Servicing tips for the Bravo family of pagers Identification, frequency changes, logic board modifications and testing, and POCSAG generators are discussed.
Around the pager service bench, boards sometimes seem to accumulate. Here’s how to quickly distinguish the Bravo receiver board from the Bravo Plus/Express receiver board. At the end of the board, next to the “jungle chip” on the Bravo receiver, are usually some five or six components. At the same location on the Bravo Plus/Express receiver board, there are just two components. Keep in mind that these two receiver boards are not interchangeable. There will be no damage inflictly if they are accidentally substituted for each other, but there will be no output at test point M1 when the “wrong” receiver board is used.
Crystal issues: co-channel operation Problem. You need to change the frequency of a Bravo pager by a single channel. Here’s how, with an interesting twist.
In many metropolitan areas, numerous paging companies operate. In some cases, the available capcode and number combinations simply do not match the frequency to which the pager is tuned.
Usually, this is overcome by means of changing crystals_but then, there are times you can get lucky.
After experiencing poor performance from one airtime supplier, I discovered that the tuning slug in the Bravo 930MHz series pagers (all of them) was capable of tuning to the next channel down from the marked frequency of the crystal. Thus, a pager operating at 931.7125MHz could easily tune down the 250kHz required to operate at 931.6875MHz.
The technician using this technique will discover that as the slug of the oscillator coil is tuned clockwise (as viewed from the foil-side of the board), the next-lower channel becomes available. Note that the slug nears the limit of the core length, making such adjustments “iffy.” To improve the fit, the slug sometimes can be removed (from the top), and a piece of cotton thread can be placed down the core. The thread acts as a “snugging” device when the slug is reinserted into the core.
When using this “trick,” be aware that “warping” a crystal in this manner might make the oscillator more sensitive to temperature and environmental changes, particularly when used with the 17.9MHz IF versions of these receiver boards.
Crystal issues: “true” conversions The logic board in the Bravo is often “stuck” at 512bps when the customer needs a 1,200bps unit. Here’s how to convert the Bravo into what I call a “cricket.”
A customer’s pager is “stuck” between two worlds_the bps rate available from the airtime supplier and the limitations of the pager. Until I tried a simple modification, many of my customers were “forced” into purchasing something new_even though their pagers worked just fine at 512bps.
Within the Bravo is a crystal-controlled oscillator on the logic board that determines the operating speed of the microprocessor. The crystal frequency is 2,048 times the bps rate_at 1,200bps the crystal frequency is 2,048 3 1,200, or 2.4576MHz. The 512bps logic boards have a crystal at 1.048576MHz, although at 2,400bps, the oscillator crystal would have to be 2,400 3 2,048, or 4.9152MHz.
The Bravo logic board is easy to modify. Simply remove the existing crystal and replace it with a suitable crystal using the math presented above.
There are a few limitations. Modified in this manner, the logic board will work only when moved up one “step”_you can move from 512bps to 1,200bps (or 1,200bps to 2,400bps), but the 512bps board cannot handle a direct conversion to 2,400bps, because the bandpass filter will not handle the higher data-rate speeds. The second limitation is one of customer convenience. The “beep” coming from the internal speaker is going to change in frequency_from a nominal 3.2kHz tone to something over 6kHz. Further, the on-off cadence is also going to become twice as fast. Hence, the name “cricket.”
When programming the modified Bravo, there are no special instructions_just program as usual. The vibrator alarm will operate for roughly half the time it did previously. Although this is not a modification for everybody, it does provide adequate service without the expense of a new unit.
(Note: The loading capacitance and mode for these crystals should be 18pF-20pF, series-resonant mode. Case styles should match, or be similar, to those removed. Moreover, the described modification is not recommended by Motorola.)
Testing logic boards The following procedures may be used to test Bravo, Bravo Plus, or Bravo Express logic boards (see Figures 1 and 2 on page 36) using Ramsey COM-6 test equipment:
Testing the logic board for the Bravo: 1) Place the logic board in an empty Motorola case, noting the “Qxx” number on the microprocessor chip. 2) Place a 1.5V battery in the case and close the battery door. 3) Place the pager in test mode. Preset the COM-6 to the appropriate capcode, along with a preloaded message. 4) Place the negative clip from the COM-6 at battery negative. 5) Set the generator to “normal” signal format output (red light off for data invert button). 6) Place the “hot” lead of the COM-6 output directly on pin 6 of the interconnect block (pin 1 is nearest to the speaker). 7) Generate the appropriate capcode and a preloaded message by using the send button. 8) With the Bravo is test mode, the logic board should emit a single beep with a momentary light. This tests the entire circuitry. A further test would be to place the logic board in “fully operational” mode (just turn it on without holding any buttons). It should give a full response using procedures 6 through 7.
Testing the logic board for the Bravo Plus and Bravo Express: 1) Read the capcode on the Bravo Plus/Express interface. 2) Follow procedures 2 and 3 given for testing the Bravo. 3) Place the negative clip from the COM-6 at battery negative. 4) Set the generator to “inverted” signal format output (red light “on” for data invert button. 5) Place the “hot” lead of the COM-6 output directly on pin 4 of the interconnect block. (Pin 1 is nearest to the clock crystal in the Bravo Express.) 6) Generate the appropriate capcode and a preloaded message by using the send button. 7) With the Bravo Plus/Express in test mode, the logic board should emit a single beep with a momentary light. This tests the entire circuitry. A further test would be to place the logic board in “fully operational” mode (just turn it in without holding any buttons). It should give a full response using procedures 5 through 6.
Other POCSAG generators The techniques outlined above also work with just about any POCSAG or Golay signal generator. When using a KNS-Cushman generator, the output level potentiometer will need to be set to 600mV-1.0V, peak-to-peak, at the output probes. The value stored in register 1 of the KNS generator determines the normal, or inverted polarity of the output signal, so to test the Bravo, do the following: 1) Perform a “0 store 1” to set the KNS generator to normal. Then perform a clr. 2) Determine the “speed” of the microprocessor in the Bravo, and set the “0” register to that speed. For example. 1,200bps POCSAG would be “5 store 0” (4 5 512bps, and 6 5 2,400bps). Perform a clr. 3) Prefix your capcode with a “1.” 4) Enter the capcode. [Therefore, a capcode of “1234567” would display as “11234567.”] 5) Using the same testpoints outlined above (“hot” on pin 6 of the interconnect lock, and gnd on the battery negative tab), generate the capcode by pressing snd.
Similarly, when testing the Bravo Plus or Bravo Express, the only differences involve reversing the signal polarity (1 store 1), and the “hot” side of the generator now goes to pin 4 of the interconnect block. As before, the pager’s response depends on whether the unit is in “test mode” or “fully operational.”
Whether using the Ramsey COM-6 or any other POCSAG/Golay generator, there may be some slight “chance” of a “short” between the input to the decoder board or chip. For safety’s sake, isolate the “hot” spot side of the signal generator with a 0.1mF capacitor before touching the appropriate pin on the interconnect block.
These procedures vastly simplify the testing the logic boards in the Bravo pagers. They are performed in the “half-shell” of the pager, and do not specifically require the use of the push-button inserts.