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Old 27th Oct 2020, 6:10 pm   #82
DMcMahon
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Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 2,356
Default Re: Brenell Purchases

Mk. 5 Series 2 Update.

Did a barrage of resistance, insulation resistance and voltage tests, will not bore you with the fine details, but everything checked out OK.

Too difficult to remove the mains transformer, using Variac adjusted to suit, set the mains voltage selection switch to the 3 settings of 110V, 220 & 240 volt and got the expected outputs. The primary winding tap various resistances also made sense.

Measured the white/pink wire using Avo wrt to both ends of the output winding and only got a few volts at most, so this result supporting strongly Lawrence's suggestion that it most likely is a transformer screen wire and the DVM high voltage readings were due to capacitive coupling effect.

The blue wire (the actual output winding centre tap) measured correct voltage wrt to both ends of the output winding using DVM & Avo.

Had a look at the Mk.5 power supply for comparison. First time I have inspected this power supply, it is a right mess, everything is very sticky and dirty covered in dead insects etc, especially the cables. Been spoilt by the Series 2 which by comparison was relatively clean.

Very similar power supply with subtle differences. The primary winding taps wire colours agree with the Series 2 schematic, the primary winding tap resistances are very similar to the Series 2, so definitely the mains transformer on the Series 2 is different from the Mk. 5, at least in terms of wire colours, with the Series 2 schematic reflecting the Mk. 5 transformer wire colours.

By resistance measurement the Mk. 5 output winding centre tap is a black wire and it correctly goes to the input side of the 47 Ohm resistor (as per schematic) with the output side connecting to earth. Just these 2 wires connecting to the 47 Ohm on the MK.5

Could not tell if there might be a transformer screen wire on the Mk. 5

Had fun and games putting the Mk. 5 Tape deck back in, it sits on 3 loose rubberised metal spacer mounts (should be 4 but 1 appears missing) and found it very difficult to get the deck in position without the mounts falling inside the case.

Now need to put everything back together on the Series 2, replacing the 470 Ohm resistor and two capacitors and correcting the wiring to the 47 Ohm, nothing so far really explains why the 470 Ohm burnt up ?
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