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Old 22nd Nov 2021, 3:38 pm   #21
SLE_71R
Diode
 
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Default Re: Help with Old Musical Christmas Lights

Apologies - just seen you have already done so! Attached are the photos.
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Old 22nd Nov 2021, 4:05 pm   #22
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Default Re: Help with Old Musical Christmas Lights

This has gone from funding spare bulbs to repairing the controller, does the wiring need replacing next? Now I'm being rather sarcastic!
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Old 22nd Nov 2021, 4:30 pm   #23
SiriusHardware
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Default Re: Help with Old Musical Christmas Lights

Number ending ...004 makes the diodes possibly 1N4004

The image resolution is a limitation we just have to deal with, if you want to show a detail like numbers on a part or group of parts you need to take a macro close-up of them or crop only that small area out of a large high resolution image of the whole board so that when the image is attached to a post and reduced to 800 x 600 maximum, the detail you want to show is still legible.

Edit: Sorry, I see you have already posted some additional good images.
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Old 22nd Nov 2021, 4:34 pm   #24
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Default Re: Help with Old Musical Christmas Lights

Quote:
This has gone from funding spare bulbs to repairing the controller!
Indeed, and is all the more interesting for that.
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Old 22nd Nov 2021, 5:57 pm   #25
Glowing Bits!
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Default Re: Help with Old Musical Christmas Lights

After looking at the 1st picture, I can see why the diodes would create more heat than usual, it's got an audio amp in there!
Edit: the big electrolytic looks like it's starting to bulge, no surprise with it being next to hot components!
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Old 22nd Nov 2021, 6:48 pm   #26
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Default Re: Help with Old Musical Christmas Lights

In addition to the above observation, the lamps DO run on the (rough) DC output from the bridge - the +Ve of the bridge diodes snakes its way around to the common 'C' terminal so that is the common +Ve supply to all of the lamps. It doesn't look as though the +ve supply to the lamps is smoothed though.

In one of the pictures one of Q4-Q7 can be seen to be an SGS-Thompson XL0840 - an SCR. the other three can be assumed to be the same type of device.

https://www.st.com/resource/en/datasheet/xl0840.pdf

The 'k' terminals of the SCRs are all commoned and go via a roundabout route to the -Ve terminal of the bridge in one direction and to the GND / 0V of the control module in the other direction.

The +ve output from the bridge also goes separately through two 560R resistors in series (R1, R2) to the +ve end of the zener diode ZD1 whose -Ve end goes directly to the -Ve side of the bridge, so this zener is the basis for the 'regulated' supply that the light sequencer / tune module runs on. That is as far as I have traced so far power-wise. One or more of the transistors near the zener may be used to buffer its output.

One of the transistors Q1-Q3 is a 2SC945 which is a common NPN transistor.
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Old 22nd Nov 2021, 8:12 pm   #27
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Default Re: Help with Old Musical Christmas Lights

Here's a slightly closer view of the track side with a few details sketched in, like the bridge diodes, the zener, and the 100uF capacitor. It looks as though the voltage regulator / stabiliser consists only of R1+R2 and the zener and the 100uF (domed) capacitor.

Red trace = raw (unsmoothed) DC from bridge +Ve
Green trace = 0V / GND track, starting from bridge -Ve

I can see that terminals of two of the transistors right in the middle of the PCB go to the speaker output terminal 'S' via an electrolytic, so that looks like the audio output stage.
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