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Coffee machine power issue

phlox

May 19, 2012
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Hi all, so im trying to fix a filter coffee machine which does not power on.

Well certain parts that are tied to mains directly llike the steamer and heater work.
the rest doesnt switch on.
the clock works but as soon as power button is pressed it tries to switch on, screen goes blank for a second then clock comes on again and repeat.

i removed the PSU, looks like no damage on it , i checked the resistors and they are good, replaced the cheap caps with brand new good name brand caps on the psu and front control panel but no change.

if i remove the relay then the device powers on like it should , except the water pump or whatever is connected to the relay doesnt work, same goes for if the transistor is removed, which i also replaced.

i measure about 7.9v at the relay coil when switched on with relay removed.

its like it loses power as soon as the power button is pressed and then switches back on.

im attaching pics of the psu and control unit.
20171108_230858.jpg 20171108_230911.jpg 20171108_230925.jpg
 

phlox

May 19, 2012
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yes, i removed the relay and put 12v across the coils, and it clicks like it should, im going to put in a different relay and maybe see if it makes any difference
 

phlox

May 19, 2012
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swopped the relay out for a 12v DC one since the original was rated for 28v DC, but the voltage drop still occurs.
 

73's de Edd

Aug 21, 2015
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Sir phlox . . . . .


This unit seems to be quite a bit of a wierd duck on the shown board in the respect that is using a MINUS 5 VDC minor and a MINUS 12 VDC main power supply but that 12V supply never leaves this board and is used just for supplying coil drive to your your power relay.

In order for me to finish parts ID asssignments on this unit, the C1 RED RING is the main electrolytic capacitor, but it is hiding the voltage of that supply above its zener, confirm that marking as 12V silk screened on the board .
Also give that caps voltage and capacitance rating.

Then move over to the other YELLOW RING cap and give its voltage and capacitance rating.

Then power up the unit and place DC metering ACROSS the 5.1 marked zener diode and confirm 5 VDC from it.
Then meter across the 12 VDC zener diode unit and confirm that DC voltage being across it is 12 VDC.

In my " reading " the boards foil on my starting to mark up the interconnecting wiring to the brains board of the unit. .

  • The top white plug connection relates to being the relay turn on voltage from the other board, coming in
via R1 ( is it being a 4700 ohm ? ). . . since it is barely visible . . . that feeds to the base of the BG1 relay driver transistor.
Its circuitry is being a variant, in the respect that the relays drive coil is placed in the emitter to ground path of that drive transistor.
  • The center white plug connection is the common + of the power supply.
  • The bottom white plug connection is the MINUS 5VDC to the logic board.

INITIAL TRIAL BOARD MARKUP . . . . . . .

Phlox_ckt_bd.png


Now . . . . . Help . .help . .me . . .Rhonda . . . . . . . . .Help . .help . .me . . .Rhonda . . . .

73's de Edd
 
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phlox

May 19, 2012
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the caps ratings, for both of them are 25v 470uf.
i replaced them with brand new ones, since i thought they were the issue and the originals were cheap chinese brand caps.

i will give the voltage readings as soon as i get home .
 

shrtrnd

Jan 15, 2010
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The 'intermittent' part of your description is what catches my attention.
73's de Edd is always thorough in his troubleshooting acumen. I'd 2nd his advice.
My thought is to check the actual connector pin contacts themselves. Sometimes I've found underrated pins in connector plugs can burn-up in higher current applications than the design engineers envisioned. (Causing an intermittent contact in partially destroyed contacts).
If you still have problems after bushtech and 73's de Edd's performance checks, Look at the connectors and the continuity of the connector wiring.
 

phlox

May 19, 2012
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thanks will check that. I also checked the 5v supply and 12v, definately an issue on the 12v supply as there is only 7.9v present however the 5v supply is fine. and 73's de edd that R1 resistor checks out a 4.6k ohms which i believe is in spec?
 

ChosunOne

Jun 20, 2010
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*shakes head* All that circuitry to make coffee. You guys do love to have things complicated. :rolleyes:

*rinses out soup can*
*punches holes in bottom of can*
*Inserts cotton sock, looping elastic over rim*
*measures one spoon of coffee grounds into sock*
*sets can on coffee cup*
*pours in one cup of hot water*

One minute later---Aaahh, coffee! :D
 

phlox

May 19, 2012
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hahaha chosunOne ....best way to make coffee... just make sure to use a clean sock !:D

the coffee machines actually a friend of mines. I said id take a look since i know a bit about electronics and the thing is basically still brand new, hasn't been used much.Just seems like a waste to throw away any piece of electronics if it can be fixed. I still have a 39" tv that i got from someone who wanted to throw it away that i want to try and fix.
Suspect it might be a easy fix, as i saw the main caps on the PSU are bulged. Will order new ones, replace and test, still switches on but only in standby.
Also i like challenges with electronics and like to learn more.
 

73's de Edd

Aug 21, 2015
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Say feller . . . . wanna go fer it . . . and blow some od yer hard earned munney for a 1 watt 12volt zener diode ?
 

phlox

May 19, 2012
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ill give that a go if you reckon thats it? maybe i might have one somehwere
 

phlox

May 19, 2012
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okay , i removed the 12v zener, and still measured 7.9v.

so i thought let me check the 12v rail, so removed the parts marked with red, and got roughly 14v up to the 12v zener pads. so i think its something on the 12v rail going to the relay.
i disconnected power and started putting components back one by one and now i have 80mV . Still get 230v before the diodes, but after them only about 80mV , even after replacing the diodes.Inked20171108_230858_LI.jpg
 

phlox

May 19, 2012
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i checked all the components again, the resistors all show correct values. Only components i couldnt test are the 104 ceramic caps, but they arent shorted though.

Also couldnt test the 275v X2 yellow capacitor and the blue ceramic as well, but i still get 230v till the diode rectifier, at the DC side of it now only 80mV.
 

phlox

May 19, 2012
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okay nevermind, was late last night, found the problem, was a shorted zener across the realy coil causing the issue.

removed it and now back to square one, 5.1v present, and still only 7.9v, replaced most of the resistors just for incase, still no change
 

73's de Edd

Aug 21, 2015
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Since your country of origin is not given, up to this moment I didn't know if you were a 120 or 220VAC person.

The back emf spike supressor across the relay coil looks to be a mere 1N4148. That is not being a Zener, but I have sooooooooooo many that I typically always use a 1N 4007 series for that function . . . overkill.

Tomorrow I will run a power flow path across the board for you to compare against to confirm no viewing errors are being made on my part..

Also give the relay driver transistor . . . . I wonder where they came up with that BG1 prefix.

Also what brand and model of unit, and I see it having to be a 2008 or newer model.
 

phlox

May 19, 2012
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hey guys, i finally got time to order parts, replaced the 12v and 5.1v zener diodes as well as the X2 1uf capacitor and all is working again.

Thanks for all the help
 

73's de Edd

Aug 21, 2015
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Got that SHINY piece of equipment going again . . . .ehhhh ? . . . . . . .KUDOS !
 
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