A quick question for Justin (probably)

[Imagine]

Afternoon all

Hope you enjoyed Coalville (I WILL be there next year)

OK - It's years since I poked inside a bulgin chaser, but I have a problem whereby when it's in sound to light mode (rather than just chasing), the bulbs are hardly lit, if at all (strangely in just ordinary chase mode, they're as bright as they should be).

I have a nagging feeling from many, many years ago that this involved changing the TRIACS? (correct me now if I'm wrong).

So, have had a quick look and the info I can glean from the microscopic etching on the side of them is that they're BTA16-600B.

Now, being a bit of a thicky when it comes to electronics, I know the first bit is to do with current, and the second bit (the 600B) is the voltage and the case style.

Bearing that in mind....I found these. Would they be a suitable replacement?

[Nakatomi]

They would indeed Wayne.

Though one thing is puzzling me. Why the gate ( the signal on the triac which controls the switching part) would decrease in sensitivity. If the chaser part works I'd not put my money on the triacs. Instead I'd go looking for a dud capacitor in the audio side of the s2l circuits.

[Imagine]

Yup - been doing a little bit more reading up since I posted this one and on third and fourth thoughts, it can't be the triacs otherwise nothing would flash.

Time to get the test meter out tomorrow and do a little more prodding methinks

[Nakatomi]

What I would likely do here if I were you is:

Equipment required: Variable voltage bench PSU. An oscilloscope or small amplified speaker

Visually locate low voltage power rails on the board. Clip power wires connected to the bench PSU onto the rails noting the polarity (you could also go onto the output of the small internal PSU's bridge rectifier). Turn the bench PSU voltage down to minimum & switch it on. Slowly & carefully increase the bench PSU voltage until the controller seems to operate correctly.

Then, trace the audio signal from the microphone (or input socket) on the controller & check each stage.

Since the controller is ancient the culprit is likely an old decoupling capacitor or 2 - they're used between stages of the circuits to block DC and only pass audio through them.

I would seriously advise against doing any kind of testing with it plugged into the mains.