Diode Designation 40

Post a close up pic of the board, close enough to see the numbers and I can help you.

Hi, thanks for your effort. No matter how I try I can not get close enough for a clear pic of the Number 40 to show up on the diode. No macro feature on this camera!

As long as you have the rating for the Caps and know the power the diods will be exposed to, all you need to do is buy any old (new actually) diode with the same power rating. A diode is a very simple device, it's just a one way valve for electrons, free to travel in one direction, with a (typical) 0.7V drop, and blocked off the other. Buy some diodes that are the same, or larger (wont hurt anything to go bigger) as the ones you pulled, Just make sure you put them in in the correct orientation, or itll never work.

As far as the Caps, You should be able to find those with the information you already have without any problem. Tell your local electronics supply the specs...

-OR- (Best Idea yet _{that I've had})

Just pull one of each of the components you need to replace and take them to your local industrial electrical supply store, hand them to the guy at the counter, and say something in the order of: "I need some of deeze pleeze"

Smells like a Voltage multiplier for an electrostatic filter (and very dangerous to mess with). Normal diodes won't do because they avalanche at a bit over 1KV or worse. You must get HV diodes or as a last resort, (and if you have the board space), use more than one normal diodes in series for every stage. (I would use four to withstand 4KV guessing from '40', providing also that the circuit uses mains frequency and not an inverter or vibrator) S.M.

Absolutely correct... thus my statement: "diode with the same power rating."

..if it's actually a diode that he has and if it isn't a generic part with an in house part number.

Sorry, but 'power rating' does NOT mean the same as 'voltage rating'. In this application it is the voltage that is the limiting factor, not the power dissipation.

He is right. IF the current consumption is below, what it can take. Otherwise the 1N4000 series is a good, cheap, larger current diode. For high voltages a series chain of diodes is correct. But, to make it sure, that leakage currents remain the same from diode to diode, 1 megohms or less ought to be parallelled with every single diode. Cheap a the price, and it works.

Watch the voltage rating!!!:

It flabbergasts me that such a short diode can have a 10kV voltage rating. The 100mA rated X100UFG from Voltage Multipliers that RS is selling for £7.15 is only 0.35" or 8.9 mm long. Sheesh, it has no creep distance!

Hah, that company likes short diodes. Yes, it's impressive that they get so many diodes in series in such a small package (the forward voltage is 15 volts at low currents), but hey, don't we need insulation distance? If I go to their 15kV 300mA part, Z150UFG, the length A is only increased 28% to 0.45" or 11.4 mm. I'm used to using diodes at least half again that long for that voltage rating.

At this voltage level, encapsulating everything is a good idea. That is what the cathode ray televisions usually did. When I was making electronic ignition for motor cars, I used to reckon that 10mm gap jumped in open air was about 25 kV. Maybe it is only mains frequency sine drive here [Tonyo has not specified] and that is how it survives? My best estimate of the maximum diode inverse voltage in the original post's equipment is 6 kV.

Ah, yes. Use small parts for a compact assembly, then encapsulate the whole mess. That makes good sense. Thanks!

From your description, this is an electrostatic device and the current is low. But the required diode reverse voltage rating is high - the capacitors are 6 kV, so 6 kV diodes would be ideal.

Farnell [www.farnell.com] list type BY8410 rated 12 kV 5 mA, but they are no longer made (may be stocks, but no price). Dimensions fit what you give. Other HV diodes are listed, but much higher current and quite expensive (£5 each).

Vishay GP02-30 is available from Farnell at a good price and rated 200 mA, but is only 3 kV. GP02-40 is 4 kV and might be what you have. Have you taken a diode off the PCB, to see if it has hidden numbers extra to "40"?

Vishay have an application note http://www.vishay.com/docs/88842/anusingr.pdf about HV doubler and tripler rectifier circuits using GP02-40 and similar.

Check out what's already been linked:

Apologies for not checking link and I rate you a good answer.

Hi, thank you for your help.

I have taken all three diodes off the board. They do check out OK.

Not wanting to go though this again I thought it prudent to replace all of the components in the power section. The caps were easily obtained, the diodes not so much. So, I'm going to follow the old advice: If it ain't broke-don't fix it---although I feel like in the not too distant future I may have to do this dance again! The only thing that is not great is the odor of the disintegrating capacitor that the furnace fan distributes throughout the facility.

Thank you all for your help!

Good. But if you need to replace the diodes, use the type from RS suggested by JohnDG in #6. It may cost more but they will last, being ample in voltage and current rating, while the originals are probably only just adequate.