Rigol DG1022 troubleshooting

[ceasar]

Hi!

I've been reading this forum for quite a while, but this is the first time I am posting.
I have studied electronics engineering, but I work in another field. I have not practiced electronics for many years, so I consider myself a begginer in the area.
This blog however gave me the inspiration to get my hands on some electronic projects, although at a novice/hobby level.

I bought a Rigol DG1022 waveform generator, described as malfuctioning, for next to nothing money.
Its firmware version is 00.03.00.08.00.02.08.
The mainboard version is ver. 2, rev. A

The unit seems to work fine and is in very good condition, apart from the fact that the LEDs that light the buttons on the front panel keypad seem to have a mind of their own.
For example, when I press the ARB button, the Pulse key lights up, when I press the Cannel 1 output button the Noise key lights up, etc. The actual buttons work fine, doing what they are supposed to. Also, sometimes buttons blink without any keys being pressed.

I am not sure if this is a hardware or firmware issue, but if I had to bet, I would bet on hardware. I tried to find another (or even the same) version firmware on the net, but no luck there. Is there any chance anyone has it or knows where I can find it? I also emailed Rigol support, but I recieved no reply.

Considering it a good experiance-building exercise, I did some investigation on the front panel board of the unit. On it there are:
        2 HC595 8-bit shift register chips, which seem to drive the LEDs (15 LEDs in total, plus 1 for the Power On button which is wired independently and is the only one operating properly.
        2 HC4051M MUX/DEMUX chips which I think sense when a button is pressed
        1 HC393 Binary counter chip which I think is also used to control the buttons.

The keypad board is connected to the mainboard via a 16-wire flexible cable. I traced the wires to be:
1: Gnd,
2: Gnd,
3: Gnd,
4: HC595 RCLK Pin (Storage register clock)
5: HC595 SRCLK Pin (Shift register clock)
6: HC595 SER Pin, (Serial input)
7: Vcc,
8:Vcc,
9:Vcc,
10:Vcc,
11: HC393 1CLK, 2CLK pins
12: HC393 1CLR, 2CLR pins
13: PWR On Button,
14: PWR On LED (This one works OK),
15: HC4051M COM IN/OUT Pin,
16: Gnd

I took some scope measurments for wires 4,5,6,11,12,15 which i attach below.
So, to sum up, my questions are:
1. Do you think this is a hardware or firmware issue?
2. Do these waveforms look OK to you (I am concerned mostly about RCLK and SER)?
3. Any suggestions about what else I should check?

A big Thank you to anyone having the patiance to read all this!