[ARC5] BC-348-Q Capacitor Testing

[Sandy]

T^he biggest bitch about a recap job in the BC-348 is removing the 
bandswitch modules!  If it were me, be  sure you replace ALL the paper 
capacitors and ALL the "bathtub" capacitors! Mylar caps are a very good 
choice and not expensive.  Will make an extreme difference in the 
receiver if it is still even functioning.

73,

Sandy W5TVW

On 1/29/2016 5:36 PM, Richard Knoppow wrote:
>    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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