brewGroup noisy on clockwise direction

[fkomat]

I know that my answer is somewere in the forum, I tried to investigate but
unfortunately I cannot read German!! sorry!
I have a Magic Deluxe problem, the brew motor runs perfectly on the counterclockwise direction, but it is
erratic and noisy on the clockwise direction. I replaced Power trasistor TIP33c and the 33v. Zener withot
success, also the fullwave bridges seem ok on a ohmmeter reading. Read voltages on Jp13, same situation
counterclockwise the voltage is smooth, motor silent, clockwise voltage jumps erratically, motor bucking
and noisy. Unless this is a microprocessor issue I have no idea of what to test next.
I hope Mr. Hmilbradt or anyone else can direct me to the right path.
Thanks!!
fkomat

 

[ksb]

Hello fkomat,

please measure carefully the voltage between

a) the both yellow and
b) the red and blue

wire of the 4-pole Motor connector (DC and AC) and tell us the result.

Is it easy possible to move the brewing unit manually ?

regards KSB

 

[fkomat]

Thanks for your reply.I forgot to mention that this is a M4AV6-7 board, all voltages were taken with machine on TEST MODE.All Triacs, diodes and full wave bridges, tested ok.The brewgroup can be moved manually, please note that on the counterclockwise direction, the motor moves the brewgroup normally without any abnormality. Below are the voltages requested on YY and R/B cables,( I am aware that the target should be for YY=80vdc and R/B=33vdc)Here is the data:yy-dc clockwise=19vdc erratic meter readingyy-dc counterclockwise=35vdc normal meter reading yy-ac clockwise= 50vac erratic meter readingyy-ac counterclockwise=40vac normal meter readingr/b-dc clockwise=12vdc erratic meter readingr/b-dc counterclockwise=26vdc normal meter reading r/b-ac clockwise=22vac erratic meter readingr/b-ac counterclockwise=29vac normal meter readingPS. voltages are approximate but reliable, taken with analog voltmeter Simpson 260.

 

[ksb]

r/b-dc clockwise=12vdc erratic meter reading r/b-dc counterclockwise=26vdc
r/b-ac clockwise=22vac erratic meter reading r/b-ac counterclockwise=29vac

please note that on the counterclockwise direction, the motor moves the brewgroup normally without any abnormality.

As you can see the voltage in ccw direction (26V) is more like the target value of 33V as the cw direction (12V). The AC voltage is too high anyway.

There are a few possible reasons for this:

1. If you have 275V-Varistors on stock, exchange the Varistor in parallel to the triac that feeds the blue wire of the motor

2. Maybe the Triac is ok while static measurement but not in reallity - exchange the triac.

3. Check that there is absolutely no connection between any of the triacs on heatsink to the heatsink itself.

 

[fkomat]

Thanks KSB
For board M4AV6-7 the triac should be T8 and varistor should be RV8, is that correct??
If yes I will replace them.Can you please explain what circuit is responsible for the
voltage reversal on the Brew Motor, It seems to me that the circuit is normal on one direction
(do not know if is on + or -) but is failing on the opposite direction.
Can you also elaborate on your step 3. the T11 triac's tab is mechanically connected on the heatsink,
however none of the pins A1, A2, Gate are shorted with the heatsink, is this your request??
Many thanks
Fkomat

 

[ksb]

T8 and RV8 is correct.

Both directions are supplied by the same component - the triac "T8" - for the change of the polarity the triac is driven at the other half-wave of the sine-voltage. If the triac is driven only while the positive half-wave of the mains-voltage the result is a positive voltage and if it is driven only while the negative half-wave the result is a negative voltage.

IF RV8 is faulty, a small conduction in one direction will be active all the time and causes the different voltage.

The triac must be passivated so that all pins have no connection to heat sink - in some cases wet dirt or small metal-parts will cause a connection - make sure that only the tab of the transistor has a connection to the heat sink.

 

[traebbe]

Hi fkomat,
to see, if the Varistor is faulty, you can run the machine without the varistor.
The Varistor is only a fuse to the Triac, and for the test it will be ok to run without the varistor.
If you get the same resilt, the varistor will be ok.

Greets
traebbe

 

[ksb]

If you are lucky the triac will survive this experiment....

 

[fkomat]

KSB
Triac T11 tab is screwed on the heatsink consequently is shorted to the heathsink, the other pins are not. All other Triacs have no shorts with the main heathsink. For the polarity issue, I understand the negative and positive AC slope, but my question is who is controlling the polarity reversal to the Triac, is it the microprocessor?? On test mode when you press key1 the brewmotor advances ccw, when you press key2 it will advance ccw, what is process? If you can explain in easy terms it will be greatly appreciated, it is driving me insane for a week now!!
tks

 

[ksb]

Yes - the triac is screwed to the sink but it must be passivated (insulated) so that no connection between tab and any pin exists.

Yes - the microcontroller does the timing for positive or negative direction.

Yes - in test mode key 1 shall do a rotation in cw and the other in ccw direction.

Is this an answer to all of your questions ?

 

[fkomat]

Yes - the triac is screwed to the sink but it must be passivated (insulated) so that no connection between tab and any pin exists.
I Confirm, there is no connections between tab and other pins.
Yes all questions have been answered, I will replace the components, and post results later.
Thanks for your help KSB

 

[fkomat]

KSB
I could be completely off on my theory, but I am confused about the Triac T8/RV8 function; These components accept and pass through both polarities minus or plus of the sinewawe, but one polarity is ok and one is not, if there was an abnormality in the varistor RV8 or triac T8, the failure should be evident on the negative or positive polarity, because the signal pass through the same components. Could it be the microprocessor is giving a distorted positive or negative level signal to the gate of the T8 triac?? Please correct me if I am completely off on this.
Thanks
Fkomat

 

[ksb]

The problem is the high ac-component of the voltage. Normaly the ac-component is about 1V or less.

The correct advice must be: replace T8 and R8 together and tell us the result.

It is wasted time to think about which change in the balance is caused by a faulty varistor.

 

[fkomat]

KSB
ok I will replace both components and report back.
Thanks for your support
Fkomat

 

[fkomat]

Hello KSB
I replaced T8 and RV8 as you suggested, it did not solve the cw rotation noisy issue.
I replaced also the +5v regulator, 470MFD cap. replaced T9, T11, RV7, RV9,
replaced the 33v regulation circuit Tip33c and 33v. Zener. Unfortunately the problem is still the same,
Brew Motor rotation is normal on CouterClockwise direction,but noisy and abnormal on the clockwise
rotation, with high AC voltage component in the DC voltage to the motor.
I have no more ideas,or what section of the circuit to focus on in order to solve this problem.
Any suggestions, ideas , help is greatly appreciated.
Thank
Fkomat

 

[ksb]

Hello fkomat,

Please make sure that there is absolutely no connection between the heat-sink and any other components.

Check the the pcb is absolutely clean - also all pins of the controller.

Run the motor with an external DC-source (9-33V) in both directions - is there any noise too ?

Regard KSB

 

[fkomat]

KSB

1-Checked, NO connection between Heatsink and components
2-Pcb top and bottom all clean
3-Tested motor with 12DC PS , motor turning normally cw and ccw

regards

 

[ksb]

Is your controller mounted in a socket ?

 

[fkomat]

Unfortunately NO, is soldered on the PCB

 

[ksb]

Do you own a scope and an insulating transformer ?