HP334A Distortion Meter - Nulling - foam problem. - UK Vintage Radio Repair and Restoration Discussion Forum

Diabolical Artificer · 22nd May 2017, 9:10 am

There's been a few threads concerning the problem of degrading foam eating into component leads on this forum. I have a HP334A distortion meter that wasn't nulling out the fundamental, degrading foam was the cause of one fault.

Whilst trying to trace the fault I opened a black box that contains one lamp, called a diode in the manual and a four photo resistors on a PCB as well as another lamp and single photo resistor. This forms part of the automatic rejection filter. In the lid of the box are two sunken sections which had expanded foam in them. This had degraded and eaten through the lead of one lamp. Luckily it had a tiny stub of the lead, which I was able to clean and solder a single copper wire from multistrand cable on to it.

This has fixed the lamp but the meter has other issues and will need more work. However if anyone has one of these meters, it would be worth checking on the foam, and removing it. I used that black anti static foam that IC's etc come on.

Andy.

Refugee · 22nd May 2017, 10:02 am

Ouch that frying pan must surely be more comfortable than the fire.

dave cox · 22nd May 2017, 11:33 am

Take care, it maybe a little conductive ...

dc

22nd May 2017, 9:10 am	#1
Diabolical Artificer Dekatron Join Date: Jul 2009 Location: Sleaford, Lincs. UK. Posts: 7,658	HP334A Distortion Meter - Nulling - foam problem. There's been a few threads concerning the problem of degrading foam eating into component leads on this forum. I have a HP334A distortion meter that wasn't nulling out the fundamental, degrading foam was the cause of one fault. Whilst trying to trace the fault I opened a black box that contains one lamp, called a diode in the manual and a four photo resistors on a PCB as well as another lamp and single photo resistor. This forms part of the automatic rejection filter. In the lid of the box are two sunken sections which had expanded foam in them. This had degraded and eaten through the lead of one lamp. Luckily it had a tiny stub of the lead, which I was able to clean and solder a single copper wire from multistrand cable on to it. This has fixed the lamp but the meter has other issues and will need more work. However if anyone has one of these meters, it would be worth checking on the foam, and removing it. I used that black anti static foam that IC's etc come on. Andy. Attached Thumbnails __________________ Curiosity hasn't killed this cat...so far. Last edited by Diabolical Artificer; 22nd May 2017 at 9:21 am.

22nd May 2017, 10:02 am	#2
Refugee Dekatron Join Date: Apr 2012 Location: Worksop, Nottinghamshire, UK. Posts: 5,553	Re: HP334A Distortion Meter - Nulling - foam problem. Ouch that frying pan must surely be more comfortable than the fire. Attached Thumbnails

22nd May 2017, 11:33 am	#3
dave cox Nonode Join Date: Jan 2009 Location: Bristol, UK. Posts: 2,062	Re: HP334A Distortion Meter - Nulling - foam problem. Take care, it maybe a little conductive ... dc