Hi All,
My TG501 1ns output died. I suspect it's CR515, the 4V hot carrier diode at the start of the 1ns section. It's just a rare sized barrier Schottky. If I understand the circuit correctly it adds some high frequency distortion by clipping the 2ns sine wave and then uses a series of LC circuits to filter out all but a clean 1ns sine wave. My question is how critical is the 4v reverse voltage and other specs in this application? Is there a suitable modern through hole replacement?
Thanks, Rick
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The Focus problem of my 465B has significantly improved by powering it down and unplugging it from AC power.
Caution: -Do the following steps at your own risk. Be sure to wear safety glasses and leather gloves.
Next the CRT socket pins are discharged to ground and the socket is Carefully pulled back away from the CRT base. This is to avoid sending DC to the High Voltage transformer.
Leave the ¡®scope switched off and disconnected from AC power during the whole process. Connect an external DC power supply voltage to a approximately 15 to 20 percent above normal rated 6.3 V filament. Note For my 465 the power supply was set to 6.3 V x 1.20 = 7.5 V to pins 1 and 14 directly to the CRT pins at the base of the CRT tube, not to the socket. Check the specs and schematics for your particular CRT. It could be different.
After an hour or so, everything was reassembled and the ¡®scope powered up with a much sharper trace.
Thanks to the guidance of members on this forum, I was able to get the 465 fully functional.
Harvey Parent
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Re: O.T. Digital scopes versus Tek analogue.
Well Sean I have three scopes on my bench right now.? Two digital and one analog.? When I want to use one of them, almost invariably I turn to the analog unit.? When I want to refine or verify a measurement I will fire up one of the digitals.
Having said that, I admit that the digital units have some very interesting and useful capabilities that are lacking in the analog.? But most of what I do doesn't require those capabilities.? Then again I am still only partway up the learning curve for digital.? My two digitals have very different characteristics, with the HP 54542A being a bit more likeable than the Tek.? It's faster and offers FFT for example.? The Tek is better at displaying an AM signal, for which the others require an external trigger.? I can save a screen on the HP to floppy disk and then print it from a computer.? (Remember floppy disks?)
Bob
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On Sunday, February 28, 2021, 03:26:16 PM PST, Sean Turner < [email protected]> wrote: Sounds like you found a great solution for you! And you found the advantage of tonnage. LOL!! I use a couple of Keysight megazoom MSOs loaded with options at work regularly. When I need to single shot trigger off some obscure protocol feature, they are fantastic and nothing old can replace them. For what I like to do in my home lab (which is largely analog on the whole), I prefer the old boat anchors. They are infinitely more satisfying to use, IMO. :o) And I sharpen my circuit design IQ every time I perform a repair or resurrect another bit of old test gear. Sean On Sun, Feb 28, 2021 at 02:08 PM, Michael wrote:
I have used Tektronix scopes since the 60s. They have always been the gold
standard, at least as far as I am concerned. Now my old Tek scopes, I have 4,
are getting old and keep requiring service. The 465Bs are particularly hard to
service. I hate having to remove the tube in order to get at parts. I have a
couple of the 2000 series, which are much easier to service. I spoke with an
old duffer like me who was working for Saelig. They sell test equipment. He
knew all about Tek scopes and their capabilities. I told him I would like to
buy their newer Siglent model 1202X-E (200 mhz dual trace), but I did not want
to see steps or noise on the display. Older inexpensive digital scopes have
that problem. He knew all about it and said I would love this model. Well, he
(John) was right. It shows a beautiful picture, plus the DC level, voltage of
the signal and frequency. It does other stuff that I keep off the display
because it just confuses me. This scope cost me about $400. The price of this
scope has increased a lot since last month. They are now $615. However,
Circuit Specialists are still selling their stock for $379 delivered. My first
1202X-E was so good I wanted another for backup so I could give away my other
analogue scopes and be done with servicing them. I managed to get an order in.
I hope they actually ship it at that price. I realize that Tektronix scopes
have an almost cult following. I have been part of that cult. At this point, I
am moving on to cheap and powerful. The only thing I don't like about the
scope is that it is too light. I will have to make some sort of frame and
fasten it down to my workbench. I want to be able to plug in and remove probes
without the scope moving away from me. The buttons have a light enough touch
that the scope remains steady when pushing buttons. I realize that my post
here might offend some, but I am just trying to let someone who might be
trying to put together a good workbench that there are choices other than
Tektronix. Again, I have been a believer in Tek scopes since the 60s. When I
went out to work on radars and sonars, I brought the very heavy 465B. I wanted
full capability when I was supposed to fix a misbehaving sonar on a ship or
submarine. These blue scopes have served me very well for decades.
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Re: 2465A CT Lessons and Leroy's Breadcrumbs
Hey Brian,
I just went thru a similar excursion with my 2467B. Only mine was more fun: I had my 'scope on and the fan seized. I didn't know it and I went out to eat and when I returned, it was stone cold dead. I removed covers and found nothing on J119. PS was dead. I removed the ps card and eventually found a shorted shottky diode. I replaced it and the fan then the ps was working but no CRT activity. I had noticed the upper RHS of board A5 (processor) had corrosion on the mounting screw. Kinda like something caustic had got to it. I Started reading this forum and came across the discussion of failing capacitors on the A5 board. I also noticed that I had a Dallas Semi timekeeper RAM that was over 20 years old. I thought that this one is either getting ready to go bad or already is so I found a new one on DigiKey. I replaced it this time adding a socket to the A5. Still no CRT. Eventually I found a -1.25 reference signal which was developed by the DAC on A5. That signal was around +0.1V. many circuits were dependent on this -1.25 reference. After probing signals on the DAC I concluded the DAC is bad. I ordered in a couple more DACs and replaced the one on A5. No help. I found a flow chart that included setting CRTs grid bias to get an image. I was able to turn it and get the CRT to light up. Out of focus and bright but at least something was there. Still I had no -1.25. J504 is a test jumper that forces circuits downstream of the DAC to be -1.25. When I moved this jumper to the test position, I could re-adjust the CRT bias and see some characters! But things needed to see the DAC working and it wasn't. So, now I started probing analog voltages feeding the reference levels into the DAC. They were correct at the components but clearly wrong on the DAC pins. There were missing connections between surface mounted parts and the DAC! One of those leaky (electrolyte wise) caps was near the resistor network for the reference current into the DAC. I ohm'ed out the DAC pads to the resistors and NO Connections!. The traces looked ok but clearly several were not connected. The solder masking on the board looked ok but the copper underneath was eaten away by capacitor ooze. So new caps, & new 30 gauge blue wire. Finally I have an image and TEST 04 FAIL 02. Time to re-cal. It took me about a day each and about 3 iterations to get it right. Then I had a CT failure and it was a separate cal.
In the end: My scope had SM caps that were ready to die, explosively. My fan quit which probably turned to case into an oven this probably encouraged the caps to squirt out their juice and the shottky to short. The RAM was probably ready to go anyway but replacing it required a re-calibration. I am up and running now: This started just before XMAS.
Many thanks go to Chuck Harris who is also a contributor to this forum. Without his help I probably would have round file'ed this machine.
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Re: Tektronix 606A that resists being repaired
Your post doesn't say if +20V at pin 5 of the transformer is checked but WF5 on your web page looks OK so +20V seems to be fine. Still worth checking. Question though. You mention that CR769 doesn't clamp if the voltage never
goes below 10V. I understand. But the voltage at R768 (on the side of C768)
definitely goes below 10V. So something on the other side of R768 (which is
the nexus of CR769, CR776 and R777) prevents that signal from going below 60V,
correct? That is also how I see it. However, looking at the waveforms I don't think it is something hard clamping to 60V, more like there is an undesired load (pulling above 60v) that is using up the charge coming from C768 before cathode of CR769 has a chance to go below 10V. Now that you removed the tube, you could try lifting R777 to figure out if the problem is to the right side of left side of R777. Could this be related to the voltage shift at C768? C768 is pure AC centered
around 0 when R768 is lifted but biased to 100V when R768 is connected?
This is expected. When R768 is lifted only DC path from right side of C768 is your probe, which has a DC path to ground. So average value will be at ground (0V). When R768 is connected your clamps (and undesired leakage) are providing DC path. Let's look at right side of R768: Its maximum is limited by top clamp at 110V (from your measurement), bottom is clamped at ~65V. The waveform is not symmetric so the average is more that (110V + 65V)/2=87V. You can ask the scope to give you an average value but ~ 100V is probably reasonable (more time is spent at 110V). Since this is the average (DC) value at the right side of R768, left side is at the same DC voltage because C768 doesn't pass DC current. Most likely one of the diodes CR776, CR782, CR780 went bad or leaky. Ozan
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Re: O.T. Digital scopes versus Tek analogue.
Sounds like you found a great solution for you! And you found the advantage of tonnage. LOL!!
I use a couple of Keysight megazoom MSOs loaded with options at work regularly. When I need to single shot trigger off some obscure protocol feature, they are fantastic and nothing old can replace them. For what I like to do in my home lab (which is largely analog on the whole), I prefer the old boat anchors. They are infinitely more satisfying to use, IMO. :o) And I sharpen my circuit design IQ every time I perform a repair or resurrect another bit of old test gear.
Sean
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Show quoted text
On Sun, Feb 28, 2021 at 02:08 PM, Michael wrote:
I have used Tektronix scopes since the 60s. They have always been the gold
standard, at least as far as I am concerned. Now my old Tek scopes, I have 4,
are getting old and keep requiring service. The 465Bs are particularly hard to
service. I hate having to remove the tube in order to get at parts. I have a
couple of the 2000 series, which are much easier to service. I spoke with an
old duffer like me who was working for Saelig. They sell test equipment. He
knew all about Tek scopes and their capabilities. I told him I would like to
buy their newer Siglent model 1202X-E (200 mhz dual trace), but I did not want
to see steps or noise on the display. Older inexpensive digital scopes have
that problem. He knew all about it and said I would love this model. Well, he
(John) was right. It shows a beautiful picture, plus the DC level, voltage of
the signal and frequency. It does other stuff that I keep off the display
because it just confuses me. This scope cost me about $400. The price of this
scope has increased a lot since last month. They are now $615. However,
Circuit Specialists are still selling their stock for $379 delivered. My first
1202X-E was so good I wanted another for backup so I could give away my other
analogue scopes and be done with servicing them. I managed to get an order in.
I hope they actually ship it at that price. I realize that Tektronix scopes
have an almost cult following. I have been part of that cult. At this point, I
am moving on to cheap and powerful. The only thing I don't like about the
scope is that it is too light. I will have to make some sort of frame and
fasten it down to my workbench. I want to be able to plug in and remove probes
without the scope moving away from me. The buttons have a light enough touch
that the scope remains steady when pushing buttons. I realize that my post
here might offend some, but I am just trying to let someone who might be
trying to put together a good workbench that there are choices other than
Tektronix. Again, I have been a believer in Tek scopes since the 60s. When I
went out to work on radars and sonars, I brought the very heavy 465B. I wanted
full capability when I was supposed to fix a misbehaving sonar on a ship or
submarine. These blue scopes have served me very well for decades.
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Re: TDS784C Signal Path Compensation Error
Well, the buyer has turned uncooperative, said something about just needing a scope to make some measurements on a current project, and has formally requested a return thru eBay. So it looks like I'm out about $120 worth of shipping, and will have a go at fixing the relays when it gets back here. Can anyone guide me as to what type relays, and how many, I need to be looking at? I have the service manual, but they don't seem to drill down to that level of detail. Also, is this a typical contact oxidation problem, that I might be able to clear by repeatedly cycling those relays? What's the best way to tackle this one?
Steve Hendrix
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At 2021-02-28 01:06 PM, EricJ via groups.io wrote: I will agree with Siggi on this one as far as one or more of those relays
being the likely cause. One of my TDS scopes had the same problem.
Replacing the relays he mentioned solved it. And yes he'll need to be
careful, the hybrid boards are made of pretty thin ceramic.
--Eric
On Sun, Feb 28, 2021, 9:19 AM Siggi <siggi@...> wrote:
Hey Steve,
The classic fault that causes SPC on these scopes is that the signal relays
on the input attenuator hybrids develop high resistance. They are used to
shunt in the internally generated calibration signal that's used for the
signal path compensation.
I replaced a few of those relays on my TDS784D, which cleared the problem.
The relays were readily available at the time, and I could readily measure
which relays were bad by a simple resistance measurement over the NC
terminals. Clipping the old relays out and soldering on the ceramic hybrid
was a little bit nerve wracking, but definitely very doable.
Siggi
On Sun, Feb 28, 2021 at 9:16 AM Steve Hendrix <SteveHx@...>
wrote:
A year or so ago I bought a TDS784C that seemed to be in pristine
condition except for a missing left rear foot. It powered up and
worked perfectly on every signal I tried it on. I found that I rarely
if ever had an actual need for its high bandwidth (1GHz) and I had
other scopes that met my needs with less bench space, so I sold it on eBay.
The buyer has been very polite and cooperative, but requests help
with finding a replacement foot, and also reports that he ran a
Signal Path Compensation which reported an error:
"A compensation error has occurred. Examine the error log and note
the message. Then refer this oscilloscope to a qualified service
technician for repair. It is possible to proceed by pressing Clear
Menu. The oscilloscope, however, may not perform according to
specifications."
According to the error log, this error has been present since 2007,
over a decade before i got hold of it.
Can anyone here offer suggestions?
Steve Hendrix
|
O.T. Digital scopes versus Tek analogue.
I have used Tektronix scopes since the 60s. They have always been the gold standard, at least as far as I am concerned. Now my old Tek scopes, I have 4, are getting old and keep requiring service. The 465Bs are particularly hard to service. I hate having to remove the tube in order to get at parts. I have a couple of the 2000 series, which are much easier to service. I spoke with an old duffer like me who was working for Saelig. They sell test equipment. He knew all about Tek scopes and their capabilities. I told him I would like to buy their newer Siglent model 1202X-E (200 mhz dual trace), but I did not want to see steps or noise on the display. Older inexpensive digital scopes have that problem. He knew all about it and said I would love this model. Well, he (John) was right. It shows a beautiful picture, plus the DC level, voltage of the signal and frequency. It does other stuff that I keep off the display because it just confuses me. This scope cost me about $400. The price of this scope has increased a lot since last month. They are now $615. However, Circuit Specialists are still selling their stock for $379 delivered. My first 1202X-E was so good I wanted another for backup so I could give away my other analogue scopes and be done with servicing them. I managed to get an order in. I hope they actually ship it at that price. I realize that Tektronix scopes have an almost cult following. I have been part of that cult. At this point, I am moving on to cheap and powerful. The only thing I don't like about the scope is that it is too light. I will have to make some sort of frame and fasten it down to my workbench. I want to be able to plug in and remove probes without the scope moving away from me. The buttons have a light enough touch that the scope remains steady when pushing buttons. I realize that my post here might offend some, but I am just trying to let someone who might be trying to put together a good workbench that there are choices other than Tektronix. Again, I have been a believer in Tek scopes since the 60s. When I went out to work on radars and sonars, I brought the very heavy 465B. I wanted full capability when I was supposed to fix a misbehaving sonar on a ship or submarine. These blue scopes have served me very well for decades.
|
Still TM500 extenders on ebay
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Re: TEK Equipment for Free
And poutine. I miss being able to drive up from Boston MA to spend a long weekend in The Great White North, Montreal, riding my bicycle, drinking beer. Not necessarily in that order. One of these days...
Arne
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Re: Tektronix 606A that resists being repaired
Thanks for your suggestions. I did the oscillator part first.
1. reducing the -5500 cathode voltage to -4400 V has no effect. Oscillation still stops at about 2 1/2 minutes
2. +120V and +30V (derived from the secondary of T710) are all good. I lifted R596 to reduce the 120V load but see no effect.
As I mentioned in my reply to Chuck, disconnecting the CRT has a very positive effect and oscillation doesn't stop anymore. I'm going to look at the DC restorer circuit with the CRT disconnected next.
Question though. You mention that CR769 doesn't clamp if the voltage never goes below 10V. I understand. But the voltage at R768 (on the side of C768) definitely goes below 10V. So something on the other side of R768 (which is the nexus of CR769, CR776 and R777) prevents that signal from going below 60V, correct?
Could this be related to the voltage shift at C768? C768 is pure AC centered around 0 when R768 is lifted but biased to 100V when R768 is connected?
JdR
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Re: Tektronix 606A that resists being repaired
Thanks for the suggestions.
1. Supply voltages check:
I remeasured the supply voltages (I repaired these earlier including rectifier diodes and a filter cap). +270V, +15V, -30V all perfect, no ripple. +120V and +30V a derived from the secondary winding of the HV transformer T710 (unusual) but look good too as long as the oscillation keeps going; +30V has a 136mV ripple (-40mV..+90mV) at the resontant frequency of 62 kHz.
2.
I added the requested measurement to (see WF5, WF6). Bottom line, the OpAmp output at the junction of R748 and R728 gets distorted after about 2 minutes, then the voltage level rises quickly until the oscillator stops.
3.
The -5500V on the secondary (measured at the anode of CR764) doesn't increase more than 50V until oscillation stops.
All these measurements were taken with P820 and R596 disconnected to reduce any load from the 120V supply taken from the secondary of T710. I noticed no difference.
I did one more test: disconnect the CRT connector from the CRT so there is no load on the secondary of T710 at all. Result is WF7 on my website. Oscillation continues forever. It does mean that transformer T710 works fine under low load conditions (only 400mV drop on R714 (modified to 1R) so about 400 mA current).
I'm going to focus on the second problem (DC restorer circuit) with the CRT disconnected now that I don't have to turn the machine off every 2.5 minutes.
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Re: Transformation TR503 into TR502
Thanks Ed,
yes, the behavior of the tracking generator is as you write, I have a maximum then the level goes down by turning the Tracking Adjust control left or right. I was careful to scan right so that the "UNCAL" light was turned off (for 300 Hz and 30 Hz resolutions I use the 7613 mainframe in STORE mode). At first I did not realize that the track must be adjusted with the Tracking Adjust control for maximum peak on the screen upwards.
If I understand correctly I should calibrate the 7L13 so that the track level is stable and in the correct position by varying Span / Div and Resolution from minimum to maximum.
Do you have any suggestions?
--Cheers
Attilio
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Ed,
Wow.
How we keep beating this to death.? I gave data on different LEDs,? gave you credit for suggesting capacitors across outputs and I used 15uF because I have lots of them, by experiment used 3W red LEDs because of higher outputs to supply enough current,? another person did SPICE evaluations on Red with wavelength recommendations.? Another mentioned that exact 1.3V wasn't important whereas my 7S14 was approximate 1.5Volts.? I gave photos for the Tek group.??
Carl Hallberg
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On Sunday, February 28, 2021, 01:02:12 PM CST, Ed Breya via groups.io <edbreya@...> wrote:
Did you include the bypass capacitors on the photo-voltaic bias outputs? There should be one across each, so four altogether. They are essential for best noise performance.? Ed
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Re: TDS784C Signal Path Compensation Error
On Sun, Feb 28, 2021 at 1:07 PM EricJ via groups.io <wyzkydd2358= [email protected]> wrote: Replacing the relays he mentioned solved it. And yes he'll need to be
careful, the hybrid boards are made of pretty thin ceramic.
I snipped the pins of the relays individually with a good pair of flush cutters, then de-soldered them individually. Even so it felt a little iffy, and one of the relay pins pulled out of its solder joint on the ceramic substrate. Maybe it was a cold joint, but you might consider cutting the pins with a dremel or some such - some method that doesn't put a lot of force on the pin or relay.
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Re: TM500 / 5000 Extenders
Is he the one that is selling them on Ebay? I just bought one there and it is NICE! You could message the seller through E-bay and see if that's him. On Sun, Feb 28, 2021 at 1:31 PM John Ackerman via groups.io <flatfoot55= [email protected]> wrote: Apparently dnmeeks has left this forum. On the off chance that he will be
selling another batch of extenders some day, does anyone have his current
email address?
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Re: TM500 / 5000 Extenders
I¡¯m interested in these extenders as well. Tried emailing Dan last night and my email bounced.
Regards,
Jeff
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On Feb 28, 2021, at 10:31 AM, John Ackerman via groups.io <flatfoot55@...> wrote:
?Apparently dnmeeks has left this forum. On the off chance that he will be selling another batch of extenders some day, does anyone have his current email address?
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Hi Ed,
1uF ceramic cap in each.
BR,
Jouko
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Did you include the bypass capacitors on the photo-voltaic bias outputs? There should be one across each, so four altogether. They are essential for best noise performance. Ed
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I have a type 284 that I am working on again to see if I can¡¯t get the td pulse side working again. Where I am at now is the last time I was in the pulser I was able to confirm that D180 is good on a curve tracer. My issue seems to be in R184 B&C. R180 seems to be good as well as R184A R184 B&C is a 2 carbon comp series resistance that should be 660 Ohms mine measure 724 Ohms if my understanding of the circuit is correct the 2 resister combination was done due to size constraints along with parasite capacitance reduction. They are carbon 1/8 Watt resisters. The challenging part is they need to be inside R184 so space is extremely critical. I can get resisters from NTE that look like they might fit. Is there any reason that I can not play with the resistance values as long as the sum total is 660 Ohms? Also given that there are IN the tunnel diode air line is resister material an important consideration given the 70 Ps rise time of the TD. In circuit this is the negative bias driver for the TD. On the positive side of things R180 is reading 749.82 Ohms so that does not need to be changed.
Thanks,
Eric
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John Williams
jrseattle
Attilio
Jeff Keyzer