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dead Philips PM3240 oscilloscope



 
 
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  #1  
Old May 8th 04, 09:52 PM
Thierry Delaitre
external usenet poster
 
Posts: n/a
Default dead Philips PM3240 oscilloscope

I have a faulty Philips PM3240 oscilloscope. The problem is that the
spot is not showing up anymore. The spot is sometimes illuminating
very rapidily for one 10th of a second as a one off and then disapears
for 1 hour. I have checked the modulation signal applied to G1 and it
seems fine. The CRT is a D14-125 GM/08 but i do not have its
characteristics and it is difficult to find out if the voltage between
the wehnelt and cathode are correct or not. There is a ZA1004 neon
which is acting as a voltage stabilizer between the cathode and
wehnelt. This ZA1004 seems to stabilise 230V but i have no idea if
this is correct or not as i cannot find any information about this
component. The voltage values of the CRT are as follows:

G1: -1500V
G2/G4: +33.4
G3: from -950 to -1120 (focus)
G5/G6: ground
G7: +45V
G8: 8KV

I've also checked the filament and it's current is constant even when
the spot is not displayed.

Any help would be greatly appreciated !

Cheers,

Thierry.
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  #2  
Old May 9th 04, 02:13 AM
Jim Yanik
external usenet poster
 
Posts: n/a
Default dead Philips PM3240 oscilloscope

Thierry Delaitre wrote in
:

I have a faulty Philips PM3240 oscilloscope. The problem is that the
spot is not showing up anymore. The spot is sometimes illuminating
very rapidily for one 10th of a second as a one off and then disapears
for 1 hour. I have checked the modulation signal applied to G1 and it
seems fine. The CRT is a D14-125 GM/08 but i do not have its
characteristics and it is difficult to find out if the voltage between
the wehnelt and cathode are correct or not. There is a ZA1004 neon
which is acting as a voltage stabilizer between the cathode and
wehnelt. This ZA1004 seems to stabilise 230V but i have no idea if
this is correct or not as i cannot find any information about this
component. The voltage values of the CRT are as follows:

G1: -1500V
G2/G4: +33.4
G3: from -950 to -1120 (focus)
G5/G6: ground
G7: +45V
G8: 8KV

I've also checked the filament and it's current is constant even when
the spot is not displayed.

Any help would be greatly appreciated !

Cheers,

Thierry.


If the neon between grid and cathode is lighting,that means the DC restorer
circuit/grid drive has problems.The neon is to LIMIT the G-K voltage in
case something in the grid drive circuit(DC restorer and Z-axis
amp)fails.The DC restorer shifts the Z-axis signal(unblanking signal) to
CRT potentials(HV). Possibly a diode breaking down under HV,or a bad HV
cap(less likely)

(My experience is with TEK scopes,though)

--
Jim Yanik
jyanik-at-kua.net
  #3  
Old May 9th 04, 04:13 PM
Thierry Delaitre
external usenet poster
 
Posts: n/a
Default dead Philips PM3240 oscilloscope

Jim Yanik wrote:
Thierry Delaitre wrote in
:


I have a faulty Philips PM3240 oscilloscope. The problem is that the
spot is not showing up anymore. The spot is sometimes illuminating
very rapidily for one 10th of a second as a one off and then disapears
for 1 hour. I have checked the modulation signal applied to G1 and it
seems fine. The CRT is a D14-125 GM/08 but i do not have its
characteristics and it is difficult to find out if the voltage between
the wehnelt and cathode are correct or not. There is a ZA1004 neon
which is acting as a voltage stabilizer between the cathode and
wehnelt. This ZA1004 seems to stabilise 230V but i have no idea if
this is correct or not as i cannot find any information about this
component. The voltage values of the CRT are as follows:

G1: -1500V
G2/G4: +33.4
G3: from -950 to -1120 (focus)
G5/G6: ground
G7: +45V
G8: 8KV

I've also checked the filament and it's current is constant even when
the spot is not displayed.

Any help would be greatly appreciated !

Cheers,

Thierry.


If the neon between grid and cathode is lighting,that means the DC restorer
circuit/grid drive has problems.The neon is to LIMIT the G-K voltage in
case something in the grid drive circuit(DC restorer and Z-axis
amp)fails.The DC restorer shifts the Z-axis signal(unblanking signal) to
CRT potentials(HV). Possibly a diode breaking down under HV,or a bad HV
cap(less likely)


(My experience is with TEK scopes,though



Hi,

Thanks for this very useful information. The neon is lighting up. Note
that the neon is connected as follows:
------
-| 2.2M |--
| ------ |
------ ------ ------ | ------ | ------
-1600V ---| 10.5 |---| neon |-----| 1.2M |----| 2.2M |-----| 5.6M |--- 0V
------ | ------ | ------ ------ ------
| |-------- ^
| - | | |
| |1| | --- |
| |0| | /_\ |--||--0V
| |0| | | |
| |K| | | |
| - K G1 G3 focus
| |
| filament
|
|---------|-----
| --- |
--- 100pF--- | |
\ / | | |1M
--- | | |
| |\ | -
---||--------| |--------|----- 1M --- 511 ---- G1
470pF |/ |
BAX17 --- 470pF
---

I've checked the two BAX17 in the DC restorer unit. I've also checked
the resistors which are in series with the neon. I've tried to
disconnected the two 470pF interfacing with the DC restorer to no
avail. I've even tried to disconnect the plug at the back of CRT with
GT8 and the neon is still lighting up with 230V accross its
pins. Could it be that the neon is faulty ? What is the normal voltage
accross it ? What is meant to be the normal voltage accross it ? Where
could i get one if it is faulty ?

Cheers,

Thierry.
  #4  
Old May 9th 04, 04:58 PM
Jim Yanik
external usenet poster
 
Posts: n/a
Default dead Philips PM3240 oscilloscope

Thierry Delaitre wrote in
:

Jim Yanik wrote:
Thierry Delaitre wrote in
:


I have a faulty Philips PM3240 oscilloscope. The problem is that the
spot is not showing up anymore. The spot is sometimes illuminating
very rapidily for one 10th of a second as a one off and then
disapears for 1 hour. I have checked the modulation signal applied
to G1 and it seems fine. The CRT is a D14-125 GM/08 but i do not
have its characteristics and it is difficult to find out if the
voltage between the wehnelt and cathode are correct or not. There is
a ZA1004 neon which is acting as a voltage stabilizer between the
cathode and wehnelt. This ZA1004 seems to stabilise 230V but i have
no idea if this is correct or not as i cannot find any information
about this component. The voltage values of the CRT are as follows:

G1: -1500V
G2/G4: +33.4
G3: from -950 to -1120 (focus)
G5/G6: ground
G7: +45V
G8: 8KV

I've also checked the filament and it's current is constant even
when the spot is not displayed.

Any help would be greatly appreciated !

Cheers,

Thierry.


If the neon between grid and cathode is lighting,that means the DC
restorer circuit/grid drive has problems.The neon is to LIMIT the G-K
voltage in case something in the grid drive circuit(DC restorer and
Z-axis amp)fails.The DC restorer shifts the Z-axis signal(unblanking
signal) to CRT potentials(HV). Possibly a diode breaking down under
HV,or a bad HV cap(less likely)


(My experience is with TEK scopes,though



Hi,

Thanks for this very useful information. The neon is lighting up. Note
that the neon is connected as follows:
------
-| 2.2M |--
| ------ |
------ ------ ------ | ------ | ------
-1600V ---| 10.5 |---| neon |-----| 1.2M |----| 2.2M |-----| 5.6M |---
0V
------ | ------ | ------ ------ ------
| |-------- ^
| - | | |
| |1| | --- |
| |0| | /_\ |--||--0V
| |0| | | |
| |K| | | |
| - K G1 G3 focus
| |
| filament
|
|---------|-----
| --- |
--- 100pF--- | |
\ / | | |1M
--- | | |
| |\ | -
---||--------| |--------|----- 1M --- 511 ---- G1
470pF |/ |
BAX17 --- 470pF
---

I've checked the two BAX17 in the DC restorer unit. I've also checked
the resistors which are in series with the neon. I've tried to
disconnected the two 470pF interfacing with the DC restorer to no
avail. I've even tried to disconnect the plug at the back of CRT with
GT8 and the neon is still lighting up with 230V accross its
pins. Could it be that the neon is faulty ? What is the normal voltage
accross it ? What is meant to be the normal voltage accross it ? Where
could i get one if it is faulty ?

Cheers,

Thierry.


To check DC restorer diodes,you need a curve tracer to check them at or
near the circuit's operating voltages,at least 100V.They could break down
under HV.

If I read your ASCII circuit right,the neon being in series with the focus
string looks like it's supposed to act as some sort of V regulator in the
focus string.
For the neon to be a protector against too large a G-K voltage
difference,the neon would have to be across the G-K.
In my experience,the neons fire at around 60V,TEK uses two of them in
series across the G-K,to limit G-K voltage difference to no more than 120V.


--
Jim Yanik
jyanik-at-kua.net
  #5  
Old May 28th 04, 06:08 PM
Thierry Delaitre
external usenet poster
 
Posts: n/a
Default dead Philips PM3240 oscilloscope

Hi,

Is there anyway i could replace the BAX17 with some kind of more
standard diodes for testing purposes ?

Thierry.

Jim Yanik wrote:
Thierry Delaitre wrote in
:


Jim Yanik wrote:
Thierry Delaitre wrote in
:


I have a faulty Philips PM3240 oscilloscope. The problem is that the
spot is not showing up anymore. The spot is sometimes illuminating
very rapidily for one 10th of a second as a one off and then
disapears for 1 hour. I have checked the modulation signal applied
to G1 and it seems fine. The CRT is a D14-125 GM/08 but i do not
have its characteristics and it is difficult to find out if the
voltage between the wehnelt and cathode are correct or not. There is
a ZA1004 neon which is acting as a voltage stabilizer between the
cathode and wehnelt. This ZA1004 seems to stabilise 230V but i have
no idea if this is correct or not as i cannot find any information
about this component. The voltage values of the CRT are as follows:

G1: -1500V
G2/G4: +33.4
G3: from -950 to -1120 (focus)
G5/G6: ground
G7: +45V
G8: 8KV

I've also checked the filament and it's current is constant even
when the spot is not displayed.

Any help would be greatly appreciated !

Cheers,

Thierry.


If the neon between grid and cathode is lighting,that means the DC
restorer circuit/grid drive has problems.The neon is to LIMIT the G-K
voltage in case something in the grid drive circuit(DC restorer and
Z-axis amp)fails.The DC restorer shifts the Z-axis signal(unblanking
signal) to CRT potentials(HV). Possibly a diode breaking down under
HV,or a bad HV cap(less likely)


(My experience is with TEK scopes,though



Hi,

Thanks for this very useful information. The neon is lighting up. Note
that the neon is connected as follows:
------
-| 2.2M |--
| ------ |
------ ------ ------ | ------ | ------
-1600V ---| 10.5 |---| neon |-----| 1.2M |----| 2.2M |-----| 5.6M |---
0V
------ | ------ | ------ ------ ------
| |-------- ^
| - | | |
| |1| | --- |
| |0| | /_\ |--||--0V
| |0| | | |
| |K| | | |
| - K G1 G3 focus
| |
| filament
|
|---------|-----
| --- |
--- 100pF--- | |
\ / | | |1M
--- | | |
| |\ | -
---||--------| |--------|----- 1M --- 511 ---- G1
470pF |/ |
BAX17 --- 470pF
---

I've checked the two BAX17 in the DC restorer unit. I've also checked
the resistors which are in series with the neon. I've tried to
disconnected the two 470pF interfacing with the DC restorer to no
avail. I've even tried to disconnect the plug at the back of CRT with
GT8 and the neon is still lighting up with 230V accross its
pins. Could it be that the neon is faulty ? What is the normal voltage
accross it ? What is meant to be the normal voltage accross it ? Where
could i get one if it is faulty ?

Cheers,

Thierry.


To check DC restorer diodes,you need a curve tracer to check them at or
near the circuit's operating voltages,at least 100V.They could break down
under HV.


If I read your ASCII circuit right,the neon being in series with the focus
string looks like it's supposed to act as some sort of V regulator in the
focus string.
For the neon to be a protector against too large a G-K voltage
difference,the neon would have to be across the G-K.
In my experience,the neons fire at around 60V,TEK uses two of them in
series across the G-K,to limit G-K voltage difference to no more than 120V.

  #6  
Old May 28th 04, 06:42 PM
Jim Yanik
external usenet poster
 
Posts: n/a
Default dead Philips PM3240 oscilloscope

Thierry Delaitre wrote in
:

Hi,

Is there anyway i could replace the BAX17 with some kind of more
standard diodes for testing purposes ?


Sure,as long as the PIV is equal or better.Small-signal diodes have better
freq. response characteristics,which would affect the risetime of the
unblanking signal to the CRT grid.
You could use the ECG recommended substitute for the BAX17.
--
Jim Yanik
jyanik-at-kua.net


Thierry.

Jim Yanik wrote:
Thierry Delaitre wrote in
:


Jim Yanik wrote:
Thierry Delaitre wrote in
:

I have a faulty Philips PM3240 oscilloscope. The problem is that
the spot is not showing up anymore. The spot is sometimes
illuminating very rapidily for one 10th of a second as a one off
and then disapears for 1 hour. I have checked the modulation
signal applied to G1 and it seems fine. The CRT is a D14-125 GM/08
but i do not have its characteristics and it is difficult to find
out if the voltage between the wehnelt and cathode are correct or
not. There is a ZA1004 neon which is acting as a voltage
stabilizer between the cathode and wehnelt. This ZA1004 seems to
stabilise 230V but i have no idea if this is correct or not as i
cannot find any information about this component. The voltage
values of the CRT are as follows:

G1: -1500V
G2/G4: +33.4
G3: from -950 to -1120 (focus)
G5/G6: ground
G7: +45V
G8: 8KV

I've also checked the filament and it's current is constant even
when the spot is not displayed.

Any help would be greatly appreciated !

Cheers,

Thierry.


If the neon between grid and cathode is lighting,that means the DC
restorer circuit/grid drive has problems.The neon is to LIMIT the
G-K voltage in case something in the grid drive circuit(DC restorer
and Z-axis amp)fails.The DC restorer shifts the Z-axis
signal(unblanking signal) to CRT potentials(HV). Possibly a diode
breaking down under HV,or a bad HV cap(less likely)

(My experience is with TEK scopes,though


Hi,

Thanks for this very useful information. The neon is lighting up.
Note that the neon is connected as follows:
------
-| 2.2M |--
| ------ |
------ ------ ------ | ------ | ------
-1600V ---| 10.5 |---| neon |-----| 1.2M |----| 2.2M |-----| 5.6M
|--- 0V
------ | ------ | ------ ------ ------
| |-------- ^
| - | | |
| |1| | --- |
| |0| | /_\ |--||--0V
| |0| | | |
| |K| | | |
| - K G1 G3 focus
| |
| filament
|
|---------|-----
| --- |
--- 100pF--- | |
\ / | | |1M
--- | | |
| |\ | -
---||--------| |--------|----- 1M --- 511 ---- G1
470pF |/ |
BAX17 --- 470pF
---

I've checked the two BAX17 in the DC restorer unit. I've also
checked the resistors which are in series with the neon. I've tried
to disconnected the two 470pF interfacing with the DC restorer to no
avail. I've even tried to disconnect the plug at the back of CRT
with GT8 and the neon is still lighting up with 230V accross its
pins. Could it be that the neon is faulty ? What is the normal
voltage accross it ? What is meant to be the normal voltage accross
it ? Where could i get one if it is faulty ?

Cheers,

Thierry.


To check DC restorer diodes,you need a curve tracer to check them at
or near the circuit's operating voltages,at least 100V.They could
break down under HV.


If I read your ASCII circuit right,the neon being in series with the
focus string looks like it's supposed to act as some sort of V
regulator in the focus string.
For the neon to be a protector against too large a G-K voltage
difference,the neon would have to be across the G-K.
In my experience,the neons fire at around 60V,TEK uses two of them in
series across the G-K,to limit G-K voltage difference to no more than
120V.





  #7  
Old June 5th 04, 10:57 AM
Thierry Delaitre
external usenet poster
 
Posts: n/a
Default dead Philips PM3240 oscilloscope

Hi,

I've replaced the 2 bax17 in the detection part by by281 but no
success. I've posted the schematic at
http://www.cpc.wmin.ac.uk/~delaitt/PM3240/circuit.jpg

and the following pictures taken with an oscilloscope:

1) http://www.cpc.wmin.ac.uk/~delaitt/PM3240/P1010339.JPG
collector of TS1308 when intensity is in maximum
voltage goes from 7v to 75v (using 1/10 probe)

2) http://www.cpc.wmin.ac.uk/~delaitt/PM3240/P1010340.JPG
collector of TS1308 when intensity is in minimum
voltage goes to 50v

3) http://www.cpc.wmin.ac.uk/~delaitt/PM3240/P1010341.JPG
emitter of TS1306
voltage goes from 8v to 28v when intensity is in maximum

4) http://www.cpc.wmin.ac.uk/~delaitt/PM3240/P1010343.JPG
emitter of TS1306
voltage is 8V when intensity is in minimum

Cheers,

Thierry.

Jim Yanik wrote:
Thierry Delaitre wrote in
:


Hi,

Is there anyway i could replace the BAX17 with some kind of more
standard diodes for testing purposes ?


Sure,as long as the PIV is equal or better.Small-signal diodes have better
freq. response characteristics,which would affect the risetime of the
unblanking signal to the CRT grid.
You could use the ECG recommended substitute for the BAX17.
--
Jim Yanik
jyanik-at-kua.net

  #8  
Old June 5th 04, 09:56 PM
The Al Bundy
external usenet poster
 
Posts: n/a
Default dead Philips PM3240 oscilloscope

"Thierry Delaitre" wrote ...
Hi,

I've replaced the 2 bax17 in the detection part by by281 but no
success. I've posted the schematic at
http://www.cpc.wmin.ac.uk/~delaitt/PM3240/circuit.jpg

and the following pictures taken with an oscilloscope:

1) http://www.cpc.wmin.ac.uk/~delaitt/PM3240/P1010339.JPG
collector of TS1308 when intensity is in maximum
voltage goes from 7v to 75v (using 1/10 probe)

2) http://www.cpc.wmin.ac.uk/~delaitt/PM3240/P1010340.JPG
collector of TS1308 when intensity is in minimum
voltage goes to 50v

3) http://www.cpc.wmin.ac.uk/~delaitt/PM3240/P1010341.JPG
emitter of TS1306
voltage goes from 8v to 28v when intensity is in maximum

4) http://www.cpc.wmin.ac.uk/~delaitt/PM3240/P1010343.JPG
emitter of TS1306
voltage is 8V when intensity is in minimum

Cheers,

Thierry.



What I don't trust is the oscillation that is on the collector of TS1308. The signals on TS1306
seems to be correct.

Did you try to disconnect the fillament from its supply? It can be that there is a short between the
fillament and the grid or at the supply of the fillament voltage, and then lighting up the neon
lamp?

Anyways, I dont know if the by281 (correct nr btw??) is a good replacement. The BAX17 cross
reference shows up this diode:
http://www.fairchildsemi.com/pf/FD/FDH400.html

When you put back the original diodes how is the signal at the collector of TS1308? Still
oscillating?

Al


  #9  
Old June 6th 04, 10:50 AM
Thierry Delaitre
external usenet poster
 
Posts: n/a
Default dead Philips PM3240 oscilloscope

The Al Bundy wrote:
"Thierry Delaitre" wrote ...
Hi,

I've replaced the 2 bax17 in the detection part by by281 but no
success. I've posted the schematic at
http://www.cpc.wmin.ac.uk/~delaitt/PM3240/circuit.jpg

and the following pictures taken with an oscilloscope:

1) http://www.cpc.wmin.ac.uk/~delaitt/PM3240/P1010339.JPG
collector of TS1308 when intensity is in maximum
voltage goes from 7v to 75v (using 1/10 probe)

2) http://www.cpc.wmin.ac.uk/~delaitt/PM3240/P1010340.JPG
collector of TS1308 when intensity is in minimum
voltage goes to 50v

3) http://www.cpc.wmin.ac.uk/~delaitt/PM3240/P1010341.JPG
emitter of TS1306
voltage goes from 8v to 28v when intensity is in maximum

4) http://www.cpc.wmin.ac.uk/~delaitt/PM3240/P1010343.JPG
emitter of TS1306
voltage is 8V when intensity is in minimum

Cheers,

Thierry.


Hi,

What I don't trust is the oscillation that is on the collector of
TS1308. The signals on TS1306 seems to be correct.


Did you try to disconnect the fillament from its supply? It can be
that there is a short between the fillament and the grid or at the
supply of the fillament voltage, and then lighting up the neon lamp?


I've disconnected the fillament, R1337, G1, G3, R21, K and neon is
still blinking. I've checked R1341, R1339, R1338 and there are
correct.

Anyways, I dont know if the by281 (correct nr btw??) is a good
replacement. The BAX17 cross reference shows up this diode:
http://www.fairchildsemi.com/pf/FD/FDH400.html
When you put back the original diodes how is the signal at the
collector of TS1308? Still oscillating?


I meant BY218! I've now put back the original BAX17 diodes and taken
pictures.

The following shows the signal at the collector of TS1308 when
intensity is at its maximum (up to 75v).

http://www.cpc.wmin.ac.uk/~delaitt/PM3240/P1010350.JPG

The following shows the oscillating signal (6us) at the collector of
TS1308. http://www.cpc.wmin.ac.uk/~delaitt/PM3240/P1010352.JPG

The following picture shows the board with neon lighting up.
http://www.cpc.wmin.ac.uk/~delaitt/PM3240/P1010353.JPG

Should i believe that the crt is not displaying anything due to the
fact that the voltage of the wehnelt is too negative relative to the
cathode ? Could it be that the neon is faulty ? Do they normally light
up above a particular current threshold ? In my case, it seems the
neon is lighting up when the current is 0.16mA (1300/8Mohm).

Cheers,

Thierry.
 




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