Zener diode markings - UK Vintage Radio Repair and Restoration Discussion Forum

IanNVJ35 · 14th Dec 2017, 4:54 pm

I have been tasked with repairing a Clare insulation tester (has two transformers to produce 5kV) and there is a short circuit zener. I'm not sure about its markings as it shows C62PH which I have not been able to look up online. It's a small glass type. The P is a small p and I'm wondering if that means Philips.

Thanks in advance for any help with these markings.

ukcol · 14th Dec 2017, 5:00 pm

Usually the number after the "C" is the reference voltage. For example a BZX61C5V6 is a 5.6 volt zener, so perhaps yours is a 62 volt zener?

Colin G8TMV · 14th Dec 2017, 5:03 pm

It's probably one of these

http://www.tekkna.it/product/20117/-...odo-Zener-.asp

Something like a BZV85-C62 would probably do as a replacement.

Maarten · 15th Dec 2017, 12:34 am

PH means Philips. If it's a small one (400mW), it is short for BZX79C62. A larger one would mean it's a 1W or 1.3W. In that case a BZV85C62 seems likely.

Radio Wrangler · 15th Dec 2017, 7:49 am

You don't want to fit a larger zener because the current they need to reach the knee in their curve is much greater, so the bigger part will start taking the amount of current the circuit is designed around at a somewhat lower voltage.

Just to make life difficult there are ranges of zeners with especially low operating current specs for the rated voltage. If replacing a zener other than with known like for like, then check the operating current of the circuit and the spec of the diode. This can save you some headscratching later.

David

IanNVJ35 · 15th Dec 2017, 2:58 pm

Thank you for the input. Sadly as its a discontinued and specialist bit of kit no circuit diagram exists. The problem arose when the mains input frequency was raised over about 100Hz then it went into shutdown (caused by this protect diode). Its only a small one so 400mA sounds about right.

Colin G8TMV · 15th Dec 2017, 3:01 pm

Quote:

Originally Posted by IanNVJ35

Its only a small one so 400mA sounds about right.

No, it's a 1 watt one, see the datasheet link I posted in post #3

turretslug · 15th Dec 2017, 5:15 pm

400mW 62V rating would imply maximum current of only around 7mA- though they apparently exist, that would seem to be low for an "electrical" piece of apparatus like this. A 1W device won't cost a fortune, if it proves to be inadequate in output or regulation terms a similarly inexpensive 400mW device could be tried. Does the surrounding circuit give any clues as to the expected operating current?

Radio Wrangler · 15th Dec 2017, 9:23 pm

400mW is a maximum rating rather than a target value. I suspect it's a zener designed for 5mA operation if used as a voltage reference.

David

Maarten · 15th Dec 2017, 10:20 pm

Quote:

Originally Posted by Colin G8TMV

No, it's a 1 watt one, see the datasheet link I posted in post #3

This can only be determined by the dimensions (or by the operating parameters of the application), not by the marking C62. A 400mW zener is about the size of an 1N4148 or slightly larger in diameter while a 1W or more zener is obviously larger and probably has somewhat thicker legs as well.

IanNVJ35 · 19th Dec 2017, 1:22 am

Thank you again for the help. Getting into work today I was able to take a photo of the diodes in place. I have ordered both the 400mW and 1.2W and to be honest I'm not really up to speed with diode characteristics and knees so this is a learning curve for me as well.

IanNVJ35 · 23rd Jan 2018, 10:48 pm

Just to wrap up I fitted the new Zener and now the unit functions as it should. Sadly though it cannot take 300Hz mains input frequency (needed for a certain test) and the diode just goes dead short if you go over about 170Hz.

jimmc101 · 23rd Jan 2018, 11:12 pm

Sounds like you may have a 'Capacitive power supply' see Transformerless-Power-Supplies
for examples.

Look for a large X2-rated capacitor and the absence of a mains transformer.

Unfortunately these are designed for a specific frequency and running at higher frequencies will cause excessive current draw as you have found.

Jim

IanNVJ35 · 24th Jan 2018, 10:23 am

It actually has two step up transformers to generate 5kV from 250V input (and a diode / capacitor array for DC) and no X2 cap so in theory it should have worked. In fact we were told what we did is standard practice but our machine did not like it. I tried a lower input voltage but then the machine did not start the test and on about 200V input the diode blew. Below 200V I just got a small electrical snap sound when test engaged but the diode did not blow. We'll just have to rent something or design our own.

14th Dec 2017, 4:54 pm	#1
IanNVJ35 Heptode Join Date: Mar 2010 Location: Hemel Hempstead, Hertfordshire, UK. Posts: 842	Zener diode markings I have been tasked with repairing a Clare insulation tester (has two transformers to produce 5kV) and there is a short circuit zener. I'm not sure about its markings as it shows C62PH which I have not been able to look up online. It's a small glass type. The P is a small p and I'm wondering if that means Philips. Thanks in advance for any help with these markings.

14th Dec 2017, 5:00 pm	#2
ukcol Rest in Peace Join Date: May 2003 Location: Harlaxton, Lincolnshire, UK. Posts: 3,944	Re: Zener diode markings Usually the number after the "C" is the reference voltage. For example a BZX61C5V6 is a 5.6 volt zener, so perhaps yours is a 62 volt zener?

15th Dec 2017, 12:34 am	#4
Maarten Dekatron Join Date: Dec 2007 Location: Haarlem, Netherlands Posts: 4,199	Re: Zener diode markings PH means Philips. If it's a small one (400mW), it is short for BZX79C62. A larger one would mean it's a 1W or 1.3W. In that case a BZV85C62 seems likely.

15th Dec 2017, 7:49 am	#5
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,857	Re: Zener diode markings You don't want to fit a larger zener because the current they need to reach the knee in their curve is much greater, so the bigger part will start taking the amount of current the circuit is designed around at a somewhat lower voltage. Just to make life difficult there are ranges of zeners with especially low operating current specs for the rated voltage. If replacing a zener other than with known like for like, then check the operating current of the circuit and the spec of the diode. This can save you some headscratching later. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

15th Dec 2017, 2:58 pm	#6
IanNVJ35 Heptode Join Date: Mar 2010 Location: Hemel Hempstead, Hertfordshire, UK. Posts: 842	Re: Zener diode markings Thank you for the input. Sadly as its a discontinued and specialist bit of kit no circuit diagram exists. The problem arose when the mains input frequency was raised over about 100Hz then it went into shutdown (caused by this protect diode). Its only a small one so 400mA sounds about right.

14th Dec 2017, 5:03 pm	#3
Colin G8TMV Tetrode Join Date: Apr 2013 Location: Cambridge, Cambs. UK. Posts: 71	Re: Zener diode markings It's probably one of these http://www.tekkna.it/product/20117/-...odo-Zener-.asp Something like a BZV85-C62 would probably do as a replacement.

15th Dec 2017, 5:15 pm	#8
turretslug Dekatron Join Date: Nov 2011 Location: Surrey, UK. Posts: 4,393	Re: Zener diode markings 400mW 62V rating would imply maximum current of only around 7mA- though they apparently exist, that would seem to be low for an "electrical" piece of apparatus like this. A 1W device won't cost a fortune, if it proves to be inadequate in output or regulation terms a similarly inexpensive 400mW device could be tried. Does the surrounding circuit give any clues as to the expected operating current?

15th Dec 2017, 9:23 pm	#9
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,857	Re: Zener diode markings 400mW is a maximum rating rather than a target value. I suspect it's a zener designed for 5mA operation if used as a voltage reference. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

19th Dec 2017, 1:22 am	#11
IanNVJ35 Heptode Join Date: Mar 2010 Location: Hemel Hempstead, Hertfordshire, UK. Posts: 842	Re: Zener diode markings Thank you again for the help. Getting into work today I was able to take a photo of the diodes in place. I have ordered both the 400mW and 1.2W and to be honest I'm not really up to speed with diode characteristics and knees so this is a learning curve for me as well. Attached Thumbnails

23rd Jan 2018, 10:48 pm	#12
IanNVJ35 Heptode Join Date: Mar 2010 Location: Hemel Hempstead, Hertfordshire, UK. Posts: 842	Re: Zener diode markings Just to wrap up I fitted the new Zener and now the unit functions as it should. Sadly though it cannot take 300Hz mains input frequency (needed for a certain test) and the diode just goes dead short if you go over about 170Hz.

23rd Jan 2018, 11:12 pm	#13
jimmc101 Heptode Join Date: Mar 2009 Location: Portsmouth, Hampshire, UK. Posts: 674	Re: Zener diode markings Sounds like you may have a 'Capacitive power supply' see Transformerless-Power-Supplies for examples. Look for a large X2-rated capacitor and the absence of a mains transformer. Unfortunately these are designed for a specific frequency and running at higher frequencies will cause excessive current draw as you have found. Jim

24th Jan 2018, 10:23 am	#14
IanNVJ35 Heptode Join Date: Mar 2010 Location: Hemel Hempstead, Hertfordshire, UK. Posts: 842	Re: Zener diode markings It actually has two step up transformers to generate 5kV from 250V input (and a diode / capacitor array for DC) and no X2 cap so in theory it should have worked. In fact we were told what we did is standard practice but our machine did not like it. I tried a lower input voltage but then the machine did not start the test and on about 200V input the diode blew. Below 200V I just got a small electrical snap sound when test engaged but the diode did not blow. We'll just have to rent something or design our own.