The IFR-1200S is fixed. It turned out to be a bad 18.8 MHz crystal, but the MV209 varactor diode and LM329 voltage reference in the 75.2 MHz reference oscillator were also bad. In case it helps anyone else: - International Crystal has the replacement 18.8 MHz crystal in their catalog under the IFR p...

I replaced Q15 and C69 with no change. After I removed the shield, I found that someone had been working on it before me. There was a SMD capacitor across the 5.5 pf capacitor at C68 that is not in the schematic. I do not know the value of the SMD part because my tester will not measure low pf value...

jry, This unit has the fast low loop. I think you've identified the problem. The 75.2 MHz oscillator is running at 75.193 MHz. I replaced CR15 because the voltage across it was 5.9V and the reference is now at 6.9V. The loop is still off frequency and the voltage at TP3 is at 6.5V. I disconnected R8...

Sorry folks. Please ignore that last message. I posted it in the wrong thread.

I am a new user to this board. I used to be a bench tech at a couple of MSS and a GESS shops back in the 1980s in the days of the Motrack, Micor, Master Exec, Master II, and Phoenix lines. We also worked on a lot of Progress Line and Aerotron tube equipment. I've worked in telecomm for one of the ma...

I didn't mention that the spectrum analyzer is also off frequency by -7KHz. If I am looking at a signal at a given frequency, the indicated signal on the spectrum analyzer is 7KHz to the left of zero. If I tune the IFR to 7KHz below the desired receive frequency, the signal on the spectrum analyzer ...

I studied the service manual and jry seems to have nailed the probably causes. I wish I had another unit to swap modules with to show me where to focus. I feel like I'm all over the place in my troubleshooting as I study each circuit after reading the descriptions in section 2. I checked the 10.7 IF...

Thanks for the replies. The external 10MHz reference starts working automatically when an external signal above 5Vp-p is applied. I have a 10MHz source so I built an amp to bring the source level up to the point where the IFR starts using the external signal. It didn't help. The only way I can get t...

I have an IFR-1200S that is consistently off frequency by -7KHz across the entire range. Here are the symptoms: - To generate a signal on (for example) 150.0000 MHz, I have to set the unit to 149.9930 MHz. If the unit is set to 150.0000 MHz, it transmits on 150.0070 MHz. - The reference output is at...