There didn't seem to be any kind of programmable regulator, but I tried a reset anyways and I got the same result. Thanks anyways.
I realized that I have an original DR-135, and not a MKII/MKIII (I got it used and wasn't sure). Looking at the schematic of the DR-135 MKII, it seems they added a new 5V regulator to run the TNC, powered off the 12V rail (but still switched by the CPU). It doesn't look like they've changed the main regulator.
I haven't wired it up yet but my plan is to get a 5V regulator with an ENABLE line (essentially doing what the MKII does) to solve this.
--- In email@example.com, Scott Miller <scott@...> wrote:
> I've been told that at least some versions of the 135 have a
> programmable regulator, and doing a factory reset on the radio has fixed
> 5v power problems.
> On 7/2/2013 10:17 AM, kg6bnl wrote:
> > Hi,
> > I have a T3-135 that I installed in a DR-135TP (I replaced the original
> > EJ-41U with the T3-135).
> > After installation I did not get any output on the serial port, the LEDs
> > did not come on, etc. I measured 3.5V on the 5V power line, which seemed
> > pretty low. If I feed 5V directly from the DR-135 regulator into the
> > power line on the T3, it comes up OK. The regulator is putting out
> > around 4.8-4.9V.
> > Looking at the schematic for the DR-135, it seems the power for the TNC
> > module is going through a transistor (Q130, type DTA114YUA) which is
> > rated for 70mA. I measured the draw at around 40-50mA running off the 5V
> > line, and about 30mA off the transistor, so it shouldn't be exceeding
> > the spec, but maybe the transistor is bad? I measured about 3.8V when
> > the original EJ-41U is on, but it seems to work OK.
> > Has anyone else seen a similar issue? I'd like to retain the ability to
> > do voice, so I'd rather not just hardwire on the 5V line to the TNC.
> > Thanks in advance,
> > -Ben (KG6BNL)