Still very broken.

Heatsink's probably bonded on, you might break the device if you remove it and it's possible the markings won't be readable anyway

Yes, this one

Not an EV, an old i10, but it has more electrical personality than any Fiat I've owned.

BTW, the reason I said transverter first is the MC145152 was very popular in transverters and the circuit's almost identical - I thought the VCO was running into a mixer - but it wasn't a mixer, it was that push-pull amplifier, which I'm kind of fascinated by - I'd love to know what that device is.

Sounds like a plan, should be fine in a basement. It might take about 30 seconds for the loop to lock, then you'll have to find it, if you don't have a spectrum analyser or a frequency counter handy (don't connect either to it unless you have the required high power attenuators). What a find!

There *may* be an audio clipper, actually, which is better than nothing. There are a couple of diodes on the right that look as if they could be performing that function.

It's missing loads more stuff that a professional broadcast exciter would have, like RF power adjustment and muting, out of lock power-down, any sort of deviation limiter, audio bandpass filters.

The guts of the amplifier itself is reasonably similar to a professional broadcast transmitter amplifier from the mid 1980s, but the lack of output filtering, forward and reflected power measurement and protection circuits suggest otherwise. The datecode on the Mitsubishi 2SC1971 says 1997, I think.

It's FM broadcast, not AM. Yes, the RCA will be audio input. You will need a 28V supply that can provide around 6A or thereabouts. Your dummy load will need to be relatively substantial. Do screw the lid on first and use good quality short cables to minimise risk of radiating that signal.

The MC145152 is a parallel load PLL synthesizer IC, DIP switches program it. I expect the small IC near the LED is a prescaler to divide the carrier frequency down to something the MC145152 can handle. The LF351 is likely the PLL loop filter, turns phase pulses into DC for tuning the VCO

It *might* be on-frequency, with the vco module on the output frequency, the push-push might just be a push-pull amplifier. I've never seen it done that way.

The output device is rated at 80W/150MHz but driving it with a 2SC1971 is just about perfect for its 10dB gain, it'll probably be slightly over-driven at 100MHz where the gain will be higher than 10dB.

Yup, it's the latter, I'm 99% sure. Just using luxury parts, I think it runs the POS-100 at 50MHz and then doubles it in a push-push doubler, that drives the 2SC1971 to maybe 10-15W and the final takes it to over 80W. There's no low pass filter, don't connect it to an antenna. 50Ω dummy load only.

Okay, I've seen all the pictures now and it's possibly transmit only. The top board has a POS-100 from MC driving a mixer, that does 50-100MHz and that drives what could be some sort of frequency doubler or mixer. I might have to draw it. Now wondering if it's a pirate FM transmitter…

The board with the chips is a ham radio frequency converter (transverter, probably), I can't tell from where to where but possibly from 28MHz to 144MHz. The lower board is a power amplifier and possibly some changeover relays. Except… I'm a bit puzzled that it uses an RCA phono as the input jack.

It has taken me several months to clear what I hope is enough space to operate it while it's open. It isn't a small synth but once you hinge the back open it's huge. So far I've established the oscillators are sending notes, but the filters, VCAs and envelopes are doing nothing, so it's silent.

The only thing I've found that helps a little with that is drinking plenty of water the night before.

Don't most switching ICs include MOSFET drivers?