Motorola R2001D won't accept any button input

[mario_b]

Hello All,
I am new to this forum but I noticed that the users are quite familiar to the Motorola R2001D Service Monitor.
I have purchased one of these devices off Ebay and I am trying to fix it (as you probably figured out, it's not working currently).
The problem:
Unit switches on but then a message appears on the screen: "Warning RF Load Over/Temp", it emits a tone that I think it's close to 1khz and it's stuck on the Spectrum Analyzer setting.
This is basically it. None of the switches are working, I tried them all, absolutely no reaction from the unit.
I've read in the service manual that the RF over load can be fixed by serial polling the GPIB interface, but unfortunately the unit doesn't have the A8 board (GPIB board).
I don't know if the freeze is caused by the RF over load error or has any other cause.
Perhaps you can help my with suggestions where to start the search.
Thank you very much for your responses in advance!
PS: I am from Romania, so I have no access to repair labs from the US!

[DJP126]

Hello Mario, Your RF Overtemp problem indicates a bad A17 RF I/O module. Either a bad attenuator chip (located behind the "N" connector) or a bad wideband amp.

[mario_b]

Hello Dave.
First of all thank you for the hint.
I plan to check the temperature sensor and the I/O board first.
I will post on my progress.

[mario_b]

Temperature sensor is ok, no voltage coming out of the op amp, meaning no over temperature, next I will check the multiplexer in the DVM/scope board and then the ADC on the RF I/O board.

[mario_b]

Hi again, i managed to fix my 2001d. The problem was in the a7 board like Dave said. The multiplexer for the signals was ok but the control line for the temp sensor select was stuck high. An op amp used between the processor address lines and the line decoder was dead. As soon as i cut the line, the processor was free and the unit came back to life. I will replace the op amp and do more tests next week. Thanks for the help, Dave.