>
>
>
>On Sat, 26 Dec 1998 19:50:02 +0800 Alek Petkovic <vk6apk@eon.net.au>
>writes:
>>
>>Hi All,
>> A friend of mine in Virginia is having the following
>>nightmare
>>with his SB220. Can anybody help?
>>My SB220 contains a small transformer with two windings. One winding
>>supplies the filament voltage for the 3-500zs and the other supplies
>>bias and relay voltage at 120volts. One side of the relay coil is
>>connected to this little half wave supply. The other side of the
>>relay
>>coil goes a jack on the back of the linear. When this jack is
>>grounded
>>it closes the relay and the linear goes into the transmit. From the
>>banded end of the diode rectifier, a 20ufd, 160 volt electrolytic
>>capacitor is connected from this point to ground. Without this
>>capacitor the relay will not close. It just chatters from the
>>pulsating dc voltage. Just what you'd expect.
>>
>>I have gone through at least 10 capacitors, and each one explodes
>>after>a short time.
>
>Starting with the obvious, you have checked or replaced the diode?
>
>>Six of them were supposedly new stock.
>
>Brand and date code?? That is a 1/2 wave supply and the ripple may be
>too much for some bargain brand caps.
? The original capacitor was a cheapo and it worked ok, Carl. We are
only talking about a 25mA load, so the ripple current is small. My guess
is that the diode is the problem. If it were a zener, it could be
delivering both polarities to the filter cap. I would measure the
breakdown V of the rectifier And check the manufacturer's. pol. marking.
If the actual cathode end of the diode does not go to the positive
terminal on the cap, the cap will be terminal.
>Have you actually MEASURED the voltage?
>Are R4 and R5 OK and in the ckt? If not the voltage will rise quite a
>bit and can exceed the cap rating.
? The secondary winding is 80Vrms. How can the peak-V exceed 160V?
- later
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
--
FAQ on WWW: http://www.contesting.com/ampfaq.html
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|