Wedg1e
They call me Mr. Bodge-angles
- Messages
- 7,739
- Location
- Teesside, England
The boss had a collection of old cars and one of them (MGA? Not sure) has a centre radio console that screws up under teh dash and houses the radio and a single elliptical speaker. Of course that was back in the olden days and with the introduction of the DIN-E fitting some previous owner had butchered the slot out to fit a different tranny. The boss wanted to return it to original so I offered to weld in a bit of tin to plug the hole so he could re-drill the proper holes.
Anyway this console was a flimsy bit of tin folded up and spot welded; I knew I wouldn't be able to MIG it without evaporating it so I opted for the TIG set. I'd got most of the job done (to my usual bodgy standards ) when the set suddenly lost its HF start.
I stripped it down and identified the HF board, whipped it out and poked a meter about the place until I'd found a blown thyristor, a blown MOSFET and an open-circuit wire-wound resistor. The semiconductors were easy, they had part numbers on but the resistor was virtually devoid of any markings - either they'd been deliberately sanded off or else age and heat had been at work. That said, although the set is 10 years old it's only had one bottle of gas through it so hardly worked hard.
I thought I'd ring the manufacturers and see if they could tell me what the resistor value should be but they were less than forthcoming, suggesting only that if I sent the board in they could fix it for me... for a fee, of course.
Having obtained and fitted new semiconductors I ransacked a big box of high-wattage resistors and selected a few to try, then starting at 25KOhm I kept on halving the value and triggering the torch.
Eventually I got some sparking but not a full arc. After a bit of meter-poking, head-scratching and double-checking it dawned on me that the Argon was turned off - turned it on, hit the trigger and nearly went blind
Ran a couple of test welds, pointed my infra-red thermometer at the replacement components and nothing got warmer than 30 degrees after a good few minutes at 120A so I'll tentatively call that a fix...
Granted it cost me the best part of an evening where a simple tip-off from the makers would have seen it fixed in minutes, but think of all the beer money saved - and even after 35 years it's still interesting to get to grips with a bit of electronics you've never seen. I have full circuit diagrams for the TIG set now, just in case...
Anyway this console was a flimsy bit of tin folded up and spot welded; I knew I wouldn't be able to MIG it without evaporating it so I opted for the TIG set. I'd got most of the job done (to my usual bodgy standards ) when the set suddenly lost its HF start.
I stripped it down and identified the HF board, whipped it out and poked a meter about the place until I'd found a blown thyristor, a blown MOSFET and an open-circuit wire-wound resistor. The semiconductors were easy, they had part numbers on but the resistor was virtually devoid of any markings - either they'd been deliberately sanded off or else age and heat had been at work. That said, although the set is 10 years old it's only had one bottle of gas through it so hardly worked hard.
I thought I'd ring the manufacturers and see if they could tell me what the resistor value should be but they were less than forthcoming, suggesting only that if I sent the board in they could fix it for me... for a fee, of course.
Having obtained and fitted new semiconductors I ransacked a big box of high-wattage resistors and selected a few to try, then starting at 25KOhm I kept on halving the value and triggering the torch.
Eventually I got some sparking but not a full arc. After a bit of meter-poking, head-scratching and double-checking it dawned on me that the Argon was turned off - turned it on, hit the trigger and nearly went blind
Ran a couple of test welds, pointed my infra-red thermometer at the replacement components and nothing got warmer than 30 degrees after a good few minutes at 120A so I'll tentatively call that a fix...
Granted it cost me the best part of an evening where a simple tip-off from the makers would have seen it fixed in minutes, but think of all the beer money saved - and even after 35 years it's still interesting to get to grips with a bit of electronics you've never seen. I have full circuit diagrams for the TIG set now, just in case...