Wanhao Duplicator i3 V2: Stud Thermistor Upgrade 

That would be your heater cartridge. You'll need a 12v 6.35mm replacement. They aren't expensive but I couldn't find a solid replacement on Amazon. Check 3dprinterwiki.info/wiki/wanhao-duplicator-i3/di3-advanced-mods/heater-cartridge-replacement/ for more detail.

Thanks a lot

You got it, PETG prints require the microswiss. The flexion is a great extruder but the PTFE tube means it's not great at higher print temps.

Except if you got the hi temp option, which is actually an additional hotend designed slightly differently around the tube flexionextruder.com/shop/flexionht/

Corrected, thanks!

No fix in temperature stability yet which leads me to believe that it's a problem with the controller itself. Still worth the ~$12 to rule out and get a more solid bonding to the hot block.

+Jim Shank I will let you know about my twisted pair cable tests. Im hoping to mitigate any interference from the stepper wires. I just need to get some connectors that will fit the melzi.

+Jim Shank twisted pair didn't make much(if any) difference. I will try and write it up when I get a chance.

Twisted pair is intended to filter noise with digital signals that go at certain high frequencies, it will have zero effect to a resistance(=voltage) measuring .

pumpalBo not exactly. twisted pair reduces the susceptibility to radiated or inductivly coupled noise. As it turns out in this case the source of the noise poor design of the melzi board. The noise is generated there when the HBP switches on/off so no amount of messing with the wires will help. Adding an external MOSFET for the heated build plate was the best fix for this. My temps are now rock solid.

There was a V1 of the Duplicator i3 that had a flat front display on the control box (not angled like the current version). It's still a perfectly good printer and most of the changes between V1 and V2 (and V2.1) can be replicated through videos like mine or other mods in the Google groups forum.

Much appreciated, thanks. I am an Instrumentation and control tech, so, modifications and upgrades is a simple and enjoyable matter to me, as long as I can get hold of the info and spares. A flat face is the least of a problem. BUT now I will be able to ask the guy a sensible question to get a valuable answer. What I did pick up is that the head may have changed from a D5 model to a D10 model. I will be able to get a nozzle for the D5, but do not know if it will fit on the D10. Probably interchangeable, but not guaranteed on thumb suck. :-( That temp problem that seems like an issue, may be just a too cold environment with a not powerful enough heater unit. A draft over it may cause the head to end up in a naturally balanced situation of heat in and heat lost to the air (moving) around the head. It will cause the heater to be full on, but unable to supply enough heat to let the head up more. An increase in airflow around the head will then explain that drop in temperature from a higher point, before set temp is reached. Maybe an enclosure or side panels around the printer can fix that if it is the case, or a slightly more powerful heater. I'd first play with some pieces of cardboard around the printer to see if it have an effect. Temp control can be a nasty monster if it want to play games. Al kinds of lags and energy "storage" in a block of metal that arrive a bit later than intended, moving from the element to the target may cause some overshoot. That is where that PID control gets into play.

Just silicon thermal pads from Amazon amzn.to/2kjyD5Y. They hold the glass in place nicelyl but I can still pop off the plate with the putty knife to clean it.

Answers in the order asked: PID tuning is "training" your processor to correlate temperature settings and actuals. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-TWsQMmJ8pB8.html. This is the same stock firmware. Upgrade to the microswiss hotend ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-S-lPVz8p6C0.html. The clamping block design provide much better heat transfer. Temperature is the key to layer adhesion in ABS. Perform a temperature test tower from ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-in_3aBWMGa.html.

Just a thought. Try keeping air movement, a draft maybe to a minimum around the head or the printer in general. I do not know what watts that heating element is, but it cannot be to high. Maybe your head cools down faster than the heat the element can supply, so you get a natural balance at that 235 degrees. It seems like that can be an explanation for that, also the dropping down instability.

Putting a dab of "heat transfer paste" on the element, and then clamping it will probably give another little bit of improvement. It is a white greasy substance that you will get at any electronic spares shop. It is mostly used between a power amp or transistor and the aluminum heat sink to help transfer heat for cooling purposes of the power components.

I just finished the same print and it has the same amount of stringing. The stringing issue may be due to another factor than temperature. goo.gl/photos/WGJjZVjswN4dBmqP7

Jim Shank Yeah I'm also having some esthetic difficulties with PETG, it's pretty solid though...

How about what I've talked about in the previous comment? Maybe some environment airflow that caused the material to solidify on one side of the nozzle and cause that string.??? Don't know, just a maybe.

MicroSwiss, slow prints (30m/s) and retraction of 1.5 did it for me.