Modifications for the Tnc MFJ-1270

19-07-1998 | TNC2C * feil i TNC2C(dansk utgave) Other language
19-07-1998 | More TX audio from MFJ1270B/1274 English language
19-07-1998 | MFJ 1270/1274 Tone Calibration Procedure English language
19-07-1998 | MFJ-1270B EMI English language
19-07-1998 | Switchable node/MFJ from a 1270b or a 1274 English language
19-07-1998 | MFJ 1270C/TheNet tips English language
24-01-1999 | Ittermittent MFJ crashes English language
24-01-1999 | Running TheNet or X1J node, using with a BBS and the Nord<>Link TF4 type EPROM English language

19-07-1998
TNC2C * feil i TNC2C(dansk utgave)

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MFJ-1270/TNC2 TNC2C(dansk)
PIN 20 PIN 5 CTS
PIN 5 PIN 4 RTS

Dersom du bruker X-ON/X-OFF er det lett nok, du kopler 10k motstand mellom pin 4 og pin 5. For node-cluster maa du ta hensyn til dette, eller hvis mulig modifisere f0r du kopler/lodder 25pin cannon kontakt. (Info fra la3fw/la5wx)

Transistorene T5/T6 brukes vanligvis ikke. Jeg kjenner ikke til at de har vaert brukt til node-clusters. Funksjonen er feil. I TNC2C skjema er de vist koplet til 'CONNECT-STATUS', de skal vaere koplet til 'DCD-STATUS'. se tidligere bulletin

I TNC2C er det brukt en strap som heter 'NODESOFTWARE', en kan udmerket godt bruke denne, men naar en er vant med MFJ-1270B/TNC-2 kan det vaere greit aa ha en kopling som er kompatibel med denne, en kopler da inn en transistor, som gj0r omkoplingen, se tidligere bulletin.

Et problem er at resetpuls (CPU-RESET) ikke virker, enten er den for kort eller saa har den feil nivaa, den skal vaere 4 klokkepulsers lengde for aa virke. Fjern C9 = 10uF, kople en 1uF elektrolyt (ikke tantal !) mellom R14 og +5V (spenning fra 7805). Dette er gjerne noe brutalt, og en kan derfor gjerne kople en 1K motstand i serie med 1uF konding. CPU faar da lang nok resetpuls ved start. (Info fra LA5WX/LA4YGA )

Med dette anser jeg alle kjente problemer aa vaere lst/beskrevet.

73 de Jan-Martin - LA8AK

If0lge OZ1FBV var det paa den tyske utgaven endel feil som maatte rettes, de er if0lge han rettet med info fra andre brukere av den tyske kopien, det synes derfor ikke rettferdig aa belaste OZ1FBV for de feil som er paa tnc2c

This modification is read 134 times.

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19-07-1998
More TX audio from MFJ1270B/1274

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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.

This modification is read 271 times.

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19-07-1998
MFJ 1270/1274 Tone Calibration Procedure

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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 alot 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:

Remove the cover of your TNC. Make sure the HF/VHF button is in the "VHF" position!

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.

Boot up your computer, and enter Command Mode (CMD:) on your TNC.

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.

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.

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).

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.

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.

Hit the "K" again, and then "Q" (to quit calibration) and then go back to CMD: mode.

Give the TNC the command:
CALSET 239 or (n= 525,000 / 2200 + 1) which equals a CALSET number of 239.

Repeat step 7. Repeat step 8, but adjust R-77. Repeat step 9.

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.

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.

Repeat step 7, this time adjusting R-79 for the best condition of the CON and STA LEDs (both lit at same time).

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 modification is read 405 times.

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19-07-1998
MFJ-1270B EMI

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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.) T4e initial esults 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 serveral of our nodes are required to operate with. In addition it may cause problem to the communications of our hosts whenwe 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.

Scrape the paint from the inside of the cover and the outside of the chassis near the four screws that hold the cover on.

Remove the circuit board from the chassis and scrape the paint from the top of the four posts that hold the circuit board.

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.)

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.

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.

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19-07-1998
Switchable node/MFJ from a 1270b or a 1274

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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.

Make all mods according to the net docs to make a node out of your 1270b or 1274

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.

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)

Connect pin 1 u24 to pin 1 u25

Connect pin 26 u24 to pin 26 u25

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..

This modification is read 672 times.

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19-07-1998
MFJ 1270C/TheNet tips

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The MFJ 1270C TNCs require a little massaging before they will run the TheNet version 2.10 or similar firmware. It seems that the problem is that the 1270C has a couple of features that the 1270B models didn't have. One of these is dedicated RAM for the mailbox feature. The other is an EEPROM selection jumper (JMP15 I think. Notes are at work!). It looks like the RAM inteferes with the node firmware. You will have to disable the mailbox RAM, which is of no use on a node anyway.

The Mod: After removing power from the TNC, remove the 74HCT374 IC (high-speed latch) from the rear left corner of the circuit board. Short pins 10 (ten) and 16 (sixteen) of the socket. This disables the chip select for the mailbox RAM. That's it.

The 1270C TNCs also allows 512k EEPROMs to be installed. There is a jumper (JMP 15, I think!) near the EEPROM socket that allows the user to switch between 256k and 512k EEPROMs. NOTE: The 512K mode is NOT compatible with the TheNet X-1 software. TheNet X-1 should be used with the jumper in the 256k position using the "bent-pin" mod described in the X-1 documentation.

MFJ is doing more testing and I may have more news later.

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24-01-1999
Ittermittent MFJ crashes

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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 didn't 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...

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24-01-1999
Running TheNet or X1J node, using with a BBS and the Nord<>Link TF4 type EPROM

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For all those that have recently purchased a MFJ-1274C or MFJ-1270C for the purpose of running a TheNet or X1J node, using with a BBS and the Nord<>Link TF4 type EPROM.

As produced, these units are not the same as the previous model that carried a B at the end of the model number, ie. MFJ-1270B. They will not function correctly as I so sadly found out after purchasing one at a Hamfest this past weekend.

This pompted a call to the MFJ technical department which produced an immediate solution to the problem. The technician (Stan) told me that they had just become aware o this problem and he way to correct it was to:

Remove the IC U40. (CD74HCT374E)

Ground Pin #16 of the IC socket.

Save the IC for future use in case you want to use the TNC for normal packet activity. To ground Pin #16 of U40, you can inert a small piece of solid wire (about the same diameter as the IC pin) between pin #16 and Pin #1 (Ground) of the socket.

This has corrected the problem with my unit and it now works as it should. I was told hat MFJ is considering making this modification a Jumper setting in future units.

To modify the MFJ-1270C for use with X1J/Thenet EPROMS follow these instructions:

You must complete all of these steps in order for Netrom firmware to function.

Note: if you are not using X1J firmware skip the first step and make sure that JP15 is set for 256k.

Bend pin 1 of 27c512 out so it will not touch socket, then jumper pin 1 of 27c512 to pin 8 of MODEM header J4. (see X1J docs)

Remove U40. Add jumper from pin 16 to pin 1 (ground pin 16)
^ > SHOULD BE PIN 10

Remove JMP9 altogether (no jumper on any pins)

Cut JMPX "PAD" to prevent node from hearing itself

Add 100ohm resistors to R14 and R15 if not already in place.

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Have you any tips, trick or modifications you can't find here, please E-mail them to me, or use the mail form.
Can't you find a mods, please don't e-mail to me. All mods i have is listed on this site.!
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