UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Test Gear and Workshop Equipment

Notices

Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders.

Reply
 
Thread Tools
Old 22nd Jun 2024, 6:13 pm   #1
AnalogueMan
Hexode
 
AnalogueMan's Avatar
 
Join Date: Jun 2020
Location: Manchester, UK.
Posts: 284
Default Weller DS801 Desoldering Station - open circuit PTC

Hello folks
I've been given a Weller DS801 Desoldering Station with attached DS3105 desoldering iron in nice condition except that the PTC thermistor in the iron is open circuit. I know that everything else works as when I pop a 39 ohm resistor in place of the PTC the iron heats up and I can control the heater with the temperature knob. The vacuum also works and I've even desoldered a few things with it but in it's current state it's not ideal.
Despite much searching the replacement sensor for these seems to be unobtanium and the bead thermistors that I can find only go up to 250 degrees.
I could wait for another Weller thermistor-controlled iron to come along and attempt to transplant the desoldering head. Or I could try to redesign the temperature control to perhaps use a thermocouple.
Am I missing something? Is there another way? What do you think?
I know someone will say "chuck it and buy another one"- I already have another one, I'd like to see if there's anything I might be able to do with this one.
All suggestions gratefully received!
TIA, Alan
AnalogueMan is offline   Reply With Quote
Old 22nd Jun 2024, 7:08 pm   #2
factory
Octode
 
Join Date: Jul 2009
Location: Cheshire, UK.
Posts: 1,829
Default Re: Weller DS801 Desoldering Station - open circuit PTC

Before spending too much time on this, check the various consumable spares are still available. I note at least two similar threads on here, with the same failure and they never got resolved.

David
factory is offline   Reply With Quote
Old 22nd Jun 2024, 7:13 pm   #3
Outrun_uk
Heptode
 
Join Date: Aug 2009
Location: Liverpool, Merseyside, UK.
Posts: 714
Default Re: Weller DS801 Desoldering Station - open circuit PTC

Standard Weller 40w 24v TCP iron should work fine, the desolder head just unscrews and transfers over. I got rid of my Weller as the tips had become unobtainium, a pity as it was a good station
Outrun_uk is offline   Reply With Quote
Old 22nd Jun 2024, 7:22 pm   #4
AnalogueMan
Hexode
 
AnalogueMan's Avatar
 
Join Date: Jun 2020
Location: Manchester, UK.
Posts: 284
Default Re: Weller DS801 Desoldering Station - open circuit PTC

Quote:
Originally Posted by Outrun_uk View Post
Standard Weller 40w 24v TCP iron should work fine, the desolder head just unscrews and transfers over
I considered that, but doesn't the TCP iron use the magnetic thermostat? The desolder head does indeed fit straight on but replaces the original bit so I'm worried that would also eliminate the temperature control
AnalogueMan is offline   Reply With Quote
Old 23rd Jun 2024, 9:05 pm   #5
m0cemdave
Octode
 
Join Date: Feb 2009
Location: Bletchley, Buckinghamshire, UK.
Posts: 1,254
Default Re: Weller DS801 Desoldering Station - open circuit PTC

There were a couple of versions of these DSxxx stations, one used the magnetic thermostats and the other (DS801) had the variable temp control.
Can you post a picture of the temperature sensor?
m0cemdave is offline   Reply With Quote
Old 23rd Jun 2024, 9:44 pm   #6
Outrun_uk
Heptode
 
Join Date: Aug 2009
Location: Liverpool, Merseyside, UK.
Posts: 714
Default Re: Weller DS801 Desoldering Station - open circuit PTC

Quote:
Originally Posted by m0cemdave View Post
There were a couple of versions of these DSxxx stations, one used the magnetic thermostats and the other (DS801) had the variable temp control.
Can you post a picture of the temperature sensor?
Ahh, my mistake then! The one I had just used 3 pin TCP iron - I’m guessing the other version had more (5?) pins for the thermistor?
Outrun_uk is offline   Reply With Quote
Old 24th Jun 2024, 3:10 pm   #7
CambridgeWorks
Nonode
 
CambridgeWorks's Avatar
 
Join Date: Jun 2010
Location: Spalding, Peterborough, Cambridgeshire, UK.
Posts: 2,968
Default Re: Weller DS801 Desoldering Station - open circuit PTC

Around 25 -30 years ago I returned 3 of those DS801 irons with faulty thermistor or element to Weller, in the North East.
This was on their advice after asking to buy spares.
They returned all 3 to me as BER!
The magnastat one might be either a DS800 or DS900??

Without taking this OT,
A few months ago I asked on here about my own DS801 that kept clicking the pump on and off at regular intervals.
I never did investigate further.
Since then, it has worked without any problems.
It wasn't the cable or plug either.

Rob
__________________
Apprehension creeping like a tube train up your spine - Cymbaline. Film More soundtrack - Pink Floyd
CambridgeWorks is offline   Reply With Quote
Old 24th Jun 2024, 4:12 pm   #8
AnalogueMan
Hexode
 
AnalogueMan's Avatar
 
Join Date: Jun 2020
Location: Manchester, UK.
Posts: 284
Default Re: Weller DS801 Desoldering Station - open circuit PTC

Quote:
Originally Posted by m0cemdave View Post
Can you post a picture of the temperature sensor?
I will, next time I have the iron apart, but as others have said and previous posts have concluded I'm pretty sure these particular PTC sensors are unobtanium.
Everything else works on the station, and by subsituting a 39 ohm resistor in place of the PTC I can get the iron to heat. If I let it heat until it melts solder then slowly turn the temp knob down until the LED flashes I can sort-of hold it at whatever temperature it has reached. With it in that state I can even desolder stuff, but it's a lottery as to what temperature I'm at, and with no closed-loop control it takes a while to recover if you suck a lot of heat out of it.
So here's my thinking - maybe build a little board with a couple of 555 timers driving reed relays that drop resistors in and out. First timer runs from power-on and allows my 39 ohm resistor to let it heat. When it expires it switches to a higher value (to be determined) to let it maintain. The initial temperature reached will be approximately a function of how long that first timer lets it heat for, again to be determined. Then each time the vaccuum pump gets run I trigger a second timer that drops back to my 39 ohm resistor giving it a few seconds pulse of heat to let it recover after use and then when that one expires it again drops it back to maintain. This is what I can do manually by riding the knob, and I'm hoping it might just make this otherwise unrepairable unit usable.
As I also said before, another option is to keep a lookout for another PTC-controlled iron and swap the desolder head onto that if I get one. A TCP iron won't work as I'd have to remove the bit to get the desolder head to fit and that would nobble the magnastat.
What do you reckon? It's do-able, but would it work in practice? How stable and predictable does the temperature need to actually be on these things to use them properly?

Last edited by AnalogueMan; 24th Jun 2024 at 4:14 pm. Reason: Spelling errors
AnalogueMan is offline   Reply With Quote
Old 27th Jun 2024, 2:26 am   #9
VT FUSE
Hexode
 
Join Date: Aug 2010
Location: Malvern, Worcestershire, UK.
Posts: 373
Default Re: Weller DS801 Desoldering Station - open circuit PTC

I mistakenly bought the handle mentioned some time back and converted it to a tcp type as the element and barrel were the same istr.
Spent 2 days looking for the sensor that fitted in the magnastat’s place and have located it. Hopefully it is the correct sort and still working.
If you would like me to send it to you so that you can check it, I would need you to pm me your address whereupon my lovely assistant can send it to you pronto.

Regards. Mike
VT FUSE is offline   Reply With Quote
Old 27th Jun 2024, 11:35 am   #10
AnalogueMan
Hexode
 
AnalogueMan's Avatar
 
Join Date: Jun 2020
Location: Manchester, UK.
Posts: 284
Default Re: Weller DS801 Desoldering Station - open circuit PTC

Quote:
Originally Posted by VT FUSE View Post
I mistakenly bought the handle mentioned some time back and converted it to a tcp type as the element and barrel were the same istr.
Spent 2 days looking for the sensor that fitted in the magnastat’s place and have located it. Hopefully it is the correct sort and still working.
If you would like me to send it to you so that you can check it, I would need you to pm me your address whereupon my lovely assistant can send it to you pronto.

Regards. Mike
That's most generous of you and extremely helpful, PM sent.
You can very easily check the sensor, just stick a multimeter across the two contacts and if it reads somewhere between about 20 to 30 ohms at room temperature then it's good. Very high resistance (Kilo-ohms) or open circuit is how they fail. It would also be good to post a photo of it as that might help someone finding this thread in the future. I'll happily do both of those and post the results on receipt.
AnalogueMan is offline   Reply With Quote
Old 27th Jun 2024, 4:21 pm   #11
VT FUSE
Hexode
 
Join Date: Aug 2010
Location: Malvern, Worcestershire, UK.
Posts: 373
Default Re: Weller DS801 Desoldering Station - open circuit PTC

Unfortunately I did not know the expected resistance profile and simply boxed it and posted it. As it was posted 1st class you should have delivery in the next 24-48hrs.
I agree that if it is the required part, a photo in your thread may prove useful in future.
Mike
VT FUSE is offline   Reply With Quote
Old 30th Jun 2024, 5:14 pm   #12
AnalogueMan
Hexode
 
AnalogueMan's Avatar
 
Join Date: Jun 2020
Location: Manchester, UK.
Posts: 284
Default Re: Weller DS801 Desoldering Station - open circuit PTC

Close, so close...

Due to the kindness and generostity of VT_FUSE I now have a replacement PTC. The one sent is exactly the same construction and dimensions as my faulty one, photos attached. However rather than a resistance of 22 ohms at room temperature going up to around 45 ohms when hot this one is 40 ohms at room temperature and goes up to about 60 ohms when hot. I'm not sure if this means it's a slightly different part or whether this is what happens as they age, but either way it's much better than mine which is totally open circuit.

I popped it into the iron and it works, in that the feedback functions and I can set a temperature which it heats up to and then maintains, however the temperature scale is unsurprisingly offset by quite a bit so that at maximum on the knob (450C) the iron is hot but not quite hot enough to melt solder.

I've had a look at the circuit (attached) and I'm not sure I entirely understand how the circuit around IC2A is working. I think I need to tweak the value of P2/R7 or maybe R3 to try to pull it into line but I'm not certain, can anyone advise? [EDIT - forgot to mention that P3 is the temperature-setting pot which according to the notes adjusts between 2 and 5 volts, P1 and P2 are trimmer pots on the PCB]

Also, for anyone with similar issues in the future, I've been getting a lot of good information from the resources mentioned in this thread: https://www.vintage-radio.net/forum/...d.php?p=961987 and I've also attached a photo of how I connected a temporary 39 ohm resistor to get the iron working when faced with an open-circuit PTC as I was initially
Attached Thumbnails
Click image for larger version

Name:	Weller PTC.jpg
Views:	65
Size:	55.2 KB
ID:	299702   Click image for larger version

Name:	Weller PTC Close.jpg
Views:	66
Size:	50.2 KB
ID:	299703   Click image for larger version

Name:	wecp-20.jpg
Views:	73
Size:	54.6 KB
ID:	299704   Click image for larger version

Name:	Weller PCB.jpg
Views:	58
Size:	65.1 KB
ID:	299705  

Last edited by AnalogueMan; 30th Jun 2024 at 5:21 pm. Reason: Spelling, forgot to mention P3
AnalogueMan is offline   Reply With Quote
Old 30th Jun 2024, 5:55 pm   #13
TonyDuell
Dekatron
 
Join Date: Jun 2015
Location: Biggin Hill, London, UK.
Posts: 5,310
Default Re: Weller DS801 Desoldering Station - open circuit PTC

My thoughts, from a quick look at the circuit diagram are :

IC2b and associated resistors is essentially a differential amplifier. The output to IC3 depends on the voltage difference between the inputs (top end of R12 and bottom end of R9). IC3 is the triac driver, depending on the input voltage on its pin 8, the element is driven for more or less of the AC half cycle.

The top end of R12 comes from the user temperature-set control. This is powered from a stable 5V rail (IC1). So that's the 'wanted temperature'.

The bottom end of R9 -- the output of IC2a -- is the actual temperature. IC2a is essentially a non-invertng amplifier. The voltage at the input (left end of R5) depends on the resistance of the PTC.

Now P2 sets the gain of this ampifier, P1 sets the offset. So P2 will effectively change the difference between min and max available temperatures, P1 will move the whole lot up and down. They will interact -- a lot!

My guess is that the calibraton procedure is something like 'set the temperature control to minimum, adjust P1 for the right temerature at the bit. Set to maximum, adjust P2 for the right temperature. Repeat until both points are right'.

In your case, since the variation of resistance of the PTC is about right, I'd start by tweakng R1 to see if you can get it near enough...
TonyDuell is offline   Reply With Quote
Old 1st Jul 2024, 12:10 pm   #14
AnalogueMan
Hexode
 
AnalogueMan's Avatar
 
Join Date: Jun 2020
Location: Manchester, UK.
Posts: 284
Default Re: Weller DS801 Desoldering Station - open circuit PTC

Thanks for that. I think the odd way the circuit was drawn was confusing me. I'll have a go at adjusting and report back.

I've attached the datasheet for the SL443A in case it helps anybody. It's a zero-crossing switch designed for heat-control applications.

All the bits are starting to hang together now and make sense but one quirky thing is the two diodes underneath the 7805. Are they lifting the supply relative to ground - and if so, why - or are they just using the forward drop across the diodes to jack up the regulator's output?

[EDIT - Ah, I think I see it - the temperature setting pot outputs 2 to 5 volts, so are the diodes there to lift up he bottom end and provide the 2 volts? Is that right, or am I becoming even more deluded the longer I look at it ]
Attached Files
File Type: pdf SL443A Zero Voltage Switch Datasheet.pdf (167.9 KB, 20 views)

Last edited by AnalogueMan; 1st Jul 2024 at 12:16 pm. Reason: Afterthought
AnalogueMan is offline   Reply With Quote
Old 1st Jul 2024, 8:52 pm   #15
Dennis M
Pentode
 
Join Date: Jun 2020
Location: Bude, Cornwall, UK.
Posts: 190
Default Re: Weller DS801 Desoldering Station - open circuit PTC

I may still have some iron bits for these in my store.
I have two complete DS801 desoldering stations one of which is my spare bought new around 1998 and only used for a week while I repaired my original one.
Dennis M is offline   Reply With Quote
Old 2nd Jul 2024, 5:54 pm   #16
AnalogueMan
Hexode
 
AnalogueMan's Avatar
 
Join Date: Jun 2020
Location: Manchester, UK.
Posts: 284
Default Re: Weller DS801 Desoldering Station - open circuit PTC

Success!

Following TonyDuell's advice I left R2 alone and adjusted R1. Reducing the resistance of R1 increases the temperature, but even with the pot at zero the iron still wouldn't melt solder. So I tried dropping the value of R8 (which sits in series with R1) by tacking resistors across it and this increased the temperature a bit more. By experiment I ended up with the total value of R8 at about 1.2k and could then tweak R1 to get a good solder melt and effective desoldering with the temperature knob at 350C. If I turn the knob above and below that then the heater responds appropriately, and if I leave everything alone it comes up and down on its own to maintain at the temperature that's set. No idea what the temperature actually is, but it desolders things quite nicely and that's what matters.

Many, many thanks to everyone who advised on this - a great result and a nice piece of kit back in working order

Quote:
Originally Posted by Dennis M View Post
I may still have some iron bits for these in my store
If you do, and you'd be willing to part with them, please send me a PM as it would be good to have some spares
AnalogueMan is offline   Reply With Quote
Old 2nd Jul 2024, 6:49 pm   #17
VT FUSE
Hexode
 
Join Date: Aug 2010
Location: Malvern, Worcestershire, UK.
Posts: 373
Default Re: Weller DS801 Desoldering Station - open circuit PTC

Nice to see a good outcome to your repair. Well done all.
Mike
VT FUSE is offline   Reply With Quote
Old 2nd Jul 2024, 7:54 pm   #18
Dennis M
Pentode
 
Join Date: Jun 2020
Location: Bude, Cornwall, UK.
Posts: 190
Default Re: Weller DS801 Desoldering Station - open circuit PTC

Quote:
Originally Posted by AnalogueMan View Post

Quote:
Originally Posted by Dennis M View Post
I may still have some iron bits for these in my store
If you do, and you'd be willing to part with them, please send me a PM as it would be good to have some spares
I'll have a look for them in the morning.
Dennis M is offline   Reply With Quote
Old 3rd Jul 2024, 9:10 am   #19
Dennis M
Pentode
 
Join Date: Jun 2020
Location: Bude, Cornwall, UK.
Posts: 190
Default Re: Weller DS801 Desoldering Station - open circuit PTC

Found a spare 50w iron less the glass tube if you need one. Found my spare unit is the later WDM 1S, never been plugged in
Attached Thumbnails
Click image for larger version

Name:	IMG_3167.jpg
Views:	43
Size:	55.6 KB
ID:	299808  
Dennis M is offline   Reply With Quote
Old 3rd Jul 2024, 10:06 am   #20
AnalogueMan
Hexode
 
AnalogueMan's Avatar
 
Join Date: Jun 2020
Location: Manchester, UK.
Posts: 284
Default Re: Weller DS801 Desoldering Station - open circuit PTC

I'd definitely be interested in a spare iron even without the glass tube. I'll send you a PM
AnalogueMan is offline   Reply With Quote
Reply

Thread Tools



All times are GMT +1. The time now is 6:11 am.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2024, Paul Stenning.