Cambridge audio a1 mk1 not powering on.

Hello so i bought a cambridge a1 mk1 (the original version) off someone and they said that the main board glass fuse blew and to change it and it would work. However after changing it the amp still doesn't turn on.
None of the other fuses had blown, it was the T3.15A which blew which is the last fuses. I also read a few youtube comments which said it could be the transformer since none of the first fuses blew.
Can anyone help me?
I have a DMM so can test things if needed be.
 
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It would help to see a circuit of the version you are working on but as a general rule the mains transformer is normally way down the list of suspects.

You can easily test the transformer by disconnecting the secondary windings and then seeing if the transformer powers up normally.

This is much more likely to be either a shorted diode in the bridge rectifier or a failed output stage.
 
This is the circuit board im working with
 

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So a few things you can check. Put your meter on the 'Diode' range and with the amp off and unplugged measure across each of those four large diodes marked 1N5402 that are next to the fuse holders.

Do any read short circuit?

Also check the four large power transistors bolted to the heatsink. Still using the diode range measure from the middle leg of the transistor to the each of the other legs in turn.

Do any of those read short circuit?

You can test the transformer by removing those 4A fuses where the transformer connects and then with your meter on AC volts switch the amp on and check the voltage between the purple wire and ground and between the yellow wire and ground.

I'm not sure what voltage the amp runs on without seeing a full circuit diagram but I would expect to see about 18 to 25 volts AC between each set of wires.
 
I have tested the diodes and i get a reading around 0.4v however when checking from cathode to anode i still get a reading which im not meant.
When checking the transistors with morocco TIP35C i get reading of 1v and then for the morocco TIP36C i get a reading of 0.49 v to 0.96v
Lastly for the transformer i get no reading at all when plugged in on either of the wires
 
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I have tested the diodes and i get a reading around 0.4v however when checking from cathode to anode i still get a reading which im not meant.
When checking the transistors with morocco TIP35C i get reading of 1v and then for the morocco TIP36C i get a reading of 0.49 v to 0.96v
Lastly for the transformer i get no reading at all when plugged in on either of the wires

The in circuit checks that I asked you to perform of the semiconductors are basic and designed to show 'short' or 'not short' which tbh would cover most failures of power devices.

So no obvious shorts and you still have doubts over that transformer.

You should be able to read the primary resistance (which will be very low) by measuring across the mains plug terminals.

What do you get?

If it is open circuit then check the primary resistance directly on the wires of the transformer.

Still open or not?
 
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The plug that goes into the wall, the mains connection...

With the plug in your hand, measure the resistance between live and neutral on the plug (make sure the amp switch is on) and see what you get. It should be just a few ohms to a few 10's of ohms.

The secondaries won't be open but you check those reading between each winding, so purple to white/red and yellow to white/red. The white and red will join on the PCB.
 
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When you say 'no difference' do you mean that you get the same 1. with the meter leads not connected? In other words open circuit.

If so then you need to measure directly now across the primary which are the brown and orangey red wires going to that little board. If it reads open circuit there then the transformer is open circuit but that would be very unusual.
 
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You are reading between these two points. Undo the board and connect the meter to the solder underneath.

If it is still open circuit then the transformer is dead, if not then you have a break in the wiring/PCB or switch.
 

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Okay so when i say no difference, i do meant 1. which you said is open circuit.
After measuring across the brown and orange colour wire the meter still shows open circuit. So I'm assuming the transformer is dead right? If that's the case could anything else be dead?
(this has all been done without the amp plugged in too)
 
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That result is pointing toward the transformer unfortunately.

(When you short the meter leads together you do see 0.00 ? (just checking your meter is working OK)

It's very unusual on a toroid for it to go open. One possibility is that the manufacturer has included what is called a thermal fuse within the windings although these are more common on small conventional transformers.

If that is the case then the fuse is normally non replaceable :( as it is buried in the windings.