I need a mains transformer (o/c primary) for a A-H300. I can source one for a A-H300mk2 do you know if they are the same? part number on the tranformer is KLT5P035YE Regards Dave

If the primary of the transformer has failed it doesn't follow that the main power supply parts are also faulty. However since the transformer is a safety part you need to replace it with the same thing.

However it seems from this website that transformers are not expensive compared to a new deck, so a look around here might solve the problem.

I know this thread is a couple of years old, but this may help someone with the same problem.
There doesn't seem to be a supply of A-H300 transformers for direct replacement, but you can utilise the transformer from the MKII version of the amplifier with a little modification.
The output voltages from the MKII transformer are exactly the same, but two of the connectors have changed, so you will need to salvage these connectors from the original transformer to modify the MKII version.
The physical size is also a little different, but it will fit. I found that I had to remove the excess 'tags' that remain on the lower circuit board to give enough space for the transformer to align with two of the original mounting holes & I drilled one extra hole in the replacement tranformer baseplate so that a third screw could be used.
Hope this helps someone!

Without Knowing the Output Chip or transistor Numbers, I don't know but Most 100 Watt anps use 60 to 70 Volt Centertap Sacondarys. Also if You Take the Cover off The Transformer you will find a Thermal Fuse in the Primary. I have bypassed the Thermal Fuse and went with a external fuse, Go for it.

These models are known for this issue.
I've had my share in the shop here.
Disconnect all speakers,turn speakers off, try headphones only
If it still persists then there is either :
1. power supply capacitors gone bad or 2. The thermal fuse in the transformer is open.
A tech can very easily find out if the thermal fuse is open by checking the primary of the transformer
if the plastic is shrinking away from the power supply capacitors then they've gone bad

I would contact Sherwood as Transformers are deemed to be safety components and should be replaced with excat parts or those recommended by the maker.

You would need to rewind the coils.Do not try to do it by yourself if you have no idea what you are up-to...this time it was transformer next time it could it could be your circuit.Take it to a professional,the charges won't be much.
Good Luck.

Probably the thermal fuse in the main power transformer. Check for ac on both the primary and secondary of the transformer. If you have 120v ac on the primary when the standby light is off and nothing on the secondary you need a new transformer.

The transformer on these units contains an internal fuse that may have blown. With the unit unplugged, measure across the primary winding of the transformer. It should read low ohms. If you get infinity, the primary is open and will require replacement.

Dan

I have replaced many thermal fuses in power transformers. Is the primary open?? If so, cut the copper shield on the primary side of the transformer with a pair of cutters and peel back the paper insulation to reveal the thermal fuse. Replace it and everythings OK!! If the secondary is bad there's no hope, of course. Anyway, in the meantime I will research your question and post again very soon. I have several old pioneer schematics and know where to find what I need.

Hi Keith

You can often replace the thermal fuse yourself often, just got to dig for it under the layers of tape and insulator. They often have tinned leads,. If you are outside the USA, you can even just bypass it, so long as the amp still has a fuse in the primary mains cct. Its about preventing fires here, so if you are not sure then don't mess with it.

regards
robotek