Complete Novice would like to ask,,,

Hi Steve,

It is a critical part, I think it should be replaced with the exact or better rated part, but trouble is knowing what the rating is, and where to get such a diode.

Even service manuals may not mention the full part code, and it may not be sold by electronics distributors - some parts are very specific, and microwave manufacturers will have their own direct source from the manufacturer.

Maybe the best approach is to call the service center for the microwave manufacturer, and ask them if they will sell one. If they won't, they may insist on repairing it themselves if under warranty, or for a charge unfortunately.

Microwave ovens are dangerous pieces of equipment - but I suppose you knew that already. Take care when working with them - I won't be held responsible for whatever that may happen if you choose to follow my advice which is provided in good faith only.

Components are normally marked with their model number (which sometimes relates to a key rating) and optionally other details including manufacturer logo, date of manufacture, place of manufacture, batch numbers etc. This is often coded in a way which may not be apparent or openly listed. I suspect SK may stand for Sanken (https://pdf-datasheet-datasheet.netdna-ssl.com/pdf-down/H/V/R/HVR-1X-40B_Sankenelectric.pdf ) who may be the original manufacturer, whereas 2024 may be a lot-code for internal tracing.

I suspect HVR-1X is probably the main important part number to worry about, with HVR possibly standing for High Voltage Rectifier. Of course, some non-standard part numbers are specific to a few manufacturers, or sometimes even a single manufacturer, while sometimes other manufacturers may make compatible parts under different numbers. Other times you might find subtle differences in the rating of the components even if they have the same number but come from different manufacturers.

• If you know nothing about the design, the easiest option is to try and replace like for like, assuming the original design is sound.

• If you want to be safe but the identical component is not available, try substituting something with the same part number but from a different manufacturer. Usually the important key specifications are identical if they share a part number.
• If you still have no luck, you could substitute entirely different parts from other manufacturers which are targeted at the same application but ensure the key specifications are met (or exceeded to provide even more margin), such as:
  • Repetitive reverse voltage
  • Average forward current rating
  • Peak current rating
  • Leakage current
  • Recovery time
  • Thermal dissipation ability

Of course, the latter requires careful consideration of the part data available in datasheets to ensure a compatible or better replacement is found.

- Gough

hi Shabaz and many thanks for taking the trouble to answer, much appriciated, Ive been able to find a data sheet for the HVR1X and it appears that they did 2 types, 10,000 and 12,000 repetitive volts and forward voltage drop of 10 and 11 v respectively, all other specs are the same. The only HVR1X I can find for sale has nothing to say which type it is, and whilst I think there may be another figure after the HVR1X its burnt and impossible to make out.I see that some places are selling "universal" diodes, and somtimes they give a few for example part ref numbers, but alas not mine, but given the job I think it does in a microwave, I wonder if they can offer universal ones because the spec is not terribly critical. ,what do you think?

Steve.

Many thanks indeed Gough, really good of you to help out, Im in the Uk and its rather late now, I will re read your note in the morning and get back to you,,part of my problem seems to be that the appliance is obsolete and I think the Diode might be too,,,but Im learning a lot as I go along,

be in touch,

Steve.

No problems.

If it is an "obsolete" appliance, then there's a good chance that the requirements are not too demanding. Keep in mind that often components do advance as the manufacturers get better at manufacturing and fabricating them, so specifications can sometimes creep up over time - older appliances may be less demanding in general. A little higher forward voltage drop = slightly less power output and a little more heat in the diode. A higher reverse voltage rating = less likelihood of damage by spikes. There is wiggle room in the specifications, as even identically badged components can vary somewhat even fresh out of the factory.

Just be aware that there is a market out there which sells "refurbished" components which may have been salvaged and used prior, others which "re-mark" components which might change their ratings and sell for higher prices, and finally even counterfeit components. Sometimes, if a repair fails, it could be down to receiving a component that does not meet the marked specification, so it can pay to source from a reputable, traceable source in a brand new condition.

Considering that you are dealing with an older appliance which has a number of other components which would have aged, suffered from accumulated heat or high voltage damage over the years, repair is likely to mean extending the life by a few years or thereabouts before something else may fail (e.g. the transformer insulation, the capacitors or the magnetron tube). Sometimes it works out better to just buy a new unit rather than repair an old one, especially as features and efficiency may have improved over time.

- Gough

Hello and many thanks to everyone who took the trouble to reply during what is Im sure for everyone a very busy period, now the last post is intresting, esp as I eventually located the identical diode rateing and make,  listed as "new old stock, never fitted" on eBay and in Russia,,,,well you can immagine my thoughts when I read your post above,,however its $14 inc postage (which is probably expensive compared to similar diodes bought at home) but was the only one advertised anywhere that I could find, and would be cheap compared to a "part" bought from say an appliance parts supplier. The problem is that its a built in microwave which although now around 15 yrs old was both very expensive when we bought it and would be extreamly difficult to replace with another and still look neat and tidy, Im also a great fiddler, and really dislike the idea of just junking somthing without at least investigating it a bit to see if its practical to fix,,and somtimes one surprises oneself.

So Im awaiting the delivery of the russian part and will go from there. Having ferreted about on the internet trying to get a grip on how these contraptions work, I think that the diode's funtion is to bleed off excess voltage, being connected between the metal caseing (earth/ground) and the hi side of the mains transformer at the point where it connects to the large capacitor, its an arrangement that made me wince a little given the multiple warnings about the dangers associated with the capacitor,,but hey-ho one assumes the the german designers knew what they were doing! But looking at the fried diode makes you wonder where all that electrickery was going the last few times the microwave operated!  Is my assessment of how it functions roughly correct? The other thing I wonder is how critical the specs of the diode would be in that situation,,provideing it was up to handleing the voltage, and what makes me think this is that it seems you can buy a "universal diode", I didnt want to chance one if I could buy the correct rated part, but it does makes you wonder.

anyway, many thanks for your help,

all the best and the seasons greetings,

Steve.

Steve,

The diode is NOT to bleed off excess voltage. The diode forms a voltage doubler circuit with the capacitor to increase the already high voltage from the MOT to one high enough to fire the magnetron. It is vitally important to the functioning of the microwave. Sure, the casing is ground but that does form a part of the high voltage circuit as well as many MOTs share one connection in common.

You might need to do some study - for example, this generic circuit diagram for a microwave oven: https://www.researchgate.net/figure/Schematic-diagram-of-the-magnetron-operation-circuit-in-a-microwave-oven-The-switch_…

The secondary loop of the high-voltage part is connected to a half-wave voltage doubler which consists of a high-voltage capacitor C 1 and a diode D 1 . From this, Ϫ 5.4 kV is produced and is applied to the magnetron cathode.

This is why the diode needs a high reverse voltage rating and relatively fast recovery as the magnetron fires a set of "pulses" and the efficiency of the whole unit vitally depends on the diode being functioning, otherwise there won't be sufficient voltage to fire the magnetron properly anyway.

It might be worth reading this as well: Notes on the Troubleshooting and Repair of Microwave Ovens

The HV diode can fail shorted (most likely) or open. It is not likely for there to be anything in between as so much heat would result that the diode would not remain that way for long.

• A shorted HV diode will likely result in a loud hum from the HV transformer when a cook cycle is initiated. The main fuse will probably not blow. However, note that the actual wattage drawn from the power line will probably be much lower than under normal conditions. Although there will be a high current flowing in the HV transformer secondary through the HV capacitor (likely causing a loud hum or buzz), the real power consumed will be reduced since the current and voltage will be out of phase (due to the series capacitor) and the power factor will be low. A reading on an AC line wattmeter of 300 W compared to the normal 1,200 to 1,500 W would be reasonable.
• An open HV diode will result in AC instead of DC across the magnetron with a peak negative value (the only one that matters) about 1/2 of what it should be. The result will likely be little or no detectable heat but no other symptoms.

 

HV diode ratings

  Most replacement microwave oven diodes are rated 12 to 15 kV PRV at .5 A. A PRV of around 8 kV is actually required even for a small oven. Here is why: Until the magnetron heats up and starts conducting in its forward direction, what you have is a half wave rectifier/filter formed by the HV transformer secondary, the HV diode, and the HV capacitor. The reverse voltage across the HV diode will be equal to: 2 * 1.414 * (VRMS of the HV transformer). This can easily be 6 or 7 kV or more! Once the magnetron start conducting, the reverse voltage goes down somewhat.

 

HV diodes rated at .5 A are adequate for most domestic microwave ovens. For example, the largest of these will have a nameplate rating of around 1,800 W power line input and a HV transformer secondary of 2,500 VAC. While there are some losses in the HV transformer, and some power is used by the magnetron filament, controller, motors, and light, this still leaves, perhaps, 1,600 W into the HV generator. However, due to the design of the half wave doubler circuit, not all the power flows through the HV diode (as would be the case with a regular power supply. Thus, even though calculations using Ohms law (I = P/V = 1,600/2,500 or .64 A) would suggest that .5 A is not enough, closer to 1/2 of the total current actually flows through the HV diode.

 

To be doubly sure that your new HV diode is happy, run the oven on full power (high) for 10 minutes with two quarts of water as a load (or a roast). Unplug the oven (while your spouse prepares the veggies), quickly DISCHARGE THE HV CAPACITOR, and then check the HV diode for overheating. It might be warm but should not be too hot to touch. Unless you have the largest oven on earth, this test is probably not needed. 

Again, I will not be held responsible for whatever you do and whatever consequences may result - information provided in good faith.

- Gough