Transceiver's performance worse after changing electrolytic capacitors. Is it me? - UK Vintage Radio Repair and Restoration Discussion Forum

MattWalker · 21st Aug 2020, 7:49 pm

I have a 40 odd year old vhf ssb transceiver and decided to remove and test a couple of electrolytic capacitors with an esr meter after noticing a dried substance near the offending items.

It was quite a job replacing all of the electrolytic caps due to the component density (some have been replaced with higher voltage as it was all I had).

Sensitivity now seems to be worse than before the replacements?

HamishBoxer · 21st Aug 2020, 8:01 pm

It should not effect performance ,unless you have a wrong value in or wrong polarity.Worth a double check.

Bazz4CQJ · 21st Aug 2020, 8:17 pm

Always the "other side of the coin" with mass re-capping is that you leave a bad joint or a bit of solder between tracks.

B

crackle · 24th Aug 2020, 8:42 pm

Double check the polarity of all the caps you replaced. On modern radial electrolytic caps the negative wire is the one that is normally marked.

Mike

The Philpott · 24th Aug 2020, 9:08 pm

..and not completely unknown for the odd electrolytic cap to creep through quality control with the polarity labelling reversed.

Radio Wrangler · 24th Aug 2020, 9:29 pm

Quote:

Originally Posted by crackle

On modern radial electrolytic caps the negative wire is the one that is normally marked.

True for aluminium electrolytics, but tantalum ones usually have the positive end marked.

David

G6Tanuki · 24th Aug 2020, 9:46 pm

Check that you've got all the screening covers properly refitted: at VHF these can be rather important.

[as an example: the Pye Westminster transmitter has a PA screening-cover made from a piece of PCB with some etching in the copper to break it up into controlled areas. Replacing a 'lost/missing' cover with a piece of plain, unetched PCB reduces the output-power by about 5dB)

GMB · 24th Aug 2020, 10:26 pm

Just to be clear on marking, they do seem to like to mark the negative on the can, but I notice that the long wire is still the positive - which was the other way it is marked (but with the snag that you loose this info after assembly)

Andrew2 · 25th Aug 2020, 12:21 am

It's also worth checking for any internal coax connections which may have come adrift. Those mini coax 'push in' types favoured by Yaesu have a habit of working loose during a service.

21st Aug 2020, 7:49 pm	#1
MattWalker Diode Join Date: Aug 2020 Location: Walsall, West Midlands, UK. Posts: 8	Transceiver's performance worse after changing electrolytic capacitors. Is it me? I have a 40 odd year old vhf ssb transceiver and decided to remove and test a couple of electrolytic capacitors with an esr meter after noticing a dried substance near the offending items. It was quite a job replacing all of the electrolytic caps due to the component density (some have been replaced with higher voltage as it was all I had). Sensitivity now seems to be worse than before the replacements?

21st Aug 2020, 8:01 pm	#2
HamishBoxer Dekatron Join Date: Aug 2007 Location: W.Butterwick, near Doncaster UK. Posts: 8,935	Re: It it me? It should not effect performance ,unless you have a wrong value in or wrong polarity.Worth a double check. __________________ G8JET BVWS Archivist and Member V.M.A.R.S

21st Aug 2020, 8:17 pm	#3
Bazz4CQJ Dekatron Join Date: Apr 2009 Location: Oxfordshire, UK. Posts: 4,935	Re: It it me? Always the "other side of the coin" with mass re-capping is that you leave a bad joint or a bit of solder between tracks. B __________________ Saturn V had 6 million pounds of fuel. It would take thirty thousand strong men to lift it an inch.

24th Aug 2020, 8:42 pm	#4
crackle Rest in Peace Join Date: Mar 2011 Location: Basildon, Essex, UK. Posts: 4,100	Re: It it me? Double check the polarity of all the caps you replaced. On modern radial electrolytic caps the negative wire is the one that is normally marked. Mike

24th Aug 2020, 9:08 pm	#5
The Philpott Dekatron Join Date: Aug 2016 Location: Colchester, Essex, UK. Posts: 4,108	Re: It it me? ..and not completely unknown for the odd electrolytic cap to creep through quality control with the polarity labelling reversed.

24th Aug 2020, 9:46 pm	#7
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 14,007	Re: Transceiver's performance worse after changing electrolytic capacitors. It it me? Check that you've got all the screening covers properly refitted: at VHF these can be rather important. [as an example: the Pye Westminster transmitter has a PA screening-cover made from a piece of PCB with some etching in the copper to break it up into controlled areas. Replacing a 'lost/missing' cover with a piece of plain, unetched PCB reduces the output-power by about 5dB)

24th Aug 2020, 10:26 pm	#8
GMB Dekatron Join Date: Aug 2003 Location: near Reading (and sometimes Torquay) Posts: 3,099	Re: Transceiver's performance worse after changing electrolytic capacitors. Is it me? Just to be clear on marking, they do seem to like to mark the negative on the can, but I notice that the long wire is still the positive - which was the other way it is marked (but with the snag that you loose this info after assembly)

25th Aug 2020, 12:21 am	#9
Andrew2 Nonode Join Date: Mar 2010 Location: Dukinfield, Cheshire, UK. Posts: 2,038	Re: Transceiver's performance worse after changing electrolytic capacitors. Is it me? It's also worth checking for any internal coax connections which may have come adrift. Those mini coax 'push in' types favoured by Yaesu have a habit of working loose during a service. __________________ Andy G1HBE.