Need help for fixing a Weller VP800 desoldering station (SOLVED)

[JacquesBBB]

Dear All,

I  got a Weller VP800 desoldering station, but  the temperatures reaches only about 200°C, not enough for
using it. I am trying to fix it, but need some help.
I found some information on http://remotesmart.wikidot.com/weller-wecp-20,
but the model is close but different. Does anybody has a VP800 schematics ?

I  attached a picture of the   board for the  heating control.
The small black chip near the triac is a 78L05.

What is the role of the two  1K pots ?

What can I do if I want to increase the temperature of the iron  ?

Thanks !

[HalfSpace]

Hi JacquesBBB,

Check the VCC supply rail with an oscilloscope across the CA358 pins 8 & 4 (LM358) it should be about 6.4V DC with no AC ripple. If there is some ripple greater than 200mV P/P the electrolytic capacitors near the 78L05 maybe faulty or the 78L05 itself.

 The 1k pots adjust maximum and minimum temperature range of the iron but unless someone has adjusted them I would think a fault in the control PCB is more likely the problem. Marking the pots with a marker so that they can be turned back to their old position would be a good idea if you want to try adjusting them.

HalfSpace 

[JacquesBBB]

Thanks HalfSpace,

Check the VCC supply rail with an oscilloscope across the CA358 pins 8 & 4 (LM358) it should be about 6.4V DC with no AC ripple. If there is some ripple greater than 200mV P/P the electrolytic capacitors near the 78L05 maybe faulty or the 78L05 itself.

I will do that tomorrow, but I have already checked the two big capacitors, and they are OK.  Nevertheless, I will  check the LM358  voltage.
I have also verified that the temperature sensor is working pretty well. I made some measures  up 170 °C and found values comparables  with what is quoted in http://remotesmart.wikidot.com/weller-wecp-20 :

Temp  normal     measured
          resistance resistance
         (ohms)

50      24,65      24.7
60      25,50      25.3
80      27,16      27.3
100    28,82      29.3
110    29,61      30.7
120    30,43      32
130    31,31      32.5
150    32,94      35.5
170    34,55      36.4

The 1k pots adjust maximum and minimum temperature range of the iron but unless someone has adjusted them I would think a fault in the control PCB is more likely the problem. Marking the pots with a marker so that they can be turned back to their old position would be a good idea if you want to try adjusting them.

Too late. This is the first thing I moved without too much understanding the function of each one.
I manage to get higher temp values, up to 340 °C, and though that was the  origin of the problem, but the next day
when I tested it, it was back in the 200°C. I will have to  tune it again, but it need first to reach high temperatures.

[JacquesBBB]

Dear HalfSpace,

You were right, the voltage was out of specs. I changed the electrolytic capacitors, and the regulator to a MCP 7102-50
which was the only one I had in hand. The voltage at the output of the regulator is now 5 V, regulated,
and at the input is 14 V  with about 200mV ripple, due to the capacitors.

The strange thing is that the LM358 is powered by the input of the LM358, not by the output.
I put a variac, and see that it was changing with  input AC voltage.
There does not seem to be any regulator on this board for the LM358 power, contrary to  some other schematics where there
is a 8.2 V zener at the INput to power the LM358. Can you confirm ?

I could run the VP800 like that, but it was still unstable. So I decided to change the triac. But I have not much experience in these  and did not realize that the one in place (which I destroyed for desoldering) TAG 226-200 is a sensitive triac,
and the one I put in place, (T810-6i) ,not. So not, I have no current at all. The triac is not triggered by the signal .

I will now try to put a transistor for amplifying the triggered current.

[JacquesBBB]

Success !

I derived the gate of the triac with a PN2222A with the collector on the 14 V power (before the  78L05),  the emitter
at the gate, and the base at the original trigger. (I tried first on the 5V power, but it seems to affect the
 board, and this did not work).

Now everything is fine. Not very pretty of course, but it seems to work OK. I do not know if I will
change it to a sensitive triac when I get hold on one.

Thanks anyway HalfSpace for you hint.

[JacquesBBB]

I was too optimistic in my previous post.
In fact, it did not work as such.

I  look at it again more carefully.

The closest schematic I found was the one of the WECP-20. One copy is here
http://remotesmart.wikidot.com/weller-wecp-20

but it is full of errors.

The correct one, hand drawing is here
http://www.uploadarchief.net/files/download/wecp-20_small.jpg

I could thus understand better the  schematic, and did a little bit of reverse engineering.
Finally, I realized that  the SL443A was not working properly.

I thus ordered some on aliexpress. These are probably of stocks as the part is no longer available.
I got a good deal at 15.5€ for 5 pcs, so I will be able to fix my desoldering station in the future.

I changed also the triac to a Littlefuse 4Q 5,5,5,10 ma L4008L6 (400V, 8A).
Now everything is working.

I  could test it and desolder a few chips on junk boards. It works perfectly. I am looking forward my
next repair that would involve desoldering of chips with large number of pins.

[Guni]

Hi,

Off topic

I'm building DIY desoldering station (+ vacuum pick and place option) little inspired by Weller VP800
I have double ASF vacuum pump, pipes, manometer, vacuum regulator and some valves from old medical instrument for strange electro-vacuum therapy . Very good base for building good desoldering station 

I would like to ask you about scheme of piping in your station. I see, there is front and back filters and some return pipe. Can you explain how they are connected?

Additional question: when pump is running? - all the time or just after pushing button on the iron like in cheap chines stations?

My idea for now is: input filter + vacuum regulator (I have it) + manometer ->pump-> output filter

I'll be very grateful for any information.

[JacquesBBB]

@Guni

You will find the schematic of the mounting of the VP800 here
http://www.uploadarchief.net/files/download/weller%20vp%20801%20ec.gif
(attached below).

There are several filters in the vacuum path.
- first filter on the solder glass reservoir mounted on the soldering Iron. (seem to be fiber glass)
- Second filter 513 435 99 at the entrance of the soldering station
- third filter    513 436 99 before the vacuum pump.

This is pretty serious.

There is a pedal for actioning the pump. When you press the pedal, you activate the pump.

Good luck for your station.

[Guni]

Thx for info.
I saw this drawing, but it's not so clear how the pipes, filters and pump are connected together 

If I good recognize your picture: from the pump's vacuum input, first pipe goes to front filter/input, next, from the site of filter's cylinder, pipe goes to back/filter input, and next from filter side to manometer (probably - its not on the picture). So, for what is the back input for? It's quite strange for me because there is no vacuum if one of the inputs are open...   

[JacquesBBB]

With the drawing and the photo  I posted above it should be clear.

There is no opening. What you see is closed by a  screwed cap. I believe that the point is to be able
to  change the  filters from the outside without dismounting the whole thing.

It is both for the front and the rear filter.

I could post some more pictures on Sunday if  you think that could be helpful.

[Guni]

If you can make some additional pictures, will nice!

[JacquesBBB]

Here are some additional pictures of the outside an inside of the Weller VP800.

[Guni]

Thx a lot. Everything is clear.
So, rear filter is just the second one to secure the pomp.  They used the same filter as on input.
BTW
Maybe it will be useful for you. Weller originally provided special aluminum filters cup - cartridges with replaceable ceramic filters. Now there is just ordinary cottonwool (or mineral)
Check this tread: 
http://www.dragonslairfans.com/smfor/index.php?topic=2411.0

[JacquesBBB]

Hi everybody !

I thought I was done with that, but yesterday the desoldering station was down again.
After searching various causes, I realize that the SL443A   was not working.

It did not last long, but I could not find an obvious reason for that so I replaced it
(I had ordered  5 of them). If it breaks down again soon, I will have to do some more
serious search.
Up to now ( 1 day), it works again.

[SeanB]

Disconnect pin 3 of the SL443 and place a 470R 1W resistor between it and the power supply, with a 100uF 25V capacitor from pin 3 to pin 1 ( ground). The original circuit is overloading the shunt regulator in the unit, and the 240R 1W resistor in the original power supply should also be replaced with a 470R 1W resistor. This will reduce the dissipation in the IC to a safe level and not cook it.

Datasheet is here.

http://www.hobbielektronika.hu/forum/getfile.php?id=36037

[JacquesBBB]

Thanks. I found very strange in this circuit that the power supply of  SL443 is not very much regulated, and at the border of
the specifications. Maybe also this was devised for 220 V and now we have 237 V which adds even more.

I will do what you suggest (next week end probably).

[JacquesBBB]

Disconnect pin 3 of the SL443 and place a 470R 1W resistor between it and the power supply, with a 100uF 25V capacitor from pin 3 to pin 1 ( ground). The original circuit is overloading the shunt regulator in the unit, and the 240R 1W resistor in the original power supply should also be replaced with a 470R 1W resistor. This will reduce the dissipation in the IC to a safe level and not cook it.

In my case, the 240 ohm resistor that appear in the schematics is replaced by two resistors in series  of 180 and  270 ohms. I have replaced the 180 ohm by 270 (after some trials for higher values). Now I have a more reasonable 12.5  to 14.5 V at pin 3 of SL443a.

I will leave it like that and see if this lasts. By the way, I realised that the SL443a that I got from aliexpress are most probably recycled, as some of them present some unusual aspect defaults.
Too late to complain...

[TJOSHI]

Hi,
I need help in repair of Weller WECP-20 soldering iron, particularly from the person
who has done the repairs on this.
Please look into the attached hand written scematic, copied from the bloger in this forum.
Both the ic,s  LM358 and SL443Awere defective, hence I replaced them and added a 220 ohms resistor in series with the existing 240 ohms after half wave rectifier as suggested by some blogger. But the iron is not functioning.
I am finding that the SL443A is not functioning with the input at pin 8, of more than about 6 volts. I don't know whether it is right.  I have replaced and tried with three numbers and all are behaving in the same manner.

The two stages of  LM358 outputs at pin 1 and 7 is high at around 13 volts and output at pin 7 is not varying by varying the temperature setting pot. I have ensured that LM358 in good worhing condition.

Inputs at the first stege pin 2 is around 1.5 volts and pin 3 is around 6 volts, as such, naturally the out put at pin 1 is high at 13 volts.. The second stage input pin 5 is around 13 volts, because it is fed from fist stage output, pin 1. Second stage input pin 6 is varying from about 3 volts to 6 volts by varying the temperature control potentiometer. Naturally the output at pin 7 is high at around 13 volts and not being able to control..
I have checked the 5volts regulator 78L05 and it is working alright. I have also checked all the resistors and diodes, all are ok. Soldering iron element is also ok. But the temperature sensor in the soldering iron is showing very high resistance, more than 2 M ohms in cold condition and around 13 k ohms in hot condition. I didn't know whether it is correct value.
To check the output states of the LM358, I put a 1.5k ohms resistor from input pin 3 to ground and found that the, both the outputs at pin 1 and 7, go low, below about less than about 1 volts. Hence the triac is getting triggered and soldering iron is getting heated up, without the temperature control. So it can be deduced that the LM 358 is working, but dont know, why the circuitry is not functioning properly.
I request any person who has experience in this, to analyze the problem and provide me the solution, for which I will be very thankful.

[JacquesBBB]

But the temperature sensor in the soldering iron is showing very high resistance, more than 2 M ohms in cold condition and around 13 k ohms in hot condition. I didn't know whether it is correct value.

This does not look right.  The value  should be between 20 and 60 ohms. This is what I got, and what is quoted in the other  blog.

I made some measures  up 170 °C and found values comparables  with what is quoted in http://remotesmart.wikidot.com/weller-wecp-20 :

Temp  normal     measured
          resistance resistance
         (ohms)

50      24,65      24.7
60      25,50      25.3
80      27,16      27.3
100    28,82      29.3
110    29,61      30.7
120    30,43      32
130    31,31      32.5
150    32,94      35.5
170    34,55      36.4

[

[stj]

that's very similar to the DS80, do a search because the full schems are out on the net.

btw, replace the cap on the back of the pump before it explodes, the resin has cracked.

[marcaurell]

Can someone give me the specification of this part. At my platine the designation is no longer readable. Reason for exchange: The PINS are broken!

[JacquesBBB]

The answer is in my above post :
 the triac is :  TAG 226-200 . It  is a sensitive triac

I could run the VP800 like that, but it was still unstable. So I decided to change the triac. But I have not much experience in these  and did not realize that the one in place (which I destroyed for desoldering) TAG 226-200 is a sensitive triac,
and the one I put in place, (T810-6i) ,not. So not, I have no current at all. The triac is not triggered by the signal .

But after too many problems with this repair, I end up with a more drastic fix
https://www.eevblog.com/forum/repair/upgrade-of-a-weller-vp800-desoldering-station/msg1114940/#msg1114940
with which I am quite happy.