Author Topic: 3D Printer problems - Monoprice/Wanhao D6  (Read 519 times)

Offline ddmckee54

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3D Printer problems - Monoprice/Wanhao D6
« on: March 11, 2020, 06:46:14 PM »
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

Offline Admiral_dk

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Re: 3D Printer problems - Monoprice/Wanhao D6
« Reply #1 on: March 11, 2020, 07:50:55 PM »
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

Offline ddmckee54

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Re: 3D Printer problems - Monoprice/Wanhao D6
« Reply #2 on: March 11, 2020, 08:42:33 PM »
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

Offline AOG

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Re: 3D Printer problems - Monoprice/Wanhao D6
« Reply #3 on: March 13, 2020, 11:30:02 AM »
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

Offline ddmckee54

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Re: 3D Printer problems - Monoprice/Wanhao D6
« Reply #4 on: March 13, 2020, 03:33:18 PM »
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
« Last Edit: March 13, 2020, 03:54:02 PM by ddmckee54 »

Offline Muzzer

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Re: 3D Printer problems - Monoprice/Wanhao D6
« Reply #5 on: March 13, 2020, 06:27:35 PM »
Take the relay out (you'll have to do that anyway) and either trace the NC track by eye to see if it is routed anywhere - or if you can't manage that, check the resistance to ground with a DVM. With the board unpowered and using a modern DVM, you should see something under 100k if there is any form of connection to that pad. I can't imagine there is but you seem uncertain.

Modern equipment is supposed to be ESD resistant, as it's such a common event - we would expect it to be tested to IEC61000-4-2. But the guys who "designed" this equipment presumably didn't see the need for it - or more likely had never even heard of ESD. Hopefully the same level of amateurs didn't "design" the mains power supply.

It should work without the heated bed, depending what filament you are using. It's usually stuff like ABS that needs heated beds, whereas the default PLA is happy with a cold bed. Why not just do without the heater altogether for now?

Offline ddmckee54

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Re: 3D Printer problems - Monoprice/Wanhao D6
« Reply #6 on: March 13, 2020, 07:30:18 PM »
I've still got my Prusa clone that I built from a kit 5 years ago, so it's not like I'm unable to print.  I plan on working on the Wanhao motherboard when I get the replacement parts from Aliexpress.  They verified my order, and told me that my order had shipped yesterday.

I've had a relay that's a drop in replacement for the original Songle relay recommended to me by a supplier in Texas.  It's identical to the original relay except it's got 20A contacts instead of 10A contacts.  I'm still waiting to hear back from the supplier about minimum order quantities and whether I'll need to sign away my first-born to get some of them.

Offline Admiral_dk

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Re: 3D Printer problems - Monoprice/Wanhao D6
« Reply #7 on: March 13, 2020, 08:20:17 PM »
I would be surprised if a 20A AC rated relay isn't good enough for at least 20A DC, as most are able to withstand more DC than AC - but there might be a contact material where the opposite is true - I just haven't got a clue witch one that would be ....

You could also find a good number off CMOS 'transistors' that are rated for much more that 20A for $2 a piece - this might demand that you also find an OPTO-Coupler to go between the "relay coil" and the "24V. Power" circuit .... if you by the DVM decide that the NC part of the relay isn't used - though I will say that I would feel more safe if the reading is infinity (as in absolutely no connection) ....

Offline ddmckee54

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Re: 3D Printer problems - Monoprice/Wanhao D6
« Reply #8 on: March 13, 2020, 09:38:17 PM »
According to the DC rule of thumb that I found on the Carling Technology website, any contact with an AC amp rating but no DC amp rating should be good for use at up to the maximum AC amp rating, when used at 30VDC or less.

It's the other way around with contact ratings, usually a contact has a higher AC rating than DC.  It's harder to extinguish the DC arc when opening the contacts since there's no zero crossing like there is with AC.  There are contact materials the are used to help extinguish the arc, but these materials take the relay out of the 2 buck per unit range that the original Songle relay was definitely well within.

If you think about it, that's actually that's not a bad racket for Wanhao to be in, as long as they can get away with it.  Selling a motherboard at $200-ish because a $1.36 relay went bad.  If it works maybe I should go into the Wanhao D6 relay replacement business?  I might make a fortune, but I don't think I'll quit my day job just yet.

Don

Offline Muzzer

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Re: 3D Printer problems - Monoprice/Wanhao D6
« Reply #9 on: March 14, 2020, 10:38:21 AM »
Yes, DC ratings are generally less than AC ratings for the same relay but low voltage DC relays are far from rocket science.

There are loads of 12V relays out there, on account of the automotive market, so 20 - 30A contacts are commonplace. I've no idea what footprint you need but there's a wide selection available for peanuts at places like CPC:

https://cpc.farnell.com/w/c/electronic-electrical-components/switches-relays-solenoids/relays/prl/results?range=inc-in-stock&st=relay%2012v

Offline ddmckee54

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Re: 3D Printer problems - Monoprice/Wanhao D6
« Reply #10 on: March 16, 2020, 08:55:54 PM »
I was able to order the replacement relay this morning.  The supplier, Picker Components only sells to distributors, but they gave me the link to one of their distributors Omni-Pro Electronics.  The relay that I ordered has exactly the same footprint as the original Songle relay but the replacement's contacts are rated at 20A, not the 10A that the Songle's contacts are rated for.

This will either fix the relay problem or show me the next weak link on the Wanhao motherboard, I'll go down that rabbit hole when I have to.

Don