Anything with a motor will run differently, usually safely but not always.

Motor speed is 120*frequency/poles.

For example, a 4 pole hair dryer motor will run at 60Hz, the fan will run at around 1700-1750rpm instead of 1400-1450rpm.

For fans specifically, this can be a problem because fan load (torque) increases to the third power with respect to speed. This means that changing the frequency to 60Hz for a fan designed for 50Hz will run it at a significantly higher load which can make it run at a worse point of the torque curve where it is less efficient and ultimately overheat.

Some electronics have filters based on their designed operating frequency, so signals may get distorted by switching frequencies (notch filters on sensitive signal chain things like ECGs devices) though many are designed for both nowadays.

Things like electric blankets are just resistive loads so there would be little effect, but if they have very cheap electronics it is possible that the timer functions would be analog AC coupled so the timers might run fast or slow.

I think it is possible, but would require a ton of trace cutting and wire bodging, even the higher current traces which is never great.

An interconnect PCB (or one per channel) might be your best bet if your current PCB is too complex to reorder and resolder. Getting it done at a cheap board house like Aisler, oshpark, jlcpcb, etc…

Design it to solder to the required pads with castellated half holes, then you can solder the new parts on top of the interconnect board, and that is also easier if you have a proto batch of 5-10.

So what are you trying to do? Are you trying to make a constant current source for the lasers or a current limited voltage source?

You are running out of voltage headroom I think Using these sort of voltage regulators as a current regulator forces a 1.25V drop across the resistors used to limit the current there. Then you have 1.5-2.5V between IN and OUT from the Darlington pair in the regulator, then 0.7 across the transistor for a total of 3.45V minimum drop before you get to the laser. That is 1.55V for the laser. It is strange that it works for the green and not the red because normally they both have a minimum of 1.8V.

Can you probe what voltage you are getting with a scope oun the laser input on J6? Profiling the laser voltage would tell you a lot.

I there are a few ways you can go with this. Since you are burning a ton off as heat anyway, just switch to a DAC controlled high side current source with a PMOS FET (+ op amp and sense resistor of course). They can do 130mA easily and have a similar amount of components.

If you want it a bit more accurate or with BJTs, you could do a current source Like described here and adjust it to your values. More components, but it works quite linearly with your DAC outputs from the arduino.

Like the other person said, it can still be very nice and useful!

However, modern (even cheap) DMMs have some quality of life or useful features like auto ranging, diode measurement, capacitor measurement, max/avg/min functions, duty cycle, etc… Like the standard low budget ANENG AN8008. And this one is certainly better quality than the cheap stuff.

Though the continuity sensor for that meter being able to select sensitivity levels is quite nice. Most multimeter’s simply use “banana plugs” so you can’t go wrong and can always use standard lab wires (that are readily available)…