Re: focus/astig off the center.
How is the screen geometry? I would check the various voltages to the CRT except the acceleration voltage with a medium voltage probe. On Sun, 22 Jan 2012 02:14:41 +0000, Luis Cupido <cupido@...> wrote: Hi,
I have two 7623b with the following
symptom: Focus adjust perfect on the
center and not so perfect near the edges
so when readout is perfect for astig/focus
the center is bad and vice versa.
Not too severe on one, but quite bad on
the second scope.
I'm sure someone will know ...
so better ask before I tweak them up too much ;-)
Many thanks.
Luis Cupido
ct1dmk.
|
focus/astig off the center.
Hi,
I have two 7623b with the following
symptom: Focus adjust perfect on the
center and not so perfect near the edges
so when readout is perfect for astig/focus
the center is bad and vice versa.
Not too severe on one, but quite bad on
the second scope.
I'm sure someone will know ...
so better ask before I tweak them up too much ;-)
Many thanks.
Luis Cupido
ct1dmk.
|
--- In TekScopes@..., "kd8dey" <kd8dey@...> wrote:
I bought a 2235 on E-bay because it had the DMM/Freq counter and the digital display is bad.
I am wondering what other models have the DMM/counter BUT display on the scope itself?
I thought a 2235 was a 2236 without the CTM board and display? Are you sure you have a 2235?
|
Re: Power supply problem with Tek 2220
Tan Chor Ming wrote: Thanks Gary,
Do you suspect that it???s a cap ESR issue? High ESR in an old electrolytic cap is a symptom, not a cause. When the ESR measures high, it means that the cap is bad, and should be replaced. Why would it cause such a behaviour? Don't think of ESR as the cause - think of the defective cap as the cause, and the high ESR as an indicator that the cap is defective. Ed I believe you can infer a lot from the behaviour than blind guesses that???s where I am trying to tap from the experienced engineers.
I suppose I have more than the basic knowledge because I am an electronics engineer with working knowledge in vacuum and solid state electronics.
I have built a scope from scratch, otherwise I would not attempt so work with EHT.
Rgds,
Chor Ming
------------------------------------------------------------------------
*From:* TekScopes@... [mailto:TekScopes@...] *On Behalf Of *Terry Gray
*Sent:* Saturday, January 21, 2012 1:11 AM
*To:* TekScopes@...
*Subject:* Re: [TekScopes] Power supply problem with Tek 2220
At least check the incircuit power supply electrolytic capacitors for ESR. If you don't have an ESR tester, buy one or build one. There is lots of ESR information on the web and also in the archives of this yahoo group. You definitely need one if you're considering working on this type of electronic equipment and problems. Otherwise give the problem to someone else who has this essential test equipment and basic electronic knowledge to assist in diagnosing your problem. You are over your head without basic skills and test equipment.
------------------------------------------------------------------------
*From:* Tan Chor Ming <jonray03@...>
*To:* TekScopes@...
*Sent:* Friday, January 20, 2012 8:45 AM
*Subject:* Re: [TekScopes] Power supply problem with Tek 2220
Has anyone seen this behaviour repairing Tek2000 series scope power
supply?
Behaviour
1. When power on from cold, it will fire up properly and stay on for
a few minutes
2. Once it warms up, the power supply shut down and try to on again
and it continues in this on/off mode
3. Pre-regulator out = 43V (between TP940 and TP950)
4. All voltages when the unit is stable for a few minutes are +8.6,
-8.6, +5.2, +100 are all ok.
What are likely problems before I start ripping the components from
the circuit?
ttesenq@... <mailto:ttesenq@...> suggested that
it could be the pre-regulator MOSFET P9070.
I though that it could be a electrolytic cap but it doe not look
likely because electrolytic failure would not have allowed the unit
to fire up for a few minutes
It is more likely a active component that weaken with increase
temperature, so ttesenq@... <mailto:ttesenq@...>
could be right. This would mean Q947 and Q946 are also likely components
Any other possible lead of similar experience.
|
Hello David,
It's getting late over here now, so others may correct me - but I have read over your voltage measurements and it seems that Jimmy has hit the nail right on the head.
Q872 e = +0.7v
c = + 64.6v
b = +1.3v
--> So the V BE should turn it on, but the V CE readings show that it does not.
Checking the parts list is easy. Sphere shows here that Q872 is a 2N3923, TO39 NPN transistor.
If you find any other 150V rated, mid-beta NPN transistor, I would try that to replace Q872...
Good Luck when searching your drawers for existing replacements.
Cheers,
Magnus
|
--- In TekScopes@..., "kd8dey" <kd8dey@...> wrote:
I bought a 2235 on E-bay because it had the DMM/Freq counter and the digital display is bad.
I am wondering what other models have the DMM/counter BUT display on the scope itself?
The 2236 also had the same display. I believe it added delta time measurement, or something similar to the display. Are you sure the display itself is bad? The device is a VFD. There were no real standards for these, so it will be nearly impossible to find a drop fit replacement. However, other than the glass breaking or the filament going open (which is not likely as they run very low power through the filiment), there is not much that can go wrong with them. More likely the problem is in the drive circuit This display will use multiplexed digits, with the individual segments bussed between the same segment in all the digits. There is a small control grid used to select which digit is being active during its display window. Should be easy to troubleshoot. The voltages will be around 20-30 volts. - Steve
|
I know the 2247A can make automated on-screen voltage and frequency
measurements. The 2246A does the same without the counter/timer
functions.
The 2445B, 2455B, 2465B, and 2467B have optional timer/counter and
voltmeter functions.
toggle quoted message
Show quoted text
On Sat, 21 Jan 2012 22:34:24 -0000, "kd8dey" <kd8dey@...> wrote: I bought a 2235 on E-bay because it had the DMM/Freq counter and the digital display is bad.
I am wondering what other models have the DMM/counter BUT display on the scope itself?
|
On 21/01/2012 04:45, jtjewell83 wrote:
?
David,
I agree with Jerry---You don't need an isolation
transformer to work on this scope. T801 provides all of
the isolation necessary.
I still beleive that you need to concentrate on the +50V
supply. Can you measure and post the voltages on driver
transistors Q869 and Q872. I'm thinking one of those may
be open, since you measured about -10V at the base of
Q874. Most likely Q872. Be careful and try not to slip
with your probe and short out something.
If you have time, posting Q860 voltages may help too.
Jimmy
--- In TekScopes@...,
Jerry Massengale wrote:
>
> Hi
>
>
> Allow me to offer a different opinion on this
isolation matter. I worked on a 7D13 with an
isolated(floating) section this weeikend. I used my
isolation gear so that I could tie my scope ground(common)
to the floating common. In such cases isolation is
desirable. In the 7603, the power supply transformer
provides all the isolation you need. Using another level
of isolation allows the 7603's chassis to float and that
is not good. It is an unneeded safety hazard.
>
>
> Jerry Massengale
> jmassen418a@...
Hello Jimmy.
I have just discovered my second mistake. I measured -10v on Q869. I
thought Q869 was Q874, because Q874 isn't actually visible on the
front of the board, it's fixed to the back of the pcb. I have also
only just realised that the transistors are marked on the pcb.
Anyway these are the readings I have just taken.
Q869???? c = +58v
?????????????? b = + 1.9v
?????????????? e = + 1.3v
Q872???? e = +0.7v
?????????????? c = + 64.6v
?????????????? b = +1.3v
Q860????? c = +2.0v
??????????????? b = - 12.7v
??????????????? e = -12.7v
Q874???? ( TO3 case )? c = + 66v
?????????????????????????????????????? e = + 0.7v
?????????????????????????????????????? b = +0.7v
I hope I have got these right and it all makes sense to you!
David
??????????????
|
Re: 7T11 trace shifting left as time/div rotated.
Hi David,
It takes some time to remember what all those circuits in the 7T11 are doing!
The shift in output of U512A in a 5-2-1 sequence corresponds nicely (as should be) to the increase in feedback resistors 10k-25k-50k, ratio 2:3. At 1 ns/div the shift is about 0.5 V and that same shift will appear at the input R647 to the Dot Position Memory. This memory should detect that systematic error and send a correction to the Slow Ramp Inverter. That in turn would (finally) result in a shift of the THT output range to correct the error. This doesn't seem to happen, or not not enough. At the faster sweep speeds U512B and D get switched in and introduce their own offsets. Again the Dot Pos Mem should correct for this.
Maybe you can check its operation/calibration. I remember it's not an easy calibration and a lot of compromise is needed.
Albert
(BTW your packet calculator needs some attention as well...)
toggle quoted message
Show quoted text
In equivalent time, sequential mode, the trace is shifting left as I rotate the time/div knob.
All measurements were made on the 50nS sweep range with the timebase triggered from Pulse Out.
Looking at the signal at TP286 which is the output of the TTH circuit, I see:
Time/Div Start V Stop V Delta V
5nS -2.22V -7.82V -5.6V
2nS -2.22V -4.62V -2.3V
1nS -2.22V -3.5V -1.2V
.5nS -2.22V -2.76V -560mV
.2nS -2.22V -2.43mV -230mV
.1nS -2.22V -2.34mV -120mV
50pS -2.22V -2.62mV -60mV (approx values)
20pS -2.22V -2.25V -30mV
10pS -2.22V -2.23V -10mV
Looking at the output of U512A (TP512):
Time/Div Start V Stop V Delta V
5nS -0.1V +5.5V 5.6V
2nS -0.3V +5.3V 5.6V
1nS -0.6V +5.0V 5.6V
.5nS -900mV +470mV 560mV
.2nS -210mV +350mV 560mV
.1nS -420mV +140mV 560mV
50pS -70mV -10mV 60mV (approx values)
20pS -170mV -110mV 60mV
10pS -340mV -280mV 60mV
I don't think the ramp start voltage should be moving down like that.
Can anyone confirm my suspicions and suggest what the fault might be?
Thanks
David Partridge
|
I bought a 2235 on E-bay because it had the DMM/Freq counter and the digital display is bad.
I am wondering what other models have the DMM/counter BUT display on the scope itself?
|
Good Day,
I have no intentions to start any long discussions here, so I decided to stay away from any.
However, I would want to give a recommendation to David: Start your own internet research on safety isolation transformers and then talk to an experienced electrician to understand the benefits of these units.
On that subject: Your VARIAC very likely provides no isolation. Here is a simple set-up how to test this: Unplug the unit completely and use cables with alligator clips to shorten the input's LIVE/NEUTRAL and another pair to shorten the output's LIVE/NEUTRAL conductor.
Now measure the resistance between both points - the shortended LIVE/NEUTRAL on the secondary side and the shortened LIVE/NEUTRAL on the primary.
Unless you measure a high resistance path, your VARIAC provides no isolation.
Cheers,
Magnus
|
Re: 7T11 trace shifting left as time/div rotated.
Joe,
Thanks for the suggestion, but I'd already found Albert's posts earlier in the day, and it really doesn't match - here we're talking about the trace shifting off screen to the left not the right. C237, C292, and C313 seem to work as expected when running through the calibration procedure.
Thanks
Dave
toggle quoted message
Show quoted text
-----Original Message----- From: TekScopes@... [mailto:TekScopes@...] On Behalf Of Albert Sent: 21 January 2012 19:37 To: TekScopes@... Subject: [TekScopes] Re: 7T11 trace shifting left as time/div rotated. Joe, Perhaps a good moment to tell whether your 7T11 indeed had a trim cap problem? Or was it another fault that would be good to know about? Albert
David,
Try searching "7T11 Failing Trim Caps" in the archives.
This contains information on shifting trace problem.
Joe
------------------------------------ Yahoo! Groups Links
|
Re: 10nF leadless ceramic capacitor
Stephan has the right idea, David. 1/4 inch dia. ceramic coated .01uF 100V ceramic disks are very common (at least over here). The ceramic easily chips off to expose the blobs of solder that attach the leads. Don't attempt to wick off the solder, you might end up with the same problem, metallization removed. Just heat the blob until the lead comes off. Trim off excess solder with a scalpel until the cap fits in place. The rest you know.
Arden
toggle quoted message
Show quoted text
This is a completely leadless 10pF ceramic capacitor about 3/8" square, Tektronix part number 283-0253-00
Where can I get something like this??? None of the distributors seem to have leadless disc ceramics.
|
Folks,
I scanned the 121 manual and the PDF file is here:
There is a scan on BAMA of the same document, but that scan is cut off in a couple of places.
As always, if you have Tektronix manuals that are not already freely available, please get in touch with me so we can make them available for everybody.
Also, if you have free PDF files that you want to share, you can drop them here: and I'll put them on Tekwiki. The goal is to make all of the classic Tektronix documentation freely available for everybody.
thanks, -Kurt
|
Re: 7T11 trace shifting left as time/div rotated.
Joe,
Perhaps a good moment to tell whether your 7T11 indeed had a trim cap problem? Or was it another fault that would be good to know about?
Albert
toggle quoted message
Show quoted text
David,
Try searching "7T11 Failing Trim Caps" in the archives.
This contains information on shifting trace problem.
Joe
|
Re: 7T11 trace shifting left as time/div rotated.
David,
Try searching "7T11 Failing Trim Caps" in the archives.
This contains information on shifting trace problem.
Joe
toggle quoted message
Show quoted text
--- In TekScopes@..., "David C. Partridge" <david.partridge@...> wrote:
In equivalent time, sequential mode, the trace is shifting left as I rotate the time/div knob.
All measurements were made on the 50nS sweep range with the timebase triggered from Pulse Out.
Looking at the signal at TP286 which is the output of the TTH circuit, I see:
Time/Div Start V Stop V Delta V
5nS -2.22V -7.82V -5.6V
2nS -2.22V -4.62V -2.3V
1nS -2.22V -3.5V -1.2V
.5nS -2.22V -2.76V -560mV
.2nS -2.22V -2.43mV -230mV
.1nS -2.22V -2.34mV -120mV
50pS -2.22V -2.62mV -60mV (approx values)
20pS -2.22V -2.25V -30mV
10pS -2.22V -2.23V -10mV
Looking at the output of U512A (TP512):
Time/Div Start V Stop V Delta V
5nS -0.1V +5.5V 5.6V
2nS -0.3V +5.3V 5.6V
1nS -0.6V +5.0V 5.6V
.5nS -900mV +470mV 560mV
.2nS -210mV +350mV 560mV
.1nS -420mV +140mV 560mV
50pS -70mV -10mV 60mV (approx values)
20pS -170mV -110mV 60mV
10pS -340mV -280mV 60mV
I don't think the ramp start voltage should be moving down like that.
Can anyone confirm my suspicions and suggest what the fault might be?
Thanks
David Partridge
|
Re: Power supply problem with Tek 2220
Yes indeed, the 2220 is virtually identical to the 2230 in most respects - just a notch down to fill the price v. performance market position at the time. The 2200 series models share the same basic power supply topology, tweaked to get more power for the digital storage add-ons.
Your equipment appears to be very limited, but you do have a working DMM and a "working" scope available for a few minutes at a time. You can use it to look at its own supplies and other circuitry, at least up to the point of shutdown.
Before delving further into the supply, I recommend that you first check your line voltage to see if it's on the high side, or possibly has transients or surges that may be causing the scopes to self-protect. I don't recall if the 2220 has the "trigger view" feature, but if so, set up for line triggering, and activate that to see roughly what the line looks like. This is band limited, so won't show fast transients. You can also look at the line voltage directly and more accurately with a X10 probe tip to the hot side. DO NOT connect the ground clip to anything, or preferably, disconnect it from the probe whenever poking around line voltage.
As I recall, the scopes should run on any line voltage between the specified limits, with no range switching needed. If you have access to a variac or step-down transformer you can try running at lower line voltage. If not, you can try loading down the branch circuit with extra lighting and appliances to see if it drops significantly, or even try something wired temporarily in series, like a space heater, coffee pot, or a large incandescent lamp.
Some background info should help:
1. Were these scopes working and then stopped, or did you just get them, and they didn't work? It seems from your initial post that they both failed at the same time. If so, one big thing in common would be line voltage problems. Do both scopes exhibit the same symptoms?
2. Is the available run time always about the same before shutting down? Does recycling the power make it run for the same length of time, or does it need to cool down first?
If the shutdown timing is fairly predictable, it may be good to monitor the outputs closely and watch to see if they sag or rise just before shutdown. Also, watch the display closely for dimming or blooming - evidence of same on the high voltage.
Also, look at the 20 kHz AC waveforms on the secondaries, ahead of the output rectifiers to see if they are nice, rounded squarish waves, and see if that shape changes just before shutdown.
That's probably enough for now.
I agree with the suggestion to revisit the 2235. It may be easier to fix, or you may luck out and find it's problem - then you'll have one fully working scope - a big improvement.
Ed
toggle quoted message
Show quoted text
--- In TekScopes@..., David <davidwhess@...> wrote:
When I was searching for a replacement channel swtich, I found that a
number of the 22xx series oscilloscopes have the same main board which
has the power supply including the 2213A, 2215A, 2230, 2232, 2235,
2236 but not the 2213 or 2215. For the analog only models, the extra
outputs which would go to the digital storage board are tied to ground
to maintain bias on the channel switches. The 2220 is much rarer with
no online service manual so I never checked it.
On Sat, 21 Jan 2012 06:28:59 -0800, "tom jobe" <tomjobe@...>
wrote:
Hi Tan,
Some one told me that the 2220 is the 60 MHz version of the 2230 100 MHz
scope. If this is true, the 2230 manual might be your best bet. It is
available from several places including:
Now that I hear about your experience level and what equipment you have on
hand, I would fix the 2235 first as it has no top board limiting your access
to the power supply (and almost everything else in the scope) while the
scope is actually running.
You mention the need for an isolation transformer. You probably do not need
an isolation transformer at this point, as its only value is to be able to
"float" the scope so you can use another scope to look at the inverter side
of the power supply. The inverter is already making the 43 VDC so what would
you need to check anyway? I know the service manual calls for an isolation
transformer (so I bought one) but my experience finds it to be fairly
useless in the 22xx repair process. Also, once you "float" the scope the
chassis of the scope is now at some elevated voltage, which is a little
scary for an amateur like me.
You mentioned that Q908 was up on the heatsink but it isn't. Take a closer
look as it only is involved in running the "gate" of Q9070.
Q9070 is up on the heatsink. Q908 is a small transistor with minor currents
through it, and Q9070 does the real work of creating the 43 VDC for the
inverter.
If you ever decide to do the external injection of the 43 VDC, you need to
disconnect Q9070, not Q908.
tom jobe...
----- Original Message -----
From: "Tan Chor Ming" <jonray03@...>
To: <TekScopes@...>
Sent: Friday, January 20, 2012 8:37 PM
Subject: RE: [TekScopes] Power supply problem with Tek 2220
Thank you Tom for taking the time to point out specifically the likely cause
of the problem.
I know it takes effort to go through the details and I really appreciate it.
Just to let you know where I come from, so that there is less to assume.
I am an electronics engineer from Singapore above 50 so very much familiar
with vacuum and solid state electronics.
I do not have the schematics for 2220 so like you I am assuming it is
quite
similar to 2235 which I have it downloaded.
I have both 2220 and 2235 and there appear to be quite similar though the
PCB layout is slightly different.
I have complete understanding of how the power supply works.
Pre-regulator - PWM driving Q908 to produce +43V across TP940 and TP950
Final Regulator - DC-DC push-pull inverter through Q947 and Q946.
I have another scope 2235, unfortunately, it too went down at the same time,
so the only instrument I have is a multimeter.
Anyway, I do not have an isolation transformer so even with the 2235
working, I will need to get an isolation transformer before I could take any
measurement.
Any idea what VA rating is needed for the isolation transformer?
Based on the power needs, it appears to be at least 200VA.
Initially, I was asking about R907, not because I was suspecting the
resistor but I intend to check the load current by putting an ammeter in
series with the resistor.
For that to be useful I need to know what is expected. Like you. I am
suspecting that the voltage at R907 has gone up after the set warms up thus
shutting down U930.
I will probably go with the cap changes you have recommended since I have
some time during the Lunar New Year break.
Unfortunately, I do not have ESR meter, but I don't think that a big issue
just replacing the caps.
I am aware of the direct 43Vdc injection, but thank you for telling me the
detail that Q908 needs to be disconnected.
Unfortunately, I do not have a power supply with this voltage output. I
only have a power supply of 18V max 2A. So I will have to hold off this
approach.
One more thing which I did not mention earlier is that I detached the +5.2V
connection to the digital board (for the storage function of 2220) and
behaviour remains unchanged.
Rgds,
Chor Ming
_____
From: TekScopes@... [mailto:TekScopes@...] On Behalf
Of tom jobe
Sent: Saturday, January 21, 2012 7:30 AM
To: TekScopes
Subject: Re: [TekScopes] Power supply problem with Tek 2220
I saw your 2220 question the first time you posted it a few days ago, and I
did not have a nice short answer for you. Since you have not gotten the
answer
you were looking for, let me comment a bit on this.
First off, I don't own a 2220 or have the service manual for it, and none of
the download sites I checked seem to have it either, including
ArtekMedia.com having it for purchase. So I will assume it is similar to the
better 22xx's such as the 2235, at least around the power supply. I will
also assume that you do have a service manual to work with. U930 monitors
the voltage drop across R907, and in your case it probably thinks the
current is too high after a few minutes, so it shuts down.
I have worked on lots of 22xx scopes and I have not seen the value of R907
drift and cause this problem, but others have reported that as a
possibility. Odds are, that this is not your problem.
An over current situation can be caused by anything after R907 within the
inverter, the transformer itself or on the secondary side of the main
transformer.
How you go about finding the problem depends on what equipment you have
available, and what your testing preferences might be.
If you don't have much to work with, just start changing components. In my
experience the components in the right rear corner of the mainboard cause
the most grief so I would start there with C925, C942 and C943. If you have
some decent soldering equipment you can change all three capacitors quickly
without removing the mainboard.
If you have access to an ESR meter you could check all of the aluminum
electrolytic capacitors in circuit. Most of the electrolytics give no
trouble, especially the six(?) 840 uF caps in front of the heat sink for
Q9070 (but you would want to check all of the electrolytic caps if you had
an ESR meter handy).
Another approach would be to put in the 43 volts DC from an external power
source until something got hot or went up in smoke. If your power supply
allowed you to adjust the current limit you could sneak up on it and just
get the problem part(s) nice and warm. You will need to at least disconnect
Q9070 when you apply the external 43 VDC at TP940 and TP 950 from the bottom
or top of the mainboard. I lightly tack on two wires to the bottom side to
make the 43 VDC connections. You can use the scope in its normal way when it
is powered with the external 43 VDC.
The external 43 VDC idea came from a fine Tekscopes member named Hakan, many
years ago, and he has an excellent document you should read at:
A couple of years ago I made up a document listing some commonly available
components you might use to replace some of the original Tektronix part
numbers that often fail. I can send you that directly or you can find it in
the Tekscopes Message archive if you like.
Another thing you might do is take resistance readings from chassis ground
to each of the voltage test points before you get very far into this repair
(with the scope not connected to the mains of course!).
There are lots of other ideas to add to this, but this should get you
started.
This will be a simple fix, so just take your time and understand what you
are doing.
tom jobe...
----- Original Message -----
From: "Tan Chor Ming" <jonray03@...
<mailto:jonray03%40singnet.com.sg> >
To: <TekScopes@... <mailto:TekScopes%40yahoogroups.com> >
Sent: Friday, January 20, 2012 6:45 AM
Subject: Re: [TekScopes] Power supply problem with Tek 2220
Has anyone seen this behaviour repairing Tek2000 series scope power supply?
Behaviour
1. When power on from cold, it will fire up properly and stay on for a
few
minutes
2. Once it warms up, the power supply shut down and try to on again and it
continues in this on/off mode
3. Pre-regulator out = 43V (between TP940 and TP950)
4. All voltages when the unit is stable for a few minutes are
+8.6, -8.6,
+5.2, +100 are all ok.
What are likely problems before I start ripping the components from the
circuit?
ttesenq@... <mailto:ttesenq%40tiscali.co.uk> suggested that
it
could be the pre-regulator MOSFET
P9070.
I though that it could be a electrolytic cap but it doe not look likely
because electrolytic failure would not have allowed the unit to fire up for
a few minutes
It is more likely a active component that weaken with increase temperature,
so ttesenq@... <mailto:ttesenq%40tiscali.co.uk> could be right.
This would mean Q947 and Q946 are also likely components
Any other possible lead of similar experience.
|
7T11 trace shifting left as time/div rotated.
In equivalent time, sequential mode, the trace is shifting left as I rotate the time/div knob.
All measurements were made on the 50nS sweep range with the timebase triggered from Pulse Out.
Looking at the signal at TP286 which is the output of the TTH circuit, I see:
Time/Div Start V Stop V Delta V
5nS -2.22V -7.82V -5.6V
2nS -2.22V -4.62V -2.3V
1nS -2.22V -3.5V -1.2V
.5nS -2.22V -2.76V -560mV
.2nS -2.22V -2.43mV -230mV
.1nS -2.22V -2.34mV -120mV
50pS -2.22V -2.62mV -60mV (approx values)
20pS -2.22V -2.25V -30mV
10pS -2.22V -2.23V -10mV
Looking at the output of U512A (TP512):
Time/Div Start V Stop V Delta V
5nS -0.1V +5.5V 5.6V
2nS -0.3V +5.3V 5.6V
1nS -0.6V +5.0V 5.6V
.5nS -900mV +470mV 560mV
.2nS -210mV +350mV 560mV
.1nS -420mV +140mV 560mV
50pS -70mV -10mV 60mV (approx values)
20pS -170mV -110mV 60mV
10pS -340mV -280mV 60mV
I don't think the ramp start voltage should be moving down like that.
Can anyone confirm my suspicions and suggest what the fault might be?
Thanks
David Partridge
|
Re: Power supply problem with Tek 2220
When I was searching for a replacement channel swtich, I found that a number of the 22xx series oscilloscopes have the same main board which has the power supply including the 2213A, 2215A, 2230, 2232, 2235, 2236 but not the 2213 or 2215. For the analog only models, the extra outputs which would go to the digital storage board are tied to ground to maintain bias on the channel switches. The 2220 is much rarer with no online service manual so I never checked it. On Sat, 21 Jan 2012 06:28:59 -0800, "tom jobe" <tomjobe@...> wrote: Hi Tan,
Some one told me that the 2220 is the 60 MHz version of the 2230 100 MHz
scope. If this is true, the 2230 manual might be your best bet. It is
available from several places including:
Now that I hear about your experience level and what equipment you have on
hand, I would fix the 2235 first as it has no top board limiting your access
to the power supply (and almost everything else in the scope) while the
scope is actually running.
You mention the need for an isolation transformer. You probably do not need
an isolation transformer at this point, as its only value is to be able to
"float" the scope so you can use another scope to look at the inverter side
of the power supply. The inverter is already making the 43 VDC so what would
you need to check anyway? I know the service manual calls for an isolation
transformer (so I bought one) but my experience finds it to be fairly
useless in the 22xx repair process. Also, once you "float" the scope the
chassis of the scope is now at some elevated voltage, which is a little
scary for an amateur like me.
You mentioned that Q908 was up on the heatsink but it isn't. Take a closer
look as it only is involved in running the "gate" of Q9070.
Q9070 is up on the heatsink. Q908 is a small transistor with minor currents
through it, and Q9070 does the real work of creating the 43 VDC for the
inverter.
If you ever decide to do the external injection of the 43 VDC, you need to
disconnect Q9070, not Q908.
tom jobe...
----- Original Message -----
From: "Tan Chor Ming" <jonray03@...>
To: <TekScopes@...>
Sent: Friday, January 20, 2012 8:37 PM
Subject: RE: [TekScopes] Power supply problem with Tek 2220
Thank you Tom for taking the time to point out specifically the likely cause
of the problem.
I know it takes effort to go through the details and I really appreciate it.
Just to let you know where I come from, so that there is less to assume.
I am an electronics engineer from Singapore above 50 so very much familiar
with vacuum and solid state electronics.
I do not have the schematics for 2220 so like you I am assuming it is
quite
similar to 2235 which I have it downloaded.
I have both 2220 and 2235 and there appear to be quite similar though the
PCB layout is slightly different.
I have complete understanding of how the power supply works.
Pre-regulator - PWM driving Q908 to produce +43V across TP940 and TP950
Final Regulator - DC-DC push-pull inverter through Q947 and Q946.
I have another scope 2235, unfortunately, it too went down at the same time,
so the only instrument I have is a multimeter.
Anyway, I do not have an isolation transformer so even with the 2235
working, I will need to get an isolation transformer before I could take any
measurement.
Any idea what VA rating is needed for the isolation transformer?
Based on the power needs, it appears to be at least 200VA.
Initially, I was asking about R907, not because I was suspecting the
resistor but I intend to check the load current by putting an ammeter in
series with the resistor.
For that to be useful I need to know what is expected. Like you. I am
suspecting that the voltage at R907 has gone up after the set warms up thus
shutting down U930.
I will probably go with the cap changes you have recommended since I have
some time during the Lunar New Year break.
Unfortunately, I do not have ESR meter, but I don't think that a big issue
just replacing the caps.
I am aware of the direct 43Vdc injection, but thank you for telling me the
detail that Q908 needs to be disconnected.
Unfortunately, I do not have a power supply with this voltage output. I
only have a power supply of 18V max 2A. So I will have to hold off this
approach.
One more thing which I did not mention earlier is that I detached the +5.2V
connection to the digital board (for the storage function of 2220) and
behaviour remains unchanged.
Rgds,
Chor Ming
_____
From: TekScopes@... [mailto:TekScopes@...] On Behalf
Of tom jobe
Sent: Saturday, January 21, 2012 7:30 AM
To: TekScopes
Subject: Re: [TekScopes] Power supply problem with Tek 2220
I saw your 2220 question the first time you posted it a few days ago, and I
did not have a nice short answer for you. Since you have not gotten the
answer
you were looking for, let me comment a bit on this.
First off, I don't own a 2220 or have the service manual for it, and none of
the download sites I checked seem to have it either, including
ArtekMedia.com having it for purchase. So I will assume it is similar to the
better 22xx's such as the 2235, at least around the power supply. I will
also assume that you do have a service manual to work with. U930 monitors
the voltage drop across R907, and in your case it probably thinks the
current is too high after a few minutes, so it shuts down.
I have worked on lots of 22xx scopes and I have not seen the value of R907
drift and cause this problem, but others have reported that as a
possibility. Odds are, that this is not your problem.
An over current situation can be caused by anything after R907 within the
inverter, the transformer itself or on the secondary side of the main
transformer.
How you go about finding the problem depends on what equipment you have
available, and what your testing preferences might be.
If you don't have much to work with, just start changing components. In my
experience the components in the right rear corner of the mainboard cause
the most grief so I would start there with C925, C942 and C943. If you have
some decent soldering equipment you can change all three capacitors quickly
without removing the mainboard.
If you have access to an ESR meter you could check all of the aluminum
electrolytic capacitors in circuit. Most of the electrolytics give no
trouble, especially the six(?) 840 uF caps in front of the heat sink for
Q9070 (but you would want to check all of the electrolytic caps if you had
an ESR meter handy).
Another approach would be to put in the 43 volts DC from an external power
source until something got hot or went up in smoke. If your power supply
allowed you to adjust the current limit you could sneak up on it and just
get the problem part(s) nice and warm. You will need to at least disconnect
Q9070 when you apply the external 43 VDC at TP940 and TP 950 from the bottom
or top of the mainboard. I lightly tack on two wires to the bottom side to
make the 43 VDC connections. You can use the scope in its normal way when it
is powered with the external 43 VDC.
The external 43 VDC idea came from a fine Tekscopes member named Hakan, many
years ago, and he has an excellent document you should read at:
A couple of years ago I made up a document listing some commonly available
components you might use to replace some of the original Tektronix part
numbers that often fail. I can send you that directly or you can find it in
the Tekscopes Message archive if you like.
Another thing you might do is take resistance readings from chassis ground
to each of the voltage test points before you get very far into this repair
(with the scope not connected to the mains of course!).
There are lots of other ideas to add to this, but this should get you
started.
This will be a simple fix, so just take your time and understand what you
are doing.
tom jobe...
----- Original Message -----
From: "Tan Chor Ming" <jonray03@...
<mailto:jonray03%40singnet.com.sg> >
To: <TekScopes@... <mailto:TekScopes%40yahoogroups.com> >
Sent: Friday, January 20, 2012 6:45 AM
Subject: Re: [TekScopes] Power supply problem with Tek 2220
Has anyone seen this behaviour repairing Tek2000 series scope power supply?
Behaviour
1. When power on from cold, it will fire up properly and stay on for a
few
minutes
2. Once it warms up, the power supply shut down and try to on again and it
continues in this on/off mode
3. Pre-regulator out = 43V (between TP940 and TP950)
4. All voltages when the unit is stable for a few minutes are
+8.6, -8.6,
+5.2, +100 are all ok.
What are likely problems before I start ripping the components from the
circuit?
ttesenq@... <mailto:ttesenq%40tiscali.co.uk> suggested that
it
could be the pre-regulator MOSFET
P9070.
I though that it could be a electrolytic cap but it doe not look likely
because electrolytic failure would not have allowed the unit to fire up for
a few minutes
It is more likely a active component that weaken with increase temperature,
so ttesenq@... <mailto:ttesenq%40tiscali.co.uk> could be right.
This would mean Q947 and Q946 are also likely components
Any other possible lead of similar experience.
|
Re: Power supply problem with Tek 2220
Hi Tan,
Some one told me that the 2220 is the 60 MHz version of the 2230 100 MHz
scope. If this is true, the 2230 manual might be your best bet. It is
available from several places including:
Now that I hear about your experience level and what equipment you have on
hand, I would fix the 2235 first as it has no top board limiting your access
to the power supply (and almost everything else in the scope) while the
scope is actually running.
You mention the need for an isolation transformer. You probably do not need
an isolation transformer at this point, as its only value is to be able to
"float" the scope so you can use another scope to look at the inverter side
of the power supply. The inverter is already making the 43 VDC so what would
you need to check anyway? I know the service manual calls for an isolation
transformer (so I bought one) but my experience finds it to be fairly
useless in the 22xx repair process. Also, once you "float" the scope the
chassis of the scope is now at some elevated voltage, which is a little
scary for an amateur like me.
You mentioned that Q908 was up on the heatsink but it isn't. Take a closer
look as it only is involved in running the "gate" of Q9070.
Q9070 is up on the heatsink. Q908 is a small transistor with minor currents
through it, and Q9070 does the real work of creating the 43 VDC for the
inverter.
If you ever decide to do the external injection of the 43 VDC, you need to
disconnect Q9070, not Q908.
tom jobe...
toggle quoted message
Show quoted text
----- Original Message ----- From: "Tan Chor Ming" <jonray03@...> To: <TekScopes@...> Sent: Friday, January 20, 2012 8:37 PM Subject: RE: [TekScopes] Power supply problem with Tek 2220 Thank you Tom for taking the time to point out specifically the likely cause of the problem.
I know it takes effort to go through the details and I really appreciate it.
Just to let you know where I come from, so that there is less to assume.
I am an electronics engineer from Singapore above 50 so very much familiar
with vacuum and solid state electronics.
I do not have the schematics for 2220 so like you I am assuming it is
quite similar to 2235 which I have it downloaded.
I have both 2220 and 2235 and there appear to be quite similar though the
PCB layout is slightly different.
I have complete understanding of how the power supply works.
Pre-regulator - PWM driving Q908 to produce +43V across TP940 and TP950
Final Regulator - DC-DC push-pull inverter through Q947 and Q946.
I have another scope 2235, unfortunately, it too went down at the same time, so the only instrument I have is a multimeter.
Anyway, I do not have an isolation transformer so even with the 2235
working, I will need to get an isolation transformer before I could take any measurement.
Any idea what VA rating is needed for the isolation transformer?
Based on the power needs, it appears to be at least 200VA.
Initially, I was asking about R907, not because I was suspecting the
resistor but I intend to check the load current by putting an ammeter in
series with the resistor.
For that to be useful I need to know what is expected. Like you. I am
suspecting that the voltage at R907 has gone up after the set warms up thus shutting down U930.
I will probably go with the cap changes you have recommended since I have
some time during the Lunar New Year break.
Unfortunately, I do not have ESR meter, but I don't think that a big issue
just replacing the caps.
I am aware of the direct 43Vdc injection, but thank you for telling me the
detail that Q908 needs to be disconnected.
Unfortunately, I do not have a power supply with this voltage output. I
only have a power supply of 18V max 2A. So I will have to hold off this
approach.
One more thing which I did not mention earlier is that I detached the +5.2V connection to the digital board (for the storage function of 2220) and
behaviour remains unchanged.
Rgds,
Chor Ming
_____
From: TekScopes@... [mailto:TekScopes@...] On Behalf Of tom jobe
Sent: Saturday, January 21, 2012 7:30 AM
To: TekScopes
Subject: Re: [TekScopes] Power supply problem with Tek 2220
I saw your 2220 question the first time you posted it a few days ago, and I did not have a nice short answer for you. Since you have not gotten the
answer
you were looking for, let me comment a bit on this.
First off, I don't own a 2220 or have the service manual for it, and none of the download sites I checked seem to have it either, including
ArtekMedia.com having it for purchase. So I will assume it is similar to the better 22xx's such as the 2235, at least around the power supply. I will
also assume that you do have a service manual to work with. U930 monitors
the voltage drop across R907, and in your case it probably thinks the
current is too high after a few minutes, so it shuts down.
I have worked on lots of 22xx scopes and I have not seen the value of R907
drift and cause this problem, but others have reported that as a
possibility. Odds are, that this is not your problem.
An over current situation can be caused by anything after R907 within the
inverter, the transformer itself or on the secondary side of the main
transformer.
How you go about finding the problem depends on what equipment you have
available, and what your testing preferences might be.
If you don't have much to work with, just start changing components. In my
experience the components in the right rear corner of the mainboard cause
the most grief so I would start there with C925, C942 and C943. If you have some decent soldering equipment you can change all three capacitors quickly without removing the mainboard.
If you have access to an ESR meter you could check all of the aluminum
electrolytic capacitors in circuit. Most of the electrolytics give no
trouble, especially the six(?) 840 uF caps in front of the heat sink for
Q9070 (but you would want to check all of the electrolytic caps if you had
an ESR meter handy).
Another approach would be to put in the 43 volts DC from an external power
source until something got hot or went up in smoke. If your power supply
allowed you to adjust the current limit you could sneak up on it and just
get the problem part(s) nice and warm. You will need to at least disconnect Q9070 when you apply the external 43 VDC at TP940 and TP 950 from the bottom or top of the mainboard. I lightly tack on two wires to the bottom side to
make the 43 VDC connections. You can use the scope in its normal way when it is powered with the external 43 VDC.
The external 43 VDC idea came from a fine Tekscopes member named Hakan, many years ago, and he has an excellent document you should read at:
A couple of years ago I made up a document listing some commonly available
components you might use to replace some of the original Tektronix part
numbers that often fail. I can send you that directly or you can find it in the Tekscopes Message archive if you like.
Another thing you might do is take resistance readings from chassis ground
to each of the voltage test points before you get very far into this repair (with the scope not connected to the mains of course!).
There are lots of other ideas to add to this, but this should get you
started.
This will be a simple fix, so just take your time and understand what you
are doing.
tom jobe...
----- Original Message -----
From: "Tan Chor Ming" <jonray03@...
<mailto:jonray03%40singnet.com.sg> >
To: <TekScopes@... <mailto:TekScopes%40yahoogroups.com> >
Sent: Friday, January 20, 2012 6:45 AM
Subject: Re: [TekScopes] Power supply problem with Tek 2220
Has anyone seen this behaviour repairing Tek2000 series scope power supply?
Behaviour
1. When power on from cold, it will fire up properly and stay on for a
few minutes
2. Once it warms up, the power supply shut down and try to on again and it
continues in this on/off mode
3. Pre-regulator out = 43V (between TP940 and TP950)
4. All voltages when the unit is stable for a few minutes are
+8.6, -8.6, +5.2, +100 are all ok.
What are likely problems before I start ripping the components from the
circuit?
ttesenq@... <mailto:ttesenq%40tiscali.co.uk> suggested that
it could be the pre-regulator MOSFET
P9070.
I though that it could be a electrolytic cap but it doe not look likely
because electrolytic failure would not have allowed the unit to fire up for
a few minutes
It is more likely a active component that weaken with increase temperature,
so ttesenq@... <mailto:ttesenq%40tiscali.co.uk> could be right.
This would mean Q947 and Q946 are also likely components
Any other possible lead of similar experience.
|
David Hess
David C. Partridge
KB6NAX