SERVICE BULLETIN
BULLETIN 93-1
APPLICABILITY: BEXT STL EQUIPMENT, FM RECEIVERS and HPT’s with built-in RECEIVERS
Purpose and general overview: Replacing some of the electrolytic capacitors that have shown to be potentially unreliable, and clarifying how to fine tune receivers for best performance.
1) ELECTROLYTIC CAPACITORS
Some of the units left the factory with a few capacitors from a bad batch; after an unspecified time period they swell and push the electrolyte out the bottom of the capacitor.
Only some specific capacitors in the units have shown to be potentially defective; they are the following ones:
For all SD R (receiver) models (includes 800 and 900 MHz SDR STL’s and 80-108 MHz SDR FM’s)
All 4 47 microfarad in the demodulator module
All 4, 220 microfarad in the demodulator module
All 4 220 microfarad in the synthesizer module
Both 47 microfarad in the synthesizer module
For all SD T (800 and 900 MHz transmitter) models:
All 4 220 microfarad in the synthesizer module
Both 47 microfarad in the synthesizer module
For all LC R (receiver) models (includes 800 and 900 MHz LCR-STL’s and 88-108 MHz LCR FM’s)
All 4 220 microfarad in the demodulator module
All 10 47 microfarad in the demodulator module
All 4 220 microfarad in the synthesizer module
Both 47 microfarad in the synthesizer module
For all LC T (800 and 900 MHz transmitter) models:
All 4 220 microfarad in the synthesizer module
Both 47 microfarad in the synthesizer module
To verify if your unit(s) have the potentially defective capacitors, you can open the synthesizer and the demodulator modules and check if the above listed capacitors bear the lettering “E K S”. If yes, it is best to replace them. We are sending a standard package of fifteen 220 microfarad and fifteen 47 microfarad high quality capacitors for replacement to every user we can trace that our records show owning either one single unit or a complete STL system (transmitter plus receiver). Please let us know if own or operate more units and you need additional capacitors.
If the capacitors at risk are not replaced, it is possible that they will fail. Should they fail while the unit is operating, you may experience failure to lock, intermittent locking, loss of output signal level or suddenly no audio altogether. A good soldering iron and standard soldering practice on PC boards will be necessary for this replacement. Should you not feel comfortable in performing this work yourself, you can of course ship your unit(s) to our service center; we will do it for you and send it/them back in the shortest time possible.
2) FINE TUNING RECEIVERS FOR BEST PERFORMANCE a) It is recommended to always fine tune the receiver to the exact transmitter frequency (STL’s 800 and 900 MHz and HPT STL models only). To do so, connect a 10.700 MHz-capable frequency counter to the 10.700 MHz I.F. output of the receiver.
By means of varying the position of the two jumpers and fine tuning the variable capacitor, located near the crystal inside the synthesizer module, adjust your receiver so that you read 10.700 on the frequency counter.
b) Bext 800 and 900 MHz STL’S, 88-108 MHz Fm receivers and all HPT’s have a selectable wide/medium/narrow RF bandwidth capability; “wide” will provide best audio performance but less protection from offending adjacent channels, “narrow” will provide best protection from offending adjacent channels but less audio performance. “Medium” is a compromise between the two. It is advised to try all to single out the best one for your application. If you experience no interference noise on “wide”, you can use it that way and take maximum advantage of the audio capabilities of your receiver. Jumpers’ location and correct positioning in the three different modes:
For SD models you need to open the “demodulator” and the 1st conversion and 1st I.F. PQ modules”.
For LC STL’s and HPT’s you need to open the 1st IF amplifier PQB module” only. For all questions and clarifications, or to arrange shipping your unit(s) to Bext, call the Bext Service Center at 619-239-8462.
