The transformer has overheated and failed. Apart from the thermal fuse in the primary those on the circuit board appear to be intact.
Toroidal transformers can fail if the mounting is compromised creating a shorted turn via the central mounting bolt. To exclude this as a possibility I suggest you check this out in line with the heading precautions in this link Design Notes
Transformers do vibrate which might have caused some movement over the life of the amplifier. Bolts can loosen for this reason.
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Mjona: "Toroidal transformers can fail if the mounting is compromised
creating a shorted turn via the central mounting bolt."
In my experience a transformer breakdown can happen when only
a small amount of rubber suspension is used, crossed wires of
outside layers are compressed and wire insulation fails. It is a short
circuit condition and the transformer or its thermal fuse will burn out.
This can be a long term phenomenon occurring after years.
I always add some rubber layer when I see this in a commercial amp.
creating a shorted turn via the central mounting bolt."
In my experience a transformer breakdown can happen when only
a small amount of rubber suspension is used, crossed wires of
outside layers are compressed and wire insulation fails. It is a short
circuit condition and the transformer or its thermal fuse will burn out.
This can be a long term phenomenon occurring after years.
I always add some rubber layer when I see this in a commercial amp.
That was me. I think you need to know why the transformer failed in the first instance and if the fault is with the transformer and how that came about.
From the image shown with post 5, the secondary winding on the outer is crimping the primary mains cable to the side of the chassis - how clever is that?
The transformer looks outsize for the space. All in all it does not look like an original fitment.
What is written on the transformer label - manufacturer, v.a. and voltage ratings and anything else.
Some research shows Mike Creek was given the job of designing the electronics in a hurry doing this within a month. There was new product receiving praise from the Hifi press and Cambridge were keen to get in on the action.
If this was a matter of urgency there would be questions of availability in quantity and cost for such components as transformers - the province of the production and purchasing.
Looking at the item shown with post 5 this looks like something in a warehouse standard product range.
If this was a matter of urgency there would be questions of availability in quantity and cost for such components as transformers - the province of the production and purchasing.
Looking at the item shown with post 5 this looks like something in a warehouse standard product range.
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The problem will be identifying the correct secondary voltages, unless they are still visible on the label. Common marking inks used in the past seemed to vanish over the years so I hope this isn't the case.
The most likely transformer secondary voltages of that period would be 2 x 22V for rails voltages of +/- 30VDC but this is no longer a standard or stock item. Closest stock products are either 2 x 18VAC for 25VDC rails and 2x24 or 2x25VAC for 33 & 35VDC rails, respectively. That's quite a wide gap in the range but RS and Farnell have plenty at around 120VA rating and quite cheap since it's only a small transformer.
The most likely transformer secondary voltages of that period would be 2 x 22V for rails voltages of +/- 30VDC but this is no longer a standard or stock item. Closest stock products are either 2 x 18VAC for 25VDC rails and 2x24 or 2x25VAC for 33 & 35VDC rails, respectively. That's quite a wide gap in the range but RS and Farnell have plenty at around 120VA rating and quite cheap since it's only a small transformer.
Part of the rubber washer is visible in the image shown in post 21 . It should be providing an evenly spread electrical insulation of the bottom of the toroid from the chassis. Of this I have my doubts.
Sorry I do not understand your post re "electrical insulation".
This may be a language problem.
I was talking about soft/rubber mechanical "insulation" of
toroidal transformers.
This has been a topic in other threads also and is expression
of my long term design and repair experience.
RS232 even reported an open primary (no thermo fuse) - I
did not see this before with transformers like this one, except
in Japanese gear (they have 100 volts ac at home). Any fuse
should fail first ..
This may be a language problem.
I was talking about soft/rubber mechanical "insulation" of
toroidal transformers.
This has been a topic in other threads also and is expression
of my long term design and repair experience.
RS232 even reported an open primary (no thermo fuse) - I
did not see this before with transformers like this one, except
in Japanese gear (they have 100 volts ac at home). Any fuse
should fail first ..
The washer is made of rubber it provides a measure of double insulation as well as being flexible to take up some of the transformer vibration and expansion due to heat in the core and copper wire in the toroid.
Anyway Bananadriller is not following this discussion and appears to have cut his losses.
Anyway Bananadriller is not following this discussion and appears to have cut his losses.
I could see a black/dark area in the primary coil so I cut the secondary to see what was going on and found the melted cooper and my conclusion was enamel failure and never seen that before or after.
What I have seen is several failed thermal fuse on the E I transformer on the MK3
the only label i could find on this transformer was this 230V other than that i could find anything on the labels.
redone this test just to make sure and it still shows open circuit.
i am in the uk. i could really appreciate it if i could have it!!!
is there a way i can make sure that it was the thermal fuse inside the transformer or is that something risky to do.
if people would like design of the bottom of the pcb then i can send pictures or even possibly make a schematic on a program.
redone this test just to make sure and it still shows open circuit.
i am in the uk. i could really appreciate it if i could have it!!!
is there a way i can make sure that it was the thermal fuse inside the transformer or is that something risky to do.
if people would like design of the bottom of the pcb then i can send pictures or even possibly make a schematic on a program.
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Post #17 giving an open circuit result is 100% conclusive the device is open circuit. You have the two primary wires direct from the transformer... no resistance between them... it is open. If there is a thermal fuse then it would most likely be that at fault, however someone has posted in this thread I think and said that failure of these transformers is not unknown and there was no fuse present in that case. So it seems to be a recognised fault.
Thermal fuses on transformers are a safety feature and so we can't really advise on any course of action other than to either replace the transformer or, if the fuse was accessible to replace with an equivalent type.
A good safety tool for working on amplifiers and so on (that is safety for the amp more than you) is a the dim bulb tester (DBT) which is simply a 60 or 100watt filament bulb in series with the mains. That limits current in the event of a fault.
Thermal fuses on transformers are a safety feature and so we can't really advise on any course of action other than to either replace the transformer or, if the fuse was accessible to replace with an equivalent type.
A good safety tool for working on amplifiers and so on (that is safety for the amp more than you
) is a the dim bulb tester (DBT) which is simply a 60 or 100watt filament bulb in series with the mains. That limits current in the event of a fault.