Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Old July 2nd 08, 11:35 PM posted to sci.electronics.repair
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Default PWM Control IC Problem (SG3525)

Hi Everybody

This chip normally puts out square pulses. In the power supply I am
working on (http://www.laserfaq.org/sam/150rcsch.pdf) it is putting
out a sawtooth wave. I am testing it in 'standby mode', in which Q4 is
off and R33 is in control of the duty cycle. Replacing the IC1 has no
effect. Does anyone have any ideas?

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Old July 3rd 08, 12:00 AM posted to sci.electronics.repair
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Default PWM Control IC Problem (SG3525)

On Jul 2, 3:35 pm, alphamnemonic wrote:
Hi Everybody

This chip normally puts out square pulses. In the power supply I am
working on (http://www.laserfaq.org/sam/150rcsch.pdf) it is putting
out a sawtooth wave. I am testing it in 'standby mode', in which Q4 is
off and R33 is in control of the duty cycle. Replacing the IC1 has no
effect. Does anyone have any ideas?


Where are you seeing sawtooths? Pin 13?

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header
above is
ignored unless my full name AND either lasers or electronics is
included in the
subject line. Or, you can contact me via the Feedback Form in the
FAQs.
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Old July 3rd 08, 01:20 AM posted to sci.electronics.repair
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Posts: 12
Default PWM Control IC Problem (SG3525)

wrote in news:16ea6110-be19-4a21-aecc-
:

On Jul 2, 3:35 pm, alphamnemonic wrote:
Hi Everybody

This chip normally puts out square pulses. In the power supply I am
working on (
http://www.laserfaq.org/sam/150rcsch.pdf) it is putting
out a sawtooth wave. I am testing it in 'standby mode', in which Q4 is
off and R33 is in control of the duty cycle. Replacing the IC1 has no
effect. Does anyone have any ideas?


Where are you seeing sawtooths? Pin 13?

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header
above is
ignored unless my full name AND either lasers or electronics is
included in the
subject line. Or, you can contact me via the Feedback Form in the
FAQs.



That is my question. Why do you have output A and output B (pin 11 and 14)
grounded?

Also, pin 13 is VC in for the transistor collectors. Why do you have this
connected as an output?

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Old July 3rd 08, 03:55 PM posted to sci.electronics.repair
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Posts: 12
Default PWM Control IC Problem (SG3525)

On Jul 2, 6:20*pm, Steve wrote:
wrote in news:16ea6110-be19-4a21-aecc-
:





On Jul 2, 3:35 pm, alphamnemonic wrote:
Hi Everybody


This chip normally puts out square pulses. In the power supply I am
working on (http://www.laserfaq.org/sam/150rcsch.pdf) it is putting
out a sawtooth wave. I am testing it in 'standby mode', in which Q4 is
off and R33 is in control of the duty cycle. Replacing the IC1 has no
effect. Does anyone have any ideas?


Where are you seeing sawtooths? *Pin 13?


--- sam | Sci.Electronics.Repair FAQ:http://www.repairfaq.org/
*Repair | Main Table of Contents:http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ:http://www.repairfaq.org/sam/lasersam.htm
* * * * | Mirror Sites:http://www.repairfaq.org/REPAIR/F_mirror..html


Important: Anything sent to the email address in the message header
above is
ignored unless my full name AND either lasers or electronics is
included in the
subject line. *Or, you can contact me via the Feedback Form in the
FAQs.


That is my question. Why do you have output A and output B (pin 11 and 14)
grounded?

Also, pin 13 is VC in for the transistor collectors. Why do you have this
connected as an output?- Hide quoted text -

- Show quoted text -


Yes the sawtooth is on pin 13. Pin 13 is being used as an output and
pins 11 and 14 are grounded because the chip is being used in single-
ended supply mode (see http://www.datasheetcatalog.org/data...a/SG3525AN.pdf
p.6 for an example of this configuration). I can see why you find that
strange--I did too!
  #5   Report Post  
Old July 4th 08, 01:09 AM posted to sci.electronics.repair
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First recorded activity by DIYBanter: Oct 2007
Posts: 12
Default PWM Control IC Problem (SG3525)

alphamnemonic wrote in
:

On Jul 2, 6:20*pm, Steve wrote:
wrote in news:16ea6110-be19-4a21-aecc-
:





On Jul 2, 3:35 pm, alphamnemonic wrote:
Hi Everybody


This chip normally puts out square pulses. In the power supply I
am working on (http://www.laserfaq.org/sam/150rcsch.pdf) it is
putting out a sawtooth wave. I am testing it in 'standby mode', in
which Q4 is off and R33 is in control of the duty cycle. Replacing
the IC1 has no effect. Does anyone have any ideas?


Where are you seeing sawtooths? *Pin 13?


--- sam | Sci.Electronics.Repair FAQ:http://www.repairfaq.org/
*Repair | Main Table of Contents:http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ:http://www.repairfaq.org/sam/lasersam.htm
* * * * | Mirror Sites:http://www.repairfaq.org/REPAIR/F_mirror

.html

Important: Anything sent to the email address in the message header
above is
ignored unless my full name AND either lasers or electronics is
included in the
subject line. *Or, you can contact me via the Feedback Form in the
FAQs.


That is my question. Why do you have output A and output B (pin 11
and 14

)
grounded?

Also, pin 13 is VC in for the transistor collectors. Why do you have
this connected as an output?- Hide quoted text -

- Show quoted text -


Yes the sawtooth is on pin 13. Pin 13 is being used as an output and
pins 11 and 14 are grounded because the chip is being used in single-
ended supply mode (see
http://www.datasheetcatalog.org/data...a/SG3525AN.pdf p.6
for an example of this configuration). I can see why you find that
strange--I did too!


I'd avoid the funky setup you have. In my opinion I'd connect pin 13 and 15
together and use either output A or B.

I'm not sure what Q4 is doing, I've never seen it used this way, but you
must know more than me since you designed this elaborte circuit.


Keep us posted at what you do to resolve the problem.


  #6   Report Post  
Old July 4th 08, 07:13 PM posted to sci.electronics.repair
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First recorded activity by DIYBanter: Jul 2008
Posts: 12
Default PWM Control IC Problem (SG3525)

On Jul 3, 6:09*pm, Steve wrote:
alphamnemonic wrote :





On Jul 2, 6:20*pm, Steve wrote:
wrote in news:16ea6110-be19-4a21-aecc-
:


On Jul 2, 3:35 pm, alphamnemonic wrote:
Hi Everybody


This chip normally puts out square pulses. In the power supply I
am working on (http://www.laserfaq.org/sam/150rcsch.pdf) it is
putting out a sawtooth wave. I am testing it in 'standby mode', in
which Q4 is off and R33 is in control of the duty cycle. Replacing
the IC1 has no effect. Does anyone have any ideas?


Where are you seeing sawtooths? *Pin 13?


--- sam | Sci.Electronics.Repair FAQ:http://www.repairfaq.org/
*Repair | Main Table of Contents:http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ:http://www.repairfaq.org/sam/lasersam.htm
* * * * | Mirror Sites:http://www.repairfaq.org/REPAIR/F_mirror

.html


Important: Anything sent to the email address in the message header
above is
ignored unless my full name AND either lasers or electronics is
included in the
subject line. *Or, you can contact me via the Feedback Form in the
FAQs.


That is my question. Why do you have output A and output B (pin 11
and 14

)
grounded?


Also, pin 13 is VC in for the transistor collectors. Why do you have
this connected as an output?- Hide quoted text -


- Show quoted text -


Yes the sawtooth is on pin 13. Pin 13 is being used as an output and
pins 11 and 14 are grounded because the chip is being used in single-
ended supply mode (see
http://www.datasheetcatalog.org/data...G3525AN.pdfp.6
for an example of this configuration). I can see why you find that
strange--I did too!


I'd avoid the funky setup you have. In my opinion I'd connect pin 13 and 15
together and use either output A or B.

I'm not sure what Q4 is doing, I've never seen it used this way, but you
must know more than me since you designed this elaborte circuit.

Keep us posted at what you do to resolve the problem.- Hide quoted text -

- Show quoted text -


It's not my design. I am trying to repair a commercial unit. I will
keep you posted.
  #7   Report Post  
Old July 5th 08, 12:23 AM posted to sci.electronics.repair
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First recorded activity by DIYBanter: Jul 2008
Posts: 7
Default PWM Control IC Problem (SG3525)

On Jul 4, 11:13 am, alphamnemonic wrote:
On Jul 3, 6:09 pm, Steve wrote:



alphamnemonic wrote :


On Jul 2, 6:20 pm, Steve wrote:
wrote in news:16ea6110-be19-4a21-aecc-
:


On Jul 2, 3:35 pm, alphamnemonic wrote:
Hi Everybody


This chip normally puts out square pulses. In the power supply I
am working on (http://www.laserfaq.org/sam/150rcsch.pdf) it is
putting out a sawtooth wave. I am testing it in 'standby mode', in
which Q4 is off and R33 is in control of the duty cycle. Replacing
the IC1 has no effect. Does anyone have any ideas?


Where are you seeing sawtooths? Pin 13?


--- sam | Sci.Electronics.Repair FAQ:http://www.repairfaq.org/
Repair | Main Table of Contents:http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ:http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites:http://www.repairfaq.org/REPAIR/F_mirror
.html


Important: Anything sent to the email address in the message header
above is
ignored unless my full name AND either lasers or electronics is
included in the
subject line. Or, you can contact me via the Feedback Form in the
FAQs.


That is my question. Why do you have output A and output B (pin 11
and 14
)
grounded?


Also, pin 13 is VC in for the transistor collectors. Why do you have
this connected as an output?- Hide quoted text -


- Show quoted text -


Yes the sawtooth is on pin 13. Pin 13 is being used as an output and
pins 11 and 14 are grounded because the chip is being used in single-
ended supply mode (see
http://www.datasheetcatalog.org/data...G3525AN.pdfp.6
for an example of this configuration). I can see why you find that
strange--I did too!


I'd avoid the funky setup you have. In my opinion I'd connect pin 13 and 15
together and use either output A or B.


I'm not sure what Q4 is doing, I've never seen it used this way, but you
must know more than me since you designed this elaborte circuit.


Keep us posted at what you do to resolve the problem.- Hide quoted text -


- Show quoted text -


It's not my design. I am trying to repair a commercial unit. I will
keep you posted.


First, I've never scoped pin 13 so don't know for sure what should be
there.

But, my guess is that one of the 3 transistors is not behaving
properly.and you're
seeing one of the caps charging.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header
above is
ignored unless my full name AND either lasers or electronics is
included in the
subject line. Or, you can contact me via the Feedback Form in the
FAQs.
  #8   Report Post  
Old July 8th 08, 01:09 AM posted to sci.electronics.repair
external usenet poster
 
First recorded activity by DIYBanter: Oct 2007
Posts: 12
Default PWM Control IC Problem (SG3525)

Steve wrote in
6:

alphamnemonic wrote in
news:ba29f199-331f-48c1-ab96-28c3a81d42d8

@i18g2000prn.googlegroups.com:

On Jul 2, 6:20*pm, Steve wrote:
wrote in news:16ea6110-be19-4a21-aecc-
:





On Jul 2, 3:35 pm, alphamnemonic wrote:
Hi Everybody

This chip normally puts out square pulses. In the power supply I
am working on (http://www.laserfaq.org/sam/150rcsch.pdf) it is
putting out a sawtooth wave. I am testing it in 'standby mode',
in which Q4 is off and R33 is in control of the duty cycle.
Replacing the IC1 has no effect. Does anyone have any ideas?

Where are you seeing sawtooths? *Pin 13?

--- sam | Sci.Electronics.Repair FAQ:http://www.repairfaq.org/
*Repair | Main Table of Contents:http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser
FAQ:http://www.repairfaq.org/sam/lasersam.htm * * * * | Mirror
Sites:http://www.repairfaq.org/REPAIR/F_mirror

.html

Important: Anything sent to the email address in the message
header above is
ignored unless my full name AND either lasers or electronics is
included in the
subject line. *Or, you can contact me via the Feedback Form in the
FAQs.

That is my question. Why do you have output A and output B (pin 11
and 14

)
grounded?

Also, pin 13 is VC in for the transistor collectors. Why do you have
this connected as an output?- Hide quoted text -

- Show quoted text -


Yes the sawtooth is on pin 13. Pin 13 is being used as an output and
pins 11 and 14 are grounded because the chip is being used in single-
ended supply mode (see
http://www.datasheetcatalog.org/data...a/SG3525AN.pdf p.6
for an example of this configuration). I can see why you find that
strange--I did too!


I'd avoid the funky setup you have. In my opinion I'd connect pin 13
and 15 together and use either output A or B.

I'm not sure what Q4 is doing, I've never seen it used this way, but
you must know more than me since you designed this elaborte circuit.


Keep us posted at what you do to resolve the problem.


I have been looking at the circuit and the datasheet.

I'm willing to bet the schematic is drawn wrong. It doesn't make any
sense to have pin 13 driving the base of a transistor.
  #9   Report Post  
Old July 14th 08, 10:10 PM posted to sci.electronics.repair
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First recorded activity by DIYBanter: Jul 2008
Posts: 12
Default PWM Control IC Problem (SG3525)

On Jul 7, 6:09*pm, Steve wrote:
Steve wrote . 136:

alphamnemonic wrote in
news:ba29f199-331f-48c1-ab96-28c3a81d42d8


@i18g2000prn.googlegroups.com:







On Jul 2, 6:20�pm, Steve wrote:
wrote in news:16ea6110-be19-4a21-aecc-
:


On Jul 2, 3:35 pm, alphamnemonic wrote:
Hi Everybody


This chip normally puts out square pulses. In the power supply I
am working on (http://www.laserfaq.org/sam/150rcsch.pdf) it is
putting out a sawtooth wave. I am testing it in 'standby mode',
in which Q4 is off and R33 is in control of the duty cycle.
Replacing the IC1 has no effect. Does anyone have any ideas?


Where are you seeing sawtooths? �Pin 13?


--- sam | Sci.Electronics.Repair FAQ:http://www.repairfaq.org/
�Repair | Main Table of Contents:http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser
FAQ:http://www.repairfaq.org/sam/lasersam.htm� � � � | Mirror
Sites:http://www.repairfaq.org/REPAIR/F_mirror
.html


Important: Anything sent to the email address in the message
header above is
ignored unless my full name AND either lasers or electronics is
included in the
subject line. �Or, you can contact me via the Feedback Form in the
FAQs.


That is my question. Why do you have output A and output B (pin 11
and 14
)
grounded?


Also, pin 13 is VC in for the transistor collectors. Why do you have
this connected as an output?- Hide quoted text -


- Show quoted text -


Yes the sawtooth is on pin 13. Pin 13 is being used as an output and
pins 11 and 14 are grounded because the chip is being used in single-
ended supply mode (see
http://www.datasheetcatalog.org/data...G3525AN.pdfp.6
for an example of this configuration). I can see why you find that
strange--I did too!


I'd avoid the funky setup you have. In my opinion I'd connect pin 13
and 15 together and use either output A or B.


I'm not sure what Q4 is doing, I've never seen it used this way, but
you must know more than me since you designed this elaborte circuit.


Keep us posted at what you do to resolve the problem.


I have been looking at the circuit and the datasheet.

I'm willing to bet the schematic is drawn wrong. It doesn't make any
sense to have pin 13 driving the base of a transistor.- Hide quoted text -

- Show quoted text -


The schematic is drawn correctly. This mode of operation is described
on p.6 of the datasheet (link is given in my post from July 3). I
removed the board and re-soldered R1 and R2, and the supply is now
working properly again. A rather boring fix, but if it works long term
I won't complain... If anyone else is having trouble with this supply,
I can send you waveforms captured with FlukeView from the working
unit. Thanks for the suggestions everyone.
  #10   Report Post  
Old July 14th 08, 11:50 PM posted to sci.electronics.repair
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First recorded activity by DIYBanter: Oct 2007
Posts: 12
Default PWM Control IC Problem (SG3525)

alphamnemonic wrote in
:

On Jul 7, 6:09*pm, Steve wrote:
Steve wrote
innews:[email protected]

6.196.97.136:

alphamnemonic wrote in
news:ba29f199-331f-48c1-ab96-28c3a81d42d8


@i18g2000prn.googlegroups.com:







On Jul 2, 6:20�pm, Steve wrote:
wrote in news:16ea6110-be19-4a21-aecc-
:


On Jul 2, 3:35 pm, alphamnemonic wrote:
Hi Everybody


This chip normally puts out square pulses. In the power supply
I am working on (http://www.laserfaq.org/sam/150rcsch.pdf) it
is putting out a sawtooth wave. I am testing it in 'standby
mode', in which Q4 is off and R33 is in control of the duty
cycle. Replacing the IC1 has no effect. Does anyone have any
ideas?


Where are you seeing sawtooths? �Pin 13?


--- sam | Sci.Electronics.Repair FAQ:http://www.repairfaq.org/
�Repair | Main Table of Contents:http://www.repairfaq.org/R

EPAIR/
+Lasers | Sam's Laser
FAQ:http://www.repairfaq.org/sam/lasersam.htm�

� � | Mirror
Sites:http://www.repairfaq.org/REPAIR/F_mirror
.html


Important: Anything sent to the email address in the message
header above is
ignored unless my full name AND either lasers or electronics is
included in the
subject line. �Or, you can contact me via the Feedback Form

in the
FAQs.


That is my question. Why do you have output A and output B (pin
11 and 14
)
grounded?


Also, pin 13 is VC in for the transistor collectors. Why do you
have this connected as an output?- Hide quoted text -


- Show quoted text -


Yes the sawtooth is on pin 13. Pin 13 is being used as an output
and pins 11 and 14 are grounded because the chip is being used in
single- ended supply mode (see
http://www.datasheetcatalog.org/data...G3525AN.pdfp.6
for an example of this configuration). I can see why you find that
strange--I did too!


I'd avoid the funky setup you have. In my opinion I'd connect pin
13 and 15 together and use either output A or B.


I'm not sure what Q4 is doing, I've never seen it used this way,
but you must know more than me since you designed this elaborte
circuit.


Keep us posted at what you do to resolve the problem.


I have been looking at the circuit and the datasheet.

I'm willing to bet the schematic is drawn wrong. It doesn't make any
sense to have pin 13 driving the base of a transistor.- Hide quoted
text

-

- Show quoted text -


The schematic is drawn correctly. This mode of operation is described
on p.6 of the datasheet (link is given in my post from July 3). I
removed the board and re-soldered R1 and R2, and the supply is now
working properly again. A rather boring fix, but if it works long term
I won't complain... If anyone else is having trouble with this supply,
I can send you waveforms captured with FlukeView from the working
unit. Thanks for the suggestions everyone.


I'd like to see them. Do you have them in a format you can easily email?




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