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Temperature variation Heller 1707 EXL

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Temperature variation Heller 1707 EXL | 13 August, 2013

We are running a Heller 1707 EXL reflow oven, but we have a temperature variation across the board.

When the oven first comes up to temperature, the centre of the board is 10degC hotter than the inside rail which is a further 10degC hotter than the inside rail.

After leaving the oven running for about 30mins, the temperature difference between the centre of the board and the inside rail is only 1 or 2 degC, but the outside rail is 12-15 degC cooler.

This is obviously not ideal for running controlled profiles, and with running lead free results in some very high temperatures inorder to get the outside edge to solder correctly.

Is this normal behaviour for the oven? Is there a way to fix or compensate for this?

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Temperature variation Heller 1707 EXL | 13 August, 2013

If it's forced air convection I'd check all the circulating fans and filters. Also if its a clam shell bonnet make sure it's closed all the way and the seal is good. You didn't specify whether it is one zone or the full length of the oven, I do not work for Heller

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Temperature variation Heller 1707 EXL | 13 August, 2013

We have a Heller 1707EXL that we use for lead and lead-free production. It has both a mesh belt and edge rails. We run 90% of our assemblies on the mesh belt (leaving the edge rails wide open). I have noticed when profiling a board on the mesh belt that the inner and outer edges can be 2-3C cooler than the middle but have never seen a 10C difference. As long as all of the zone blower motors are working correctly, there should not be a 10C degree temperature difference across 1 zone.

One possibility is making sure the hood (clam shell) is fully closed so that no air is leaking in/out around the edges.

Another possibility...Are you reflowing boards with components on both sides? In the hottest "reflow" zone heavier parts on the bottom side can fall off. Over time if there is enough of them falling off they can accumulate and start to disrupt the air flow from the bottom side heater in that zone. Would be good to check and make sure there is nothing obstructing air flow on the bottom zones. This not only means the holes where the air blows out, but also check the screens that cover the air intake for the bottom zones as well. If those screens are plugged, you will not get proper air flow/circulation for the bottom zones.

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Temperature variation Heller 1707 EXL | 13 August, 2013

We are seeing this the full length of the oven.

We run a lot of double sided boards, so we cannot run them on the wire mesh. I checked inside the oven to ensure there was no build up of dropped parts that could block it.

The temperature difference seems pretty uniform and steady, which is not what I would expect if there was a problem with air leakage at a certain point

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Temperature variation Heller 1707 EXL | 13 August, 2013

Is this a new issue? You could run a wide piece of masking or duct tape along the oven seal on the outside just to see what happens. What is the heating plate configuration. Are they solid from front to back or split. My thought here is if there is a front row of plates they could have a separate power source which is not turning on. Just some thoughts.

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Temperature variation Heller 1707 EXL | 13 August, 2013


Please give a call to Bilal Malhi Service Manager at Heller. +1-973-377-6800 EXT 312

Bilal and his team can walk you through some easy steps to determine the cause.

Should be relatively quick to get to the bottom of it!



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Temperature variation Heller 1707 EXL | 14 August, 2013

Most of this you have probably covered, but these are what have caused heating issues for us in our 1707 EXL.

First, you would probably notice, but check that all blowers are turning by looking at there cooling fans in the top and bottom, Our 1707 has only 2 remaining original blowers out of 10 on the top, the other 8 all failed sense we bought the oven.

Heller is very good about getting you blowers for there very good warranty. 2 we replaced because they had severe vibration, and the shafts ended up having 1/16 inch of play when we pulled em. (The old blowers are black silicon power, New blowers are silver pot metal)

Pull the belt off, and open the zones on both ends, Odds are there is a lot of flux build up in there. Also sweep out the components once a month(Don't need to take the belt off for this).

There are 3 non heat blowers in the 1707, 2 for fume extraction to the chimney, 1 for cool down, All 3 of these attract a lot more flux and dust than any other blower, we clean them every other year.

Make sure your draft inducer is running well.

The cool zone intake has a baffle on it, make sure the baffle is in place and on ours covers 1/2 the intake.

There are baffles behind that rail on each end to block air coming in behind it, Make sure these are in place.

There are no rail heaters on our 1707, we run most of our boards on the belt, but the outside rail dose indeed have heating issues, 5C to never more than 10C is normal on that far edge. Our 1809 III dose not have this as much.

I am rather certain you can move this rail in several inches, if you do not need the full width, there are 2 collars holding it in place on each end.

Hope something in there helps


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Temperature variation Heller 1707 EXL | 14 August, 2013

Generally the heller exl range has issues in cross profile, some machines more than others. I have see as bad as 15 deg c and as low as 5 deg c ranging from entire length to a few zones. They never match the specification in reality.

The markiii is better in this area as they changed the blower recirculation technique which helps balance out thermal transfer vs old exl series

The fix i have seen is customers do is move the fixed rail into the oven more and then have each zone ballanced by tweaking air flow diffusers that are in each zone that are used to try and ballance air flow across the zone. As each machine is slightly different a one size fits all ie factory set may not fit all machines.

At end day exl was not very good in terms of cross profile machine to machine from my exoerience. Mark iii is better, but still not 100%

They are low cost ovens so at end day..... will solder most pcb but always last 5 10% of more difficult pcbs thermally challanging etc cross profile of 5 to 10 deg not good....for getting correct profile balance.

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Temperature variation Heller 1707 EXL | 20 August, 2013

I moved the fixed rail in by about 2 inches and it seems to have done the trick.

Rail movement is easy, moving machine to keep all conveyors in line not so easy

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