Hello,
I recently repaired a Pod Disco Light, because, instead of sequencing each lamp in turn, they were all lighting at the same time, appearing slightly brighter as the sequence rotated.
On inspecting the PCB, I noted that many of the resistors and capacitors had rusty component legs (possibly due to storage in a damp environment, or excess flux when soldering). Initially I was unsure what the fault was, so I ended up replacing the 100nF capacitors, the electrolytic capacitors (in case they'd dried up), resistors, ICs, triacs and transistors, just in case. Upon further inspection, I noticed that one of the 4 diodes (placed in a bridge rectifier configuration) was actually reversed, thus only providing half wave rectification of the mains to the logic circuitry. I also made sure that there were no dry joints, by heating up all of the solder connections and allowing the solder to re-flow. After giving the underside of the board a clean, I was ready to test the board again and was pleased to see that this had indeed rectified the issue.
I then decided that it would be a good idea to replace the filament lamps with Equivalent LED Lamps. However, after only a short time operating, the same fault re-occurred. I then tested the transistors and triacs and discovered that one transistor and 4 of the triacs had failed. So, at this point, I swapped the LED bulbs back for the filament lamps and replaced the damaged components. As the transistors were a type that I haven't come across before (S9013), I decided to try swapping one out for a BC549B (as I have loads of these) and the circuit still worked. It wasn't until I measured the gain of both a new S9013 and new BC549B, that I realised the collector and emitter were reversed! Therefore, I needed to put them in back to front, for them to work as required (I suspect that the incredibly low gain, when used in reverse was still sufficient to switch the triac, but not enough to amplify the microphone input, for sound operation).
I've attached a picture of the front of the board and one which I started to make, showing the tracks, as I intend to draw out a schematic at some point, to fully understand how the circuit works... So far, my understanding is that the input from the microphone is being amplified and driving the schmitt NAND oscillator at full speed, which sequences a decade counter through the six outputs and I've attached a CSV, detailing the components that I've been able to identify.
So, now I have a dilemma. Do I leave the circuit working as is, with the filament bulbs, or should I look for a solution to get it to work reliably with the LED replacements? I noticed on the PCB, that each output is missing a series resistor/capacitor across the anodes of the triacs. I suspect that the LED replacement's driver circuitry is inducing a voltage spike, that exceeds the 600V rating of the triacs? It would seem the series resistor/capacitors were removed from the original design (presumably to reduce cost), however I don't what values they would have been? But I'd welcome any thoughts on this?
I look forward to hearing your thoughts/suggestions.
Kind Regards
Edward
MOD:Made the Front image viewable.E
I recently repaired a Pod Disco Light, because, instead of sequencing each lamp in turn, they were all lighting at the same time, appearing slightly brighter as the sequence rotated.
On inspecting the PCB, I noted that many of the resistors and capacitors had rusty component legs (possibly due to storage in a damp environment, or excess flux when soldering). Initially I was unsure what the fault was, so I ended up replacing the 100nF capacitors, the electrolytic capacitors (in case they'd dried up), resistors, ICs, triacs and transistors, just in case. Upon further inspection, I noticed that one of the 4 diodes (placed in a bridge rectifier configuration) was actually reversed, thus only providing half wave rectification of the mains to the logic circuitry. I also made sure that there were no dry joints, by heating up all of the solder connections and allowing the solder to re-flow. After giving the underside of the board a clean, I was ready to test the board again and was pleased to see that this had indeed rectified the issue.
I then decided that it would be a good idea to replace the filament lamps with Equivalent LED Lamps. However, after only a short time operating, the same fault re-occurred. I then tested the transistors and triacs and discovered that one transistor and 4 of the triacs had failed. So, at this point, I swapped the LED bulbs back for the filament lamps and replaced the damaged components. As the transistors were a type that I haven't come across before (S9013), I decided to try swapping one out for a BC549B (as I have loads of these) and the circuit still worked. It wasn't until I measured the gain of both a new S9013 and new BC549B, that I realised the collector and emitter were reversed! Therefore, I needed to put them in back to front, for them to work as required (I suspect that the incredibly low gain, when used in reverse was still sufficient to switch the triac, but not enough to amplify the microphone input, for sound operation).
I've attached a picture of the front of the board and one which I started to make, showing the tracks, as I intend to draw out a schematic at some point, to fully understand how the circuit works... So far, my understanding is that the input from the microphone is being amplified and driving the schmitt NAND oscillator at full speed, which sequences a decade counter through the six outputs and I've attached a CSV, detailing the components that I've been able to identify.
So, now I have a dilemma. Do I leave the circuit working as is, with the filament bulbs, or should I look for a solution to get it to work reliably with the LED replacements? I noticed on the PCB, that each output is missing a series resistor/capacitor across the anodes of the triacs. I suspect that the LED replacement's driver circuitry is inducing a voltage spike, that exceeds the 600V rating of the triacs? It would seem the series resistor/capacitors were removed from the original design (presumably to reduce cost), however I don't what values they would have been? But I'd welcome any thoughts on this?
I look forward to hearing your thoughts/suggestions.
Kind Regards
Edward
MOD:Made the Front image viewable.E
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