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Old 28-10-2016, 23:16   #1
PhilipOneL
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Capacitors blowing in MorphyRichards 27024

I brought my MorphyRichards 27024 in to my local electronics repair shop a week ago and it finally moved up to the top of the queue for repair today. I had ordered (thanks to Neil GOSVN) and received a new rotary encoder and the plan was for the technician to install it for me.

When he opened it he discovered the top of one capacitor had been blown off (by overheating?) and the cover of another was swelling. He is going to replace both of them for me.

This set was at our out-of-town weekend place which we don't get to for weeks on end sometimes. I wonder if the damage was a case of the radio turning itself on in my absence, running unobserved for weeks, and finally overheating itself. Has anyone had similar experiences? (Certainly the MR27024 is well known for its turning itself on.)

Apparently both capacitors continued to work because, except for tuning troubles on the rotary encoder, the set continued to function.

. . . Or: is it possible that the lack of one or both capacitors caused the (otherwise good) rotary encoder *not* to do its job?


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Old 30-10-2016, 08:58   #2
Digger
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Did you take note of the component numbers (i.e. C100)? Electrolytic capacitors are prone to swell or even explode if the voltage rating is too low. I would think those two were in the power supply region of your Morphy.
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Old 31-10-2016, 16:38   #3
PhilipOneL
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That is interesting, but - no - I didn't note the capacitors' values or other numbers. The technician, however, read them both when I dropped by and he was looking for replacements. I believe I saw three similar-looking capacitors on the board when he showed me. Two were smaller than the third. One of the two small ones (the one closest to one of the sides of the circuit board) and the big one (which was closest to the other side) were the failed ones. The one in the middle seemed to be okay.

On the power rating, when I originally received my MR set, it came with an AC adaptor that was made for the UK mains supply. I tried several new ones before I found one that neither overheated, since the MR draws so much power, nor produced too much noise for the DRM to be decoded. I am using a linear adaptor made by Triad, a 9 volt, 2.3 amp jobby. It's large, and runs just barely warm but perfectly silently with regard to RFI.

The technician tells me he'll have some more word on my radio the end of this week.


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Old 17-11-2016, 13:46   #4
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Update, 17/11/16.

My MR27024 is still in the neighbourhood electronics shop. The manager called yesterday to say it was ready and that he had good news: replacing the condensers (and a transistor in another circuit) made the rotary selector work. So he didn't replace the selector.

But, sigh, when I arrived and checked it out, the rotary selector was still almost entirely inoperative. (It *is* a complicated radio that he had no idea how to operate fully.) So I await their work on replacing the rotary selector as I wanted them to do three weeks ago. . . .

But there is something learnt from this. The condensers (capacitors) have a tendency to blow up and burst and my local electronics shop does not know why. ("That just happens sometimes; we see it a lot in TVs too.") If it is a matter of low power, as Terje suggests (above), then I wonder if it happens when the radio turns itself on unattended (a very common complaint about the MR27024). When it turns on like that, everything seems to be operating except that no sound makes it to the speaker, while unamplified sound *does* get delivered to the Line Out. If this oddity is a matter of coming on with low power, too low to drive the amplifier, then it may explain the exploding condensers problem.

In turn, I wonder if this can help explain why the MR27024 turns itself on.
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Old 12-12-2016, 18:46   #5
PhilipOneL
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Just to complete the record here:

Today I picked up my fully operational MR27024. Testing it, I have it working in one room with only its own whip antenna, and it seems to be as good as my other MR27024 in another room with an outdoor wire attached.

It took the shop nearly two months to get it all fixed. In putting it back together two weeks ago, the technician did something that kept the left-most bank of front buttons from operating. That's all corrected now.

I don't mind that they had so much trouble getting it working. It's a two-brothers-outfit and it must be the most peculiar model of radio they've ever had in their shop. I was pleased to be able to turn it on in their shop today and (just with the whip antenna) pick up a perfect signal of AIR's DRM to show them what it does. The brother I was dealing with was impressed.
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Old 18-10-2019, 20:22   #6
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Hi.
I opened my radio to replace RTC super capacitor with a AA/AAA battery, and found a blown capacitor (EC100 3300uFx25V). Replaced by a 2200uFx25V from my junk box.
I don't know how or when this happened.
https://i.imgur.com/ZtSwJ4H.jpg
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Old 21-10-2019, 20:30   #7
PhilipOneL
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Is the replacement of the RTC super capacitor in order to retain the time & date information after unplugging the set?
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Old 23-10-2019, 21:17   #8
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Quote:
Originally Posted by PhilipOneL
Is the replacement of the RTC super capacitor in order to retain the time & date information after unplugging the set?

Yes, I removed super capacitor and replace by a 1.5V alkaline battery, to avoid charging, add a 1K resistor in series. Positive side of battery is available on pin 48 of module header.
This pin rated to 1.6V and output 1.47V when plugged to AC.
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Old 08-11-2019, 01:13   #9
PhilipOneL
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Thanks, Paulino.
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