Can anyone help me to work out what’s going wrong here? Happy to asnswer any questions - am new to soldering in general, so I dont have a voltmeter but can get one if it’s a good idea and would help isolate the issue.
I have emailaed the museum to see if they have any other circuitboards lying around, this one was a b-stock left over, could be broken , or more likely I broke it!
multiple sharp hi-rez photos of the both sides would be helpful.
I gotta say, seeing the ICs soldered in really bummed me out after hearing that “wrong components” were used at one point – but that’s not your fault. Just for the future … always socket your chips if you can. It’ll save you so much headache if you end up needing to replace them. If you have a multimeter what voltage do you see between VCC and Ground on each of the chips? 
EDIT: I see now that you don’t have a voltmeter, so we’re doing this visually. Let’s get some good photos.
Thanks! Here are some high res pics. If you want more let me know - I also have a multimeter coming tomorrow so I can answer on the voltage, I imagine that will be more helpful.
Impulsively, I went without the sockets as when I had time for the project initially, they were the only thing I didnt have. So yes, lesson learnt. That said, it’s one of the things I didn’t have to mess around with, and happy I got them the right way in and (I think) the right chips, but that could be my problem. I got NE556 instead of LM 556 but apparently they’re interchangeable..?
Everyone learns this lesson the hard way i think so dont sweat it lol.
Some things leap out to me:
This joint looks like it could be re-flowed. (add a bit more solder to use the flux inside to pool the solder with surface tension to apply across the pad more universally)
Possibly this point too (the middle 556 chip):
With it making sound, but being wonky, its usually something like this. When you dont have a clean solder joint, the voltage could be inconsistent. The way this circuit works, the 555/556 timers work off the
This is a video by ben eater on making an astable 555 timer. He covers how this works in more detail. Essentially if the voltage is off because of a floating or semi-floating solder joint it messes with the comparisons. Like, the circuit is built such that a comparison is made between voltages and will oscillate when it latches etc.
It sorta working is a good sign.
thanks for all your help so far - i tried resoldering these joins, but the output is the still the same.
I would reflow EVERY joint for what it’s worth.
Have you ever powered this (or attempted to) with anything other than the 9v battery?
If you mean all the 556 pins on each chip, then I did that at the same time, alongside the cap you pointed out. I haven’t gone over the whole thing, but I can do that next.
Many thanks,
Sam
I mean the entire thing. I still end up doing that as a first step when I finish a module and “shit don’t work” right away.
thanks - it’s like glue of some sort, i took a little bit off but i’ll try and get it all off and ensure nothing is damaged underneath.
Hi I’ve checked each one with a multimeter:
U1 = 8.14V
U2 = 8.13V
U3 = 8.07V
my battery read 8.40V
@Caustic I can confirm this is a little bit of glue it rubs off and no damage underneath.
tried it with a DC power supply of 12V, I get 10.xx V between each VCC and GND on each chip, and it sounds different, but still high pitched and very low dB.
Is it center positive? I’m not sure I can be much more help here. My guess is that either something got fried early on or isn’t soldered well. Those voltages are fine now but if they ever went negative for whatever reason (wrong polarity supply) then the chips don’t look like they’d be tolerant of that. At this point I’d whip out my scope to see what’s coming out of the chips
Thanks very much. I’m throwing in the towel and putting it down to a learning experience. I’ve emailed the museum to see if they have another circuit board knocking around in case I feel like giving it another go!
DEF pick up and solder the IC sockets this time!
Carefully cut the legs off the chips one at a time with sharp snips, then desolder each individual leg. Add more solder to each leg to make this process easier, and so that no traces are lifted from the PCB.
Clear out all of the holes with solder braid or a vacuum desolderer (you can get cheap non-electric ones that can work well). Again adding more solder before removing it will make things easier.
Clean any solder braid flux residue with PCB cleaner and a brush. Automotive brake cleaner is great for this if you happen to have any.
When the PCB is clean and the holes are clear, fit chip sockets and try with new ICs throughout.
