Modern resistors with spalled paint..? - UK Vintage Radio Repair and Restoration Discussion Forum

The Philpott · 9th Apr 2018, 7:08 pm

Within a cheapie late 20th Century DMM I see several small (probably 1/4w) resistors that have shed part of their (light blue) paint, and also some on which the colour bands have a melted appearance, having apparently slid down the body of the resistor.

Is this likely to have been evident since day one (ie cheap manufacture) or is it symptomatic of long term heat cycling or other deterioration? Is their rating likely to be compromised?

Thanks
Dave

joebog1 · 9th Apr 2018, 11:58 pm

I would suggest it has happened in storage. I have used over the years, many types of resistor, from ultra cheap and nasty, to .01% super metal films.

Never seen smeared colour bands yet. BUT you may have picked up a lot from some disposals type store.

Joe

Terry_VK5TM · 10th Apr 2018, 3:34 am

Only time I have seen that, it has been when they have been pushed past their specs.

Having said that, I have seen photo's on the regular auction sites of some pretty sad looking parts in much the same condition (and supposedly new).

The Philpott · 10th Apr 2018, 7:57 am

Certain ranges have been displaying odd and random results which at the next try correct themselves, so the DMM was on its way to the bin when I decided to have a look inside. (which is fatal, of course.)

Next time it rains (won't have to wait too long) I will snip free one end of the worst affected ones (which are little beige ones of 150k, 220k, 510k, 1meg, with 5% tol.) and see where they have drifted to.

The Philpott · 10th Apr 2018, 7:27 pm

The DMM is the lowest of the low, the legendary DT830. Not worth fixing but it was worth meddling for interest.

Snipped and tested 3 of the worst looking 220k resistors and they were well within their 5% tolerance, (renewed them with 1% 1/4w) Also spotted a 50k resistor which didn't match the legend on the board; the board states 150k but the '1' is obscured slightly. Changing this component to 150k threw out the basic DCV calibration slightly so i assume the rest of the meter was set up to compensate for this error! Changing back to 50k and flushing the double sided circuit board with iso, liberated a sticky deposit which must have been hiding in places not easy to clean. It took 3 flushes and wipes to clean away the goo, i don't know what it was but no corrosion was evident anywhere.

The meter has a trim pot and after tweaking has now stabilised. (One assumes all other ranges rely on the basic DCV trim)

I now wonder if i have spilt something on this meter in the dim and distant past and the residue was causing current to go astray.. it certainly seems improved following a thorough clean.

Conclusion: flaking paint or colour-code rings sliding off a resistor doesn't necessarily mean it's beyond further use.

9th Apr 2018, 7:08 pm	#1
The Philpott Dekatron Join Date: Aug 2016 Location: Colchester, Essex, UK. Posts: 4,107	Modern resistors with spalled paint..? Within a cheapie late 20th Century DMM I see several small (probably 1/4w) resistors that have shed part of their (light blue) paint, and also some on which the colour bands have a melted appearance, having apparently slid down the body of the resistor. Is this likely to have been evident since day one (ie cheap manufacture) or is it symptomatic of long term heat cycling or other deterioration? Is their rating likely to be compromised? Thanks Dave

9th Apr 2018, 11:58 pm	#2
joebog1 Banned Join Date: Jun 2015 Location: Mareeba, North Queensland, Australia Posts: 2,704	Re: Modern resistors with spalled paint..? I would suggest it has happened in storage. I have used over the years, many types of resistor, from ultra cheap and nasty, to .01% super metal films. Never seen smeared colour bands yet. BUT you may have picked up a lot from some disposals type store. Joe

10th Apr 2018, 3:34 am	#3
Terry_VK5TM Nonode Join Date: Oct 2010 Location: Tintinara, South Australia, Australia Posts: 2,339	Re: Modern resistors with spalled paint..? Only time I have seen that, it has been when they have been pushed past their specs. Having said that, I have seen photo's on the regular auction sites of some pretty sad looking parts in much the same condition (and supposedly new). __________________ Terry VK5TM https://www.vk5tm.com/

10th Apr 2018, 7:57 am	#4
The Philpott Dekatron Join Date: Aug 2016 Location: Colchester, Essex, UK. Posts: 4,107	Re: Modern resistors with spalled paint..? Certain ranges have been displaying odd and random results which at the next try correct themselves, so the DMM was on its way to the bin when I decided to have a look inside. (which is fatal, of course.) Next time it rains (won't have to wait too long) I will snip free one end of the worst affected ones (which are little beige ones of 150k, 220k, 510k, 1meg, with 5% tol.) and see where they have drifted to.

10th Apr 2018, 7:27 pm	#5
The Philpott Dekatron Join Date: Aug 2016 Location: Colchester, Essex, UK. Posts: 4,107	Re: Modern resistors with spalled paint..? The DMM is the lowest of the low, the legendary DT830. Not worth fixing but it was worth meddling for interest. Snipped and tested 3 of the worst looking 220k resistors and they were well within their 5% tolerance, (renewed them with 1% 1/4w) Also spotted a 50k resistor which didn't match the legend on the board; the board states 150k but the '1' is obscured slightly. Changing this component to 150k threw out the basic DCV calibration slightly so i assume the rest of the meter was set up to compensate for this error! Changing back to 50k and flushing the double sided circuit board with iso, liberated a sticky deposit which must have been hiding in places not easy to clean. It took 3 flushes and wipes to clean away the goo, i don't know what it was but no corrosion was evident anywhere. The meter has a trim pot and after tweaking has now stabilised. (One assumes all other ranges rely on the basic DCV trim) I now wonder if i have spilt something on this meter in the dim and distant past and the residue was causing current to go astray.. it certainly seems improved following a thorough clean. Conclusion: flaking paint or colour-code rings sliding off a resistor doesn't necessarily mean it's beyond further use.