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Hi I'm just getting to the bottom of breaker tripping out and have put it down to a diode but it's very burnt and I can't identify it maybe someone can its diode D7 please see the pictures of it on and off the board.
Barry
The four diodes together right above the "victim" on the board look like they are a full wave bridge rectifier. One like the blown-up one out by itself in the middle of what is probably a power supply is likely a Zener diode to either produce a regulated voltage or catch voltage spikes before they harm something sensitive.
I see a "6" or a "5" on the "horizon" of the device in your middle picture. Can you read the other digits in this number?
("IR" stands for International Rectifier: Power Semiconductor manufacturer for many decades, even if I'm semi-guessing at the "R".)
"1Z22 T5" is basically everything we need to know. For example, if you look at D7 in the schematic above, "1Z22" is scrawled handwritten next to the device (Back when people created schematics with pencil! I did in high school.), so we are definitely on the right track here.
This device is wonderfully obsolete: I found it in a 1962 International Rectifier catalog on a website called "Steam Powered Radio":
(Catalog page 10, Right hand column, almost to the bottom)
It is in there as a Zener Diode, 22V, 1 Watt, 5%.
If my parents had bought me semiconductors as a baby, this may have been one of them! (-I wasn't ready until I was a teenager.)
We are probably never going to find you one of these, but that's OK. There should be many modern, better, commonly available equivalents that weren't designed when Winston Churchill was still alive.
This device is polarity sensitive: if it gets mounted backwards you will be just as bad off as when you started. There is a black band marked on one end of the device body. In your picture up at the top of the thread, this band would be on the right-hand end of the device if properly mounted.
Putting an ohmeter on R3 and verifying 600 Ohms is a good plan too. When D7 shorted it probably got very hot.
Thank you very much for all your help with this one.
I'm sure it's a Heat problem as the thermal fuse had also blown this was all due to running the machine with no fan belt being fitted.
as soon as the new diodes arrive ill message you with the resorts.
Barry
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