It is useful to have a 240v current-limiter to insert between the amp
and the mains to facilitate troubleshooting HV PS problems such as
this. Such a limiter requires a 240v plug, a 240v socket, a 10 by 12
or so inch square of 3/4" plywood, two Edison medium screw-base lamp
sockets, #16 wire, and two 300W 120v incandescent lamps.
One lamp goes in series with each half of the 240v source. Under
standby condition, with the tubes removed, the lamps should not glow or
glow barely. If a short is present somewhere is the PS, or if the
interlock is not disconnected. both lamps will glow brightly.
On Mar 30, 2006, at 12:37 PM, Georgens, Tom wrote:
> Thanks to all for the responses.
>
> In response to the questions, The amp does have a retrofit step start
> installed by a previous owner. A guest had reported that the amp did
> not turn on at all and had verified that the interlock and the fuses
> were OK.
>
> My guess was the step start resistor or a bad connection. When I
> opened
> the unit, the step start resistor was indeed fried. I replaced it but
> the new one failed instantly as well. I thought that it may be the
> step
> start relay failing so I shorted the step start resistor but the fuses
> blew instead.
>
> At this point I disconnected the HV connection at the transformer
> secondary, and the primary side of the AC (Fan, step start relay,
> lights, etc) all worked fine. It is then I started measuring the other
> stuff and found the blown rectifiers.
>
> Also the diode between HV- and Gnd was also shorted.
>
>> From the feedback, it is probably likely the one diode failed and took
> the rest with it. I will replace them all and bring down a bunch of
> spare diodes and step start resistors.
>
> 73, Tom
>
> -----Original Message-----
> From: R; Measures [mailto:r@somis.org]
> Sent: Thursday, March 30, 2006 8:25 AM
> To: Georgens, Tom
> Cc: Amps
> Subject: Re: [Amps] AL80A
>
>
> On Mar 30, 2006, at 7:15 AM, Georgens, Tom wrote:
>
>> Hello -
>>
>> My AL80A in Barbados failed after years of reliable service.
>>
>> It looks like all of the diodes on the rectifier board are shorted. I
>
>> also noticed that one of the diodes had a chunk blown out of it. I
>> can obviously replace the diodes but I would like to know why they all
>
>> failed. Is it possible that if one diode fails, they all fail?
>
> Yes, which is the usual case because series rectifiers are like
> dominoes.
>
>> Or, should I be concerned about a problem further down stream.
>
> This is a possibility -- especially with an AL-80 because it uses no
> glitch R in the +HV to limit fault-I during an anomaly -- such as an
> intermittent +HV arc to ground.
>
>> Rudimentary ohmmeter checks of the capacitor bank/load looked normal
>
> A white deposit near the pressure vent indicates a kaput electrolytic.
> When one or more electrolytics in a string goes bad, it's best to
> change
> out all of 'em.
>>
>> Thanks for your help.
>>
>> Tom W2SC 8P5A
>> _______________________________________________
>> Amps mailing list
>> Amps@contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
>>
>>
>
>
>
> Rich Measures, 805.386.3734, AG6K, www.somis.org
>
>
Rich Measures, 805.386.3734, AG6K, www.somis.org
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