Does anybody know what the switch and the two potentiometers do on the back of the fan control pcb on a potterton suprima 120L. I have such board where the 250mA fuse blows every 5 or 6 days, have replaced the fan and still it blows. I presume it is now either the transformer or the PCB or both !! But am intriguied by the switches and the potentiometers...
Potterton Suprima 120L Fan PCB
- Thread starter brinzlee
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The switch is to put the fan in set up mode..Hence the two dials to adjust the min and max fan speeds.
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Are you sure it was the bridge?
It would normally be either shorted or not!
I dont have a stock PCB to check but sometimes the surge limiting VDR will operate at too low a voltage and give that effect. They are mostly rated at 275 VAC so only a small margin over 240 VAC.
I went to a boiler yesterday and both 3.15 A fuses had blown on a massive overcurrent. After checking all the components I reapplied power with a lighter fuse of 1.6 A and left it on test for a week to see what happens next.
There was no evidence of any lightening storms or power surges at the time the fuse blew.
Tony
It was the fuse on the Fan PCB that kept blowing....not the main fuse...it was very frustrating as I thought it was the fan going overcurrent through wear and tear...but it was definitely the Bridge....I think one of the diodes in it was hovering around a short which taking out the fuse.....but its now blown open circuit.....changed the 2200 capacitor as well just in case the extra ripple did any damage...
Sounds like you have an interesting fault on your one too
Sounds like you have an interesting fault on your one too
That's just a 4 or 6 Amp ordinary thing iirc, but the lumps of silicon inside can be quite big abd move about a bit, causing intermittent shorts. They'd hardly be avalanche diodes.
Mending your own board is up to you, but not something that's often wise to do for a customer, imho.
Mending your own board is up to you, but not something that's often wise to do for a customer, imho.
Same thing...if you cut one open you'll see it for yourself...ok its not a conventional off the shelf diode but it can only be arranged in the same way...embedded or not...
As to the movement...I'll take your word on that one....never seen if for myself....but then with my eyesight..well lets not go there !!
As to the movement...I'll take your word on that one....never seen if for myself....but then with my eyesight..well lets not go there !!
I have just been looking at the data sheet and see that its only a 600v diode! It IS an industry standard off the shelf component!
Its not clear exactly how the bridge is encapsulated. It says the case is "moulded plastic". That is probably fully moulded around the diodes but it would not exclude a hollow plastic case with the diodes embedded in epoxy.
However, I have looked at a sample of the later PBU605 and thats a fully moulded case so I would expect the earlier model to have been the same! I dont see any scope for movement in that kind of case!
It was always practice ages ago to use 800v diodes for mains even in consumer equipment.
However, more recently it has been usual to fit a 275v surge limiter on the supply after the mains fuse and perhaps, if one is incorporated on your pcb, thats why they choose to only use a 600v bridge.
I do have to say that for the extra 1p or 2p I would have used an 800v bridge to increase the reliability BUT to a boiler manufacturer who makes a lot of money out of spares, too high a reliability is unfortunately not a desirable feature.
I have this feeling that if it was on the Space Shuttle they would have used a 1000v bridge!
Tony
Its not clear exactly how the bridge is encapsulated. It says the case is "moulded plastic". That is probably fully moulded around the diodes but it would not exclude a hollow plastic case with the diodes embedded in epoxy.
However, I have looked at a sample of the later PBU605 and thats a fully moulded case so I would expect the earlier model to have been the same! I dont see any scope for movement in that kind of case!
It was always practice ages ago to use 800v diodes for mains even in consumer equipment.
However, more recently it has been usual to fit a 275v surge limiter on the supply after the mains fuse and perhaps, if one is incorporated on your pcb, thats why they choose to only use a 600v bridge.
I do have to say that for the extra 1p or 2p I would have used an 800v bridge to increase the reliability BUT to a boiler manufacturer who makes a lot of money out of spares, too high a reliability is unfortunately not a desirable feature.
I have this feeling that if it was on the Space Shuttle they would have used a 1000v bridge!
Tony
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