Date   
Re: Switching power supplies

Tom Gardner
 

On 26/03/19 20:37, Brendan via Groups.Io wrote:
I have a few questions about power supplies and would like some opinions. Are switching powers supplies inherently harder on components than linear power supplies? If you picked up a 70's-80's vintage scope with a SMPS would you replace power supply components before using it as a daily driver? Or do you treat all power supplies the same and visually inspect, check for ripple and call it good? From my reading it seems that when a SMPS melts down the chain reaction damage has the possibility of being bad.
Replace Rifa mains interference suppression delayed action smoke generators on sight; if there is any sign of cracking in the transparent case, don't even turn it on.

Where there are tantalum beads that are operating near their rated voltage (e.g. a 15V tant on a 13V rail), replace those with a higher voltage.

Visually inspect, measure, replace if there's a problem.

Otherwise, if it ain't broke, don't fix it.

11801 calibrator rise time

Reginald Beardsley
 

I think I figured out why the calibrator rise time measurement doesn't read to spec. I warmed up the 11810 for about 40 minutes to do the Enhanced Accuracy adjustments. That seemed to go fine except afterwards when I measured the rise time I was getting >400 ps. The 11801 will remember the incorrect settings through a power cycle.

If you do the Loop Gain adjustment in the Enhanced Accuracy menu it resets something which results in incorrect values. If you go to the Utility menu and press Initialize you should now be able to set the Trigger to Internal, press Autoset, adjust the time base, turn on Hardware measurement and get <35 ps rise time.

Unfortunately, it does not appear to be possible to measure the rise time on more than one one channel.

I think a bunch of the Chinese DSO designers must have spent a lot of time using an 11801 and thought that was what a scope UI should look like. Even after reading all the way through the User manual the UI is still confusing because of the strange locations of various settings.

The tip off came from this line on p 82 of the User manual:

"Whenever you begin a new task using the 11801. you should initialize the system so that all the settings are at "factory default" . That way you do not get unexpected results because of settings remaining from the last use of the 11801."

BTW I have a 2 port divider feeding the upper channel of my SD-22s and the waveforms look to be exactly the same. The pieces of hardline from the divider to the heads are different lengths and I have not been able to shift one relative to the other to see how closely they overlay as there is a 340 ps delay between the two. The divider increases the rise time to 42 ps. It's an MBC Technology unit. No frequency rating specified.

I just discovered that it reset the time base readings when I removed the splitter and turned off one channel to take a look at how much of the 7% overshoot was the splitter which it turns out is about 5% of the total.

There's a little bit of ringing on the calibrator step at 12.2 GHz which is probably the result of reflections where the semi-rigid SMA cable connects to the 3.5 mm calibrator and sampling head connectors.

I am quite agog at how precise this thing is. Getting the full performance out of it will take some serious skill.

Re: Switching power supplies

Glenn Little
 

My take on this after replacing thousands of surface mount electrolytic capacitors is replace them all when you get a new to you device that is more than ten or so years old.

Switchers are harder on electrolytics because they run at a higher frequency than a linear supply and the bean counters usually required the least expensive part to be installed to get the instrument out of warranty.

My take on surface mounted electrolytics is that the fail for two reasons. The seal where the positive lead exits the case was violated during the reflow process. Or the capacitors was not properly selected for the task at hand.

When I replace power supply capacitors in switchers, I select the highest temperature capacitors available with the highest ripple current rating that will fit into the available space. I do not use 85 degree C capacitors unless they are all that is made in that value and voltage.

When doing repair work on cameras and tape decks in TV stations, I never saw a failure of a capacitor that I replaced with the above guidelines. I may have not waited long enough or may have been lucky.

Large computer grade electrolytics are the exception. Do not replace unless needed. These do not usually cause board damage that cannot be repaired.

See: https://www.eetimes.com/author.asp?section_id=183&doc_id=1279791#

Hope this helps.

Glenn

On 3/26/2019 4:37 PM, Brendan via Groups.Io wrote:
I have a few questions about power supplies and would like some opinions. Are switching powers supplies inherently harder on components than linear power supplies? If you picked up a 70's-80's vintage scope with a SMPS would you replace power supply components before using it as a daily driver? Or do you treat all power supplies the same and visually inspect, check for ripple and call it good? From my reading it seems that when a SMPS melts down the chain reaction damage has the possibility of being bad.


Brendan


--
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Glenn Little ARRL Technical Specialist QCWA LM 28417
Amateur Callsign: WB4UIV wb4uiv@... AMSAT LM 2178
QTH: Goose Creek, SC USA (EM92xx) USSVI LM NRA LM SBE ARRL TAPR
"It is not the class of license that the Amateur holds but the class
of the Amateur that holds the license"

Re: Repairability of SD-24, SD-30 & SD-32 sampling heads

Jim Ford
 

Hmmm...  Did he die-bond, wire-bond, and package the FPGA or just solder it onto the board?  Not so impressive if it's the latter.  Still, the link to the website shows microwave devices being bonded in hybrid packages to repair mixers in spectrum analyzers - now that's impressive!Jim FordSent from my Verizon, Samsung Galaxy smartphone

-------- Original message --------From: Craig Sawyers <c.sawyers@...> Date: 3/25/19 5:07 PM (GMT-08:00) To: TekScopes@groups.io Subject: Re: [TekScopes] Repairability of SD-24, SD-30 & SD-32 sampling heads He clearly knows what he is doing. You don't knock up something with an Altera FPGA unless you have a major development lab at your disposal https://www.qsl.net/ct1dmk/gw_04.jpgCraig> -----Original Message-----> From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Jose Luu> Sent: 25 March 2019 23:29> To: TekScopes@groups.io> Subject: Re: [TekScopes] Repairability of SD-24, SD-30 & SD-32 sampling heads>> https://www.qsl.net/ct1dmk/wbond_ex.html>> This guy seem to have made a home hybrid lab and repairs. Could former professionals comment ?>> Best> Jose>>> On Mon, Mar 25, 2019 at 9:30 PM Bob Koller via Groups.Io <testtech= yahoo.com@groups.io> wrote:>> > How well I know. My last job in the hybrid business was at Teledyne> > Microelectronics. Space Qual parts had reams of paperwork, x-rays,> > PIND test,photographs, etc...> > Tek, Keysight, and many other still , out of necessity, use hybrid> > technology with custom parts, in the front ends, and other places, of> > very high frequency instruments. But, commercial hybrid production> > has, I think, largely been supplanted by ASIC, FPGA, and more modern,> > more reliable, less expensive technology.> >> >> >> >>>

Re: Switching power supplies

Kevin Oconnor
 

I have to agree with Chuck. Most test equipment with imbedded/integrated switchers are going to be very difficult to qualify parts if working. Their functionality can be extremely subtle. Blanket replacement of components will more likely cause additional reliability issues.
My 1978 Tek 485 has had spot repairs, but it’s still working fine. I’d never replace caps in it without good reason.
I have an HP 500MHz digital scope with one of this 3rd party modular switchers. (I forget the HP model but 5digits). Switcher went bad. No docs, no schematics. Really hopeless to diagnose. Best option was an eBay replacement switcher. $50 and never looked back.
Now if you are talkin about bad caps in an LCD monitor or TV, that’s where “replace em all” will serve u well! Lots of crap used in those devices.

K

Sent from kjo iPhone

SD-26 disassembly, how to separate sampling gate block from pcb

Albert Otten
 

Does anyone know how to remove the complete sampler block from the printed circuit board? I ask since I'd like to replace the channel select switches. The solder lips are hidden between sampler block and pcb. I removed the 6 block attachment screws but still I can't remove the block with reasonable force. Maybe more force is needed because there are several contact pins between this block and the pcb. The nice close-up repair photos by Leo Bodnar show the internals of the sampler block but not how to remove the block (the block perhaps was still in situ during repair).
It seems that the tiny plastic push pins of the switches have been cut away deliberately. I guess this has been done to prevent any accidental touches by an operator. I can still activate the switches using a small screw driver, so I don't want to take the risk of damaging the otherwise functioning head.

Albert

Re: Switching power supplies

Chuck Harris
 

SMD electrolytic capacitors are a tricky problem in several ways:

First, they are easily damaged by the heat of the reflow oven,
and solvents that may be used in cleaning flux,... though cleaning
flux isn't done much if at all, on consumer grade equipment.

Second, it is almost impossible to find out what was originally
installed. There are no standardized markings to identify the
manufacturer, or what grade capacitor was installed.

Third, it is hard for a re-worker to find a complete spectrum of
ESR values from which to select replacement capacitors.

When you grab an assortment of SMD electrolytic capacitors off
of ebay, you are unlikely to be able to match more than just the
capacitance and voltage of the original. Never the ESR or lifetime
rating.

When you buy from Mouser, or DigiKey, you will find that cute
little 20uf, 16V cap you need to replace, (because its ESR is 3 ohms
while its cohorts are all 0.5 ohm), can only be had with ESR's of
0.7 ohm, 3 ohms, and 12 ohms! Replace the 0.5 ohm ESR caps with a
0.7 ohm cap, and you have taken the expected life of the cap and cut
it in half (or more). Put in a 3 or 12 ohm version, and you will have
improved nothing.

Tricky indeed!

-Chuck Harris

Kevin Oconnor wrote:

I have to agree with Chuck. Most test equipment with imbedded/integrated switchers are going to be very difficult to qualify parts if working. Their functionality can be extremely subtle. Blanket replacement of components will more likely cause additional reliability issues.
My 1978 Tek 485 has had spot repairs, but it’s still working fine. I’d never replace caps in it without good reason.
I have an HP 500MHz digital scope with one of this 3rd party modular switchers. (I forget the HP model but 5digits). Switcher went bad. No docs, no schematics. Really hopeless to diagnose. Best option was an eBay replacement switcher. $50 and never looked back.
Now if you are talkin about bad caps in an LCD monitor or TV, that’s where “replace em all” will serve u well! Lots of crap used in those devices.

K

Sent from kjo iPhone



Re: Switching power supplies

David Kuhn
 

Switching supplies can be a problem when they fail. I recently had a
Agilent VXI E4808A chassis that the main power supply failed, at least
its 12 volts out did. That power supply is huge with a logic board mounted
about it ( I think it's a power supply monitor board). It's a lot of
physical work just to get it apart to check caps. Anyway, I doubt
HP/Agilent made that power supply themselves. I really don't know, as to
get information out of them is like pulling hen's teeth. They no longer
sell, or support, those 4 slot VXI chassis's, so it would be nice of them
to release the schematics, or service information. I think you can only
hope to buy a used chassis somewhere. I would love to have the schematics
for them.

In other switches that fail to start, I often find what I call the
"start-up" capacitor in the primary is open or leaking or has a high ESR.
I call it the "start-up cap" as I do not fully understand switching
supplies, and often if there are schematics, there is not a theory of
operation with them, but there is often a capacitor in the primary circuit
that looks to be a short to ground and then charge-up to create the initial
switch swing to get it going and then afterwards, the power supply self
sustains.

So a lot of times with a dead switcher, I have been able to fix them by
replacing the small electrolytic in the primary side of the circuit. It is
usually a 4.7uf or 10uf. Other than that, if the rest are not physically
leaking or swelled and the supply is working I don't touch it.

One instrument that I work on has an on-board +5volt switching regulator
circuit. It is very reliable. Two times (since 1999) I have seen the
switch regulator fail where the output drive to the FET shorts to ground
allowing the supply voltage (~+12volts) go through to the output with no
over-voltage protection, not even a +5.6volt zener to short. It blows
every TTL chip on the +5volt rail, and some some regulators that follow it.
Stupid, stupid German design. You have to be very urber careful probing
that +5volt switching regulator circuit. One slip of the scope probe and
you can simulate the switching regulator IC output shorting to ground
turning on the pass FET full time. So, I've learned "If it aint broke,
don't fix it"!

Sorry it that was slightly off topic.

Dave

On Wed, Mar 27, 2019 at 8:29 AM Chuck Harris <cfharris@...> wrote:

SMD electrolytic capacitors are a tricky problem in several ways:

First, they are easily damaged by the heat of the reflow oven,
and solvents that may be used in cleaning flux,... though cleaning
flux isn't done much if at all, on consumer grade equipment.

Second, it is almost impossible to find out what was originally
installed. There are no standardized markings to identify the
manufacturer, or what grade capacitor was installed.

Third, it is hard for a re-worker to find a complete spectrum of
ESR values from which to select replacement capacitors.

When you grab an assortment of SMD electrolytic capacitors off
of ebay, you are unlikely to be able to match more than just the
capacitance and voltage of the original. Never the ESR or lifetime
rating.

When you buy from Mouser, or DigiKey, you will find that cute
little 20uf, 16V cap you need to replace, (because its ESR is 3 ohms
while its cohorts are all 0.5 ohm), can only be had with ESR's of
0.7 ohm, 3 ohms, and 12 ohms! Replace the 0.5 ohm ESR caps with a
0.7 ohm cap, and you have taken the expected life of the cap and cut
it in half (or more). Put in a 3 or 12 ohm version, and you will have
improved nothing.

Tricky indeed!

-Chuck Harris

Kevin Oconnor wrote:
I have to agree with Chuck. Most test equipment with imbedded/integrated
switchers are going to be very difficult to qualify parts if working. Their
functionality can be extremely subtle. Blanket replacement of components
will more likely cause additional reliability issues.
My 1978 Tek 485 has had spot repairs, but it’s still working fine. I’d
never replace caps in it without good reason.
I have an HP 500MHz digital scope with one of this 3rd party modular
switchers. (I forget the HP model but 5digits). Switcher went bad. No docs,
no schematics. Really hopeless to diagnose. Best option was an eBay
replacement switcher. $50 and never looked back.
Now if you are talkin about bad caps in an LCD monitor or TV, that’s
where “replace em all” will serve u well! Lots of crap used in those
devices.

K

Sent from kjo iPhone





Re: Switching power supplies

Chuck Harris
 

In switcher parlence, the "start up" capacitor is called the
bootstrap capacitor because the supply picks itself up by its
bootstraps. It is often charged by using a high wattage resistor
connected to the power line, with a diode, capacitor, and zener
to limit its DC voltage. It supplies power to the control PWM
circuitry. When the supply starts, the bootstrap will be taken
over by voltage from a winding on the switcher transformer.

Half wave rectifying creates a lot of ripple current in these
capacitors, and they very often... and I mean VERY often go open
circuit, preventing the supply from starting.

I have fixed many tens of thousands of dollars of equipment ranging
from sewing machines to TV sets by replacing the bootstrap capacitor
and sometimes the bootstrap resistor.... Even HP supplies ;-)

Competently designed switching power supplies are a delight to
behold. They seem to protect themselves from everything, including
stupid technician mistakes.

-Chuck Harris

David Kuhn wrote:

Switching supplies can be a problem when they fail. I recently had a
Agilent VXI E4808A chassis that the main power supply failed, at least
its 12 volts out did. That power supply is huge with a logic board mounted
about it ( I think it's a power supply monitor board). It's a lot of
physical work just to get it apart to check caps. Anyway, I doubt
HP/Agilent made that power supply themselves. I really don't know, as to
get information out of them is like pulling hen's teeth. They no longer
sell, or support, those 4 slot VXI chassis's, so it would be nice of them
to release the schematics, or service information. I think you can only
hope to buy a used chassis somewhere. I would love to have the schematics
for them.

In other switches that fail to start, I often find what I call the
"start-up" capacitor in the primary is open or leaking or has a high ESR.
I call it the "start-up cap" as I do not fully understand switching
supplies, and often if there are schematics, there is not a theory of
operation with them, but there is often a capacitor in the primary circuit
that looks to be a short to ground and then charge-up to create the initial
switch swing to get it going and then afterwards, the power supply self
sustains.

So a lot of times with a dead switcher, I have been able to fix them by
replacing the small electrolytic in the primary side of the circuit. It is
usually a 4.7uf or 10uf. Other than that, if the rest are not physically
leaking or swelled and the supply is working I don't touch it.

One instrument that I work on has an on-board +5volt switching regulator
circuit. It is very reliable. Two times (since 1999) I have seen the
switch regulator fail where the output drive to the FET shorts to ground
allowing the supply voltage (~+12volts) go through to the output with no
over-voltage protection, not even a +5.6volt zener to short. It blows
every TTL chip on the +5volt rail, and some some regulators that follow it.
Stupid, stupid German design. You have to be very urber careful probing
that +5volt switching regulator circuit. One slip of the scope probe and
you can simulate the switching regulator IC output shorting to ground
turning on the pass FET full time. So, I've learned "If it aint broke,
don't fix it"!

Sorry it that was slightly off topic.

Dave

Re: Switching power supplies

Tom Gardner
 

On 27/03/19 06:05, Kevin Oconnor wrote:
My 1978 Tek 485 has had spot repairs, but it’s still working fine. I’d never replace caps in it without good reason.
Personally I'd replace C911: 22uF 15V tant bead on a 13V PSU rail, diagram 17 (not the PSU diagram!), and IIRC there are a couple of others on that rail, hidden on the other diagrams 7, 9, 11, 16.

When C911 shorted, it toasted R965.

Re: 11801 calibrator rise time

Albert Otten
 

Reg,

If you display the two channels simultaneously then they share the same time base speed and position. I don't see how you tried to align the rising edges. On my CSA's I do this: display both channels CH1 and CH2, then Store CH1 en turn CH1 off, then Recall the stored trace of CH1. Now the displayed stored trace is "frozen" and remains in position regardless how you change the time base of the CH2 trace. (Note you can select one of the displayed traces by touching the trace somewhere.)

Albert

On Tue, Mar 26, 2019 at 11:10 PM, Reginald Beardsley wrote:


BTW I have a 2 port divider feeding the upper channel of my SD-22s and the
waveforms look to be exactly the same. The pieces of hardline from the
divider to the heads are different lengths and I have not been able to shift
one relative to the other to see how closely they overlay as there is a 340 ps
delay between the two. The divider increases the rise time to 42 ps. It's an
MBC Technology unit. No frequency rating specified.

Re: 11801 calibrator rise time

Reginald Beardsley
 

That was my conclusion. But the UI is so bad that I thought there might be a variable delay line in there somewhere that would adjust channel skew. I've also discovered it is buggy as all hell. You pretty much have to reinitialize the scope for a bunch of operations. I tried switching from vector to dot mode. Menu said vector was off, but the display said otherwise. Once I initialized the scope I was able to set it to dot mode.

I've had the 11801 running for 4-5 hours with the calibrator feeding an SD-22 with cursors set on the peaks of the reflection in the cable. I've noticed that the internal timebase varies by a little over 1 ps over the course of 5-10 minutes. I have a postit on the screen and the cursors are not moving. The waveform is moving. I've got the internal clock output connected to my 5386A with the OCXO option and that confirms the internal time base period is changing.

From looking at the block diagram in the service manual, it appears to me that the OCXO is not as stable as the one in my 5386A which I have compared to a GPSDO over long periods.

This has me considering whether installing one of Leo Bodnar's single output GPSDOs in place of the 200 MHz OXCO would be worthwhile. In particular in improving the jitter spec from the factory 1.1 ps.

Watching the clock period vary by 100 femtoseconds over the course of 15-30 seconds with a 1 s gate time is rather interesting.


Reg

--------------------------------------------

On Wed, 3/27/19, Albert Otten <aodiversen@...> wrote:

Subject: Re: [TekScopes] 11801 calibrator rise time
To: TekScopes@groups.io
Date: Wednesday, March 27, 2019, 12:57 PM

Reg,

If you display the two channels simultaneously
then they share the same time base speed and position. I
don't see how you tried to align the rising edges. On my
CSA's I do this: display both channels CH1 and CH2, then
Store CH1 en turn CH1 off, then Recall the stored trace of
CH1. Now the displayed stored trace is "frozen"
and remains in position regardless how you change the time
base of the CH2 trace. (Note you can select one of the
displayed traces by touching the trace somewhere.)

Albert

Need Help repairing a 7104 oscilloscope

 

Hello all

I just got a 7104 for 30 dollars. With all 4 plugins. Including the 1ghz
one.

I need help fixing it. It powers on but the trace is wide and choppy . I
created a video. Please see it and let me know. I will start with
checking the volts on the different rails.


https://youtu.be/wMGDOzYwLys


Thx in advance for your help

Re: Greeting from Stan

 

Hello, I'm Armando

I'm new here.. I just bought a 7401 for 30 bucks. , it turns on, and if I play with the buttons and give a little smack , I get a distorted, extra wide and chopped up trace.
anyways. I will be doing the dismantleling soon and visual inspection, looking forward for some help, getting this puppy up and working. :}

Armando

Re: Hello World

 

Welcome, I'm not afraid, my name is Oscillator Sherman

You have any vidoes or PIctures of the monster oscilloscope
I just bought a 1ghz tektronix 7104 for 30 dollars Partially working.
Here is my video

https://www.youtube.com/watch?v=wMGDOzYwLys

Re: New: Member Intro

 

Welcome, I have 1 7401 with this Plug ins: 7A18A , 7A29 , 7B53A , 7b15
I need help rebuilding it.
It turns on, and If I give a little smack and play with the buttons, eventually I got a distored glitched out Fat and chopped trace. :(
wil start with the visual inspection and cleaning first.. we'll how to goes from there

Any one with experience on this is Local " Los Angeles, CA"

Tek 2465B Calibrator issues

Marcial Gomez Varas
 

Hi everyone,

I bought some time ago (2017) a TEK 2465B that I didn't have too much time to play with (having 2 kids and a travelling job doesn't help!)
I have been toying with it lately, and I've discovered that the calibrator is showing some really awful square signal.

It's clearly NOT square ! It has quite a bit of slope in the rise and fall lines, and bouncing on the high level.
I have checked and both the output levels and frequency seem to be OK, but somehow the signal is distorted.

Could it be some capacitor? Looking at the service manual it shows to be in the A1 board, section 5 (That should be in the middle left side, am I right?)

Any help would be appreciated !

Cheers,
Marcial

Tek 2710 focus issue

john@...
 

Hi,
I have tried adjusting the rear focus control to get a good focus on the screen, but it just 'jumps about'

I have tried the trimmer on the main PCB underside of the unit which allows me to adjust to focus, but power down and focus is blurr!

Any help would be much appreciated.

Regards

John

Need Help fixing my newly acquired 7401

 

Hello guys

I just bought a 7104 fully loaded with plugin for 30 bucks from this guy on offer up in California. But its partially working.

I posted a video of what it does.
I'm excited to get some pointers on where to star and get this Vintage Gem working again. Voltage rails any specific capacitors. It's the issue the plug ins ?


https://youtu.be/wMGDOzYwLys

Re: Tek transformer 120-0866-02

Richard Katezansky
 

According to the recently scanned and released transformer list on VintageTek it's for the 408, 412, or 414 portable patient monitors.
Mid to late 70's vintage.

Richard