PWM Control IC Problem (SG3525)

Discussion in 'Electronic Repair' started by alphamnemonic, Jul 2, 2008.

  1. 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?
     
    alphamnemonic, Jul 2, 2008
    #1
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  2. alphamnemonic

    Guest

    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.
     
    , Jul 3, 2008
    #2
    1. Advertising

  3. 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/datasheet/motorola/SG3525AN.pdf
    p.6 for an example of this configuration). I can see why you find that
    strange--I did too!
     
    alphamnemonic, Jul 3, 2008
    #3
  4. On Jul 3, 6:09 pm, Steve <> wrote:
    > alphamnemonic <> wrote innews::
    >
    >
    >
    >
    >
    > > 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/datasheet/motorola/SG3525AN.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.
     
    alphamnemonic, Jul 4, 2008
    #4
  5. alphamnemonic

    Guest

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

    >
    > > > 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/datasheet/motorola/SG3525AN.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.
     
    , Jul 5, 2008
    #5
  6. On Jul 7, 6:09 pm, Steve <> wrote:
    > Steve <> wrote innews:Xns9AD0CDEF8F97Fnobodynobodycom@216.196.97.136:
    >
    > > 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/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 Formin 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/datasheet/motorola/SG3525AN.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.
     
    alphamnemonic, Jul 14, 2008
    #6
  7. On Jul 14, 4:50 pm, Steve <> wrote:
    > alphamnemonic <> wrote innews::
    >
    >
    >
    >
    >
    > > On Jul 7, 6:09 pm, Steve <> wrote:
    > >> Steve <> wrote
    > >> innews:Xns9AD0CDEF8F97Fnobodynobodycom@21

    > > 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/datasheet/motorola/SG3525AN.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?-Hide quoted text -
    >
    > - Show quoted text -


    Yes: .rtf
     
    alphamnemonic, Jul 16, 2008
    #7
  8. On Jul 16, 6:12 pm, Steve <> wrote:
    > alphamnemonic <> wrote innews::
    >
    >
    >
    >
    >
    > > On Jul 14, 4:50 pm, Steve <> wrote:
    > >> alphamnemonic <> wrote
    > >> innews:e7294911-213d-4734-b0cd-

    > > :

    >
    > >> > On Jul 7, 6:09 pm, Steve <> wrote:
    > >> >> Steve <> wrote
    > >> >> innews:Xns9AD0CDEF8F97Fnobodynobodycom@21
    > >> > 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.or

    > > g/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 F

    > > orm
    > >> >  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/datasheet/motorola/SG3525AN.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?-

    > >  Hide quoted text -

    >
    > >> - Show quoted text -

    >
    > > Yes: .rtf

    >
    > I phrased that incorrectly.
    >
    > I meant can you post them on here for downloading or on a site?
    >
    > Thanks- Hide quoted text -
    >
    > - Show quoted text -- Hide quoted text -
    >
    > - Show quoted text -


    I don't have a website, but I will post them here if you tell me how.
     
    alphamnemonic, Jul 17, 2008
    #8
  9. On Jul 17, 11:08 am, "Michael A. Terrell" <>
    wrote:
    > alphamnemonic wrote:
    >
    > > I don't have a website, but I will post them here if you tell me how.

    >
    >    This isn't a binary newsgroup, and you can't post pictures through
    > Google Groups.
    >
    >    Sign up for a free photo hosting service and post the link to the
    > pictures.
    >
    > --http://improve-usenet.org/index.html
    >
    > If you have broadband, your ISP may have a NNTP news server included in
    > your account:http://www.usenettools.net/ISP.htm
    >
    > Sporadic E is the Earth's aluminum foil beanie for the 'global warming'
    > sheep.


    The pics are up at http://sites.google.com/site/scientificelectronicsrepair/
     
    alphamnemonic, Jul 17, 2008
    #9
    1. Advertising

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    jeffrun
    Oct 8, 2007
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