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3D Printer problems - Monoprice/Wanhao D6

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ddmckee54:
I'm posting this on several forums, so for some of you this might be a repeat.

I've got a Monoprice printer that is actually a re-badged Wanhao D6.  I managed to kill my printer last week, I static ZAPPED it  - but that's not the only problem.  As I was plugging in the SD card to load a new G-code file I felt a shock through my finger tips and the LCD screen went dark at the same time.  I remember I said "Oh Fudge", or something like that because those two events occurring at the same time are NEVER a good thing.  I tried cycling the power to the printer but that made no difference.  I tried the turn it off for a few seconds and then turn it back on trick, still no screen.  I tried turning it off for over  a minute and then turning it back on but still no joy.  By this time it was past my bed-time and I'd run out of the expletives that I've learned in the past 65 years,  so I planned on trying it one more time in the morning before I left for work.  The next morning, this was Friday, when I turned on the printer the screen came to life.  I said Praise Jesus, turned off the printer, and went to work.

After I got home from work that evening I tried to actually do something with the printer and discovered that I had no cursor on the screen and apparently no way to control the printer.  At this point I opened up the printer to see if I could find any part numbers to order replacements.  The D6 uses two proprietary PC boards, through my research into these boards I found that they call them the control board and the motherboard.  I think the control board is the one that I ZAPPED.  It has the SD card hardware, the LCD hardware, and the control knob/button hardware and would have been the first in line when the static charge hit.

BUT, and it's a big BUT, I also found reference to a relay problem on the motherboard.  It seems that Wanhao cloned the motherboard from another of their printers and didn't quite do their due diligence in the design.  They used a relay with contacts rated for 10 amps maximum at 30VDC, this is a problem when just the heater load is 12.5 amps.  Having designed industrial control systems for over 30 years, I can assure you that relay is going to fail.  It's not a matter of IF it's going to fail, it's a matter of when.   One of the messages the failure of this relay will generate is a Heater Error message, which I had been getting on rare occasions for several months.

So my motherboard relay was failing, along with a dead control board.  I try to avoid the long shipping delays by buying from suppliers on this side of the pond - no such luck.  The only place that I could find that had the control board in stock was Aliexpress.  Even with UPS Expedited shipping I won't see my parts until the end of the month at the earliest.

I'm pretty sure that the only thing wrong with my motherboard is the relay.  I have not been able to find a relay that meets the power requirements, both coil and contact.  I'm leaning towards using a remote mounted something, either a relay or a DC rated SSR, there's plenty of room available in the base of the printer.  The problem I've got is that I think the existing relay has both a NO (Normally Open) contact, and a NC (Normally Closed) contact.  I'm not sure if Wanhao is using the NC to do anything.  Anybody know if somebody has already gone to the work of figuring out the schematics of the motherboard?  I could eventually get it figured out, but if somebody's already done it, why re-invent the wheel?

Don

Admiral_dk:
Hi Don

That is a very annoying thing that happened to you there  :zap:

In my youth that would have killed ALL the IC's - especially if they where of the CMOS variety ....
But much changed during the next ten years where the internal protection in the IC's where improved dramatically - so much so, that it I can't be bothered to do any precautions in may daily handling off IC's ....
That said - there is always a limit to how effective the protection can be or put another way - increase the energy that do the damage enough, and all thing will eventually break - including the relay.

I must admit that I prefer not to try and repair stuff I don't have any documentation for .... but the relay should be possible. One useful source here is www.digikey.com - we use them quite a bit, as they ship same day from the US and we usually have the items two days later here in Denmark  :)
That said - relays are one of these components that has dramatically disappeared from all suppliers in the last 5 years .... so a lot of those I have searched for lately are not available from anybody but the manufacturer .... and China.

You probably know that relays can have many different ways to do the 'limit data' and most are with inductive load -> they will last a lot longer with a resistive load, like a heater .... (this might help others).

Best wishes

Per

ddmckee54:
A direct replacement for that relay is not really possible, I've looked at Digi-key, Newark, and Allied.  The 10 amp contact rating is the limit for that relay foot print.

I've been thinking about remote mounting a larger relay or even a DC rated SSR, one with the proper rating.  I HAVE found relays and SSR's that have a suitable rating.  The problem with the larger relay is I'm not sure how large of a coil load that the motherboard can drive.  I know that the existing coil is about a 0.36 Watt load, 71.4mA @ 5VDC.  Any relay that I can find with contacts capable of handling a 20A load at 30VDC has a coil load of about 1 Watt, I doubt the motherboard could drive that type of a load directly.

The other problem is whether or not Wanhao is using the NC relay contact on the existing relay for anything, like triggering those stinkin' error messages maybe?  If they aren't using the NC contact then a suitably rated SSR is looking better and better.

Most inexpensive SSR's contain Triacs which use the zero crossing point of AC to turn the Solid State Relay off.  With a 24VDC system a zero crossing isn't going to happen, so once triggered the relay would never turn off.  There are DC rated SSR's that do not use a Triac, but they are about 3-5 times the cost.  They don't have the voltage drop across the SSR that the Triac version does either, so that's an added benefit.  The load to drive an SSR from the motherboard would be WAY less than the current 71-72 mA load.

That's why I'm looking for the schematics, to see the NC contact on the existing relay is tied to anything.  If they aren't using it for anything, I can drop a suitably rated DC type SSR in there and forget about it for years.

Don

AOG:
There is another option if you are willing to put in some work. From what I remember, the motherboard on that printer is a variant of the Arduino with with the RAMPs shield combined on one board. You could always replace it with something like a MKS gen L running Marlin and some proper remote power relays.

Tony

ddmckee54:
True, but I'm trying to get the printer back in operation - and keep it operating -  with a minimum of hassle.  I've got a  replacement motherboard ordered, Aliexpress verified the order and told me it shipped yesterday.  Now I've just got to wait for the slow boat from China to get here.

You're right though, according to Wiki the motherboard is based on the ATMega2560.  Plus I've found a version of Marlin on Github that's specifically for the Wanhao D6 motherboard.  This makes me wonder if a 24V RAMPS board could be plugged into the Wanhao control board?

But then again, other than the relay issue I really don't have a problem with the Wanhao motherboard - other than the replacement cost.  I may have found a direct replacement for the Songle relay.  I had one recommended to me that's rated at 20A.  It doesn't have a DC rating so the jury's still out on that part.  My gut feeling says it should work, but I'm waiting to hear back from one of the other engineers that I work with to see what he thinks.

Don

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