Mulja tv repair portal
General => General Forum => Topic started by: OldLes on August 11, 2012,17:19:36
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My Panasonic SD-255 bread machine gave a seriously under baked loaf this morning. I have established there was no mains supply "outage", so I think I need to repair it. First thoughts are temperature sensor, but it would be useful if anybody could help me with a service manual.
OldLes.
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Hi Les,
Know little apart from the fact they were recycing sites best biz a year or two ago.
Best thought - there is always a thermal fuse somewhere on all modern stuff, programmed to phut a week after guarantee expires,
Or so it seems - plenty of thermal fuses on Ebay, if it's the biz - Chris.
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Hi Turnip. I have had a few BMs from our amenity site in the past. Hinari, Morphy Richards etc., then I picked up apanasonic SD253, without the tin. A pal (an inveterate amenity site scourer) already had an earlier model, so I borrowed his tin, and was very impressed with the results.
There came up this NEW SD255 on Ebay two years ago, but "Damaged case, not tested" so I put in a £24 bid 6 seconds before the end, and got it for £16. I just had to bodge up the bit of broken plastic, and fit it all together. Two years of good healthy wholemeal bread (I make the best bread in the world), so not happy when it played up.
My pal has meanwhile collected a couple of SD254s, which are identical except for not having the automatic nut and raisin dispenser, which I use. I collected them off him this morning, to get bits from and compare.
The control panel and the "main board" have very minor differences, such that the Sd254's could probably be modded to fit SD255 if required.
So far, thermistors read the same, and the elements, and the fuses are intact. However, on my machine, the thermistor was not properly in place. Has it moved? Would it matter? It may sense radiated heat, it may require good conductive connection, I don't know.
The on-board battery (capacitor) reads zero volts, which it should surely not be down to since Saturday. But does it matter?
Tonight, the old SD253 is baking, with my own tin inside, giving me time to see if the capacitor will take and hold a charge.
I have an ancient Rayburn OF22, so on Saturday, I stuck the unbaked loaf in there for an hour so we had bread, so no disaster. With the SD253 there is time to sort it out properly, and now plenty of spare bits to use. It already has new plastic bits from one of the SD 254s, so at least it will look better if I fix it.
But that manual just might give some clues.
OldLes.
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Hi Old-Les, you're a hero.
Confess I get bread - reduced from 'Morrison's' - not so healthy but doesn't give me 'New bread Gypp'
Your thermisters however, get me confused -They were originally an 'N' device to stop dial lamps burning out on valve radios on switch-on - they then morphed to became 'P' PTC with early colour degauss circuits to give an initial surge.
Still see a few in modern tellies (N) types to prevent surges, not yet seen one in a breadmaker, and if so - why - Over-temperature fuses however are much the biz to prevent spurious houses into 'toast' claims
Off to Morrison's - again - Chris.
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Turnip, the thermistor has long been used for temperature control.
Resistance varies with temperature and so it is a simple matter to have various control points programmed into the microprocessor. The 26K is the room temperature value. It is NTC, so falls a little for the "rise" period(s), and even lower during the "bake" period.
I had a Minolta photocopier 30+ years ago, and as I recall, it had a thermistor to control the temperature of the heated output (fixing) rollers.
If you dig out one of your little "Mullard data books" (I have a 1979-80 version open right now) they give details of the various NTC and PTC types available back then. If you go back to the "Theory", then, with the "beta" values shown there, you could use any of those available back then for temperature measurement.
I put the SD255 back together last night, and will probably try it out on Friday evening, and see if it is now fixed (why???) or still faulty (why???) and will report back later.
OldLes.
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Hi Old Les,
Glad you put me to rights, had forgotten so much 'till reminded. Not seen many thermistors in recent years, but there again, as only mend stuff that doesn't generally use 'em.
Will try get out more and find decent flour - Thanks, keep it up, will re-read my Mullard Data books, if I can still find 'em - Better than '50 shades', most folks say - Chris.
PS - Changed Varistors to Themistors eventually remembering they are quite a different beast.
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Well, we baked another loaf in the "faulty" Panasonic SD-255 overnight, and all was OK.
As I said previously, I had found nothing amiss, so it was a bit of a mystery. There was just one thing I remembered, and that was its indicator LED was "ON", whereas it normally beeps about six times then goes quiet, but the LED flashes. When I removed the loaf today, I left the machine switched on, and five hours later, it was still flashing.
Conclusion: There must have been a temporary mains failure early within the final hour, long enough to discharge the memory capacitor, so the programme did not resume. I had made a point of ringing the local board, as I suspected this as it seemed to fit all the symptoms, but was told "no outages". Now I don't believe them.
Over the next weeks, I will monitor progress, but I am pretty sure!
Meanwhile, it would still be reassuring if a manual ever did come to light. Who knows, one day it may really fail.
OldLes.
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Hi Old Les,
Guess mains powered clocks would have given the 'outages' game away - spent an extra day in bed after the last one when the morning alarm didn't fire - Missed BBC4's 'Sunday' where world might well have ended before I enjoyed my usual breakfast toast - Toast was still great - ever Optomistic - Chris.