Q:
- decoupling? (100uF and few 100nF ceramics close to 1284 and MAX pins)
- voltage? 1284 without P might have a problem at 3.3V and 16MHz
- upload speed? - start with 38400 or 57600 when possible (115200 @16MHz is 3.7%off - a potential issue when your crystal is off)
- Xtal capacitors?
- is the automatic reset (dtr to reset via a 100nF cap) working?
- 10k pullup on reset
- 10k pullup on RxD (optional)