[ARC5] BC-348-Q Capacitor Testing

[Richard Knoppow]

    To properly test a capacitor one end must be disconnected.  If you 
can manage that without unsoldering fine. I have not looked over the 
schematic you attached.  For the most part old paper caps will have some 
leakage, often a lot. Depending on the application leakage, which is 
parallel resistance, may be more important than series resistance.  
Modern plastic film caps have vanishingly small leakage and generally 
better performance than paper caps.  if you want to actually _use_  the 
receiver I think you will be ahead by just replacing these caps.  I 
understand wanting to keep the thing authentic but if its more than a 
shelf queen you may have to tolerate some change. At least under the 
chassis.  Of course, this is just my opinion.

On 1/29/2016 2:51 PM, Mark K3MSB wrote:
>
> I would like to keeps the inside of my BC-348-Q as stock as possible, 
> so I don’t want to replace caps if I don’t need to.
>
>
> The tubular bypass and coupling caps are of the aluminum cylinder 
> variety, as shown below:
>
>
> http://www.k3msb.com/temp/bc348q_underside.jpg
>
>
> From previous discussions about the BC-348-Q it seems that these types 
> of caps do not always need to be replaced. Instead of unsoldering each 
> one, I think this can be done by considering the entire circuit as 
> composed of several individual circuits separated by the various 
> switch positions as shown below:
>
>
> http://www.k3msb.com/temp/bc348q_caps.jpg
>
>
> My testing will conducted with the Dynamotor and tubes removed and the 
> AVC-OFF-MVC Switch in the OFF position.
>
> I plan on using my IT-28 Cap tester in "Leakage" mode as it provides 
> current limiting.I’ll probably use a series millameter as well.
>
> So, here’s my proposed tests:
>
> Test 1 - Inject voltage into relay pin 6 to test caps on the Blue circuit.
>
> Test 2 - Inject voltage into relay pin 2 to test caps on the Red circuit.
>
> Test 3 - Inject voltage into non grounded end of 61-7 or 61-6 to test 
> those two caps in the AVC circuit (Yellow).
>
> Test 4 - Caps 61-9 (near 28V input) tested individually
>
> Test 5 - Caps 63-2 (Audio Bypass) tested individually
>
> Test 6 - Cap 61-8 (Audio Filter, Relay Pin 1), needs to be unsoldered 
> to test.
>
> Test 7 - Cap 61-1 (RF Module), needs to be unsoldered to test.
>
>
> I want to make sure I won’t inadvertently damage anything…….
>
>
> Comments welcome.
>
>
> 73 Mark K3MSB
>
>
>
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-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL

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