Re: SC502 Trace Issues - Beginning and ending of trace connected.
Barry,
Look at the crt circuit in the schematic. The diodes can/should be replaced with 1N4937 and I strongly suggest replacing R888 with a Vishay VR37 series 22meg resistor. That carbon will be out of tolerance. I would also suggest replacing the 1mfd condensers for the 70V supplies with a Nichicon ULD type and can be higher in capacitance, e.g. 2.2mfd, and the 1mfd decoupling from the crt bias with a 250V film type. Check the crt bias pot to make sure it is still good. The pot could be open. I have found these and a few others open in the 7000 series then replace them with a 10 turn 3/4W type. Yours does not need to be this type, unless you want it and the pot is bad.
Mark
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Re: SC502 Trace Issues - Beginning and ending of trace connected.
I am clearly out of my league... How do I find the "intensity DC restorer" circuit?
Thanks!
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Re: 7704A - Readout Stretches Vertically
Disable the high voltage, unplug the CRT, certainly defocus the CRT, If there's a fuse in the HV supply, you might try removing that.
The problem is (on a bright spot), the density of the electron beam.? Diffused over a relatively large area, it won't hurt the phosphor.? Unplugging the CRT may be one of the easiest things.
The above is for checking the character generator.
if you have no sweep, then unplug the CRT and check the voltages everywhere.? Horizontal and vertical positioning controls should be able to move the (invisible) spot around.
You can check the CRT voltages at the socket (be very careful, high voltage!), with the thought that the grid/cathode voltage never goes negative (grid volts = cathode volts => very very bright spot).? The CRT is not needed to check the voltages.? The grid ought to be able to be driven negative with respect to the cathode to turn off the tube.
Some of the diodes coupling the blanking signal into the CRT can go bad, as has been mentioned.
Ought to be a start.
Apologies if you already know this.
Harvey
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On 3/4/2024 3:58 PM, Albert Otten wrote: On Sat, Mar 2, 2024 at 11:04 PM, Harvey White wrote:
Another trick you can pull is to take the second scope, put it in XY mode, and
look at the outputs of the character generator, I'd initially suggest the
connectors to the V and H boards.? Should get the whole vertical/horizontal
amplifier question out of the way. Harvey,
Regrettably this is almost impossible without blanking the (otherwise extremely bright) central dot. It would require the use of one of the control signals (perhaps Z-axis Inhibit) in the 7704A to drive Aux Z of the test scope.
Even locating the bright dot outside the visible CRT area is of no help here.
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Re: 7704A - Readout Stretches Vertically
On Sat, Mar 2, 2024 at 11:04 PM, Harvey White wrote: Another trick you can pull is to take the second scope, put it in XY mode, and
look at the outputs of the character generator, I'd initially suggest the
connectors to the V and H boards.? Should get the whole vertical/horizontal
amplifier question out of the way. Harvey, Regrettably this is almost impossible without blanking the (otherwise extremely bright) central dot. It would require the use of one of the control signals (perhaps Z-axis Inhibit) in the 7704A to drive Aux Z of the test scope. Even locating the bright dot outside the visible CRT area is of no help here.
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Re: SC502 Trace Issues - Beginning and ending of trace connected.
If the intensity control doesn?t work the blanking problem is a consequence of it.
With a high degree of probability one or more diodes of the intensity DC restorer are leaky. Since testing it is quite difficult, I would replace all.
This problem happens in several Tek models and also in scopes of other makers (Who copied the circuits designed by Tek).
Regards,
Ignacio
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El 04/03/2024 a las 16:48, Barry Breaux escribi¨®: Interesting that you mention intensity. The intensity adjustment does nothing. I am troubleshooting that now.
Barry
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Re: SC502 Trace Issues - Beginning and ending of trace connected.
You might want to see if the unblanking pulses are doing what they're supposed to.? (or blanking pulses).? In some older scopes, there are diodes that have gone bad.? Do be careful, since they may run the cathode and grid at elevated voltages (like 2KV).
Grid - cathode voltage *should* change with the intensity settings.?? Hmmm......
Harvey
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On 3/4/2024 10:48 AM, Barry Breaux wrote: Interesting that you mention intensity. The intensity adjustment does nothing. I am troubleshooting that now.
Barry
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Re: SC502 Trace Issues - Beginning and ending of trace connected.
Interesting that you mention intensity. The intensity adjustment does nothing. I am troubleshooting that now.
Barry
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Re: SC502 Trace Issues - Beginning and ending of trace connected.
blanking problems.? You might want to check the CRT bias adjustments and similar voltages.? Turning down the intensity should make it vanish.? If not, then definitely blanking problems.
Harvey
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On 3/4/2024 10:07 AM, Barry Breaux wrote: I posted a phot of my new problem. Someone with more experience than I will probably know!
Please have a look.
/g/TekScopes/album?id=293496
Thank You!
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SC502 Trace Issues - Beginning and ending of trace connected.
I posted a phot of my new problem. Someone with more experience than I will probably know! Please have a look. /g/TekScopes/album?id=293496Thank You!
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Re: Help with floppy drive
I solved the issue... Digged out my oldest Apple laptop, a 3400c, from about the same era than the AM700 and still working with MacOS 8. Once I formatted a floppy in that laptop the AM700 was perfectly happy, reading and writing as told in the manual and still readable on OSX. Meanwhile I also found a method to do it on OSX - I had to create an image of the working disc and copy it on another one. OSX seems to be formatting DOS discs with FAT12 as required, but adding a partition the AM700 (and an old Apple laptop) are unable to see. I added some pics here ( /g/TekScopes/album?id=293272), showing some screenshots of the low-level tests. Now the question is: what the heck is the AM700 doing when it says "formatting floppy"? BTW, the lithium battery of the NVRAM, with date code from 1994, still delivers exactly 3,0 volts as written on the battery. It seems there is nothing vital on NVRAM (like calibration constants), most folders are empty. Anyone knows for sure? cheers Martin
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Re: I've done it! Finally, a real Tektronix book!
Is the 456 a typo in the table of contents?
I think the issue you'll have is someone else recently done a very similar book and gave it away for free.
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Re: about those vintage ceramic terminal strips...
Silver solder is still made and some RoHS lead free may qualify. See AIM
We designed the 500 kHz Metcal SP-200 solder station in 1990, constant current resonant supply.
20 sec warmup time, excellent temperature reg with large thermal mass work.
These were also sold by OK industries, etc.
Hakko Japan also made great irons, the odlper digital 926, 936 etc.
Still have some huge Hexacon irons....
Bon chance,
Jon
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Re: Tek "CONSOLE PORT" TDS 5/6/7xx Oscilloscope Debug Card RS-232
I've thought about emulating the MC68681 for a 'proper' console debug card, but didn't need it bad enough. Not sure if it would be possible to meet timing requirements with a microcontroller, but it looks like someone started an HDL implementation for FPGAs :
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Re: I've done it! Finally, a real Tektronix book!
Thanks to everybody!
@Grayson: they are preparing a better sample pdf and yes, they ship everywhere. Congratulation for your book! Such more scientific than I am. It will be of great hep to me in the future.
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Re: about those vintage ceramic terminal strips...
3% appears to be optimum.
Here is a table of soft silver alloys:
Sn/Pb/Ag Solid - Liquid(C)
60/36/4 179-246
61.5/35.5/3 179-227
62/36/2 179-189
62.5/36.1/1.4 179 (eutectic)
The temperature range of 4% is significantly higher. The silver contents of 2% and 1.4% are lower; although their temperatures are lower. For reference, the 63/37 Sn/Pb melts and solidifies at 183C
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Re: F.S.: Tek "CONSOLE PORT" TDS 5/6/7xx Oscilloscope Debug Card RS-232
On Sat, Mar 2, 2024 at 07:39 AM, rivet_head wrote:
hey maurizio, glad to see your still fighting the good fight!
Anybody have a spare Option 13 board they wouldnt mind parting with? Hell, id
even be will to put a deposit down to borrow one for a week or three. I would
like to dig a little deeper into my 684B.
I have a spare one I can sell you, shipped from Japan. It's small so shipping shouldn't be too bad as it can be sent as a 'small packet'. Jared
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Re: about those vintage ceramic terminal strips...
Excerpt from the Tek Type Z plug-in manual:
"Soldering Precautions
In the production of Tektronix instruments, a special silver-bearing solder is used to establish a bond to the ceramic terminal strips. This bond may be broken by the repeated use of ordinary tin-lead solder, or by the application of too much heat. Occasional use of ordinary solder will not break the bond however, if too much heat is not applied.
If continued maintenance work is to be performed on Tektronix instruments, it is advisable to have a stock of solder containing about 3% silver. This type of solder is used often for work on etched-circuit boards and should be readily available. It may also be purchased directly from Tektronix in one pound rolls (part number 251-514).
Because of the shape of the terminals on the ceramic terminal strips, the soldering iron should have a wedge- shaped tip. A tip such as this allows the heat to be applied directly to the solder in the terminals and reduces the amount of heat required. It is important to use as little heat as is possible. Do not use force or twist the tip in the slot as this may chip or break the ceramic strip."
Greg
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Re: 7704A - Readout Stretches Vertically
Hi Albert,
I can certainly try that. I'm almost to the point of just living with this. I've had the boards off and back on all too many times for this little bit of annoyance but I would still love to know why it's doing what it's doing.
Thanks again,
Barry - N4BUQ
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----- Original Message ----- From: "Albert Otten" <aodiversen@...>
To: "tekscopes" <[email protected]>
Sent: Saturday, March 2, 2024 3:51:29 PM
Subject: Re: [TekScopes] 7704A - Readout Stretches Vertically Hi Barry,
With the same setup you can add a second input (plugin or channel) in the
monitoring scope and display there the amplified signals present further on at
the vertical amplifier board. Triggering as before (R4470) should remain
unaffected when you change 7704A vertical position up/down. I would start with
the deflection plates. With DC coupled input the observed actual character
wave forms fragments will remain at the same vertical position while the
normal trace moves up/down when you change the vertical position in the 7704A.
Again you may see or not see an effect of that on the character waveform
fragments.
Albert
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Re: 7704A - Readout Stretches Vertically
I've been through checking most of that but there is certainly the possibility of something I haven't checked. I get proper waveforms for the timer chip (U33433). I could always try swapping U3480 to see if that helps.
Regarding your other, later, email, I didn't think of trying XY mode to see the characters. I've tried to make sense of the squiggles for just the vertical signals and, to some extent, I think I can see how those are working but to see the entire character would be nice as well.
Thanks again,
Barry - N4BUQ
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The same vertical amplifier drives the display for both trace and
characters.? If, while displaying a triangle wave, you do not see any
non-linearity when the trace is within the zone of the readouts, then
it's the readouts.
Looking at J3405 on the Y readout connection to the vertical amplifier
suggests that if Q4470 on the vertical amplifier is odd, then you've got
some problems.? What I would suspect is non-linearity either around
Q4470? (possible, check waveforms on good and bad scopes), or back in
the Y readout.? I'd think that Q4479 and Q4485 might be well behaved,
although they are not in the signal path except for the readout.? One
presumes that the capacitors C4427, C4424, and pots R4427, R4423 are
well behaved.
On the readout board, I'd hope that U3480 is ok, that's the stroke
generator.? That leaves you with checking Q3486 and Q3489 for bad
biasing.? If you have a good board (I think you do), then comparison
between boards is going to be a key, also looking at waveforms.
Q3486 is an example of a grounded base system, where the voltage gain
has to do with the emitter resistor to +15 and collector resistor
(effective) to -15.? Q3493 looks to be more of an emitter follower than
anything else, so it generally gets non-linear if it's leaky or it runs
out of headroom.? Again, voltage and waveform comparisons are likely the
key.
Hope this helps a bit.
Harvey
On 3/2/2024 12:59 PM, n4buq wrote:
I have monitored the signal at that point and cannot see any difference there
when positioning the trace at the top or bottom. Yes, fully CW or CCW is most
likely overdriving the vertical amplifier and the stretching is at its worst at
those settings; however, the stretching is quite noticeable even when a trace
is positioned at the top or bottom of the screen. The stretching is worse on
the characters at the top when the trace is at the bottom and vice-versa. I
can see a very small bit of this effect on the characters in my other 7704A but
it is much worse in this one.
Thanks,
Barry - N4BUQ
Hi Barry,
It should be not too difficult to check whether or not the incoming signal at
R4470 is affected by vertical position changes.
I tried this (and saw no effect, of course) viewing and triggering that incoming
signal, also with delayed sweep. It's best to have all readouts in the same
row since then you can enlarge the waveform without overdriving the monitoring
scope. The actual observed character height can be twice that of the height on
the 7704A.
By the way, 7704A positions fully CW and fully CCW might also be at the border
of overdriving the vertical amplifier. I would not go beyond top and bottom of
the CRT.
Albert
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Martin
Jean-Paul
fenugrec
Jared Cabot