TR-2400 Unwanted Noise: Tone or burst at tx                        2-13-80

For complaints of a tone burst type noise, or simply a noise, at initial
key down, suspect either a broken losse component, or incorrect valued
component on the RX TX  unit.

On the RX TX unit, Q16 emitter, check C82, a 33 uf tantalum cap for broken
connection.

If you find a 22 uf cap at C82 replace it with a 33 uf cap.

TR-2400 Display or Keyboard trouble                        2-20-80

Display

An intermittent or blank digit may be caused by either a broken lead, or
intermittently shorting lead on the PLL unit.

On the PLL unit, look in the area of Q12, the touchtone generator.  Between
Q12 and the board edge locate the D1-D4 lines.  Inspect this area for
either an open (Broken) lead, or shorted (pinched) lead.  Repair as
necessary, and check lead dress before reassembly.

Keyboard

An intermittent or inoperative keyboard row or column may be caused by a
torn or pinched lead, or a cracked diode.

Again, in the area of Q12, inspect the "T" and "Y" lines for shorts or open
connections, and inspect diodes D19-D26 for physical breakage.

TR-2400 RX low, INtermittent, or distorted                        2-20-80

For any of the above complaints, suspect a broken loose component in the RX
IF or audio output circuit on the RX TX unit.  Simply pull up on the leads
and resolder.

Adjacent to Q9, the audio output IC, find C49, a 1uf cap.  If broken loose
from the board, audio output may be down, while current consumption may be
up from the normal 30mA to about 100mA due to the audio output amp
oscillating.

Adjacent to L10, the discriminator, locate C33, a .033uf cap.  If this
component is broken loose, audio output may be up approximately 6 dB with
excessive high frequency audio response.