Weller WESD51 digital soldering station - intermittent failure to turn on

[dhakajack]

Hello. I come to you haggard and desperate, having wrestled with a diabolical WESD51 soldering station. It's a 230V model, which worked fine for months, but starting a few months ago, would intermittently not turn on. That is to say, that I'd flip the switch on and no LEDS would light and the iron would not heat. Subsequent investigation has shown that when this happens, power is being drawn, and regulated 5V is available on board. Flipping the switch back and forth bunch of times sometimes brings it back. Waiting a while and then flipping the switch sometimes brings it back. This condition happens whether the iron part is plugged in or not, so it's an issue in the base unit and the iron. I've written up my attempt at fixing it (http://blog.templaro.com/?p=1773) and my realization that I hadn't (http://blog.templaro.com/?p=1788) in some detail. I'd appreciate any suggestions. Thanks - Jack

[Sbampato12]

Check the control signal of the triac. If it has the gate voltage burst than could be the triac. If not, it could be the pic, one or twice I saw a program memory get corrupted... Or a intermitent 5V Vreg maybe?

[Smith]

Have you tried the caps and soldering connections?

[dhakajack]

Thanks Smith & Sbampato for suggestions.

Smith - I have inspected the board closely and don't see any obvious solder issues. Almost all the caps on the board are surface mount ceramics, so I think unlikely to be an issue. I will check out the two electrolytics. I have the sense that the large one is doing its job in the power supply, as the wave form downstream of it and into the voltage regulator looks smoothed.  As both you and Sbampato have suggested, there could still be some ugliness on the power supply. I suppose that one way to explore this would be to just bypass the power section and feed a known, good 5V after the regulator and see if it powers up. I didn't mention it above, but I live in Madagascar, and the power grid here is pretty hard on the front end of power supplies.

Sbampato - When the unit does power up, it works correctly. Given that, I don't think there is a problem with memory corruption. As far as I know, the triac is working correctly. Are you suggesting that the triac could somehow affect the digital section of the board? I will look more into the 5V rail, as above.

Thanks,

Jack

[DmitryL]

Hello. I come to you haggard and desperate, having wrestled with a diabolical WESD51 soldering station. It's a 230V model, which worked fine for months, but starting a few months ago, would intermittently not turn on. That is to say, that I'd flip the switch on and no LEDS would light and the iron would not heat. Subsequent investigation has shown that when

Have you tried replacing the quartz oscillator rather that fiddling with load capacitors ?

[amyk]

Hello. I come to you haggard and desperate, having wrestled with a diabolical WESD51 soldering station. It's a 230V model, which worked fine for months, but starting a few months ago, would intermittently not turn on. That is to say, that I'd flip the switch on and no LEDS would light and the iron would not heat. Subsequent investigation has shown that when

Have you tried replacing the quartz oscillator rather that fiddling with load capacitors ?

This, and I'd also reflow the MCU. Soldering defects are not always visible.

[DmitryL]

Also, I heard somewhere that Weller doesn't protect PIC from reading (not sire though)... It this is the case, it is possible to replace controller as well.

[Sbampato12]

Also, I heard somewhere that Weller doesn't protect PIC from reading (not sire though)... It this is the case, it is possible to replace controller as well.

Yep, they don't. I've managed to get a entire copy of the firmware from mine. Same model.

That could be a good suggestion. First, get a copy of firmware. Then change the cristal and reflow the PIC.

If that doesn't work, change the PIC.

That seems to be a good workflow...

[Smith]

For future reference, the Weller WDM 1 and 2 have unprotected firmware in them too. Comes in handy as their controllers tend to break prematurely.

Ontopic: Measure the SMD caps too, they are less likely to break than their trough hole counterparts, but they do fail.

[dhakajack]

Thanks all for replies. I had to leave last night on a business trip, so I tried the most expedient fix - I used a rework station to reflow the PIC. Afterwards, it powered right up... but again, it was a tease. I came back half an hour later and it would only intermittently turn on.

I looked at the crystal, and looks like it isn't a simple crystal - it has three terminals and the center one does not ground the case. I think it's more likely that the small metal box is a resonator rather than simply a quartz crystal (that would explain absence of flanking caps, right?). I don't have the exact same piece, but I can forage in my junk box for a color burst crystal, which I think would be near enough at 3.579 Mhz. This will have to wait a week until I'm back.

I'm not as familiar with the PIC and not really equipped to read/upload firmware to it. Just to put this in context, I'm trying to make this repair in my garage workshop in the middle of the Indian Ocean, where it's difficult to ship parts and equipment around. I'll try the simple fixes first :-)

Thanks,

Jack

[dhakajack]

Update: After mucking about with the board for a while, I'm afraid I've only compounded problems. When I plugged it in, I released a certain amount of magic smoke from the largish, presumably current-limiting 27 ohm resistor upstream of the voltage regulator. I traced the short down to pic pins 19 and 20, which unfortunately are Vss and Vdd, so the microprocessor is toast. At this point, I'm resigned to writing to the company to see if I can get a replacement board 

[Tomorokoshi]

Oh, that's too bad.

I had a similar set of problems with my WES51. It has a 7-pin connector on the base unit (only 5 pins populated). Mine would appear to be off, but it was actually the heater not running, so the tip would get cold.

What seemed to happen was that the spring pins on the base unit slowly expanded, eventually leading to intermittent or no contact. I bent them back towards the center, so now the connection seems to be fairly reliable.

[JoeB83]

Oh, that's too bad.

I had a similar set of problems with my WES51. It has a 7-pin connector on the base unit (only 5 pins populated). Mine would appear to be off, but it was actually the heater not running, so the tip would get cold.

What seemed to happen was that the spring pins on the base unit slowly expanded, eventually leading to intermittent or no contact. I bent them back towards the center, so now the connection seems to be fairly reliable.

The exact same thing happened to me. Unfortunately I thought it was the actual iron itself, not just the connector, and ordered a new heating element. $$

[dhakajack]

Epilogue: I was able to order a replacement board for $30USD. Installation was pretty easy and the soldering station is now back in service. Details on my blog: http://blog.templaro.com/?p=1867. - Jack

[alank2]

Interesting.  I found out this morning that you can buy the replacement boards from tequipment directly:

http://www.tequipment.net/Weller/WES206/Soldering-Accessories/

http://www.tequipment.net/Weller/WES207/Soldering-Accessories/

[dhakajack]

Dusting off this crusty topic because I think I know the original cause of the problem - bad grounding.

The soldering station with the replacement board worked fine for a couple months, then one day refused to turn on. Déjà vu. Thinking back, I had a strange incident a few days before while soldering 2n7000's - two in a row went bad after soldering, failed closed. That made me curious. I tested the ground pin on the socket versus a cold pipe: 90 volts.

I forced the ground pin to that reference earth ground and the station powered up with no problem. This explains my original observation that the soldering station could be "brought to life" by touching the pins on the clock crystal with something metallic - that must have been enough to effectively ground them or at least dampen out the noise on them. I more formally tested the garage grounding and found out that there was none (construction records indicated that it had been grounded in a system involving the house and generator, but the underground cable must have corroded over time). I had the garage professionally grounded and I'm back in business with a soldering station that consistently works (and, to boot, no longer zaps components). So, there you go. Only took me like a year to figure this one out 

[Emrtech]

Attached is the schematic of the WESD51. I prepared it when I had to repair my unit a few years ago. Hope it helps.

[Emrtech]

Here are some WESD51 Scope Images from testing.