Date   

Re: Question re: capacitor in Tek 181

Harvey White
 

Hmmm, they had a big box full of them?  Wouldn't be the first time that overstock got used like that.

Harvey

On 5/2/2020 11:08 AM, Brad Thompson wrote:
What was Tek thinking? Capacitor C420 in the 181's schematic gets spec'ed as an electrolytic cap of
6.25 uF at 300 volts, -10%-+100% tolerance. It's filtering the -25-volt line, so 10 uF at 450 V should
do nicely. as a replacement.

I can't figure out why a Tek engineer would specify a nominal value of "6.25 uF", considering that electrolytics
aren't that precise to begin with.

Any insights would be welcome.

Thanks, and 73--

Brad  AA1IP



Question re: capacitor in Tek 181

Brad Thompson
 

What was Tek thinking? Capacitor C420 in the 181's schematic gets spec'ed as an electrolytic cap of
6.25 uF at 300 volts, -10%-+100% tolerance. It's filtering the -25-volt line, so 10 uF at 450 V should
do nicely. as a replacement.

I can't figure out why a Tek engineer would specify a nominal value of "6.25 uF", considering that electrolytics
aren't that precise to begin with.

Any insights would be welcome.

Thanks, and 73--

Brad  AA1IP


Re: Which type of transistor is SG503 Q190 151-0614-00?

boid_twitty
 

The suggestion that darlington-type voltages were being measured
in-circuit suggest another type of measurement error.

The base of the Q109 part is biased below ground, adding a few hundred
millivolts into the circuit to give observers more chance for error..

A saturated collector, or CB short will also introduce a terminal voltage
somewhere between the emitter and base potentials.

Live measurements will also be dependent on accurate bias settings
and (hopefully not) active signal conditions.

Values of the emitter ballast resistors is unspecified, but measurements
between one open bonding wire and another are typically 1.5 ohms,
suggesting 750mR per contact.to the emitter mech terminal.

RL


Re: 2445 EPROMs

Chuck Harris
 

It's not like it is hard to get an A5 card for a
2465. PM me an address, and I will send you one
for the postage.

-Chuck Harris

christopherbath@hotmail.com wrote:

Hi Mark & Others,

I have finally managed to program new EPROMs after a bit of a nightmare in having misplaced my old programmer and also loosing the software for another one.

The bad news is the re-programmed EPROMs don't fix the issue. I was starting to get a bit suspicious now about the processor itself which is a S68A08 and having looked around on the web for a possible replacement I found a few other posts where people had issues with the S68A08 processor in the 2445.

The IRQ waveform is not as expected as per the trouble shooting procedure in the service manual. I have run the NOP and the address lines do seem to have a binary count on them but I am still not convinced yet that the processor is working correctly.

Do you have any recollection of what the faulty processor was you had mentioned previously? This one is an AMI (American Microsystems) S68A08. From what I can tell that specific microprocessor was not very common.

Sorry for the very belated reply.







Re: Another miserable tantalum!

Shailendra Krishan
 

Ernesto,

You forgot to mention the "dynamic timer" of the IBM 407 / 447 tabulators, and also found on some other machines of its time. It was a functional equivalent of a dual channel oscilloscope, implemented as an electromechanical device. It displayed timing of up to two signals at a time on a round display scale, marked 0 degree to 360 degree, representing one machine clock cycle. It had two neon lamps mounted on a rotating disc, getting electrical connection through slip rings.

You sure can call it a electromechanical oscilloscope!

Just recalling the early years of my job as a maintenance engineer fixing IBM unit record data processing equipment.

Shailendra


Re: Large number of people unsubscribing to YAHOO TekScopes

Chuck Harris
 

Hi Dennis,

I remember how it was, so I didn't mean to criticize, just inform.

Sign into yahoo. you should end up in groups home.
In the list of yahoo groups you own, moderate, or are subscribed to,
click on "tekscopes".

The heading should now have tabs for Aout, Membership, and Management.

Click on "Management".

The heading should now have tabs for Group Settings, Email Template, About Group.

Click on "Group Settings".

Make group type "Restricted"
Make Who can Join: "By invitation only"
Who can see: Unclick both boxes.

You also want to set (but, this is by memory):

Attachments not permitted
Membership requires approval (or closed?)
Messages are moderated
Not listed in Yahoo Groups Directory

and I think there are some more restrictions that are beneficial, but I can't
see them, or remember them. I think one is closing the group to new messages.

If you can't do that, make a filter in your email reader that catches the moderate
requests, and dumps them in your trash folder.

Domain Restriction: "Restrict membership by email domain"

Which will open up some new boxes for you to set the email domain.
Pick a nonsense email domain, and nobody that isn't using that domain
will be able to ask to join.. (this might lock you out...)

Leave, and the group should remain quiet.

As I said earlier, I no longer own any yahoo groups, so some of the settings
are not visible to me... and I have no desire to start a group just to kill it.

-Chuck Harris

Dennis Tillman W7PF wrote:

Hi Chuck,
When we left Yahoo for Groups.io there were so many new issues to deal with that what would happen to the Yahoo TekScopes was the last thing I was thinking about. Once the move was completed and the initial chaos settled down and the world didn't end we all breathed a sigh of relief. By then my entire focus was discovering all the new features and help that Groups.io provides. I never looked back.

I didn't realize I could lock the Yahoo TekScopes down. Yahoo stopped providing help and support long before we left them - that was a significant reason we chose to leave so there was no one at Yahoo who might have suggested it would be wise to lock it down.

If it isn't too late to "lock it down" do you know how to do that? I am still the administrator of the Yahoo TekScopes so I should be able to do if as long as I know what is required.

Dennis Tillman W7pF


Re: 2445 EPROMs

 

On Sat, May 2, 2020 at 02:32 PM, <christopherbath@hotmail.com> wrote:


Do you have any recollection of what the faulty processor was you had
mentioned previously? This one is an AMI (American Microsystems) S68A08. From
what I can tell that specific microprocessor was not very common.
AFAIK AMI's S68A08 was just a second source for the Motorola MC68A08, IOW an MC68A02 with unusable/defective/disabled internal (128 byte) RAM. The A refers to a version with a slightly higher maximum clock frequency.
I'm not sure if a 68A02 (or 68B02) would just work but that should be easy to find out, because the data sheets are available on the 'net.

Raymond


Re: 2445 EPROMs

christopherbath@...
 

Hi Mark & Others,

I have finally managed to program new EPROMs after a bit of a nightmare in having misplaced my old programmer and also loosing the software for another one.

The bad news is the re-programmed EPROMs don't fix the issue. I was starting to get a bit suspicious now about the processor itself which is a S68A08 and having looked around on the web for a possible replacement I found a few other posts where people had issues with the S68A08 processor in the 2445.

The IRQ waveform is not as expected as per the trouble shooting procedure in the service manual. I have run the NOP and the address lines do seem to have a binary count on them but I am still not convinced yet that the processor is working correctly.

Do you have any recollection of what the faulty processor was you had mentioned previously? This one is an AMI (American Microsystems) S68A08. From what I can tell that specific microprocessor was not very common.

Sorry for the very belated reply.


Re: Large number of people unsubscribing to YAHOO TekScopes

 

Hi Chuck,
When we left Yahoo for Groups.io there were so many new issues to deal with that what would happen to the Yahoo TekScopes was the last thing I was thinking about. Once the move was completed and the initial chaos settled down and the world didn't end we all breathed a sigh of relief. By then my entire focus was discovering all the new features and help that Groups.io provides. I never looked back.

I didn't realize I could lock the Yahoo TekScopes down. Yahoo stopped providing help and support long before we left them - that was a significant reason we chose to leave so there was no one at Yahoo who might have suggested it would be wise to lock it down.

If it isn't too late to "lock it down" do you know how to do that? I am still the administrator of the Yahoo TekScopes so I should be able to do if as long as I know what is required.

Dennis Tillman W7pF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Chuck Harris
Sent: Friday, May 01, 2020 8:31 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Large number of people unsubscribing to YAHOO TekScopes

It is nothing important. I unsubscribed from the old group because I got tired of getting fooled into responding to accidental posts from there.

Others got tired of their email browsers auto selecting the yahoo group when they meant to address the groups.io group.

Really, you should have locked it down when you left it abandoned and adrift.

-Chuck Harris

Dennis Tillman W7PF wrote:
Is there something going on at Yahoo that would cause several people
to unsubscribe from the YAHOO (not the Groups.io) TekScopes all at the
same time?
Of course it hasn't been active for over 2 years but that hasn't
stopped a handful of new people from trying to subscribe to it each month.
I still get those requests from Yahoo and, of course, I politely tell
the potential new Yahoo TekScopes member where we moved to.
Dennis Tillman W7pF







--
Dennis Tillman W7PF
TekScopes Moderator


Re: Large number of people unsubscribing to YAHOO TekScopes

Chuck Harris
 

It is nothing important. I unsubscribed from the old group because
I got tired of getting fooled into responding to accidental posts from
there.

Others got tired of their email browsers auto selecting the yahoo group
when they meant to address the groups.io group.

Really, you should have locked it down when you left it abandoned and
adrift.

-Chuck Harris

Dennis Tillman W7PF wrote:

Is there something going on at Yahoo that would cause several people to
unsubscribe from the YAHOO (not the Groups.io) TekScopes all at the same
time?
Of course it hasn't been active for over 2 years but that hasn't stopped a
handful of new people from trying to subscribe to it each month.
I still get those requests from Yahoo and, of course, I politely tell the
potential new Yahoo TekScopes member where we moved to.
Dennis Tillman W7pF




Re: Large number of people unsubscribing to YAHOO TekScopes

Ed Breya
 

Maybe yahoo is bumping everyone out automatically and gradually?

Ed


Re: TDS784D not booting, never seen this before

amirb
 

My instrument does not have any SMD electrolytics on the CPU board and acquisition board. Only a handful on the front panel and option 13 and they are all very clean and proper. The boards are all very clean and I cannot spot any crack or damage anywhere. But as I said, I am sure someone has replaced the two NVRAMs.
The schematics for this CPU board (679-4003-00) do not exist (in public at least) and is quite a bit different than 520B. This one uses two E28F016SA flash memories.

I traced all the 32 data lines from the two flash memories to four bidirectional buffers (74F245) and started checking I/O in those buffers (triggering on the chip enable pin) one by one. I only used my Siglent teo channel scope with external trigger and segmented memory to capture the input and output bit on each data line. Before I made sure that during all transactions the direction is always from the flashrom to the data bus (only read is happening) and I also checked to see where the FlashROM CE and OE are activated which was in sync with the buffers CE.

There is not enough time to view much activity on the flash roms because after 2-3 seconds when the DSACK test fails, there is no activity anymore and everything goes dead silent on the FlashROM data lines (not on the other side though). In fact I found out during this time only two read attempts are made and both read the exact same data (see my boot log) which is 0x2540001c. After 2-3 hours of turning the instrument on and off 30-40 times I finally confirmed that this data is exactly what is read from the flash rom and transferred to the CPU. So there is nothing wrong with the data bus to the flash ROMs. I got tired and didn't check the address lines but I really dont think the address bus is bad either.

I dont know what to look for on the address bus either. If someone has a suggestion, please comment

I am curious that where the "should be" data (0x4e714ef9) is located? Is it in the NVRAMs? is it in the bootloader? can someone please comment?

Because if it is in the NVRAM, it is possible that whoever replaced them, made a mess of it and the data is corrupt, so the "should be" value is indeed the problem!! but my gut feeling is that this info is hard coded in the bootloader.


Large number of people unsubscribing to YAHOO TekScopes

 

Is there something going on at Yahoo that would cause several people to
unsubscribe from the YAHOO (not the Groups.io) TekScopes all at the same
time?
Of course it hasn't been active for over 2 years but that hasn't stopped a
handful of new people from trying to subscribe to it each month.
I still get those requests from Yahoo and, of course, I politely tell the
potential new Yahoo TekScopes member where we moved to.
Dennis Tillman W7pF


Re: 2465B post-recap issues.

Chuck Harris
 

I would carefully check to make sure that the cabling is
correct for the GPIB option. It is generally very reliable,
which means of all of the 2465's with the GPIB option that
have darkened my door step, I haven't seen one that crashed
the scope... I can't say that I tested them for proper function,
though.

-Chuck Harris

Andy Warner wrote:

Disconnected the GPIB option and the 2465B is back working like a champ.

Thanks for pointing me in the direction of the option, not the logic main
board.

I know for a fact I will never need GPIB on this 'scope, so problem solved.

On Fri, May 1, 2020 at 9:56 AM Andy Warner <andyw@pobox.com> wrote:

Thanks for that, reading the section of the manual around the diagnostic
tests is not very clear to me - I have a hunch that at some point the penny
will drop and then I can see what the text was trying to tell me, but I am
not there yet. I have zero plans to use the GPIB interface on this scope,
so I will plan an initial re-test with the GPIB option disconnected, if
that resolves the issue, I might stop looking at that point.

My de-oxit comment was more about the CH 2 trace missing, since that pot
was noisy, I wondered if it had hard failed.
I found the front panel exerciser test, and it looks like the pot is
working fine, at least as far as the micro is concerned.

Will learn more when I get it on the bench this weekend.

On Fri, May 1, 2020 at 7:51 AM Chuck Harris <cfharris@erols.com> wrote:

U2160 is not the problem. It is a spare 2764 pad left just
in case Tektronix needed more EPROM space for some option.

The options buffer would be located in the first option board.

What options do you have?

Odds are pretty good that your GPIB card is probably not
installed properly.

DeOxit won't hurt anything. If anything it can be messy, but
electrically it is nonconductive.

-Chuck Harris

Andy Warner wrote:
I recently re-capped my 2465B and replaced the DS1225 (copied the
contents
over.)

All seemed to go well, and the unit performed well in my post-rework
testing.

However, when I turn it on now, about 2 weeks later, it reports a
diagnostic failure:

TRIG'D flashes, and the following pattern is displayed:

Ready - Off
+ - Off
- - On
CH 1 - On
CH 2 - On
CH 3 - On
CH 4 - On

Reading Section 6 of the service manual, I think Tables 6-6 thru 6-8
are
telling me the problem is with U2160, Buffer ROM. Am I decoding that
correctly ?

Pressing TRIG A/B moves things along, but I am unable to see a trace
for
Channel 2, all other channels seem to work correctly.

Before I clear space on the bench and tear into the unit again, I
thought I
would check with the group for advice on these issues. Whether they are
likely to be connected or separate and coincidental (I don't usually
believe in coincidences.) I am not even sure what U2160 does, I need to
look that up.

I did not remove or recap the main board, it looked like a whole raft
of
hassle that I did not want to get into. I did recap the PSU, A5, A9 and
the
GPIB option card.

It is possible that some de-oxit got where it shouldn't have, I was
careful, but perhaps not careful enough. While I had the case open, I
gave
a couple of the switches and pots a shot (including the CH2 position
pot),
because they were noisy.

Regards,


--
Andy




Re: Which type of transistor is SG503 Q190 151-0614-00?

Chuck Harris
 

Mini Circuits has the ERA series and the MAR series of
MMIC RF amplifiers based on darlington configurations.

They are in plastic micro-X cases.

DC to 8GHz, 50 ohm input and outputs.

-Chuck Harris

Jim Ford wrote:

Hi, Albert.

I don't know about discrete RF Darlingtons, but Avantek (bought by HP, spun out as
Avago Technologies and then merged with Broadcom) used to have RF amplifiers based on
the Darlington configuration.

Incidentally, I've run across the Motorola/Freescale/NXP MRF transistors elsewhere as
well.  We use the MRF275G 150 Watt UHF devices in some of our radios at Raytheon
Technologies; they are made by MACOM now.  The MACOM transistors seem to be pretty
bulletproof; we also use one PolyFET device, which is not as robust, so I don't
recommend them.

I looked up the MRF511; it looks like several manufacturers are still making it.  I
wasn't able to get a datasheet (I didn't try very hard), but I did see that it was in
the micro-X package.  The 4 leads are probably Base and Collector 180 degrees apart
and 2 Emitter leads to reduce inductance to GND.

HTH.

Jim Ford
Southern California
USA


Re: Troubleshooting and repairing a 7704A instrument

Harvey White
 

Most RF transistors, and RF front ends, have a limited voltage input tolerance.  Running DC into a spectrum analyzer generally kills the front end, because of the DC.  To prevent that, people tend to use DC blocks, which is a selected capacitor in series.

The front ends also have a limited power input tolerance, even if it's not DC.  Many microwave or HF circuits have a limited tolerance for voltage, DC or otherwise.  Many amateur radio operators have killed a spectrum analyzer by hooking up their trasceiver to a dummy load, then hooking that to the spectrum analyzer.  Then they key the transmitter and go looking for repairs.

Many times, people will put a DC block and an attenuation pad on the front end to protect the front end from excessive voltages.

A surprisingly small antenna (if you want to go that way) can be used to monitor a transmitter's output.  Needless to say, the static charge accumulated on an antenna can also kill the input of a spectrum analyzer.

On a different piece of equipment, the 1502 TDR is particularly sensitive to over voltages, and once blown, the internal tunnel diode is extremely hard (if not impossible) to replace.

The 1503 TDR, which deals with 10 times the cable length, has a different method of generating the pulse, not a tunnel diode, and is less subject to damage.

The bottom line on TDR, sampling oscilloscopes, and spectrum analyzers is to be very careful with the front end.

Harvey

On 5/1/2020 9:31 PM, Ernesto wrote:
Thank you Greg, Raymond for your teaching of 7L13 precautions.

It will take me a good while of studying the details of the RF, microwave circuits, attenuators, filters, mixers, oscillators and other more mundane details of the 7L13, including ways to protect the input (maybe a pair of schottky diodes, preceded by bipolar diodes, to limit input to 0 dBm or less), all this stuff BEFORE I ever plug this triple unit into the mainframe.

And better there be no tantalum capacitors in there! I'm not looking forwards to disassemble this monster to look for them.

Ernesto



Re: Troubleshooting and repairing a 7704A instrument

 

Thank you Greg, Raymond for your teaching of 7L13 precautions.

It will take me a good while of studying the details of the RF, microwave circuits, attenuators, filters, mixers, oscillators and other more mundane details of the 7L13, including ways to protect the input (maybe a pair of schottky diodes, preceded by bipolar diodes, to limit input to 0 dBm or less), all this stuff BEFORE I ever plug this triple unit into the mainframe.

And better there be no tantalum capacitors in there! I'm not looking forwards to disassemble this monster to look for them.

Ernesto


Re: R561B rectangular trace, I'm baffled, please help

WastelandTek
 

OK, data

The +300 and +125 rails are at spec with 5mV and 3mV ripple respectively.

The -12 and -100 rails are a little over at 3 and 4mV respectively. The spec is 2.

Interestingly, the ripple I see is primarily a 50KHz triangle wave with some higher frequency hash on it, but these amplitudes are near the limit of my ability to measure so perhaps this is uncertainty creeping in.

All rails are well in spec voltage wise under load.


Re: Troubleshooting and repairing a 7704A instrument

Jim Ford
 

Good to know, Greg.

At the risk of taking this further off-topic (but to an area that may be of interest to many on this group), what about areas like Southern California where I live that have very little lightning activity and very low ground conductivity? I understand that this area is about the least likely place on earth to experience lightning damage. I do have a 65 V neon bulb on the input to the 70 cm band LNA up on my chimney mast, just because it was recommended by a friend and was easy enough and cheap enough to install inside the LNA housing. I have a receive-only setup for now.

Thanks for your help.

Jim Ford
Laguna Hills, California
USA

------ Original Message ------
From: "Greg Muir via groups.io" <big_sky_explorer=yahoo.com@groups.io>
To: TekScopes@groups.io
Sent: 5/1/2020 3:18:44 PM
Subject: Re: [TekScopes] Troubleshooting and repairing a 7704A instrument

A note on connecting test equipment (namely spectrum analyzers) to an outdoor antenna.

There is little that can save an instrument from external environmental electrical effects (mostly static) that will wreak damage to the front end unless properly protected. But then damage may still occur so it is a gamble one must make if wanting to do so.

As was mentioned, one need not be near an active lightening event to sustain sizeable static buildup on an external antenna. Clouds characteristically possess static charges as they move through the atmosphere. This creates a hidden potential difference between the cloud and the earth. The electric field is normally not a problem since the other electrode – the earth – is a solid ground point. But when you add an ungrounded antenna (such as a longwire or ungrounded element antenna) significant potentials can build until they find someplace to go to the earth ground.

DC blocks are rated for low voltages. As you may well be aware of, these items are usually very compact devices with low voltage rated internal component(s) that will not withstand overvoltage conditions. The main internal component, usually a capacitor, has a small geometry which means the input-to-output distance can be a very easy “spark gap” to jump when a sizeable static discharge is impressed upon it.

Risetimes of the rogue voltage can also be a problem. Even if one fabricates a high-voltage blocking device, any rapid cloud-to-ground or ground-to-cloud discharges far off in the distance can create a transient that can couple to the antenna. Given the fast risetime of these transients and their higher frequency characteristics this will more effectively couple through the capacitive element used in the blocking device thereby presenting a more significant voltage spike to the input of the connected instrument.

One way to overcome these problems would be to fabricate an inductive coupler between the antenna and instrument. The primary (input) winding can be grounded on the low end thereby passing any static buildup on the incoming coax to ground. But there would still be an issue with any external transients that may couple into the antenna since they are not DC potentials.

Off-the-shelf coaxial line transient suppressors are usually rated for normal lightning suppression purposes and can have a characteristically high breakdown voltage much more that the relatively low maximum voltage permitted by the instrument input. Many instruments may display a warning on the front panel near the input connector sporting maximum voltage levels anywhere from a few upwards to 50 volts or more before damage will occur. These levels should be heeded lest one be faced with costly instrument repair or none at all given the legacy ages of much of the equipment possessed by members on this list.

As the well-known Clint Eastwood once said – “How lucky do you feel?”

Greg



Re: Tek 5440

WastelandTek
 

I have converted 2 5000 series scopes to the rackmount form factor.

It is not hard, you have to fabricate a couple simple parts if you don't have a donor unit going the other way, and it requires a fair amount of disassembly to untangle the wiring loom.

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