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TR-7950 mods | Radioaficion Ham Radio

TR-7950 mods

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Modifications for the Kenwood TR-7950

TR-7950 PA module mod

Just found a Kenwood screwup on the tr-7950. On the power-output board where the PA module is connected is a 470 uf Cap designated C 1. The silkscreen on the board shows the + terminal going to gnd.

The origional cap that was factory installed was installed with the positive lead going to the + on the board. This is obviously wrong as the Gnd Foil is the minus lead not the + lead. The cap had swolen up and burst due to incorrect installation. Almost blew another cap till I verified that the MINUS goes to the foil, not the way its marked on the PC board.

If you have a 7950 or 7930 you would do well to pull off the back and inspect the Cap installed at C1. Its the only large filter cap on this board so its easy to locate. If the case looks bulged, better get another cap and install it correctly. 73, N5WX @ N5WX.OK


TR-7930/7950 transceiver for packet/rtty operation


Circuit modification for Kenwood TR7930/7950 transceiver
for packet/rtty operation
by: WA4IXN
This modification provides controlable audio output to pin 5 of the mic connector for single plug packet/ rtty operation.

Remove top cover of transceiver and carefully disconnect speaker lead plug from "rx unit" board.
Locate plugs"j-13" on the right front of the "rx unit" board and "j-18" on the left rear side of the board.

Notice which wire goes to pin "8-m" on "j-13" and to pin #5 on the mic connector.
Remove plug "j-13" from the board and locate the spring tab on the side of the plug that holds the "8-m" connector in place.

Using a small awl or pointed tool, press the tab down and carefully pull the "8-m" connector from the plug.

Work the wire from the harness so it will reach back along the left side of the board to plug "j-18".
Using the awl or small pointed tool, carefully spread the "8-m" connector a slight amount so it can be fitted Like a sleeve over another connector of the same size.
locate terminal "ap" on plug "j-18".

Insert the spread terminal "8-m" into the top of plug "j-18" so it fits around the top of terminal "ap". This is a fairly tight fit, so use care not to bend the terminals by using too much pressure.
About half of terminal "8-m" will stick up above the top of terminal "ap". The lower part will be firmly sleeved around terminal "ap" inside the plug.

Dress the wire around the left side of the board.
Replace speaker plug and install top cover.

plug tnc cable with ptt/audio in/audio out/ground connectons into mic connector and it's ready to go on packet/rtty.

No soldering is required and unit can be returned to original state at any time if necessary.


TR-7950 screwup on the power-output


Just found a Kenwood screwup on the tr-7950. On the power-output board where the PA module is connected is a 470 uf Cap designated C 1. The silkscreen on the board shows the + terminal going to gnd.

The origional cap that was factory installed was installed with the positive lead going to the + on the board. This is obviously wrong as the Gnd Foil is the minus lead not the + lead. The cap had swolen up and burst due to incorrect installation. Almost blew another cap till I verified that the MINUS goes to the foil, not the way its marked on the PC board.

If you have a 7950 or 7930 you would do well to pull off the back and inspect the Cap installed at C1. Its the only large filter cap on this board so its easy to locate. If the case looks bulged, better get another cap and install it correctly. 73, N5WX @ N5WX.OK



TR-7950/30 RX Interference

Some users have reported FM Broadcast or TV video carrier interference to the receiver. Normally the TR-7950/30 has excellent two signal intermodulation characteristics. For a reported case of Broadcast or TV IMD the following modification may reduce or eliminate the interference.


Parts Required

Qty Description
1 MI-308 Diode

Procedure

  1. REmove the top and bottom covers.
  2. Remove the 4 screws that secure the heat sink assembly to the rear of the set. Gently pull the heat sink assembly to the rear, to allow access to the final unit X54-1270-1-,11.
  3. Remove the 5 screws securing the PC board to the heat sink. Remove the 2 screws securing the final module (M57733/M57726) and remove the screw that secures Q2 to the heat sink. Carefully desolder L9 from the antenna connector. (Dont change the spacing of the coils!!!)
  4. Gently fold the assembly over to allow access to the foils side of the final assembly and remove D2, and replace it with the MI-308 diode.
  5. Reverse steps 1-3 to reassemble. Reconnect L9 but don't change the spacing of the coils. Use heat sink compound when replacing the final module.

This is an optional change and may not be performed in warranty.



TR-7850/30 RX interference

Author: Trio-Kenwood Communication, inc.

Service Bulletin no. 870 (8-4-1983)

Some users have reported FM broadcast or TV video carrier interference to the receiver. Normally the TR-7850/30 has excellent two signal intermodulation characteristics. For a reported case of broadcast or TV IMD the following modification may reduce or eliminate the interference.

Parts required

Qty        Description
1          M1-308 Diode

Procedure

  1. Remove the top and bottom covers.
  2. Remove the 4 screws that secure the heat sink assembly to the rear of the set. Gently pull the heat sink assembly to the rear, to allow access to the final unit (X54-1270-10,11).
  3. Remove the 5 screws securing the PC board to the heat sink. Remove the 2 screws securing the final module (M5733/M57726) and remove the screw that secures Q2 to the heat sink. Carefully desolder L9 from the antenna connector.
  4. Gently fold the assembly over to allow access to the foil side of the final assembly and remove D2, (figure 1), and replace it with the MT-308.
  5. Reverse step 1 - 3 to reassemble. See figure 2 for proper connection of L9. Use heat sink compound when replacing the final module.

TR-7850/30 RX interference

Note: This is an optional change and may not be performed in-warranty.

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