Paper shredder - diode question, circuit question
 

I'm attempting to fix a Royal Orca 3500 5-sheet crosscut paper
shredder that's eating fuses within half a second in either forward or
reverse directions. I was unable to find a 125V 3.5A mini glass fuse
in this size, so I replaced hte original with a 125V Littelfuse 3.5A
Picofuse.

I've testing various diodes on the board -- the 4 rectifier diodes
appear to be ok, but there are several others... many of which test at
a relatively low resistance in the reverse direction when tested
in-circuit. Without reverse engineering the schematic off this board,
or desoldering a bunch, I can't say for sure, but this appears to be a
Very Bad Thing telling me it's time to send this thing off to the
local landfill (though with the heft of that cutter, the tree hugger
in me would like to restore it to life if at all possible).

I have 3 questions:
Are these circuits likely to have diodes in parallel with a
resistive path (i.e. is it posible the diodes could be ok)?

Does anyone know if Royal actually stocks replacement boards
for these things?

Curiosity--anyone know the most likely root-cause failure
modes in these circuits?

The circuit in this one has one dual op amp, big diodes, little
diodes, electrolytic caps, 2 high power resistors, bunch a little
ones, 5 transistors, and a blue, square RW-SS-124D--apparently a
relay--likely for the overload protection circuitry is claims to have.

TIA for any info or shared experience!

Best Regards,
--
Todd H.
http://www.toddh.net/

Paper shredder - diode question, circuit question
 

"Todd H." wrote in message

Are these circuits likely to have diodes in parallel with a
resistive path (i.e. is it posible the diodes could be ok)?
-----------

Todd H.
Yes the diodes are probably good..... to be certain, remove one leg of the
diode and test it again.
--
Best Regards,
Daniel Sofie
Electronics Supply & Repair
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Paper shredder - diode question, circuit question
 

Can you test the motor alone. A shorted motor winding would be
a likely cause of fuse blowing.

--- sam | Sci.Electronics.Repair FAQ Home Page: http://www.repairfaq.org/
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Paper shredder - diode question, circuit question
 

Sam Goldwasser writes:

Can you test the motor alone. A shorted motor winding would be
a likely cause of fuse blowing.

Hey Sam,

Thanks for the response.

I disconneted the motor and slapped a meter across it and it reads 0.1
ohm across the motor terminals. Have I found the smoking gun?

What's a more normal motor reading?

Best Regards,
--
Todd H.
http://www.toddh.net/

Paper shredder - diode question, circuit question
 

(Todd H.) writes:

Sam Goldwasser writes:

Can you test the motor alone. A shorted motor winding would be
a likely cause of fuse blowing.

Hey Sam,

Thanks for the response.

I disconneted the motor and slapped a meter across it and it reads 0.1
ohm across the motor terminals. Have I found the smoking gun?

What's a more normal motor reading?

What voltage is the motor supposed to run on? DC or AC? It does sound
low but not totally out of the quesiton depending on the answers to the
above questions.

--- sam | Sci.Electronics.Repair FAQ Home Page: 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 Site Info: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: The email address in this message header may no longer work. To
contact me, please use the feedback form on the S.E.R FAQ Web sites.

Paper shredder - diode question, circuit question
 

Sam Goldwasser writes:

(Todd H.) writes:

Sam Goldwasser writes:

Can you test the motor alone. A shorted motor winding would be
a likely cause of fuse blowing.

Hey Sam,

Thanks for the response.

I disconneted the motor and slapped a meter across it and it reads 0.1
ohm across the motor terminals. Have I found the smoking gun?

What's a more normal motor reading?

What voltage is the motor supposed to run on? DC or AC?

DC...or at least rectified AC. The AC line comes onto the board and
hits a bridge rectifier. The circuit board components and motor leads
are all downstream of that. There isn't an enormous amount of
capacitance on the board.

--
Todd H.
http://www.toddh.net/

Paper shredder - diode question, circuit question
 

(Todd H.) writes:

Sam Goldwasser writes:

(Todd H.) writes:

Sam Goldwasser writes:

Can you test the motor alone. A shorted motor winding would be
a likely cause of fuse blowing.

Hey Sam,

Thanks for the response.

I disconneted the motor and slapped a meter across it and it reads 0.1
ohm across the motor terminals. Have I found the smoking gun?

What's a more normal motor reading?

What voltage is the motor supposed to run on? DC or AC?

DC...or at least rectified AC. The AC line comes onto the board and
hits a bridge rectifier. The circuit board components and motor leads
are all downstream of that. There isn't an enormous amount of
capacitance on the board.

Can you tell what type of motor it is. Does it have brushes? Is there
perhaps a capacitor or other component across its leads that is the
real culpret being shorted? 0.1 ohms sounds really low even for
a burnt motor.

--- sam | Sci.Electronics.Repair FAQ Home Page: 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 Site Info: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: The email address in this message header may no longer work. To
contact me, please use the feedback form on the S.E.R FAQ Web sites.