Topics

Tektronix 2230


Saroj Pradhan
 

Hi everybody
I have a tektronix 2230 that I got from one of my friends and that was lying with me for one year. Last week I tried to put on it. But unfortunately the ac line tripped. I opened the scope and with tedious effort  got access to the power supply section. Checked it with multimeter found the following:
Two bridge rectifiers shorted.
Q9070 shorted
CR907 shorted
Q908 shorted
R909 opened
U930 cracked
CR908 shorted

I replaced all the defective components and all electrolytic and other fixed capacitor capacitors in both inverter section and low voltage side. I have not changed the capacitor in the line filter, C908, C904, C922 and C919.
After doing that I again put on the scope this time it took away q9070 Cr907and all the rectifier diode.
Then checked the resistance between tp950 and tp940 it was very low around 8Ohms.it turned out that cathode and anode of Q935 was shorted. I did not have the correct replacement so just desoldered  Q935. According to the manual this transistor protects the power supply from high voltage at tp950 and hi current of Q946 and Q947.
After replacement of other burnt components I put on the scope this time with current limiter bulb.i experienced following behaviour:
Bulb was flashing with a ticking sound at the frequency of around 60 times in one minute. I could see two of the small bulbs in the main board also flashing in same frequency.
Measured some voltages at different points
At every points of measurement voltages were jumping.
Measurements are as follow:
Voltage at C906 varies from around 130 to 285v
Voltage across C925 varies from 12 to 20v
Voltage across tp950 and tp940 varies from 1 to 9v
U930 pin voltages with respect to u930 ground pin
Pin 1 0v
Pin 2 0.1  to 0.8v
Pin 3 0 to 0.3v
Pin4 0v
Pin5 almost 0v
Pin6 0 to 1.5v
Pin 8 12 to 20v
Pin 9 5 to 7v
Pin 10 0 to 3v
Pin 11 12 to 20v
Pin12 0 to 6.6
Pin 14  0 to 1.8v
Pin 15 0v
Pin 16 0v
I red some where to test u930 with external power supply so I wanted to checked the voltages at u930 pins with externally applying voltage across C925 so I put off the scope and connected external power supply across C925 and increased the voltage at around 23v I could see few milliamp in the display of external power supply. I then decreased the voltage to 14 volt and did measure voltages at different pins of u930 and they are as follow
Pin1 0v
Pin2 4.37v
Pin3 0v
Pin4 0v
Pin5 1.66v
Pin6 3.57v
Pin8 13.9v
Pin9 12.6v
Pin10 11.78v
Pin11 13.9v
Pin12 13.9v
Pin13
Pin14 4.9v
Pin16 0v
As suggested in u930 testing document there was no pulse in pin5 and pin10.
I have 50 MHz keysight. Till now I was hesitating to scope around tek 2230 because I do not have isolation transformer. Because u935 was supplied with external supply I Scoped at test point 44 and 45.At point I got the ramp and 56KHz pulses at 44 with 94%duty cycle.
I will put Q935 once I have the proper replacement. People are using mcr72 scr as Q935. I have some tyn series scr shall I select one with proper voltage and current rating and replace for Q935?
And please some suggest and me to rectify my issue with tek2230.
By the way for cr908 I used 1n4148 and for cr908 I used 1n4007.
Sent from my Huawei phone


Saroj Pradhan
 

Hi everybody
I have a tektronix 2230 that I got from one of my friends and that was
lying with me for one year. Last week I tried to put on it. But
unfortunately the ac line tripped. I opened the scope and with tedious
effort got access to the power supply section. Checked it with multimeter
found the following:
Two bridge rectifiers shorted.
Q9070 shorted
CR907 shorted
Q908 shorted
R909 opened
U930 cracked
CR908 shorted

I replaced all the defective components and all electrolytic and other
fixed capacitor capacitors in both inverter section and low voltage side. I
have not changed the capacitor in the line filter, C908, C904, C922 and
C919.
After doing that I again put on the scope this time it took away q9070
Cr907and all the rectifier diode.
Then checked the resistance between tp950 and tp940 it was very low around
8Ohms.it turned out that cathode and anode of Q935 was shorted. I did not
have the correct replacement so just desoldered Q935. According to the
manual this transistor protects the power supply from high voltage at tp950
and hi current of Q946 and Q947.
After replacement of other burnt components I put on the scope this time
with current limiter bulb.i experienced following behaviour:
Bulb was flashing with a ticking sound at the frequency of around 60 times
in one minute. I could see two of the small bulbs in the main board also
flashing in same frequency.
Measured some voltages at different points
At every points of measurement voltages were jumping.
Measurements are as follow:
Voltage at C906 varies from around 130 to 285v
Voltage across C925 varies from 12 to 20v
Voltage across tp950 and tp940 varies from 1 to 9v
U930 pin voltages with respect to u930 ground pin
Pin 1 0v
Pin 2 0.1 to 0.8v
Pin 3 0 to 0.3v
Pin4 0v
Pin5 almost 0v
Pin6 0 to 1.5v
Pin 8 12 to 20v
Pin 9 5 to 7v
Pin 10
Sent from my Huawei phone


satbeginner
 

Hi,

Try this very good document of Håkan :

http://www.hakanh.com/dl/docs/troubleshooting_tips_on_2200_ps.pdf

If you remove the switching transistor, you can feed a 43VDC into the scope to temporarily bypass the grid power supply.
That way you can eliminate possible overloads further down into the scope.

Succes,

Leo


Saroj Pradhan
 

Hi satbeginner
Thanks for the response
I saw that document. But I do not have a suitable power supply right now. I
will try that later when I get a suitable power supply.
Tell me one thing how important are those capacitors in the line filter,
c904 and c908 when we talk about the situation like I have right now. I
wanted to change those capacitor but it is hard to find in my area. They
categorize those capacitor as X2 safety. Shall I replace those capacitor
with normal polystyrene 250v type.
Thanks
Saroj

On Sat, Jun 27, 2020, 10:14 PM satbeginner <@satbeginner> wrote:

Hi,

Try this very good document of Håkan :

http://www.hakanh.com/dl/docs/troubleshooting_tips_on_2200_ps.pdf

If you remove the switching transistor, you can feed a 43VDC into the
scope to temporarily bypass the grid power supply.
That way you can eliminate possible overloads further down into the scope.

Succes,

Leo




satbeginner
 

Hello Saroj

for now you do not need to bother about the line filter capacitors, if they ae not broken now, let them rest for now.
Let's concentrate on the active power supply.

This power supply is a switching power supply, so the active components you use must be of enough speed to be able to work in this region.
(44-50 kHz)

So the protection diode CR908 you replaced with a 1N4148, that should be OK (recovery-time = 4ns, this means it is fast enough)

If you replaced CR907 with a 1N4007, I would say this is not good, that diode should be able to follow the used frequency as well.
An 1N4007 is a normal, Line frequency rectifier diode, not suited for use in fast switching situations.
I would look for at least a UF4007, or one of the diodes mentioned in Hakan's document, like the BYD73G.

Also, many times a fast enough diode can be harvest from an old switching power supply from a broken television set or laptop PS.

When you have time,read this thread about this Power Supply, a lot of information can be found there too.

https://groups.io/g/TekScopes/topic/23804512#149922

Good luck,

Leo


Saroj Pradhan
 

Hi satbeginner
Thank you for good suggestion.
I will find some suitable diode for cr907 and replace. By theime I am looking for a power supply to connect to the inverter. I will get back to you after I get and test the inverter.
Saroj


Saroj Pradhan
 

Hi Leo
I made myself a old style transformer type power supply to connect to the
inverter section. Here are my findings.
1. Un loaded external power supply out put voltage---44v
2. Loaded external power supply voltage--- 38.7v
3. Got the trace.
4. Front panel knobs have effect.
5. Fan doesn't rotate.
6. Measured out put voltages at low voltage side which are
+7.7v at +8.6v
- 7.66v at - 8.6v
+ 4.58 at +5v
- 4.46v at - 5v
+91v at +100v
+26.9v at +30v
7 collector voltage of Q946 and Q947 is 37.6v
8 base voltage of Q946 and Q947 is 0.5v
9 voltage across R949 is 0. 85v which gives around 1.66A current at
emitter of Q946 and Q947. I think that is quite normal.
10 text in the screen wobbles.
11 I can see some noises on the trace and is significant in 2mv/div
12 put on the equipment for 30 minutes
Q946 and Q947 were hot but I could touch them.

What will be the cause of out of spec voltages at low voltage side. Low
voltage at tp950(38v) makes so much difference.
Check the fan motor with external 10v supply, the fan motor gives initial
torque but does not spin and draws nearly 500mA.
It seems some has already replaced Q947 and q946.
Please advise me what shall be my next step.
Thank you very very much for your time and suggestion. At least I could
conclude that there is no dead short in the inverter section.

Regards
Saroj

On Sun, Jun 28, 2020, 1:00 PM Saroj Pradhan via groups.io <sarojman.Pradhan=
gmail.com@groups.io> wrote:

Hi satbeginner
Thank you for good suggestion.
I will find some suitable diode for cr907 and replace. By theime I am
looking for a power supply to connect to the inverter. I will get back to
you after I get and test the inverter.
Saroj




satbeginner
 

Hello Saroj,

this is a good start! You confirmed your scope has the typical issue, it's almost always the primary power supply with problems.

The Power Supply are basically TWO switching inverters after each other.
By means of bypassing the first - what you now did- you narrowed your problem down to the first one.

First about the fan:
The fan is just a simple 60mm 12VDC fan, and usually draws about 150-160mA, and in the scope its running at a slightly lower voltage.
Did you use the proper polarity when you tested the fan? The board layout and diodes in the scope create a negative voltage in respect to ground.
But, I assume you unplugged it to test, and if it does not turn and draws 500mA, I would say it is broken.

Smaller scopes in the 22xx range do not even have this fan, so again, for now leave it disconnected until you got a proper replacement.

The wobbling of the screen, and lower DC voltages in the secondary PS are probably due to the fact your temporary power supply is not regulated, a bit low (38,7V) and therefor probably has a significant ripple, I would not worry about these things right now.
The most important thing is: the second stage of the power supply works. :-)

Now we concentrate on the first stage of the power supply:

I looked at all the different versions of the power supplies used in the 2213 2215 2215A 2230 etc scopes, and they are all similar, but not of great design (Sorry for this remark, Tek!!)
I choose to use the following approach:

I changed R909 to 4,7 Ohm, instead of 39 Ohm.
This charges and discharges the input capacity of the FET Q9070 faster, so it will switch ON and OF faster, therefor it will dissipate a bit less power during switching.
You will find this lower value of R909 in some f the scopes I mentioned.

Furthermore: I replaced Q9070 by a FQPF4N90C.
This FET has a slightly lower ON-resistance (again, less dissipation while ON) AND it has a full plastic housing.

Because of the plastic housing I put it directly on the metal mounting plate while I added a TO-220 heatsink as well.
I even put a TO-220 heatsink at the other side of the metal plate, to increase the cooling surface.

Recently I used the following components to repair this power supply:

CR907 MUR460 (a bit difficult, because of the thicker wires on this diode)
Q908 2N5401 (EBC) same pinout, so easy to replace
Q9070 FQPF4N90C Higher voltage, Lower ON resistance, plastic TO-220 housing, better mounting (IMHO)

But obviously, others will work too.

My first option would be:
Find suitable components, and leave the suspected fan disconnected for now.
See if it works, and while working on the repair, find another 60mm fan, maybe from an old PC or other device.

God luck, you will get it up and running.

Leo


Saroj Pradhan
 

Hi leo
Thanks once again for guiding me through repair process.
Regarding the voltage issue you are right that my power supply has poor
regulation.
As you suggested I will try my best to replace those component and get
back to you hopefully with good news.
Saroj

On Mon, Jun 29, 2020, 12:52 PM satbeginner <@satbeginner> wrote:

Hello Saroj,

this is a good start! You confirmed your scope has the typical issue, it's
almost always the primary power supply with problems.

The Power Supply are basically TWO switching inverters after each other.
By means of bypassing the first - what you now did- you narrowed your
problem down to the first one.

First about the fan:
The fan is just a simple 60mm 12VDC fan, and usually draws about
150-160mA, and in the scope its running at a slightly lower voltage.
Did you use the proper polarity when you tested the fan? The board layout
and diodes in the scope create a negative voltage in respect to ground.
But, I assume you unplugged it to test, and if it does not turn and draws
500mA, I would say it is broken.

Smaller scopes in the 22xx range do not even have this fan, so again, for
now leave it disconnected until you got a proper replacement.

The wobbling of the screen, and lower DC voltages in the secondary PS are
probably due to the fact your temporary power supply is not regulated, a
bit low (38,7V) and therefor probably has a significant ripple, I would not
worry about these things right now.
The most important thing is: the second stage of the power supply works.
:-)

Now we concentrate on the first stage of the power supply:

I looked at all the different versions of the power supplies used in the
2213 2215 2215A 2230 etc scopes, and they are all similar, but not of great
design (Sorry for this remark, Tek!!)
I choose to use the following approach:

I changed R909 to 4,7 Ohm, instead of 39 Ohm.
This charges and discharges the input capacity of the FET Q9070 faster, so
it will switch ON and OF faster, therefor it will dissipate a bit less
power during switching.
You will find this lower value of R909 in some f the scopes I mentioned.

Furthermore: I replaced Q9070 by a FQPF4N90C.
This FET has a slightly lower ON-resistance (again, less dissipation while
ON) AND it has a full plastic housing.

Because of the plastic housing I put it directly on the metal mounting
plate while I added a TO-220 heatsink as well.
I even put a TO-220 heatsink at the other side of the metal plate, to
increase the cooling surface.

Recently I used the following components to repair this power supply:

CR907 MUR460 (a bit difficult, because of the thicker wires on this diode)
Q908 2N5401 (EBC) same pinout, so easy to replace
Q9070 FQPF4N90C Higher voltage, Lower ON resistance, plastic TO-220
housing, better mounting (IMHO)

But obviously, others will work too.

My first option would be:
Find suitable components, and leave the suspected fan disconnected for now.
See if it works, and while working on the repair, find another 60mm fan,
maybe from an old PC or other device.

God luck, you will get it up and running.

Leo




Saroj Pradhan
 

Hi Leo
I am still searching for the component.
I got 4.7 Ohms resistor an 2n5401transistor.
Replaced 39 Ohms resistor and 2n2907.
For the time being I replaced q9070 by irf 830 which is very close to the
one you suggested in terms of switching time
and has better voltage and current performance. For cr 907 I replaced by
two 1n4936 in parallel which has switching time of 200ns which is quite
higher than switching time of Byz73g.
And put the scope on with same current limiter bulb. This time the bulb
lights on continuously bright (does not flash Ann no ticking sound) and I
could hear high pitch sound which is not very loud. But all the voltage
dropped across the limiter bulb. I could get around 7 v across c906. I
might be wrong but what I am thinking is
q907 fired on and never came to off state or there is a dead short in the
preregulator.
Of course I Wil replace those two component when I get them.
Saroj

On Mon, Jun 29, 2020, 3:25 PM Saroj Pradhan via groups.io <sarojman.Pradhan=
gmail.com@groups.io> wrote:

Hi leo
Thanks once again for guiding me through repair process.
Regarding the voltage issue you are right that my power supply has poor
regulation.
As you suggested I will try my best to replace those component and get
back to you hopefully with good news.
Saroj

On Mon, Jun 29, 2020, 12:52 PM satbeginner <@satbeginner>
wrote:

Hello Saroj,

this is a good start! You confirmed your scope has the typical issue,
it's
almost always the primary power supply with problems.

The Power Supply are basically TWO switching inverters after each other.
By means of bypassing the first - what you now did- you narrowed your
problem down to the first one.

First about the fan:
The fan is just a simple 60mm 12VDC fan, and usually draws about
150-160mA, and in the scope its running at a slightly lower voltage.
Did you use the proper polarity when you tested the fan? The board layout
and diodes in the scope create a negative voltage in respect to ground.
But, I assume you unplugged it to test, and if it does not turn and draws
500mA, I would say it is broken.

Smaller scopes in the 22xx range do not even have this fan, so again, for
now leave it disconnected until you got a proper replacement.

The wobbling of the screen, and lower DC voltages in the secondary PS are
probably due to the fact your temporary power supply is not regulated, a
bit low (38,7V) and therefor probably has a significant ripple, I would
not
worry about these things right now.
The most important thing is: the second stage of the power supply works.
:-)

Now we concentrate on the first stage of the power supply:

I looked at all the different versions of the power supplies used in the
2213 2215 2215A 2230 etc scopes, and they are all similar, but not of
great
design (Sorry for this remark, Tek!!)
I choose to use the following approach:

I changed R909 to 4,7 Ohm, instead of 39 Ohm.
This charges and discharges the input capacity of the FET Q9070 faster,
so
it will switch ON and OF faster, therefor it will dissipate a bit less
power during switching.
You will find this lower value of R909 in some f the scopes I mentioned.

Furthermore: I replaced Q9070 by a FQPF4N90C.
This FET has a slightly lower ON-resistance (again, less dissipation
while
ON) AND it has a full plastic housing.

Because of the plastic housing I put it directly on the metal mounting
plate while I added a TO-220 heatsink as well.
I even put a TO-220 heatsink at the other side of the metal plate, to
increase the cooling surface.

Recently I used the following components to repair this power supply:

CR907 MUR460 (a bit difficult, because of the thicker wires on this
diode)
Q908 2N5401 (EBC) same pinout, so easy to replace
Q9070 FQPF4N90C Higher voltage, Lower ON resistance, plastic TO-220
housing, better mounting (IMHO)

But obviously, others will work too.

My first option would be:
Find suitable components, and leave the suspected fan disconnected for
now.
See if it works, and while working on the repair, find another 60mm fan,
maybe from an old PC or other device.

God luck, you will get it up and running.

Leo






Saroj Pradhan
 

Forgot to tell
I replaced u930 by tl 494.


satbeginner
 

Hi,

I think that should be ok.
As far as I can see in the 494 the reference has a bit more room, compared to the 595.
But being in the first stage of the power supply, maybe it's not so critical.

Un saludo, Leo


Saroj Pradhan
 

Hi
Did you go through my previous message?
There I described some of the activity and results.
I appreciate if you comment on that.
Thanks saroj


satbeginner
 

Hello Saroj,

the high pitch sound should indicate it is trying to oscillate and turn on the FET.
The one you have should be OK too.

The thing is, the inrush current of these switch mode PS is very high, so it could be the bulb preventing it to switch on properly...

If you don't find any obvious shorts around the FET and other transistor, I would try it without the bulb...
Connect a voltmeter to the expected 43V and see what happens :-)

Good luck,

Leo


Saroj Pradhan
 

Hi Leo
Put on without limiter bulb.
Took away q9070, cr901and cr903.

On Tue, Jun 30, 2020, 12:31 PM satbeginner <@satbeginner> wrote:

Hello Saroj,

the high pitch sound should indicate it is trying to oscillate and turn on
the FET.
The one you have should be OK too.

The thing is, the inrush current of these switch mode PS is very high, so
it could be the bulb preventing it to switch on properly...

If you don't find any obvious shorts around the FET and other transistor,
I would try it without the bulb...
Connect a voltmeter to the expected 43V and see what happens :-)

Good luck,

Leo




Saroj Pradhan
 

Hi Leo
I put on the scope without limiter bulb, it took away q9070, cr901and
cr903. Fuse also blown away and ac mains tripped.
I could not see any obvious short circuit
near Q9070.
At the beginning, before we started talking to each other I had checked
the u930 for its operation with external supply across C925. That time I
measured the ramp at pin 5.
The frequency was 56KHZ with 52%duty cycle and the pulse frequency at pin
10 was also 56KHZ with duty cycle of 94%.
Is that a normal situation or the duty Cy le of both the ramp frequency and
pulse should be same.
I could not see any circuit path for that limiter bulb light so bright.
And one thing more, in the circuit diagram +I've rail for inverter
input(Tp950) and circuit ground is always confusing.
Regards
Saroj

On Tue, Jun 30, 2020, 3:29 PM Saroj Pradhan via groups.io <sarojman.Pradhan=
gmail.com@groups.io> wrote:

Hi Leo
Put on without limiter bulb.
Took away q9070, cr901and cr903.

On Tue, Jun 30, 2020, 12:31 PM satbeginner <@satbeginner>
wrote:

Hello Saroj,

the high pitch sound should indicate it is trying to oscillate and turn
on
the FET.
The one you have should be OK too.

The thing is, the inrush current of these switch mode PS is very high, so
it could be the bulb preventing it to switch on properly...

If you don't find any obvious shorts around the FET and other transistor,
I would try it without the bulb...
Connect a voltmeter to the expected 43V and see what happens :-)

Good luck,

Leo






chipbee40
 

I don't see in your messages where you have checked C906? Usually if 2 bridge rectifiers fail it burns out C906 (Large can), so you get rippled volts going through the power supply causing damage.
I'm guessing you are on 220Vac?


Saroj Pradhan
 

Hi chipbee40
Thanks for your concern and suggestion.
For c906 I had replaced by 100uf 450v type. And now I checked out of the circuit the esr meter shows 98uf and 0.34 esr.
Thanks
Saroj


Saroj Pradhan
 

Hi chipbee40
Yes, I am on 220v
Thanks


satbeginner
 

Hello Saroj,

sorry to hear about the breakdown of your replaced parts... :-(

Since you already confirmed that the scope worked when fed from a secondary power supply, and I assume it still does?
If that's the case, there still must be something wrong with the first switcher...

I would check all surrounding parts, and when necessary, remove them before checking, because in-circuit checking can give distracting results.

At the moment I do not have other suggestions than to check if the scope is still running on the external 43V power supply, and check again very thoroughly all other parts and their polarity in the first switching part of the power supply...

Good luck,

Leo

Again, sorry for