I probably have 400mW zeners in voltages which would add up to 22 or thereabouts, Mooly. Amongst others, I have some 5v6, 9v1, etc., but, as I have to get some 22R Fusible resistors, I may as well at the same time get a 21 or 22v ZD,
You might find the fusibles hard to come by and they are often expensive. If the fusible had failed then it seems likely the original fault was with the transistor, perhaps a C to B short or leak and that in turn zapped the zener. A zener failure alone would not take out the 22 ohm.
The fusibles are a 'safety' item but in low voltage stuff like this it is as much to stop the customer seeing or smelling smoke as much as anything should a fault arise. An ordinary quarter watt resistor can make quite a bit of smoke and smell if it burns, and that scares the punters 😉
The fusibles are a 'safety' item but in low voltage stuff like this it is as much to stop the customer seeing or smelling smoke as much as anything should a fault arise. An ordinary quarter watt resistor can make quite a bit of smoke and smell if it burns, and that scares the punters 😉
CPC sell 22ohm fusible resistors at reasonable prices, but are out of stock until late November. Oh, well, that's life! However I have found a pack of 10 Vishay F.R's on eBay for under £2.00, so have ordered them instead. Should now be able to repair the HK1400 by the end of this week or early next week.
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