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Re: Help with (another) broken 7B92 please
Harvey White
I can give some general answers, but perhaps not as helpful as you'd want.
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Considering the trigger circuits: A good approach is to take the input waveform, compare to a level, then produce a waveform that is above or below a threshold. For slope, if the trigger is > than the threshold, it's + going, if not, it's minus going. At this point, you might have used a fast comparator (with hysterisis), or possibly a tunnel diode (which also provides hysteresis). This comparator output (possibly a square wave) is differentiated to produce a very fast rise time pulse. The way the older scopes worked (and this may still be valid), was that there would be a coupled monostable multivibrator, think a self triggering flip flop that could be in one of two states (for bias), one is not running, the other is self triggering. Putting a trigger pulse into the multivibrator causes it to trigger, which then makes the ramp generator run. With the ramp running, the ramp cannot be triggered again until the ramp is over, and a holdoff period (often variable) has elapsed. So the question for the multivibrator is threefold: 1) is it biased so that the trigger pulse cannot trigger it? (ain't running) 2) is it biased so that the trigger pulse is high enough to trigger the the sweep? (triggered mode) 3) is it biased so that without a trigger, it will retrigger itself (auto mode) The general trigger diagnostics path is to put in a known waveform, and taking the waveforms in the schematic (if any), trace them through. You should see trigger level, trigger shaping, and then the generation of a fast trigger pulse. NB: I had a telequipment scope that had a very fragile trigger threshold. The cause was an open 10 pf capacitor that differentiated the trigger pulse. Putting a capacitor across that gave a trigger pulse with sufficient amplitude to trigger the sweep. I don't think that the sweep mechanism varies much in concept (but does in implementation) from 7000 series plugin to another. What I have described may be more suitable to the old 500 series tube scopes, but the concepts should be close. Once the trigger pulse is there, you need to look at the sweep generator to see if it works at all. If it does, then that's one thing, if not, then likely the ramp generator is never triggered (or perhaps it is never reset). Harvey
On 10/26/2021 9:13 PM, Jeff Dutky wrote:
I have a general question about the diagnostic approach to this instrument: how are people figuring out what should be seen at a given test point?
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Re: Help with (another) broken 7B92 please
I have a general question about the diagnostic approach to this instrument: how are people figuring out what should be seen at a given test point?
There are lots of test points on the sweep board, but I don't see any central guidance in the service manuals for what I should measure at them. The service manuals for the 7B92 seem awfully short on diagnostic guidance, unlike some Tek service manuals I have used. -- Jeff Dutky
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Re: Help with (another) broken 7B92 please
Ozan
Hi Bruce,
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1.4V across CR750 is not a good sign, it is most likely in open circuit. You can short across CR750 with an ammeter and make sure the current is not excessive (I think parts list says ~ 10mA) because of some other fault. If that looks good and you have a tunnel diode available you can replace CR750. Another option is to carefully swap with CR950. Diode CR750 is main trigger, CR950 is delayed trigger. With this change main trigger should work, then you can install the replacement diode in CR950 location later. Regarding your question about hold-off: In this state of the circuit most likely ramp is railed at the top (i.e. TP408 is at max) and Q398 is not resetting the ramp. As soon as hold off ends (Q349 turns off) HO start is triggered again because ramp is already at its final voltage. That is why you see hold off ramp running and it is independent of timing switches (ramp is not reset so there is no setting dependent ramp). Ozan
On Mon, Oct 25, 2021 at 01:25 PM, Bruce Atwood wrote:
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Re: Help with (another) broken 7B92 please
Miguel Work
https://groups.io/g/TekScopes/photo/260881/3326552?p=Created%2C%2C%2C20%2C2%2C0%2C0
Horizontal is in volts, Vertical 10mA/div Good diode has a resitance <10 ohms, in this example 4 ohms in reverse, bad diode > 20 ohms Regards!
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Re: Help with (another) broken 7B92 please
Miguel Work
I use a simple x y octoupus to check in board these diodes
I have fix recently a 7T11 with bad TD outuput diiode, I replaced it with a 10mA russian diode and it now works. https://groups.io/g/TekScopes/photo/249051/2975689?p=created%2C%2Cs51%2C20%2C2%2C0%2C0 Some bad TD diodes has high resistance, this can explain the high voltage that you see https://groups.io/g/TekScopes/photo/260881/3326552?p=Created%2C%2C%2C20%2C2%2C0%2C0
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Re: 4051 Rampack Solid-state Tape Replacement
stevenhorii
If enough people want them, a data recovery service might be able to read
the tapes and rewrite them on fresh tape cartridges or another medium. I think the cost would be too high for one set of tapes with one fresh set rewritten, but I don’t know. This is one outfit that claims to do this: https://www.ontrack.com/en-us/tape-recovery No conflict of interest with this company. On Tue, Oct 26, 2021 at 10:18 Gary Robert Bosworth <grbosworth@...> wrote: What we really need are new fresh magnetic tapes loaded with original
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Re: 4051 Rampack Solid-state Tape Replacement
What we really need are new fresh magnetic tapes loaded with original
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software for the Tektronix 4041. My old tapes (all 6 of them) are no longer readable by the tape drive. Gary Bosworth grbosworth@...
On Mon, Oct 25, 2021 at 2:02 PM Bob Haas <robeughaas@...> wrote:
The vintageTEK Museum has just released a new version of the 4051 Rampack, --
Gary Robert Bosworth grbosworth@... Tel: 310-317-2247
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Looking to buy Tektronix 661 plug-ins
Hi , I am wanting to find a couple of old Tektronix plug-ins . They are from the rather old 661 sampling oscilloscope . I need a 4S2A and also a 4S3 plugin to complete my system :- please note that I am not asking for these to be working plug-ins , all I ask is that they are as complete as possible - the 4S3 does not need to have the P6038 probes although they would be most welcome also . Any other plug-ins for this oscilloscope will be considered as possible backup and spares . I would be very pleased to hear from anyone wishing to part with these .
Many thanks in advance . Brian (UK)
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Re: Help with (another) broken 7B92 please
Roger Evans
I am not sure I understand what is happening so these are no more than comments.
Have you set the P308/P309 jumper for 'non 79xx' mainframes? If you set the trigger mode to normal then do the repeating hold off pulses stop? The voltage on TP321 is suspiciously high. Apart from the 51R resistor R765 it is equal to the voltage across the gating tunnel diode CR750. Germanium tunnel diodes normally have a voltage drop of 50-100mV when armed and around 500mV when triggered. GaAs tunnel diodes go as high as 1.1V when triggered. The parts list says that CR740 and CR750 are Silicon diodes - I have never seen a Silicon tunnel diode, but a Google search says they do exist and would have an on state voltage drop around 700-800mV. Regards, Roger
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Re: Help with (another) broken 7B92 please
Miguel Work
I´m waiting to receive one 7B92 that I have bought cheap beacuse I need pulse diodes, and this time base has 6 fast TD diodes.
I don´t understand what you neen to know. what does it mean free run hold off? It seems that this time base don´t have a variable hold off control.
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TM506 + WR501 (without cables) + DD501 + LA501 is looking for a new home
Dr.-Ing. Stephan Massner
Hello Rick,
may you use the e-mail massner@... please. Best regards, Stephan
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Re: tek 2215 trace position issues
Paul M3VUV
the voltages on the vert position pot wipers is as follows fully ccw=3.6v,halfway point =1.2v,fully cw =3.6v.
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Re: TM500 tester switch - Attn. Jared Cabot.
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Here is a PDF of the datasheet for the Greyhill 71BDF30-02-2-AJN switch
that was recommended for the tester. The stop pins are shown on page 11. < http://www.farnell.com/datasheets/20309.pdf> If your switch doesn't have the adjustable stop pins then you may have a different model switch. On Mon, Oct 25, 2021 at 5:38 AM Colin Herbert via groups.io <colingherbert= blueyonder.co.uk@groups.io> wrote: Ah, But that order was from Mouser, not DigiKey like mine. My switch was
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Re: TM506 + WR501 (without cables) + DD501 + LA501 is looking for a new home
Greetings Stephan,
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A quick message to ask whether the TM506 is still available and, if so, whether I can put in my request 🙏 Thank you, Rick.
On 26 Oct 2021, at 07:57, Dr.-Ing. Stephan Massner via groups.io <massner@...> wrote:
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4051 Rampack Solid-state Tape Replacement
The vintageTEK Museum has just released a new version of the 4051 Rampack, It is the same form factor as a rompack, and can store 2MB (equivalent to 7 DC300 tapes) of programs and data in rewritable flash memory. It comes preloaded with 140 demos, utilities and graphics files. It is on the vintagetek Ebay store.
-- Bob Haas
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TM506 + WR501 (without cables) + DD501 + LA501 is looking for a new home
Dr.-Ing. Stephan Massner
Dear all,
if anybody is interested in the following parts, please write me a PM, please. Mainframe TM506 (working unit) including Word Recognizer/Delay WR501 (without cables) Digital Delay DD501 and Logic Analyzer LA501 (P6450 included but without further accessories) Probably, I'ld find the cable for the WR501 within the next days while clearing our old lab - but I'm not sure. We're encouraged about a donation for our kitty (thank-you box). Best regards, Stephan
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Re: 7000 series parts hulks
Oz-in-DFW
All teh plugins are spoken for as are the 7603 and 7613
-- Oz (in DFW, Texas USA) N1OZ
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Tek 308 data analyzer - serial data
Paul Amaranth
I have a small device that uses a 9600 baud rs-232
connection for communication that's not working correctly. I thought I could use my 308 to take a look at the data stream and I can't seem to get the right setup for it to recognize the data. All I get are "+++" marks. I have it connected on the TTL side, not the external +/- 12V side. The trigger LED does flicker, but no data is displayed. Any one ever use this to look at a serial data stream? Any ideas on the setup? There are not a lot of parameters to fiddle with here, but I haven't found the right combination yet. thanks -- Paul Amaranth, GCIH | Manchester MI, USA Aurora Group of Michigan, LLC | Security, Systems & Software paul@... | Unix/Linux - We don't do windows
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Re: Help with (another) broken 7B92 please
Bruce Atwood
7B92, S/N B052568, No Sweep, Help!
Thanks Miguel, TP321, and R765, have ~60mv, ½ usec pulses. So pulses but probably not functional. I went back and checked carefully on all pins of U310 and found, in addition to those noted below, several volt 200 nsec pulses on 16 and 17. All are at the same frequency and in phase with the HO ramp. Since it has been almost a year since my 7B92 arrived in my new-to-me 7904 I’ve decided that it is time to make it work. I’ve re-posted with a new title since it may have been confused with “..no repeating sweep” The first question might be is it normal for the Hold-Off circuit to free run? I have not found a configuration where it does not free-run at a frequency determined by timing switches 7, 8, 9 and 10. Test setup ‘92 installed in right-most slot of a 7603. No vertical plug-ins installed. (The 7603 has been tested with a 7B53A in the right-most slot and a 7A26 in the left-most slot.) The side covers have been removed from the ‘92. The side covers are removed from the 7603 giving good access to the main trigger board and the sweep board. The external trigger is driven by the cal-out of a 7904 set to 1kHz and 0.4 volts. The termination is off. Trigger is set to Auto, DC coupling, External. The “Alt” and “Level” controls are pushed in. Sweep speed set to 20 uSec/division. The “Triggered” light is off when powered-up but come on and stays on if single-sweep is selected. U310 Voltages, taken with Fluke 115, Waveforms observed with 7409/7A26/7B53A combo: Pin # name Voltage 1. +TD input 1.159 2. -TD input 0.232 3. + TD Auto 0.331 4. - TD Auto 4.890 5. -5V -4.980 6. Auto timing 0.022 7. Tgd Lamp 4.602 8. HO timing 2.239 + Hold-Off ramp, ~4V P-P, 40 uSec 9. 0.001 10. HO out 0.289 + 0.5 usec 6V pulses at HO frequency (25kHz) 11. SS ready 4.663 12. 0.013 13. 0.216 14. Reset timing 4.716 15. Reset start 0.762 16. 0.074 2V 200 nsec pulses 17. SWP disable 1.686 3 V 200 nsec bipolar pulses 18. Lockout input -0.006 19. Auto Mode 0.001 20. +5V 4.889 And: TP 392 4.367V TP 321 1.429V C 1.61V + Hold-off pulses E 0.115V + Hold-off pulses CR740 (TD) ~1.5uSec, ~600mv pulses at Hold-Off ramp freqeuncy Q754 base 0.747V Q748 base 0.790V
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Re: 2445B vertical non-linearity other issues.
Robin Szemeti
I'm building a replacement U400 from discrete surface mount components. I'll let you know how it works out.
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