LCM4 selected vend motor moves slightly, then stops without vending.

[keithn]

Hi all, I am a newcomer to vending machines, but I am a retired professional electronics engineer, with over 50 years experience in analog, digital & embedded micro-electronics such as this vending controller. I am trying to help the owners of this machine (made in 1997) to try and get it working. The machine has been working for years with no issues, until now.

The problem is that when a selection is made in test vend mode, the selected motor moves fractionally, but does not complete the cycle by turning a complete revolution and the vend fails. If I put the machine into Diagnostic Vend Test (mode button press followed by #6) it sequentially moves each motor present in the configuration, but only slightly as described above, however it passes the test and only fails on the ones that are not present in the configuration and so no motor is fitted. The machine is configures as 2 rows of 6 then 1 row of 10 snack items on rows A,B & C and 2 rows of cans on G & H

I have tried setting the machine to free vend and individual dispensers to free vend, but nothing works.

 

I now have the control board with just 1 motor (wired to position A1) on my test bench and can confirm that when it is selected during a test vend, the motor is driven for precisely 100mS before stopping. I am guessing that a full vend would require the motor to run for about a second or so.

Can anyone think of any reason why the vend motor time is being cut short, other than a control board fault?

I would appreciate any help or advice on any suggestions for other tests I could try?

Many Thanks,

Keith

[AZVendor]

You are doing a motor test which only does what you are describing.  In order to free vend a motor you have to set the selection price to zero and then you can press the selection and have it "free vend."  This is how LCM machines work.  If you still only get incremental motor movement with a zero price vend (which excluded the coinage)  then you either have a bad power supply or bad logic board.  Get the manual and check for proper power supply voltages first.  Make sure you select the proper DC and AC scales.

[keithn]

Thank you for responding.

I will look into the power supplies in more detail. It maybe that the full wave bridge smoothing capacitor is failing (it is 25 years old after all!).

Thanks again,

 

Keith

[tblake05]

1 hour ago, keithn said:

Thank you for responding.

I will look into the power supplies in more detail. It maybe that the full wave bridge smoothing capacitor is failing (it is 25 years old after all!).

Thanks again,

 

Keith

Wow! You may be talking over our heads Keith! But welcome aboard.

ive always been amazed at the lack of support for vending machines. Like look at arcade games.... full schematic down to the control board and every component on it.

ive got a nayax telemeter on the bench right now that has a shorted b+ to ground after the regulator. No (public) schematic, no help from tech support, and I t’s filled with shotty Chinese junk parts which google turns up nothing. No data sheets. Frustrating.

keep up the battle. You know more about it than I do- though given capacitors from the 90’s, I believe your on the right track.

[keithn]

Agreed - it's a pain in the what'sit not having schematics. Already for this repair attempt I've had to reverse engineer about 2/3rds of the circuitry just to figure out how it should work - very time consuming, but as I'm retired, not a problem. As to component supplies, I recently worked on an xbox series s console that had been water damaged and even though I managed to get hold of complete schematics, two of the chips I knew were damaged are simply not available anywhere,  even in China. so my efforts were wasted. C'est la vie I guess.

Good luck with your repair efforts!

Keith

[lacanteen]

That's a known problem with the LCM. Motor drivers on the board are bad. Time to replace the computer board. 

[keithn]

Problem is I'm here in UK and the cheapest I can get a replacement board for including shipping from the US  is more than $200. 

The motor drivers on the board I have are made by Allegro in the US and are a UCN5890A (8 channel source drivers) for the rows paired with a UCN5842 (8 channel sink drivers) for the columns. So, following lacanteen's message, I am going to replace both devices and see if that fixes it. The devices are not easy to get hold of in the UK, so I may have to wait due to having to get them from China (2-3 weeks).

If AZVendor is reading, I have checked the AC voltage to the board (26v rms) and have replaced the main smoothing capacitor and the 5v step-down converter's capacitors (just in case) - but no joy. If I have success after replacing the above drivers, I will report back here in case it helps someone else.

Thanks,

Keith

[keithn]

Hi all, Sorry to bug you again with another question, but on an LCM4, when you enter service mode (by pressing the mode button), what does the diagnostic number displayed actually mean? I've got a board on my workbench, with no motors connected and I'm getting a display of '12', but when I connect a motor (say across A1 connections) and I power off and then on again, I get '13' displayed. What is it telling me?

Many Thanks for any replies.

 

Keith

[AZVendor]

When you press the mode button it displays the motor count (number of valid motors the board sees.)  Yours saying 12 with nothing connected means your board is bad or maybe 12 is a default.  I've never seen that low a number before.  In most machines you would see between 4 and 10 motors less than you actually have if one shelf wasn't seen by the board.  In real life, the way you finish servicing an LCM is by entering and exiting the service mode 4 times to ensure the display shows all of the motors in the machine before you close and lock the door.  If it doesn't then you have to reseat all the shelves and try the motor count again.  Most vendors don't even know of this as it's not in the manual.  They just come back later to find entire shelves that didn't sell anything and then wonder why.

[keithn]

Thank you. So, if the board is fitted into a machine with 2 rows of 5 snacks, then 1 row of 10 snacks and 2 rows of 5 cans, should I see the diagnostic number 30, meaning 30 motors have been detected?

Keith

[AZVendor]

Yes, if all of the motors, harnesses, etc. are good.

[keithn]

Thank you Sir. Any idea why would I get a display of '12' with no connected motors? - You mention a default condition maybe - Is there a way to reset the board to known factory values (i.e. clear the system of all previously programmed settings)?

Keith

[AZVendor]

None that I know of.  There isn't a battery to pull as it uses non-volatile memory.  I wouldn't worry about that unless you put it back in the machine and it is off by 12 motors. 

[keithn]

OK - Thanks AZV!