Repairing a toaster - theory and practice. (Also repairing televisions and the ST9400C Honeywell central heating programmer.)

Replacing failed electrolytic capacitors.

This webpage is mainly about mending toasters, and replacing electrolytic capacitors in general.

I  have mended probably a dozen toasters for various friends (usually female ones).

Here are a few tips, for cases where the operating lever refuses to stay down - which is the usual problem.

WARNING - if you take a toaster to pieces you need to know what you are doing. Be careful if you plug it in for testing while it is still in pieces. There can be many exposed and live electrical connections. If it is unplugged from the mains, the dangers are mainly from sharp metal objects.

1. Toasters are not meant to be taken to pieces. Manufacturers claim this is for safety reasons. They really want you to buy a new toaster. So toasters are usually screwed together with 'tamperproof' screws of various designs. You need a set of special screwdriver tips to circumvent this issue! Available on eBay for about £4.

2. It is usually necessary to use brute force to remove the operating knob (the knob or lever you push down to start the toaster) from the metal bracket to which it is attached. This is often most easily done when you have the toaster partially taken to pieces, and there is easier access.

3. Older toasters do not include electronic components. They operate simply by means of a current through an electromagnet holding down a metal plate. The most usual cause of the lever refusing to stay down is a build up of bread crumbs or other residue on the metal plate or the electromagnet itself. Sultanas can be particularly troublesome! Simply clean both the surfaces, scraping off all the deposits, and any rust, and all will be well (usually).

4. Modern toasters have electronic control of the hold down as well as the timing function, but the same problem as above can still be the sole cause of the lever refusing to stay down. So try that first. You can sometimes do this with the toaster in bits - but be careful not to touch any live wires or connections.

5. Where the electromagnet and plate surfaces are clean and the lever still refuses to stay down, the most likely problem (one I have fixed on at least six occasions on different models) is failure of a smoothing capacitor. The cost is about 70p, but you need to know something about electronics, and you need a small soldering iron. Or (much easier if you are a woman) you need to know someone like me.

Capacitors are essential components of almost all electronic circuits, anything from central heating programmers, televisions, radios, and microwave ovens. And much more besides. They vary in size from a small garden pea up to a can of soup, or larger......... The high voltage capacitors inside a microwave oven are VERY DANGEROUS. So don't take a microwave oven to pieces unless you know what you are doing. But toasters are much less dangerous - once they have been unplugged from the mains.

Capacitors can be grouped roughly into electrolytic and non-electrolytic types. This is a gross oversimplification as there are many different sub types. Electrolytic capacitors have a high capacitance for their size and are much used for smoothing waveforms in switched mode power supplies, for example. A glut of inferior capacitors made in Taiwan was alleged top be responsible for what is called the Capacitor Plague (ask Google for hundreds of references). Probably millions of computer monitors and computers were junked in the years 2002 to maybe 2010 simply because people either didn't know how, or couldn't be bothered, to replace a few capacitors. I have mended many switched mode supplies in television sets - often a television can be fixed for about £3. If you know how! These days (2025), electrolytic capacitors still fail, but less frequently. When you study how they are made, the miracle is that they work at all, let alone sometimes for 20 years or more. In many circuits, neither the exact capacitance value nor the ESR (Equivalent Series Resistance) is critical, hence devices continue to operate even with degraded capacitors. Whilst the capacitor plague was a specific series of problems within a specific time frame, problems with capacitors of this generic type continue, albeit at a lower level.

A lucid video explaining the early years is here - and read many of the comments also, especially those describing how lucrative the computer and electronics repair business was in those days!

In 2025, all the old problems of electrolytes should be history - but failed capacitors are still a regular cause of failure of televisions, for example. Poor circuit design, excessive ripple loads and fake capacitors are probably all factors. In buying replacements from eBay and similar online stores, you never really know if the capacitors you use to try to fix a failed TV are going to be any better than the ones you replace. Fake products affects car parts also - genuine NGK iridium spark plugs for example can cost almost £50 each but fakes are widely sold.

For anyone interested in planned obsolescence and car engine manufacturing - try this video. It makes the manufacture and repair of televisions and toasters seem rather tame.

But back to toasters.

Modern toasters have an electronic circuit board that controls hold-down and timing, as well as extra functions such as defrost and reheat. These circuit boards often cannot be repaired - except (helpfully) for the one component that often is the sole cause of the problems - an electrolytic smoothing capacitor. Sometimes toaster circuit boards will have two capacitors, one for timing and one for smoothing, but the timing function is often digital anyway. What happens (and this is the problem in televisions, central heating programmers and many more devices) is that partial failure of an electrolytic capacitor can degrade the quality of the DC power supply to a microprocessor or other sensitive bit of electronics, so it then refuses to work properly, if at all. Replacing the capacitor can, as if by magic, make the rest of the circuitry work again. It is quite satisfying to do this!

	Here are a few pictures of modern toasters. You need to find the electrolytic capacitor, read the values on it (microfarads and voltage, maybe 100uF and 25V) and replace it with one of similar or slightly better rating. And preferably use a high temperature rated capacitor (105C). If the old one was 10V or 16V, you can replace it with 16V or 25V, but not the other way around. The voltage rating must be at least as great as the original. If the capacitance was 100uF (microfarad) you could probably use a slightly larger valve (150uF for example) but a smaller value might not work. It need not be the same physical size - in  my own Philips toaster (shown here, and which is a very well made unit) I used a capacitor that was physically too large to fit where the original one had been, and it works fine. This one is 470uF and 16V rated. I cannot remember if the original was less than 470uF. You MUST replace electrolytic capacitors the right way round - see below.
	This is the circuit board from a cheap 'TOWER' brand toaster, the sort of thing that is sold by discount stores and on-line for about £12. Two capacitors are on the right of the picture, The small one at the top was not replaced, the longer one marked 100uF and 25V was the cause of the malfunction. The resistors (grey, with stripes) are a very crude way of dropping mains voltage down to a level that can be utilised by the electronics - a cheap and cheerful design, and all made in China, of course. You MUST replace electrolytic capacitors the right way round. The board will usually be marked, but take a note of the old capacitor before you unsolder it. The negative side often has a stripe down the side with a - (minus) sign on it. This board has a clear + sign.
	The reverse side of the circuit board. The chip with about 16 soldered legs is a tiny microprocessor and cannot be diagnosed or repaired if it goes wrong. But the usual problem is simply its power supply - and, often, that can be fixed just by replacing the smoothing capacitor. The rest of the components are diodes or tiny surface mounted resistors or capacitors - again these cannot easily be diagnosed or replaced. If replacing the smoothing capacitor doesn't make the toaster work properly again - simply throw the whole thing away! You can buy electrolytic capacitors on eBay for about 50p each, plus postage.
	And now - a true story for every woman who would doubt my abilities. In early December 2024, a dance partner telephoned me to say that her Honeywell ST9400C central heating programmer had stopped working - no display, no heating, nothing. I went round to check the fuse and basic connections, but concluded that the programmer itself was at fault. She refused to have her boiler system temporally wired so that it would still work while I tried to mend the programmer - but she did say I could have the old unit. Subsequently, she has refused to tell me how much she paid for a local firm to replace her programmer with an identical model - I would guess £100 plus £100, or more, call-out fee and labour charges. It probably took them about 5 minutes to snap the new programmer into the existing housing, no rewiring would have been necessary. When I was eventually given the old unit, it took me less than an hour to dissemble it, replace a couple of electrolytic capacitors, and have it working again. (Cost =£1) Honeywell made it quite difficult to take their programmer to pieces, and 1:1 capacitor replacements were impossible, owing to how the originals had been fixed in place. I had to prise out the old units (shown at the top of this picture) because unsoldering their bases was impossible, the board having originally been flow soldered.
	I used a couple of equivalent capacitors, soldered to alternative locations and glued in place, and with bits of cardboard as an insulating layer. These are 63V and 22uF each, and located across the 48VDC supply rail. Helpfully, there were four linked locations for capacitors on the circuit board so I could mix and match where I soldered in the new capacitors, some of the original locations having been damaged when the old capacitor bases were forcibly removed. The large blue X2 rated capacitor at the bottom of this photo is the main voltage dropping unit to provide low voltage for the electronics from the 240VAC mains supply. This too can give problems (as do similar units in very badly designed Sunvic actuators) and cause low voltage to the 48VDC relay coils. This will in turn lead to irregular operation - sometimes the heating will come on, sometimes it will not, as the relays fail to operate. The cure here is simply to replace the blue capacitor with an equivalent X2 rated unit. The back-up battery for the internal clock is a CR2032 - as used in all desktop computers. So I had several in stock! I subsequently sold the repaired programmer.

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Repair of Sunvic motorised actuators in central heating systems.

Mending an old Honda lawnmower  I just wanted to see if it was possible - three years later the mower is still working perfectly.

Various links to mending of Saab 900 classic cars