UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio 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.

Closed Thread
 
Thread Tools
Old 16th Sep 2018, 7:32 pm   #1
Chris Wilson
Heptode
 
Join Date: Nov 2011
Location: Whitchurch, Shropshire, UK.
Posts: 581
Default Metcal RF soldering base unit playing up.

After singing this RF soldering station's praises here and elsewhere it has decided after many years good service to play up. Whilst tips et hot, probably to full temp, they do not retain heat when touched to joints. I have tried several tips, one brand new and my RF tweezers on their own RF co-ax seem to do the same. I suspect whatever part of the circuitry is supposed to maintain heat when a junction is taking it from the tip is not working properly, but that's merely a guess. It's an earlier version than some I have seen mentioned in here, a
STSS-P2V-O2 but I would imagine the schematic of the later ones will be similar unless anyone has the correct diagram / service manual?

http://colinoflynn.com/wp-content/up...MX-500P-11.pdf

Any ideas where to look and has anyone had this issue themselves and fixed it? Thanks
__________________
Best Regards,
CW. 2E0ILY
Chris Wilson is offline  
Old 16th Sep 2018, 10:53 pm   #2
MrBungle
Dekatron
 
MrBungle's Avatar
 
Join Date: Jun 2016
Location: London, UK.
Posts: 3,510
Default Re: Metcal RF soldering base unit playing up.

I've fixed a couple of these for people. The schematic is about right AFAIK. Are you blessed with LEDs on your unit? If so what are they doing.
MrBungle is offline  
Old 17th Sep 2018, 12:58 am   #3
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 4,232
Default Re: Metcal RF soldering base unit playing up.

I use a Metcal all the time at work and one of their few downsides is that the tip / cartridge is also the 'element'. The most common failure mode for the cartridges, apart from the tip becoming physically worn out, is for the cartridge to start running merely quite hot, rather than very hot. This symptom is, on my Metcal station, accompanied by the green LED being lit as usual, but the amber LED also coming on. To my frustration, this often starts to happen while the physical tip is still in good condition.

If you had this problem with just one tip I would be adamant that the tip / cartridge was your problem: But in light of the fact that you have this problem with a number of tips including a new one I am somewhat mystified.

As always, a major suspect with any cable connected hand tool should be the cable which gets wriggled around constantly in use, especially where it exits the base station and where it enters the handpiece.
SiriusHardware is online now  
Old 17th Sep 2018, 7:24 am   #4
Radio Wrangler
Dekatron
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 14,533
Default Re: Metcal RF soldering base unit playing up.

Where I work, it's almost impossible to get people to turn off Metcals. So there is a steady supply of dead Metcal bases with dead power transistors (and sometimes the drivers).

I've come across enough tips that just run too low in temperature and a new tip fixes that.

This sounds different.

I have a little Metcal power meter which goes in-line between the iron and the base. It's good for seeing when you're up to temp, and very useful for diagnosis.

I think you have a problem in the base. Either it can't make enough power at 13.5MHz in the RF bits, or else the feedback control system is awry.

David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is offline  
Old 17th Sep 2018, 8:38 am   #5
wd40addict
Heptode
 
wd40addict's Avatar
 
Join Date: May 2009
Location: Stevenage, Herts. UK.
Posts: 797
Default Re: Metcal RF soldering base unit playing up.

Interestingly the frequency used on the baby Metcals has dropped to 470kHz...

Now you can solder and tune your IF amp at the same time!
wd40addict is online now  
Old 17th Sep 2018, 8:51 am   #6
MrBungle
Dekatron
 
MrBungle's Avatar
 
Join Date: Jun 2016
Location: London, UK.
Posts: 3,510
Default Re: Metcal RF soldering base unit playing up.

I’ve got a PS900, the 470Khz one. Can’t tune it - have tried! The case is a big chunk of aluminium though and there’s somewhat extensive shielding. Really nice iron. Better than my TCP was.
MrBungle is offline  
Old 17th Sep 2018, 11:48 am   #7
Chris Wilson
Heptode
 
Join Date: Nov 2011
Location: Whitchurch, Shropshire, UK.
Posts: 581
Default Re: Metcal RF soldering base unit playing up.

Quote:
Originally Posted by MrBungle View Post
I've fixed a couple of these for people. The schematic is about right AFAIK. Are you blessed with LEDs on your unit? If so what are they doing.
Yes, it has two LED's. From memory a green and a yellow. The green shows "all OK" the yellow seems to come on with no iron plugged in or if the iron touches something with a charge in it. Turning the main unit power switch off and on resets to all OK. They seem to be functioning as they should though. Thanks for the reply.
__________________
Best Regards,
CW. 2E0ILY
Chris Wilson is offline  
Old 17th Sep 2018, 11:53 am   #8
Chris Wilson
Heptode
 
Join Date: Nov 2011
Location: Whitchurch, Shropshire, UK.
Posts: 581
Default Re: Metcal RF soldering base unit playing up.

Quote:
Originally Posted by SiriusHardware View Post
I use a Metcal all the time at work and one of their few downsides is that the tip / cartridge is also the 'element'. The most common failure mode for the cartridges, apart from the tip becoming physically worn out, is for the cartridge to start running merely quite hot, rather than very hot. This symptom is, on my Metcal station, accompanied by the green LED being lit as usual, but the amber LED also coming on. To my frustration, this often starts to happen while the physical tip is still in good condition.

If you had this problem with just one tip I would be adamant that the tip / cartridge was your problem: But in light of the fact that you have this problem with a number of tips including a new one I am somewhat mystified.

As always, a major suspect with any cable connected hand tool should be the cable which gets wriggled around constantly in use, especially where it exits the base station and where it enters the handpiece.

The normal iron's cable shows continuity at DC even when waggled about, and the fact the tweezers which have their own co-ax seem to have the same problem makes the cable seem unlikely, sadly. I have read two opinions on the base unit's functionality. Some say it outputs full power all the time and only the Curie effect of the tips affect their running temperature. Others, with who I tend to side, say ther's circuitry that regulates the voltage to the output FET for the purpose of temperature control. Whether that control is linear or a simpler two state, full power or idling, I do not know. Does anyone know what the RF connector type is? Or if the things can be powered up out of their case, I suspect the case is also the heat sink for some semiconductors. Thanks!
__________________
Best Regards,
CW. 2E0ILY
Chris Wilson is offline  
Old 17th Sep 2018, 1:36 pm   #9
Radio Wrangler
Dekatron
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 14,533
Default Re: Metcal RF soldering base unit playing up.

The RF connector is Type-F

Once, when giving a talk, I covered what the different RF connector names meant and someone asked what 'F' stood for. "Very bad" I replied.

The metcal has an RF output stage whose power is controlled by a detector which is part of a directional coupler on the RF output. The winding on the heating part of the tip is wound so that it looks close to 75 Ohms when the metal core is below working tempaerature (the Curie point) at theat temperature, the impedance changes rapidly and the load ceases to be a match for the impedance of the directional coupler and coax (75 ohms) and so power is reflected from the tip back to the base unit. The base unit detector senses this and throttles back the power supply voltage reaching the power output stage.

If a tip fails in a way which changes its cool impedance (EG a shorted turn) then the impedance looks bad, relfected power holds the level of RF from the base down and the thing never gets to temperature. The mismatch is such that the tip cannot take the full designed power from the base, and also the base senses this and reduces the available power as well.

David

Oh, and the mains switch on top switches only the secondary of the mains transformer, so it's as well to shut off the power from the socket when not in use.
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is offline  
Old 17th Sep 2018, 2:03 pm   #10
merlinmaxwell
Dekatron
 
merlinmaxwell's Avatar
 
Join Date: Jul 2008
Location: Maidenhead, Berkshire, UK.
Posts: 9,402
Default Re: Metcal RF soldering base unit playing up.

One of the worst drawn circuits I have seen, very hard to follow. A expect S1 to have a short life because it is charging a 100uF capacitor from a 1000uF one, lots of DC current all at once.
__________________
Cats have staff, it's dogs that have owners.
merlinmaxwell is offline  
Old 17th Sep 2018, 3:16 pm   #11
Skywave
Dekatron
 
Skywave's Avatar
 
Join Date: Jun 2006
Location: Chard, South Somerset, UK.
Posts: 6,818
Arrow Re: Metcal RF soldering base unit playing up.

Quote:
Originally Posted by merlinmaxwell View Post
One of the worst drawn circuits I have seen; very hard to follow.
Agreed, and, unfortunately, all too common. Usual cause is a draughtsman/woman who has not the slightest understanding of the operation of the cct.

Al.
__________________
Chard, Somerset - The home of powered flight and prosthetic limbs.
Skywave is offline  
Old 17th Sep 2018, 4:16 pm   #12
Chris Wilson
Heptode
 
Join Date: Nov 2011
Location: Whitchurch, Shropshire, UK.
Posts: 581
Default Re: Metcal RF soldering base unit playing up.

Glad you think it's a bit of a random schematic too I thought it was just me! There's something wrong with the F type socket on the main unit. One tip is definitely gone but the new one and the tweezers start to work fine and hold temp when applied to a cold joint if I wiggle the connector about, so I need to get inside and see how the socket connects to the PCB, I think light exists down this `ere tunnel! Thanks for the guidance
__________________
Best Regards,
CW. 2E0ILY
Chris Wilson is offline  
Old 17th Sep 2018, 7:08 pm   #13
hysteresis
Tetrode
 
Join Date: Feb 2007
Location: Liverpool, Merseyside, UK.
Posts: 96
Default Re: Metcal RF soldering base unit playing up.

Quote:
Originally Posted by merlinmaxwell View Post
One of the worst drawn circuits I have seen, very hard to follow.
When you consider that it is a reverse engineered drawing, drawn by someone unconnected to Metcal, I think that it's a pretty good effort.
hysteresis is offline  
Old 17th Sep 2018, 10:15 pm   #14
Skywave
Dekatron
 
Skywave's Avatar
 
Join Date: Jun 2006
Location: Chard, South Somerset, UK.
Posts: 6,818
Arrow Re: Metcal RF soldering base unit playing up.

Yes, O.K., it may indeed have been a 'reverse-engineered' drawing and, yes, it is better than nothing, but the point is this: what is the prime purpose of a circuit diagram? Answer: So that someone who has a basic working knowledge of electronics circuitry will be able to easily understand how it works. That requires a layout that reasonably reflects the functionality of all items shown in that circuit and the 'logical signal flow' thus arising. The circuit - as shown here - simply fails that critical test in every respect. My post #11, q.v., still applies.

Al.
__________________
Chard, Somerset - The home of powered flight and prosthetic limbs.
Skywave is offline  
Old 17th Sep 2018, 11:14 pm   #15
Herald1360
Dekatron
 
Herald1360's Avatar
 
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 14,518
Default Re: Metcal RF soldering base unit playing up.

Think of it as an opportunity- turn it into what you would like it to be and post it in the forum.......
__________________
....__________
....|____||__|__\_____
.=.| _---\__|__|_---_|.
.........O..Chris....O
Herald1360 is online now  
Old 18th Sep 2018, 7:57 am   #16
MrBungle
Dekatron
 
MrBungle's Avatar
 
Join Date: Jun 2016
Location: London, UK.
Posts: 3,510
Default Re: Metcal RF soldering base unit playing up.

It’s not actually bad. I can read it fine and work out what the logical blocks and functions are.

I reckon this is power supply stalling if it’s an old unit. Check the voltage on the top of C8 when the iron drops out. DMM should sufficient. There’s a TI simple switcher which provides the higher voltage to the PA. see if it dips significantly. If it does replace the C6 and C8 with equivalent low ESR units.
MrBungle is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 9:49 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 - 2020, vBulletin Solutions, Inc.
Copyright ©2002 - 2020, Paul Stenning.