I would think a good working used KX170B is appx the same as the $300 repair.
I love mine. Cast Iron mofos that never stop working.
That's not to say that I don't covet when I walk through Aircraft Spruce's avionics shop at CNO. That's when I start telling myself about the resale impact of a GTN750 on my airframe.... sigh.
Sounds like an easy fix check with Avionics shop for a price.
I have the MAC1700 in my airplane, which is the digital conversion of a KX170B. Absolutely bulletproof. I also have a newer/more costly NAV/COM, but I use the MAC exclusively. If you can find one, worth the money. I keep the KX170B that I took out as a slide in replacement if needed.
Mac = too much money for this customer.
The decent ones look to be getting 400ish on eBay.
you could just trade with this guy for 200.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&vxp=mtr&item=270881974152#ht_1039wt_1397