BID: 580_WB4D Subject: Intermittent MFJ crashes... Those of you that are using the older MFJ 1270 with the mini phone connector for the DC input would be wise to replace this connector with a "coaxial" type. For the past 2 weeks, I've been fighting an intermittent BLOCK TIMEOUT error which was caused by this cheap connector.. It wasn't bad enough to completely reset the TNC - but did confuse hostmode protocol. Physically moving the TNC didnt reveal this problem. The mini phone connector was a poor choice for a DC connector and should be replaced even if you don't show any problems --now... *** TNC 2 - MFJ 1270 - and some Clones *** Tone Calibration Procedure Have you ever wondered to yourself whether or not the Packet TNC you are using may or may not be generating correct mark and space tones in reference to the proper frequency? As the owner of 5 MFJ 1270/1274 TNCs, the above question came to mind. I am not equipped to make adjustments on these TNCs with the use of various testing devices, and turned to the MFJ Owners Manual for a possible remedy. They tell you in the Manual how to adjust the tones if you desire HF operation (300 Bps) using their 1270B, or 1274 Model, but when trying to find out how to check for proper calibration on the VHF/220 Mhz/UHF (1200 Baud) -- it's not there. The TNC 2 has a couple of GREAT features built in to its software. CALSET and CAL are in the list of Parms, but not explained in detail that would enable the average packeteer to do his own calibration. 1. 1200 Hz. - MARK TONE (Low tone ) 2. 2200 Hz. - SPACE TONE (High tone) 3. 1685 Hz. - CENTER TONE (Demodulator) On the CENTER FREQUENCY tone, it states in the TNC 2 Manual that 1700 Hz is ideal. Continued experimentation has shown that 1685 Hz is best. If you are experiencing a lot of retries, and having a difficult time with connects, chances are that your TNC is not generating compatible Mark and Space tones. To calibrate the 1200 Baud tones on your TNC 2 or Clone. Follow these instructions: 1. Remove the cover of your TNC. Make sure the HF/VHF button is in the "VHF" position! 2. Get a screw driver small enough to adjust the trim pots R-76 through R-79 located toward the rear center of the TNC circuit board. 3. Boot up your computer, and enter Command Mode (CMD:) on your TNC. 4. Try to listen on another Transciever, possibly a Hand Held Radio or monitor of some kind, and pick a clean freq. (simplex) with LOW pwr. This is helpful, but not required. 5. Enter this command from command mode: CALSET 438 or (n=525,000 / 1200 + 1) which in either case will equate to 438 or therabouts. This is your MARK tone CALSET number or 1200 Hz tone. 6. Remove the jumper from JMP 8 and place on JMP 9 Pins 1 and 6. (If you are facing your TNC pins 1 and 6 are on the far right). 7. Type CALIBRA or CAL. Hit the letter "K" and then the space key to get the lower of the two tones. NOTE: you may want to remove the jumper from JMP 5 to use on JMP4 to override the watchdog timer circuit. 8. Adjust R-78 until the you hear a change in pitch of the transmitted tone, AND both the CON and STA led's light up and stay lit, or at least alternate back and forth the same rate. Ideally, they should both stay lit simultaneously. 9. Hit the "K" again, and then "Q" (to quit calibration) and then go back to CMD: mode. 10. Give the TNC the command: CALSET 239 or (n= 525,000 / 2200 + 1) which equals a CALSET number of 239. 11. Repeat step 7. Repeat step 8, but adjust R-77. Repeat step 9. 12. NEXT - REMOVE the jumper from JMP 9 (Pins 1 and 6) and place the jumper on Pins 2 and 5. - the center two pins of JMP9. 13. Go to CMD: mode and type this: "CALSET 157" or (n= 262,500 / 1685 + 1) which would equate to a CALSET number of 157. This is your Demodulator/or center freq of 1685 Hz. 14. Repeat step 7, this time adjusting R-79 for the best condition of the CON and STA LEDs (both lit at same time). 15. Replace JMP 8 (from JMP9) and replace JMP 5 (from JMP4). Once you have done all of the above, you have successfully calibrated the TNC's tones. LAST BUT NOT LEAST...follow the MFJ or TNC 2 Manual on how to properly set the deviation level adjustment (R-76) so that your transmitter puts out in the neighborhood of 2.8 to 3.0 kHz of deviation. THIS MOD WILL MAKE A SWITCHABLE NODE/MFJ FROM A 1270B OR A 1274 NOTE:TNC MUST BE UPGRADED TO 32K MEMORY FOR THIS MOD... PARTS REQUIRED : 1 27C512 EPROM 1 EXTRA 32 MEMORY CHIP FOR THE MFJ 1 1K RESISTOR 2 10K RESISTORS 1 DPDT MINI SWITCH HOOKUP WIRE. 1. MAKE ALL MODS ACCORDING TO THE NET DOCS TO MAKE A NODE OUT OF YOUR 1270B OR 1274 2. USING YOUR EPROM PROGAMMER, READ YOUR MFJ EPROM. BURN THE FIRST HALF OF THE 512 CHIP WITH THE MFJ DATA...BURN THE SECOND HALF OF THE EPROM WITH THE NET (2.06 OR 2.08 ARE BEST). CONSULT THE DOCS ON YOUR PROGRAMMER AS HOW TO DO THIS AS IT WILL VARY WITH THE TYPE OF PROGRAMMER. 3. FOLLOWING ALL SAFETY PRECAUTIONS FOR CMOS DEVICES CUT THE FOLLOWING TRACES. A:CUT TRACE FROM PIN 26 TO PIN 28 OF U24 B:CUT TRACE TO PIN 7 ON U12 C:CUT TRACE TO PIN 6 ON U12 D:CUT TRACE TO PIN1 U24 (IF ANY EXIST) 4. CONNECT PIN 1 U24 TO PIN 1 U25 5. CONNECT PIN 26 U24 TO PIN 26 U25 6. INSTALL PARTS PER FOLLOWING CIRCUIT DIAGRAM: U13 PIN 4 ------------- DPDT +5V 1K _____________ +5V 10K |------\ -------XXXX---===| PIN 1 | -------XXX--- \ | | | O O----------------- | 27C512 | U12 PIN 7 | | ---------------------O O-------\ | | \ | | U13 PIN 8 O O ----- | | ------------- / --- | | +5V 10K |------/ - | | -------XXX--- -------------- NOTE:PIN 1 ON THE 27C512 IS BENT OUT AND THE PARTS SOLDERED.. PLACE THE EXTRA 32K RAM CHIP IN SOCKET U24 TO SWITCH BETWEEN MODES POWER DOWN, FLIP SWITCH AND POWER UP..MEMORY IS DIVIDED 32K FOR EACH MODE.. WE HAVE 2 OPERATING NOW AND 2 MORE BEING CONVERTED.. THANKS TO TO THE FOLLOWING HAMS FOR THIS MOD.. WA6OTP JIM McNUTT WA6IKO JOHN OLSON WB7VMS JERRY KIME WB7VMS @ WB7VMS.#MURPHY.OR.USA.NA ------------- From : W3CSG @ WB4D.VA.USA.NA Subject : More TX audio from MFJ1270B/1274 Need more TX audio to drive a commerical radio or inject past the limiter? The following mod will increase the stock output from a MFJ1270B or 1274 TNC from about 200mv with tone twist to about 500mv with no tone twist. Change R56 from 7.5K to 4.7K Jumper out cap C71 Remove cap C73 Install 1mfd caps at C34 and C35 (caps shown on board but missing) The above changes will make the TNC TX audio the same as the older MFJ1270 and TAPR TNC2 units. I am presently using this mod in order to drive Motorola and GE radios in my node stack. 73 Royce W3CSG @ WB4D.VA.USA.NA ---------------- FILE NAME: MFJ1270B.001 @ VE3EUK I have recently taken the opportunity to observe electromagnetic compatibility of the MFJ-1270B as used by several of our NET/ROM nodes. (some of this may apply to other brands also.) The initial results were not as good as they should have been. The question was 'Do the TNC's cause interference to co-located sensitive VHF receivers?' The answer is YES, depending on the situation. In two different sites measured, the noise coming from the TNC was sufficient to cause 4-7 db worth of desense to a 0.2 uv (12 db SINAD) receiver (145.01). There are two types of noise that are that radiate from the MFJ-1270B. One type is broadband in nature (probably due to data/address bus activity and DC-DC converter operation) the other kind is harmonics from the crystal oscillator and sub-multiples thereof ((4.9152/2) * 59 = 144.998 MHz). The broadband noise can cause interference on all frequencies if a sufficiently sensitive receiver in a quiet location is involved. The harmonic energy can cause problem on specific frequencies. This interference is detrimental to the weak singals that several of our nodes are required to operate with. In addition it may cause problem to the communications of our hosts when we share a commercial site. It is relatively easy to determine if you have a harmonic problem because the receiver noise will quiet when the TNC is turned on. The broadband noise usually can not be heard unless you observe the noise level in the presence of a weak signal. (With the normal antenna connect, inject a signal that provides 10 db of quieting then turn on the TNC and observe the change in noise level. If you have a 0.5 uv receiver or are in an otherwise noisy location you may not be affected. With a 0.2 uv receiver you may lose 6 db of quieting.) CLEANING UP THE MFJ-1270B Sufficient reduction in the energy emitted by the 1270B can be had with some relatively simple modifications to the 1270B. These modifications should reduce the broadband noise level to a insignificant level for most sites. Harmonics that cause problems to specific frequency can usually be moved far enough off frequency by 'rubbering' the crystal with the trimmer in the TNC. 1. Scrape the paint from the inside of the cover and the outside of the chassis near the four screws that hold the cover on. 2. Remove the circuit board from the chassis and scrape the paint from the top of the four posts that hold the circuit board. 3. Add a low inductance strap from the mounting hole near the power switch to the ground trace at the edge of the circuit card. (The bottom side of the card works the best.) 4. On the bottom side of the card add a 'small' 0.001 uf capacitor from each of the four active pins on the DIN connector to the ground foil immediately adjacent. 5. Add a ground strap from the foil on the bottom side of the card under the DIN connector. The ground end of this strap can be left dangling until the card is reinstalled and then looped to the outside of the chassis and grounded with a small self tapping screw on the lip just below the DIN connector. If you are at a shared site, you owe it to the other services to be a good neighbor. Subject: MFJ-1274 crashing solution A few weeks ago I placed a bulletin on the boards regarding a problem with the MFJ-1274 crashing from time to time. I received lots of replies and suggestions. I tried them all, and all of them failed to correct the problem. The was one which touched upon power failure, so I decided to look into the power supply. At no time was there a power failure or drop in voltage, but I removed the small 12v, 500ma supply that comes with the MFJ, and replaced it with a battery. The TNC ran fine until the voltage dropped on the battery 14 hrs later. The result was the TNC reset itself, and just sat there not doing anything. At this point I replaced the power supply with my PK-232 supply rated at 1 amp, and the MFJ has been running 100% for the last 4 days. It is possible that the TNC is drawing more current then it's suppose to but in any case the 1amp supply is not running hot at all. So keep this in mind if something similar happens to your 1274. The problem may not appear if your TNC is not on continiously as mine is. Thanks to all for all the suggestions. KD2EJ Winston.. PORTED AND REALIGNED FROM PC TO AMIGA FORMAT BY BOB G0LBQ - N6XDI.