Well, heres a start to what I have on mods for the HR 2510.
Unlocking the Clarifier......This will allow the transmit and receive to be on the same frequency, allowing ease of use on SSB transmissions.
(it should be noted that I have not tried this mod, but got it from a 2510 newsletter)
1. Remove the top from the 2510 and set it aside. Remove the bottom cover, de-solder the speaker leads and set the cover aside.
2. Find D150 on the main circuit board. With the radio right side up, it will be found in the front, right-hand coener of the board. Lift (or clip) one end of this diode.
3. Find the Orange wire coming form the RIT/RF Gain circuit board(PB-120). From there it goes to the main circuit board to a four-wire connector (yellow/orange/red/brown) located on the left side of the main circuit board near the center of the radio. Clip the orange wire from the connector and feed it throught to the other side of the radio, Solder it to pin 3 of the IC311. This will be a three-pin voltage regulator chip located just to the right of the large microprocessor chip (IC315). The pins on IC311 are numbered from left to right.
4. Tune in a signal known to be on center frequency on one of the sidebands. If the line on the RIT control doesn't point to the dot at the 12 o'clock position, it can be adjusted as follows, if desired. WIth the radio right-side up, locate the three tuning coils in the front left corner of the main circuit board. The extreme left coil is labeled L116and adjusts USB. The center coil is labeled L118 and adjust LSB. The coil on the right is labeled L117 and adjust CW, It will not be adjusted. With the RIT control pointing at 12 o'clock and while listening to a signal known to be on center frequency, turn MODE switch to LSB and adjust it's corresponding tuning coil until the signal is perfectly tuned. Repeat the steps for USB. There will be some interaction between the tuning coils, so it may be necessary to repeat the above steps a few times until both sidebands are properly centered at 12 O'clock.
5. Re-solder the speaker leads to the speaker and install both covers. This completes the modification. You will have an approximate + or - 3khz slide with the RIT control. The digital display will not change, but the transmit frequency will now move relative to the position of the RIT control.