[Elecraft] Help! Rescue me from stupid error!

[Josh Fiden]

Typical on these type of supplies is the voltage selector switch is 
single pole which converts between being a bridge to the filter caps to 
a voltage doubler configuration. So, where you should have had about 
320VDC, you would be in doubler mode and gotten 640VDC (230V*1.4*2).

Protection devices prior to the bridge should be okay to 240VAC. ZNR1 & 
2 are most likely across each of the filter caps which are in series for 
the doubler. Hopefully they did their job before killing anything else. 
They would be identical.

73,
Josh W6XU


On 9/9/2014 10:59 AM, Vic, K2VCO wrote:
> Took the second one out. It is labeled TVR07241, which is a 240v
> varistor! I can get these to replace them.
> I think this one is undamaged (at least, it isn't blown up or 
> shorted). I wonder if the other one was a 115V one which was only in 
> the circuit when the switch was set for 115. That would certainly 
> explain it blowing when I plugged it into 230!
>
> On 9/9/14 8:41 PM, Fred Townsend wrote:
>>
>> Vic: Sorry you passed the smoke test. Your mystery components sound
>> like transient suppressors. They are not needed for normal operation.
>> They are there to suppress lightning or other power line
>> disturbances. To find out carefully cut out ZNR1&2 and clean up any
>> ashes. Then replace the fuse and try the computer. If you are lucky
>> the computer will run. Don't forget to change back to 120 VAC
>> setting.
>>
>> Good luck, Fred, AE6QL
>>
>> -----Original Message-----
>>> From: "Vic, K2VCO" <k2vco.vic at gmail.com> Sent: Sep 9, 2014 10:23
>>> AM To: Elecraft Reflector <elecraft at mailman.qth.net> Subject:
>>> [Elecraft] Help! Rescue me from stupid error!
>>>
>>> I just did one of the dumbest things I've done since I tried to
>>> swim across the Susquehanna river with all my clothes on. I
>>> survived that, but I need help with something else.
>>>
>>> I just turned on a computer plugged into 230v with the switch on
>>> the power supply set to 115v. Result: bang, smoke, house breaker
>>> (16a) pops.
>>>
>>> I took the power supply apart (it is a funny size so I have little
>>> confidence I could replace it). I found two obviously bad
>>> components: 1) an 8a fuse -- no problem. 2) something marked znr1
>>> on the board, a component wrapped in heatshrink tubing. It was
>>> completely destroyed. Next to it is a similar part labeled znr2. I
>>> haven't removed it yet -- so I am not sure it is good. It might be
>>> the same as the first one and it might be marked under the
>>> heatshrink.
>>>
>>> There is a bridge rectifier nearby which checks good. All traces
>>> look ok. I am hoping there is someone out there who is familiar
>>> with these supplies who can suggest what these are (zener diodes?
>>> What voltage?) The board is made in such a way that it is difficult
>>> to trace the wiring -- but these parts are right near the power
>>> input.
>>>
>>> -- Vic, K2VCO/4X6GP Rehovot, Israel http://www.qsl.net/k2vco/
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>