Hmm, interesting. I think I can find some uses for that part.
Bill, while I understand that you like the look of incandescent, there are some technical considerations that you should think about with what you are doing. At the factory, they installed a momentary switch. However it's not like JVC doesn't know how to rig up a normal on/off switch. It's because the current consumption of incandescents is high enough that it can affect battery life. My LED system consumes probably about 20-25mA. A single grain of wheat bulb consumes about 100mA. If you put a total of 4 of those bulbs, you are consuming 400mA of current. If you think about it for a sec.... 20 vs 400 mA, that's a huge difference. The second issue is that it looks like you are powering the circuit from the meter board. If you consider where the circuit gets it's power from, studying the schematic shows that it is powered through the X505 voltage regulator, which is a Sanyo 2SD439e. Look at the datasheet:
2SD439E
- Sanyo Semiconductor
- Si NPN Power HF BJT
- V(BR)CEO (V)=18
- V(BR)CBO (V)=20
- I(C) Abs.(A) Collector Current=1.2
- Absolute Max. Power Diss. (W)=8.0
- I(CBO) Max. (A)=1.0u
- h(FE) Min. Static Current Gain=100
- h(FE) Max. Current gain.=200
- @I(C) (A) (Test Condition)=500m
- @V(CE) (V) (Test Condition)=2.0
- f(T) Min. (Hz) Transition Freq=150M
- Package=TO-126
- Military=N
The absolute max power dissipation is 8W and the max collector current is 1.2 amps. At the absolute ratings, it is presumed that the only safe way to handle that is with heat sinks clipped to the transistors, which I'm pretty sure they do not.
Using ohms law and presuming the constant of 100mA published by several grain of wheat bulb specs I saw in a quick search, I come up with .4A consumption and 4.8w for 4 bulbs@12v. Both figures are within the limits published in the transistor datasheet.
HOWEVER. That regulator also powers the following:
- Tuner light
- Power LED indicator
- MMS system including the control system
- Cassette Motor
- Cassette Auto Stop system including the plunger
There is no way for me to calculate the power consumption of all those other systems, much less if they are all being used simultaneously. Suffice to say however that with an added 400mA load (on a system with max 1.2A total rating), there is a risk of blowing that regulator, or running it very hot for an extended period which could cause scorching of that area of the board.
The alternative is to power your incandescent lights from a non-regulated rail. However, then power concerns manifest. The X505 rail is regulated to exactly 12V. The unregulated rails could range from 15v (on batteries) to over 19v (on AC). Since that adafruit states 14v max, and there is a concern that any of those 2 figures could run the bulbs too hot, maybe blow them, it seems that you'll then need to rig up a separate regulator system as well.
None of this suggests that you can't operate your setup in the manner you currently are. Much the same as to suggest that it's not safe to operate a boombox with 2-ohm woofers (ignoring minimum impedance guidelines recommended by the factory and most any technical guru's). However, I'm just looking at this from a technical aspect and of course, that involves future reliability of the project. Blowing that regulator isn't the end of the world, but it is in a very difficult spot to access on the board without extricating the main PCB which is a real pita. And of course battery life would be a concern with that large of a power consumption jump. Just food for thought.....
