IFR 1200S Frequency Meter Bounce

[w9ac]

I've been reading the archives to try and isolate a problem I'm having with a IFR 1200S Service Monitor. In a nutshell, the frequency meter needle quickly bounces down at intervals of about 3 seconds or so. It's fine for about the first 15 minutes of operation, then the problem starts as the unit warms up.

The archives suggest replacement of Y1, the 18.8 MHz crystal on the Fast Low Loop Board as well as CR15 which is an LM329 - 6.9V Zener regulator in a TO-92 case. A temporary fix seems to involve lowering C18 from 47 pF to a slightly lower value like 33 pF.

If I need to replace Y1, where on earth can I find a new 18.8 MHz crystal? ICM had the original crystal loading specs but they are now out of business. If necessary, I can find an alternate source to manufacture the crystal, but I need to know more about tolerance, series v parallel loading, etc.

Many thanks for any suggestions.

Paul, W9AC

[Andy Corbin]

Check with Kurt Graber at http://kgelectronics.com/. He is top notch on the IFR 1200 and 500.

Andy

[jry]

normally I increase the Zener diode value to get more range on the PLL which uses the crystal as part of a VCO.

If the crystal is too far gone than you may have to find alternative to ICM as a source. Believe there are still some out there reading through the forums.

Usually just a slight increase in voltage is enough so going from the roughly 6 volts to 8.2 should work.

[w9ac]

Many thanks for the info. The display checksum error is now cleared after replacing the 3V lithium coin battery.

Kurt at KGelectronics has an inventory of 18.8 MHz crystals so I ordered one today. But thanks for the Zener info. Looks like CR15 is in a TO-92 package and I assume only 2 of the 3 pins are used if substituting with a common Zener diode.

Is there a quick way to determine the options installed in the 1200S?

Paul, W9AC

[w9ac]

Thanks to the input received here, my IFR 1200S is working well again. In addition to the checksum fix, replacing the 18.8 MHz filter on the Fast Low Loop Board cured the frequency meter bounce problem. It's now stable after the unit warms up. The crystal was sourced from Kurt at kgelectronics.com who made a large purchase from ICM just before they closed the business.

Replacing the crystal is not an easy exercise. Extracting the module from the mainframe is easy enough, but the area on the solder side of the crystal is housed in a metal shield that's completely soldered to the board ground traces. I heated the soldered edges with a Weller controlled-temp soldering station, and raised the heat level to its maximum setting. Then, as I heated along the shield's edge, I used a jeweler's screwdriver to gently lift the shield away from the PC board. Five minutes later and the shield was off, with complete exposure to the solder side of the crystal for removal with a de-soldering station. The new crystal was soldered in and that fixed the frequency meter problem.

Paul

[greyhound]

Thank you for posting this. I have the identical issue on my IFR 1200S and this helped me a lot.

[w9ac]

> "...replacing the 18.8 MHz filter on the Fast Low Loop Board..."

Sorry, what I meant to write:

"...replacing the 18.8 MHz crystal on the Fast Low Loop Board..."

Pau