577 Phantom Base Current. Notice the first picture how there is a vertical positive offset on the IV curve, this doesn't appear to be normal. Notice the second picture where the step generator is set to single but some form of current exists. If I pull the transistor the phantom current disappears, if I install another transistor the same phantom current appears once more. If I adjust the step amplitude then I notice a proportional effect on the phantom current, increasing amplitude increases the magnitude of the phantom current. I have the offset controls disabled. Any thoughts on this, thanks

https://groups.io/g/TekScopes/photo/255355/0?p=Created,,,20,2,0,0


Re: Early 577 service manual needed.

Eric
 

Bob,

    I did not realize that the preferred was the 10X10 which was option 10. This was the 8 X 10 1.25cm I do have a newer model that is the 10 X 10. Dialing in the amp was adjusting the horizontal and vertical amps for the CRT. Also getting them balanced.  It might be reading a little off due to it not being the better CRT. If i check the 177 on the other curve tracer it reads correctly so I suspect the resisters are fine. Though on this 177 half of the 22 Ohm current scene resisters were burned in half.

Eric

On 10/18/2020 1:20 PM, robeughaas@gmail.com wrote:
Production serial numbers started at B010101, so B010124 is a production instrument, just a very early one. The suffix on the CRT part number designated different phosphors and graticule types. The preferred graticule for a 577 is 10x10 1 Cm centered horizontally. There is also a variant of this CRT that has an 8x10 1.25 CM graticule. Usable, but not the best. There is also probably a variant of this CRT with no graticule. Check the 154- RPR's on the vintageTEK website.

If by "dialing in the amps" you mean the vertical sensitivity on the higher-current ranges is wrong, check the high-current shunts, which are on a board plugged into circuit board in the 177 adapter. It's a piece of thin PCB material with scribe lines to adjust the resistances.



Re: Early 577 service manual needed.

 

Production serial numbers started at B010101, so B010124 is a production instrument, just a very early one. The suffix on the CRT part number designated different phosphors and graticule types. The preferred graticule for a 577 is 10x10 1 Cm centered horizontally. There is also a variant of this CRT that has an 8x10 1.25 CM graticule. Usable, but not the best. There is also probably a variant of this CRT with no graticule. Check the 154- RPR's on the vintageTEK website.

If by "dialing in the amps" you mean the vertical sensitivity on the higher-current ranges is wrong, check the high-current shunts, which are on a board plugged into circuit board in the 177 adapter. It's a piece of thin PCB material with scribe lines to adjust the resistances.



--
Bob Haas


Re: Is my Tek 468 beyond repair?

Harvey White
 

replies interleaved:

On 10/18/2020 11:09 AM, John wrote:
According to the Service manual, page 5-38 (volume 1 if you have the version split across volume 1 and volume 2) the service ROM is fitted in place of U565.

It has been 4 days and I seem to be no closer to solving the X_Y mode problem. Any help would be greatly appreciated.

For example, could someone please explain to me how Q760 and Q772 on the Horizontal Display Logic & A&B Sweep Generators diagram work. Both bases are connected to chassis/GND so how do they conduct?
You're looking at a configuration called common base (can be common base, common emitter, common collector).  Common collector is an emitter follower, common emitter is what most people think of as a transistor amplifier.

Look at Q772 for example, the transistor is PNP, so the emitter should be more positive than the base (base more negative than emitter).  It's fed through two resistors from the +15 volt supply.  the current going *in* to the collector will be about the same as the current going into the emitter (ignoring transistor beta).

so about 2.3K gives roughly 6 to 7 ma.  That same current will want to flow into the collector.  Looking at the horizontal amplifier, the base of the lower differential amplifier is the source (as well as any resistors connected to it from a negative supply).  What you see looking into the emitter is a very low impedance, so the waveform at point 65 generates a current that adds or subtracts from the emitter current on Q772, which then changes the collector current.

To turn OFF the sweep, Q781 is turned ON, which shorts the emitter to ground (VCE saturation on Q781 is less than VBE on Q772, so the transistor is off), killing the A ramp voltage/current into Q772, and effectively disconnecting the horizontal amplifier.

The first stage of the horizontal amplifier is a differential pair, which takes the input (which is effectively a current), mirrors it with the upper transistor, and runs a differential output to the plates.  All the magic is in that first stage.



With both traces centered both horizontally and vertically, the oscilloscope in analog mode and then switching to X_Y mode, test points 65 and 67 are both at +12.5V but Q772_e is at 160mV whereas Q760_e is at 45mV so there is a difference. The common point at Q740_c/Q772_c/U564_2 is at 180mV, rising to approximately 640mV when U564 (first stage of horizontal amp) is removed. I would have expected close to or at 0V at this point and as previously mentioned, grounding U564_2 brings the spot to dead centre which would tend to suggest that the horizontal amp, including U564 transistor array, ought to be fine.

If BOTH U564 and Q760/Q772 are removed, then this common point is at 0.02mA which demonstrates that other feeds into this point are having little or no effect. This is as expected because the position control is dead centre and no signal is being fed into the X or Y inputs.

This tends to suggest that the problem might be somewhere within the Horizontal Display Logic & A&B Sweep Generators sweep part of the circuit but I am not sure how to troubleshoot this.
Note that the horizontal amplifier is playing with a current input, not really voltage.

Had you looked at Q781 and Q782?  the trigger view offset voltage goes through a diode or so (as does the trigger view offset enable) and that contributes to the offset of the horizontal amplifier.

Harvey


Notwithstanding, when U564 is plugged back in without Q760/Q772 being present, the voltage at the common point drops to -170mV so its presence/abscence does affect the balance of the circuit. Consequently, I am not sure whether the transistor array is leaky or whether the problem is at the earlier stage or whether both parts of the circuit are contributing to the problem but I suspect it to be related to Q760/Q772 and that part of the circuit. Swapping or substituting those transistors has no effect.

The scope otherwise operates perfectly fine in triggered modes.





Re: Is my Tek 468 beyond repair?

 

On Sun, Oct 18, 2020 at 06:10 PM, Roger Evans wrote:


Q760 and Q772 are PNP common emitter amplifiers, they have very close to unity
current gain and they conduct because their base is positive with respect to
the emitter so the BE junction is forward biassed.
That should be *negative* for PNP's.

Raymond


Re: Is my Tek 468 beyond repair?

Roger Evans
 

Q760 and Q772 are PNP common emitter amplifiers, they have very close to unity current gain and they conduct because their base is positive with respect to the emitter so the BE junction is forward biassed. In XY mode (see page 3-26 of the manual) the sweeps are disabled, the BE junction should be reverse biassed, there is almost no collector current and they just look like a high impedance from the output side.

If you look at the outline of the X amplifier on page 3-26 there are three inputs to the X amplifier all connected to the base of U564A. According to the operating mode two of the inputs should be 'off' ie high impedance and the X signal comes from whichever input is active. If the display is OK in normal Y vs time, sweep mode then the X amplifier from U564A/B onwards looks OK.

In analogue XY mode the X input comes via Q582/Q583 and the manual shows the DC switching signals (+5V and -8V) to turn on this input (and disable the sweep). So you need to check that the +5V, -8V switching signals are present and that Q582, Q583 are OK.

Roger


Re: OT Hameg HM103 blanking

Jean-Paul
 

Hello again all!

Ray thanks for the PM,


I Have just posted schematic markup and trace image in album "HM103 Hameg"

I now suspect the 68 pF coupling cap C705 is leaky and has damaged the NPN transistor.

But am traveling and Limited in tools and parts to disassemble main board and replace the 68 pF 2kV caps.

Open to your kind advise!

Jon


Re: Is my Tek 468 beyond repair?

John
 

According to the Service manual, page 5-38 (volume 1 if you have the version split across volume 1 and volume 2) the service ROM is fitted in place of U565.

It has been 4 days and I seem to be no closer to solving the X_Y mode problem. Any help would be greatly appreciated.

For example, could someone please explain to me how Q760 and Q772 on the Horizontal Display Logic & A&B Sweep Generators diagram work. Both bases are connected to chassis/GND so how do they conduct?

With both traces centered both horizontally and vertically, the oscilloscope in analog mode and then switching to X_Y mode, test points 65 and 67 are both at +12.5V but Q772_e is at 160mV whereas Q760_e is at 45mV so there is a difference. The common point at Q740_c/Q772_c/U564_2 is at 180mV, rising to approximately 640mV when U564 (first stage of horizontal amp) is removed. I would have expected close to or at 0V at this point and as previously mentioned, grounding U564_2 brings the spot to dead centre which would tend to suggest that the horizontal amp, including U564 transistor array, ought to be fine.

If BOTH U564 and Q760/Q772 are removed, then this common point is at 0.02mA which demonstrates that other feeds into this point are having little or no effect. This is as expected because the position control is dead centre and no signal is being fed into the X or Y inputs.

This tends to suggest that the problem might be somewhere within the Horizontal Display Logic & A&B Sweep Generators sweep part of the circuit but I am not sure how to troubleshoot this. Notwithstanding, when U564 is plugged back in without Q760/Q772 being present, the voltage at the common point drops to -170mV so its presence/abscence does affect the balance of the circuit. Consequently, I am not sure whether the transistor array is leaky or whether the problem is at the earlier stage or whether both parts of the circuit are contributing to the problem but I suspect it to be related to Q760/Q772 and that part of the circuit. Swapping or substituting those transistors has no effect.

The scope otherwise operates perfectly fine in triggered modes.


FTAGH: National Instruments DAQCard DIO-24 PCMCIA digital I/O card and cable

Oz-in-DFW
 

Free to a good home: National Instruments DAQCard DIO-24 that I can no longer use. It's a PCMCIA digital I/O card. I no longer have any laptops with PCMCIA slots. Yours if you want it. It's complete with interface cable and docs.

Pick up in Southlake, TX or for the cost of shipping. I'll ship outside the US if you accept any risk and pay additional fees it involves.

Oz (in DFW near the airport.)


Re: OT Hameg HM103 blanking

Ray
 

Jean,Well ... I can attest that Hameg scopes and owners :) also exist in the US.As I used to own a 204 and still own a 507.Alas I have not run into the specific problem you discribe.By they way the button labeled CT activates a build in component tester. It puts pn junction curves as well as capacitor and res respomses onto the screen. (In circuit as well)One of the reasons I got the 204 & the 507 which also have this.This function alone is worth fixing your 103.Bon chance.RaySent from my T-Mobile 4G LTE device------ Original message------From: Jean-PaulDate: Sun, Oct 18, 2020 03:16To: TekScopes@groups.io;Cc: Subject:[TekScopes] OT Hameg HM103 blankingBonjour a tous:

Have a Hameg HM103 scope found at a flea market in Paris for EU7, dead unblanking circuit but otherwise OK.

I have replaced the optocoupler, CQY80N, NPN, BF199 PNP BF440, and checked resistors and trimpot, all are fine.
Blanking logic input pulse OK, so quite a puzzle.

Last possibility: leaky coupling caps 68pF/2kV, I have seen many posts on EEVblog referring to their failure.
But I have no way to test caps here. I have only a variac, VOM and soldering iron!

I ask any Hameg veterans (perhaps in Germany or elsewhere in EU) to please inform me:

Could a failed cap just kill blanking, but scope works fine and traces is good otherwise?
How to diagnose if a cap has failed?
Will a failed 68 pF/2kV kill the semiconductors?
where else to look for the problem?

Your assistance is greatly appreciated!

Jon


OT Hameg HM103 blanking

Jean-Paul
 

Bonjour a tous:

Have a Hameg HM103 scope found at a flea market in Paris for EU7, dead unblanking circuit but otherwise OK.

I have replaced the optocoupler, CQY80N, NPN, BF199 PNP BF440, and checked resistors and trimpot, all are fine.
Blanking logic input pulse OK, so quite a puzzle.

Last possibility: leaky coupling caps 68pF/2kV, I have seen many posts on EEVblog referring to their failure.
But I have no way to test caps here. I have only a variac, VOM and soldering iron!

I ask any Hameg veterans (perhaps in Germany or elsewhere in EU) to please inform me:

Could a failed cap just kill blanking, but scope works fine and traces is good otherwise?
How to diagnose if a cap has failed?
Will a failed 68 pF/2kV kill the semiconductors?
where else to look for the problem?

Your assistance is greatly appreciated!

Jon

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