I was happly working away on an old radio receiver (Eddystone EC958), when there was an almighty bang! It made my ears ring, the tinitus is bad enough as it is.
View attachment 64813
Everything still seemed to be working, but there was a bit of a flash from inside the radio and a distinct smell of dead electronics.
I switched off everything, I have one handy switch which kills to power to my workbench, disconnected the radio and opened up the back panel where the flash appeared to come from, there I found a mains filter capacitor which had blown wide open.
View attachment 64814
OK, no big problem, this can be easily replaced.
Then I got to thinking.
This radio was designed and built in the early 1970s, these are not "Y" rated capacitors.
They are just 400v rated paper capacitors. The parts list in the handbook shows them as 0.47μF, what was fitted was 0.047μF. The 0.47 sounds a bit on the large side for these applications.
Looking at the fragment of the PSU schematic in the attachment, there is also what should be an "X" rated capacitor at the transformer winding. It is actually a 3000v rated disc ceramic.
Not having and suitable capacitors on hand, I snipped out the dud and its evil twin and re-assembled the backpanel of the radio. It still appears to work OK, just that the mains noise filtering will be compromised.
I can get some new capacitors sometime mañana.
Maybe I can carry on trying to align the RF circuits again now.
Always worth remembering when working on older equipment like this, some of the safety aspects are not up to modern standards.
In this case the connector on the end of the mains lead would definitely not pass the "little finger" test.
(Not pining for the "good old days", just saying.
JimB
View attachment 64813
Everything still seemed to be working, but there was a bit of a flash from inside the radio and a distinct smell of dead electronics.
I switched off everything, I have one handy switch which kills to power to my workbench, disconnected the radio and opened up the back panel where the flash appeared to come from, there I found a mains filter capacitor which had blown wide open.
View attachment 64814
OK, no big problem, this can be easily replaced.
Then I got to thinking.
This radio was designed and built in the early 1970s, these are not "Y" rated capacitors.
They are just 400v rated paper capacitors. The parts list in the handbook shows them as 0.47μF, what was fitted was 0.047μF. The 0.47 sounds a bit on the large side for these applications.
Looking at the fragment of the PSU schematic in the attachment, there is also what should be an "X" rated capacitor at the transformer winding. It is actually a 3000v rated disc ceramic.
Not having and suitable capacitors on hand, I snipped out the dud and its evil twin and re-assembled the backpanel of the radio. It still appears to work OK, just that the mains noise filtering will be compromised.
I can get some new capacitors sometime mañana.
Maybe I can carry on trying to align the RF circuits again now.
Always worth remembering when working on older equipment like this, some of the safety aspects are not up to modern standards.
In this case the connector on the end of the mains lead would definitely not pass the "little finger" test.
(Not pining for the "good old days", just saying.
JimB