Shredder very slow to start

[jinu_j]

Hi Folks

I have a shredder, the problem is after putting the paper it takes about a minute for the motor to start and shred.

I trouble shooted a lot and figured out that the problem is the voltage at the coil end of the relay is taking time to reach 24V. It rises very gradually and as soon as it reaches 20V the motor starts.

The question is what component could be causing this ? Could caps be the problem. Please see PCB images below

[petehall347]

try new solder on those bad joints .
if that doesn't fix it then you may as well change all 3 electrolytic capacitors .
if that hasn't worked change relay driver transistor

[R_J]

Also check that the gears etc. are not full of paper dust and causing things not to operate, Check the motor to make sure it is turning freely and that the bearings are not causing the fault.

[jinu_j]

Thanks. This is a new shredder and not used much so no issue with gears. I have ordered the replacement CAPS. will replace those and update once done. Thanks folks

[eccerr0r]

Other possibility is that one of the resistors went open or one of the tracks broke. Some of the tracks on the bottom looks corroded or something weird is going on with them ... could they be to blame?

[budm]

I see some crappy solder joints too.

[jinu_j]

Hi Folks

I have replaced the caps with new ones. and resoldered some of the joints showing poor solder. But still the same problem, infact replacing the capacitors seems to make it worse. Now the voltage across the coil of the relay is stuck at 10V. i believe it has to reach 24 volts for the relay to trigger. What else could be the problem ?

I looked at the transistor. All that written on it is A44 B331. Cant find the data sheet for this transistor. Is there an equivalent you are aware off.

Some voltages i have recorded
- Voltage at the receiver end of the IR recerive when path is blocked : 2.5V
- Voltage at Base of Transistor (pin 2) : 1 V
- Voltage between C and E (Pin 1 and 3) : 30V
- Voltage across coil of relay : 8v (This should be around 24) but this is gradually very gradually increasing and climbing upwards

[eccerr0r]

I'd also make sure the paper sensor is actually working properly too...

[jinu_j]

Paper sensor is working fine. Without the paper blocking the path between the sensors i see volts 0.5v and when i put the paper the voltage rises to 2.5V

[eccerr0r]

what's the reference point of base of transistor when you say 1V ?

[petehall347]

transistor looks duff . try shorting emitter to collector and see if relay clicks in .

[jinu_j]

Originally Posted by eccerr0r

what's the reference point of base of transistor when you say 1V ?

The problem is i cant find the specs on the Transistor. It is just numbered as A44 B331.

I think its ground. Please see image below. The voltages measured are:

- Voltage at the receiver end of the IR receiver when path between IR Transmitter and receiver is blocked (Points C and D : 2.5V
- Voltage at Base of Transistor (pin 2) Points C and H : 1 V
- Voltage between C and E (Pin 1 and 3)Points G and I : 30V
- Voltage across coil of relay Points E and F : 8v (This should be around 24) but this is gradually very gradually increasing and climbing upwards
- Points A and B are points to the IR Tranmitter - 1V
- The transistor is at points G, H, I

[jinu_j]

Originally Posted by petehall347

transistor looks duff . try shorting emitter to collector and see if relay clicks in .

Actually it did. When i shorted the Emitter and collector the Shredder started working. Thanks a lot.

So can i assume the transistor is bad and needs replacement. If so the problem is i cant find the replacement of a transistor with the name A44 B331 is there an equivalent.

[R_J]

This could be it. Either the transistor is bad OR the base is not being turned on enough.

[jinu_j]

Originally Posted by R_J

This could be it. Either the transistor is bad OR the base is not being turned on enough.

Is there anyway i can test for the second issue (base not being turned on enough) ?

[R_J]

Check the voltage between emitter and base. It should be around 0.7 volts or a bit more, also what is the voltage across C2

[jinu_j]

Originally Posted by R_J

Check the voltage between emitter and base. It should be around 0.7 volts or a bit more, also what is the voltage across C2

The voltage between the Emitter and base is 0.45V

[R_J]

That seems too low to turn on the transistor, check the voltage across C2 (or R6) also check R7 10k, it could be open
Check that the trace that goes from R9 to D5 to R6 to ZD1 is not open, this is the ground or common point
C1+ seems to be the low voltage supply (5V?) It then goes through R5, through D6 to C2+

[jinu_j]

Voltage across C2 is 1.8V. R7 is 10k and is not open. That would indicate a a problem with the diode D5? If I check the voltage between points after R7 and before D5 it about 1V, but i move it to after D5, it drops to 0.45V

[R_J]

D5 has nothing to do with the base circuit, it connects the emitter of Q1 to ground.
Check the voltage across C1. C1 negative is the ground of this circuit.
There are 2 wires next to the relay (Violet and Grey) where do they connect? The violet wire connects to ground, and the grey wire seems to control the voltage going to the Q1 base