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Old 19th Feb 2021, 5:16 pm   #1
Electronpusher0
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Default Weller EC2000D repair

I purchased a Weller EC2002DA base unit from Julesomega, the left hand one here:
https://www.vintage-radio.net/forum/...43&postcount=8

The fault was described as "briefly flicks up a display before going blank"

The EC2002DA base unit takes the EC1201P iron and makes the Weller EC2000D.

When it arrived I stripped it down and cleaned up the case. I then reassembled and started testing.
The EC2002DA base is easy to work on as the two modules, the control board and the display board are independent and can be tested separately.

I tested the control board by connecting a 24V bulb to replicate the iron element and a 51ohm resistor to replicate the sensor.
On testing the bulb was on continuously at all settings of the pot. It turned out the Triac was short circuit.
I replaced this with a BT136, same pinout. - That got the Control board working.

The display board fault was exactly as described. The circuitry mainly consists of a pair of chips that form a DVM. The chips are now obsolete and replacements are expensive and of suspect provenance.
I decided to go back to basics and see what the display actually did.

The Display board takes a voltage from either the temperature set pot or (after amplification) the sensor as selected by a “SET / READ” switch. The sensitivity is set by a pair of pots and displays 400 for an input of just over 5V.

I decided to make a new display board using a 3 digit Chinese DVM module. These are 3 wire, Red is the supply, Black the common 0V and Yellow the input to the DVM.
The sensitivity as supplied is 0 to 100V auto ranging. The lowest range being 0 to 9.99V

Testing this on the bench I discovered that putting a 50K pot in series with the input allowed me to set the sensitivity to the same as the Weller display board.

The replacement display board consists of a half wave rectifier and capacitor for the supply to the DVM module, using the same ac input the original board used, a switch and two 50k pots, could not be more simple.
I did however put a drop of black paint on the decimal point to blank it out.

I then calibrated the control board and new display board according to the procedure in the manual (slightly modified in the case of the display).
The Base unit was then fully working and calibrated.

The pictures show before and after.

Peter
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Old 19th Feb 2021, 10:18 pm   #2
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Default Re: Weller EC2000D repair

Excellent work. Someone gave me one of these base stations a while ago and although it works I've never been able to find a suitable iron to go with it. Interested to know what plans you have in that regard.

Alan
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Old 20th Feb 2021, 7:44 am   #3
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Default Re: Weller EC2000D repair

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Originally Posted by ajgriff View Post
Excellent work. Someone gave me one of these base stations a while ago and although it works I've never been able to find a suitable iron to go with it. Interested to know what plans you have in that regard.

Alan
I plan on using one of the cheap Hakko clones, they come in two versions, one with a thermistor sensor (like the Weller) and one with a thermocouple.

The thermistors used in both the Hakko and Weller are positive coefficient but different slope, I am pretty sure tha Hakko can be modified with resistors to mimic the Weller slope over the range 200 to 400 deg C.

I will report on my findings.

Peter
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Old 20th Feb 2021, 9:24 am   #4
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Default Re: Weller EC2000D repair

I'd wondered about that as a possibility and look forward to finding out how you get on.

Alan
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Old 20th Feb 2021, 11:20 am   #5
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Default Re: Weller EC2000D repair

A splendid outcome to your labour of love Peter. You will be able to maintain that indefinitely, and the element and bits will be available for a long time to come, unlike my Antex TC50. I wanted a third iron to use with it to save swapping hot bits, and their website now shows most parts as discontinued. Seems like they have moved to industrial rework stations and the like.
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Old 20th Feb 2021, 3:14 pm   #6
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Default Re: Weller EC2000D repair

Quote:
Originally Posted by ajgriff View Post
I'd wondered about that as a possibility and look forward to finding out how you get on.

Alan
I recall these used an expensive temperature-sensor (were > £20 for spares - around half the price of a new iron > 20 years ago). And they have 2 gold-pins on the 5pin DIN, for connections to this, to avoid problems with dissimilar metals and electro-potentials / contact-resistance

The smaller 20W? EC1301 series irons (May only work on EC3000/4000 bases) did seem to have (small ceramic-tube sprung-into-tip) sensors that were rather prone to failure (I've got 3 that were scrapped due to this, so need a lower cost solution), compared to original magnastat tip-set solution.

But the larger (EC1201?) 45W? Irons usually supplied with the old EC2000 bases, with larger metal tube sprung-into-tip sensor seem to be better (I've still got one back at parents house, for when I need to fix something there)

I thought they actually used (more expensive) Pt100 etc. Platinum thermocouples, rather than cheaper non-linear thermistors. I do recall they measure about 22R - about the same as the element on the small ones?
But Weller have mostly moved onto (integrated sensor / heater / tip) expensive cartridges, so I expect have long discontinued spares for the old EC range (which had been superseded by WSP80 etc Irons > 20years ago)
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Old 20th Feb 2021, 3:50 pm   #7
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Default Re: Weller EC2000D repair

The cal procedure for the EC2002D base quotes the sensor resistances as:
0 deg C - 20Ω
200 deg C - 36.5Ω
400 deg C - 51.8Ω

I am pretty sure I can tailor the Hakko to match over the limited range of 200 to 400 deg.

Peter
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Old 20th Feb 2021, 4:46 pm   #8
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Default Re: Weller EC2000D repair

Any idea what the temperature/resistance profile is for a Hakko clone?

Alan
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Old 20th Feb 2021, 10:21 pm   #9
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Default Re: Weller EC2000D repair

I have an example iron and plan to plot it over the next few days.

Peter
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Old 21st Feb 2021, 10:35 am   #10
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Default Re: Weller EC2000D repair

I still plan on plotting the curve, especially as there is a definate thermal gradient between the element (where the thermistor is) and the tip of the bit.
This is due to the relatively loose fit of the bits over the element on the Hakko clones.
Some users have reported an improvement using thin copper or aluminium (cut from a drinks can) wrapped around the element to fill the gap.

I did find the attached curve on line.
As I say I will plot my own.

Peter
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Old 21st Feb 2021, 2:51 pm   #11
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Default Re: Weller EC2000D repair

I have now plotted the curve.
I used a bit of aluminium foil wrapped round the element to fill the gap between the element and the bit. I used a modified bit with a hole drilled in it into which I fitted a type K thermocouple connected to a commercial temperature meter.

Allowing for the thermal gradient between the element and the bit the measured values are in reasonable agreement with the data I found on the net.

It would be very difficult to tailor the Hakko to mimic the weller exactly but if a 78 ohm resistor (68 ohm plus 10 ohm in series) is connected across the Hakko thermistor then the error vs the Weller is 6% low at 400 deg, 0% at 350 deg plus 4% at 300 deg and plus 14% at 200 deg.

Probably good enough to be useable.

I attach the Excel spread sheet with the calculations and a picture of the graph.

Peter
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Old 21st Feb 2021, 5:22 pm   #12
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Default Re: Weller EC2000D repair

Impressive analysis Peter. Presumably you measured the sensor's resistance by monitoring current and voltage. If the 78Ω resistor works in practice I wonder if you could reveal the source of your particular Hakko type iron?

Alan
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Old 21st Feb 2021, 5:46 pm   #13
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Default Re: Weller EC2000D repair

Thiking about it, if I decide to commit to the Hakko clone then the 78 ohm can be wired internal to the base and the unit can be calibrated to be correct for the Hakko clone.

I attach the manual, the calibration procedure calls for 2 resistors, Resistor A which corresponds to 200 deg C and resistor B which coresponds to 400 deg C
If the unit was calibrated for resistor A = 41.2 ohm and resistor B = 48.5 then it would be correct for the Hakko with the 78 ohm.
That's the next thing to try.

In theory the Hakko Iron type 907 (without an A) is the version with a thermistor and the 907A has a Thermocouple.

However the chinese suppliers seem ignorant of this. I successfully bought a 907 for another project which was indeed with a thermistor but when I bought another from the same supplier it was a thermocouple type.

I currently have a replacement element and sensor on order which should be a thermistor type.
If I find a reliable source I will post it.

Peter
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Old 22nd Feb 2021, 7:43 am   #14
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Default Re: Weller EC2000D repair

Quote:
Originally Posted by ajgriff View Post
Presumably you measured the sensor's resistance by monitoring current and voltage.
Alan
Actually I powered the element of the iron from a variable bench power supply and increased the voltage from zero in small increments, allowing it to stabilise temperature each time, and measured the resistance of the thermistor with a DVM.

Peter
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