>> It blew the fuse and I gave the user two more fuses  which reportedly
>> also blew in short order.

>> On examining the speaker I found the power transformer primary was
>> open circuit. (Toroidal about 150 VA)

> Er, how is it blowing fuses with an open primary? Further investigation
> is indicated.

Indeed!!! :-)
"Further investigation" is what I'm attempting.
This is from a church that has a number of similar units.
Some years ago another one started blowing fuses. It was repaired by
the local dealer, took 3 months and $300 to repair, and they replaced
the power transformer.
A reasonable implication (sample of two, margin of error ~=3D +/- 70% if
population is normally distributed :-) ) is that transformers go short
circuit internally initially, but if persuaded enough by
re-re-applying mains will then go O/C.

I'll be doing a (hopefully) controlled power up to check that
something on the PCB has not caused the problem but dealer comment
suggests that some of the transformers "just die". Mounting rather
heavy toroidal power transformers with mechanically & electrically and
thermally insulating washers backed by large metal washers adds
stresses which may contribute if not done adequately.

>> ...BUT to then  remove the PCB seems to require the removal
>> of the driver from the "horn" speaker. The horn body is integral with
>> the solidly cast speaker front face and there are no obvious screws.
>> It is not clear whether removal requires twisting pulling or general
>> beating to death. Modest amounts of each produce no results.

> Is the PCB physically blocked by the horn, or is it simply being restrain=
ed
> by the wires going to the horn? A picture might be helpful.

Wires we heed not ... :-)
Most things have no problem falling apart in my hands with little effort.
Wires are no impediment.
Being fit for reassembly seems attractive :-).

I was hoping for some specific experience of this range of products.
The PCB has a curved cutout that fits around the tapering horn body.
The PCB is attached to a large heatsink block by (at least) a row of
MOSFETs etc by mounting screws so there is an L shaped assembly that
seems to resist every topological variation attempted to try to
persuade it to clear the horn body, main body casting find etc.
Removing all the semiconductor screws would allow the unit to be
removed but as this would dislodge decade plus old insulating hardware
and thermal grease etc unnecessarily it seems a bad idea [tm].

Removal of the horn driver must be possible. 'How to do it non
fatally' is my question.


                 Russell
--=20
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