Akai power board diodes

[brymac]

Two diodes on the MC-5208 power board of my Akai GX1820 have gone up in smoke. They are listed in the service manual as ED224526 - can't find that reference outside Akai..

What are the correct replacements please?

[paulsherwin]

I think these are just silicon rectifier diodes like the 1N4007. I'd take a look at why the originals failed before proceeding though.

[brymac]

Thanks - what happened is that after many years of regular use, I accidentally left the unit on all night and in the morning there it was dead with the 1amp fuse blown. I replaced the fuse and was greeted with smoke coming out from the vents at the top. Stripped it down (I have the service manual and have had to take it apart often over the past 10 years!) and found two frazzled diodes!!

I've ordered a replacement power board from the US, but it will take a time to arrive. so I thought I'd try replacing the diodes on the duff board to see what happens......

[AC/HL]

The Google trail seems to indicate IR 10D1, a plain old 1.5 Amp diode

[ms660]

As Paul said, you need to investigate as to why the diodes went duff, C4 is the reservoir capacitor for the DC output which as far as I can make out supplies the audio power output transistors TR1 & TR2 and there oppo's in the other channel, it also supplies power for the erase/bias oscillator via the record switch and also via the transfer switch if the transfer function is selected.

If it should turn out that the audio output transistor or transistors are shot then I would also think about checking or replacing the loudspeaker coupling capacitor C6 or it's oppo. in the other channel if the loudspeakers were connected when the fault occurred.

Lawrence.

[brymac]

Many thanks - I saw IR 10D1, but didn't realise the significance.....

Bryan

[brymac]

Lawrence - thanks, but this is the 1820 - the one without the amps or speakers, not the 1820D which has them!

Bryan

[brymac]

Sorry - another senior moment!!!!

This is the 1820D - the one without the amps or speakers, not the 1820 which has them!

[ms660]

It's best to include the make and model in the thread title.

Lawrence.

[brymac]

Indeed - sorry!!

Attached are some photos of the burnt out diodes in situ, together with the overall and more detailed power board schematics. The burnt out diodes are D1 and D2.

I have a replacement board on order from the US, but meanwhile will remove the existing board and test the other components - although I am aware the cause may be elsewhere - or not to be found at all if the diodes have self combusted when the thing as left on all night!!

I'll then replace the diodes and and other suspect components and then reconnect the old board to see if that resolves it - but will have the back up of a new board arriving from the US.

Bryan

[paulsherwin]

There has been some serious overcurrent there. The only component on the board I can see that would cause this is C4.

[brymac]

Yup - I have my beady eye on C4!!!

Bryan

[brymac]

Yup - C4 S/C; it's a big fellah 2200uF 35V. It took out the two diodes by frying them....!!

Thanks all...

Bryan