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Old 27th Oct 2020, 1:50 pm   #76
DMcMahon
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Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
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Default Re: Brenell Purchases

The two 47uF 350V capacitors checked out fine capacitance and ESR wise (not checked on Meggar), but still will renew them, the 470 Ohm resistor is open circuit.

Decided to double check the mains transformer output to the EZ 80 and have found something very confusing. I disconnected the transformer output wiring (have never disturbed this area before) designated B and measured the centre tap of the output winding to each end of the winding and got totally unbalanced voltages 380V and 165V. Previously (before this fault occurred) with everything connected had measured balanced voltages OK.

Did resistance checks of the output winding and found that the centre tap wire was not the centre tap, there being no resistance between that wire and either end of the output winding (winding itself measures OK).

The Series 2 schematic shows the centre tap connecting to a 47 Ohm resistor (I will call it the input here) and then on the output side of the 47 Ohm resistor the schematic shows connections to the wiper of the humdinger, earth and one side of the loudspeaker.

I do not really know the function of the 47 Ohm.

The transformer wire connected to the input of the 47 Ohm is white/pink, according to the schematic should be the output winding centre tap, but as explained it is not, however somehow it has a connection voltage wise.

Found another transformer wire (green) connected to the output side of the 47 Ohm which by resistance measurement seems to the centre tap of the output winding, so the centre tap connection is on the output side of the 47 Ohm as opposed to the input side as shown on the schematic. There are no other transformer wires shown on the output side (apart from the 2 sets of heater windings) so the white/pink wire is currently a mystery. The schematic does not show a transformer connection to the output side of the 47 Ohm.

I had mentioned early on in the Thread that some of the primary winding wire colours do not match the schematic, unfortunately the schematic does not show wire colours for the 3 output windings.

So first need to find out what the mystery white/pink transformer wire is, will recheck all the primary winding taps. Will have a look at the older Mk. 5 Power supply transformer wiring also.

Last edited by DMcMahon; 27th Oct 2020 at 1:59 pm.
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