Fault on Motorola R2600B

[PSmith]

motorola r2600b

Hello All

Can anyone help, I have a fault on a Motorola R2600B communications test set so far I have not been able to find a workshop manual so fault finding is just about impossible. So maybe someone has come across this fault before.

The set functions just fine apart form the following -Spectrum Analyzer, Sweep Generator and Tracking Generator display, regard less of the band width I select the display will show a line across the screen at the input R,.F level.

Regards

Paul

 

[E-design]

motorola r2600b

Can you post a picture of the display?

 

[E-design]

motorola r2600b service manual

I guess not

 

[VSWR]

Message is unavailable.

 

[E-design]

This model uses the RSSI level from a NE615 if I can remember correctly (long time ago) for the log value of the spectrum analyzer sweep levels. If he is getting just a line there is no sweep action and it is like being in zero span mode.

I found this diagram that I copied from a service manual between my papers.

 

[PSmith]

Hello

Thank you for the information I did up- load 3 pictures of the display, can you tell me which module I can find this circuit in, has I still cannot find a workshop manual and have even contacted Motorola and General Dynamics.

Regards

Paul

 

[E-design]

From what I can find the spectrum analyzer module is the (A11) module

I have some rough notes that the sweep in is on U17(MC34072) may be same as TL072 which is also the LPF on the block diagram. You should see a sawtooth sweep signal on this opamp in/out.

Sweep out is on U10(MC34072) Here you should see a variable amplitude sawtooth as you vary the span on the spectrum analyzer.

I have also noted that there are two switches U18(DG211) that should be checked as they switch in the gain settings. It looks like your problem is that you not getting the sawtooth in for a start. You should check with a scope.

I think this signal gets generated on the interface module by a D-A chip (module right on the side) that is not enclosed. I will scratch more and see if I have more notes on this.

I also know someone who was on the original design team in Germany for these monitors. I will give him a call and see what more I can get.