Hot Air Station - Air Pump Failing

[redwire]

Re: Hot Air Station - Air Pump Failing

If it's low or full-blast only, then I think most likely the pot has failed, or its soldering connections. It could be a low quality lazy BT137 triac, I did see that once.

I would check the (hot air) potentiometer with an ohmmeter and see if the wiper might be going open or it's noisy. Halfway should be around half value etc. but in-circuit it will read lower and non-linear and I would lift one end pin of the pot to take readings.

Part of the problem is the crappy design - a (hot air) 500k pot is best for 220VAC, and 250k for 120VAC, to give a good range of control (with 0.1uF gate cap). So a 500k pot on 120VAC has a huge dead zone, nothing really happens until you are past 3/4 rotation. The minimum-air trimpot is to help cover that up but it just keeps things at a minimum until the pot is way past that.
I'm not sure if you are running 120V or 220V.

[caphair]

Re: Hot Air Station - Air Pump Failing

If it's low or full-blast only, then I think most likely the pot has failed, or its soldering connections. It could be a low quality lazy BT137 triac, I did see that once.

I would check the (hot air) potentiometer with an ohmmeter and see if the wiper might be going open or it's noisy. Halfway should be around half value etc. but in-circuit it will read lower and non-linear and I would lift one end pin of the pot to take readings.

Part of the problem is the crappy design - a (hot air) 500k pot is best for 220VAC, and 250k for 120VAC, to give a good range of control (with 0.1uF gate cap). So a 500k pot on 120VAC has a huge dead zone, nothing really happens until you are past 3/4 rotation. The minimum-air trimpot is to help cover that up but it just keeps things at a minimum until the pot is way past that.
I'm not sure if you are running 120V or 220V.

I’m on 120v. I can’t tell which pins are being used as it’s soldered from the front so would need to remove from the housing. But measuring 1st and 3rd pins it reads 120k as well as pins 2 and 3, and no change really until it’s on the max air setting then it jumps to 10 ohms.

Comparing to the other two pots they read 2.2k and gradually change as expected. But about half way on them reads 3k then it drops down as you continue. Maybe in circuit it’s giving those readings. But the one for air speed doesn’t have a smooth change

[sam_sam_sam]

Re: Hot Air Station - Air Pump Failing

I’m on 120v. I can’t tell which pins are being used as it’s soldered from the front so would need to remove from the housing. But measuring 1st and 3rd pins it reads 120k as well as pins 2 and 3, and no change really until it’s on the max air setting then it jumps to 10 ohms.

Comparing to the other two pots they read 2.2k and gradually change as expected. But about half way on them reads 3k then it drops down as you continue. Maybe in circuit it’s giving those readings. But the one for air speed doesn’t have a smooth change

This tell me that the trim pot is bad and that more than likely your biggest problem with it

But did you pin one to pin two because pins two and three might be tied together

[caphair]

Re: Hot Air Station - Air Pump Failing

If it's low or full-blast only, then I think most likely the pot has failed, or its soldering connections. It could be a low quality lazy BT137 triac, I did see that once.

I would check the (hot air) potentiometer with an ohmmeter and see if the wiper might be going open or it's noisy. Halfway should be around half value etc. but in-circuit it will read lower and non-linear and I would lift one end pin of the pot to take readings.

Part of the problem is the crappy design - a (hot air) 500k pot is best for 220VAC, and 250k for 120VAC, to give a good range of control (with 0.1uF gate cap). So a 500k pot on 120VAC has a huge dead zone, nothing really happens until you are past 3/4 rotation. The minimum-air trimpot is to help cover that up but it just keeps things at a minimum until the pot is way past that.
I'm not sure if you are running 120V or 220V.

It is a 500k pot B500k and they have the first two pins tied together. Finally took the front off. So looks like a bad pot as it reads 120k till the very end of its travel which is then 10 ohms.

Should I replace it with a 250k or would that require messing with the trim pot? How do I make sure I'm getting equivalent replacement? Are they all the same size for the value? There's a ton on eBay makes it hard to know which one to get

[stj]

Re: Hot Air Station - Air Pump Failing

that's an american value, in europe the closest would be 470k
frankly, anything is better than what you have!

[caphair]

Re: Hot Air Station - Air Pump Failing

Out of circuit at the lowest setting on the meter it reads .830MOhm so 830kohm and doesn't gradually decrease to 370k and then to 0 ohms with a hair turn after that.

Only pot I have is a B20k could that be used?

Would these from Amazon work? Pretty similar size specs expect for the leads and the back mounting piece the original has

[redwire]

Re: Hot Air Station - Air Pump Failing

Those potentiometers are weird chinese stuff because it is a dual-potentiometer housing, right angle, PCB mount, but only the one top wafer is used. The WH148 family is a pretty generic chinese ripoff of Alps.

I haven't seen the exact same part for sale, ever. You could ask vendors if they can supply one.

What could be done is take out the pot, take it apart (bend up 4 tangs) and swap out just the phenolic wafer/shaft from a new potentiometer. Just keep the old housing and transplant the wafer/shaft portion. It's really no fun and I use a hammer/screwdriver to bend the tangs back down flat putting it together. Note hazardous live mains on its 3 pins, so the pins should not touch other stuff.

If you stay with 500k, I would change the cap from 0.1uF to 0.047uF for better control. Or go 250k and keep the original 0.1uF part. 20k is too low

I had the same pot failure in a 4000W ebay "SCR" controller, exact same circuit but bigger triac. I took it apart and there was a defect/crack in the carbon track, just a cheap build.

[stj]

Re: Hot Air Station - Air Pump Failing

50c pots for 5$ with some gold vapor deposition?
actually they may not work.
audio pots are supposed to be logarithmic, and you need a linear track.

[caphair]

Re: Hot Air Station - Air Pump Failing

50c pots for 5$ with some gold vapor deposition?
actually they may not work.
audio pots are supposed to be logarithmic, and you need a linear track.

Doesn't the B in B500k indicate it's a linear pot? Every 500K I found says it's for guitar use but labeled B500k?

[stj]

Re: Hot Air Station - Air Pump Failing

no idea,
but audio is supposed to be log, every other use should be linear.
i doubt audio makers care anymore though.
they probably dont even understand the difference.

[redwire]

Re: Hot Air Station - Air Pump Failing

OK the pots are Alpha so a "B500k"
"A" is audio (logarithmic) taper.
"B" is linear taper.
"C" is reverse audio (antilog) taper.

It's been many years since I listened to audio gear with a decent log pot lol

[caphair]

Re: Hot Air Station - Air Pump Failing

OK the pots are Alpha so a "B500k"
"A" is audio (logarithmic) taper.
"B" is linear taper.
"C" is reverse audio (antilog) taper.

It's been many years since I listened to audio gear with a decent log pot lol

So these would work fine even though the description says it's for audio yet they're labeled B500k? Confusing

5 B500k Guitar OHM Potentiometer Split Taper Audio POTS Gold 18mm Shaft Base Dia 16.5mm https://www.amazon.com/dp/B0191AGY68..._0uvMCb92QMEZ1

[redwire]

Re: Hot Air Station - Air Pump Failing

It's for audio and guitar use, but not necessarily audio taper. Note the vendor sells A250k, A500k as well.

BUT the threaded shaft looks too long (it's for guitar use through thick wood).
Short shaft is 15mm, long shaft 18mm. I think yours is the short one.

[caphair]

Re: Hot Air Station - Air Pump Failing

It's for audio and guitar use, but not necessarily audio taper. Note the vendor sells A250k, A500k as well.

BUT the threaded shaft looks too long (it's for guitar use through thick wood).
Short shaft is 15mm, long shaft 18mm. I think yours is the short one.

Little longer shaft shouldn't be an issue. I ended up buying them just because I'm a prime member and get free two day shipping. Need this station up and running ASAP

[stj]

Re: Hot Air Station - Air Pump Failing

you may want to resolder the connector pins - some have ghost-rings in your picture.

[caphair]

Re: Hot Air Station - Air Pump Failing

you may want to resolder the connector pins - some have ghost-rings in your picture.

Which pins?

[stj]

Re: Hot Air Station - Air Pump Failing

the 3.96mm molex connectors

[caphair]

Re: Hot Air Station - Air Pump Failing

you may want to resolder the connector pins - some have ghost-rings in your picture.

Are ghost rings the greyish cloud looking things in solder joints? I see that a lot in various pcbs. What caused them? I always thought they were normal from lead-free solder

[sam_sam_sam]

Re: Hot Air Station - Air Pump Failing

Yes and even the ones that are not shine

It probably would not hurt reheat all the other solder joints as well

[caphair]

Re: Hot Air Station - Air Pump Failing

Well new pot is in. Had to solder the ends of the old leads onto the new one so they’d reach the PCB.

Oddly the air control seems weaker. I have full range again but just seems weaker than before. Is it possible for a new pot to cause this or?