TK-5710 External Mic Issues

[KB9LMJ]

Hello,

I am trying to wire an external mic to the tk-5210s DB25 port and am having several issues.

The schematics for the KMC-35/36 and the KMC-28 give the pinouts as:

1 - BLC
2 - SB
3 - GND
4 - PTT
5 - ME
6 - MIC
7 - HK
8 - DM

I have the KMC-27 non-DTMF, KMC-28 DTMF, and KMC-35 non-DTMF mics, and when testing them, I am getting some unusual behaviors:

First, I wired the KMC-35 as:

MIC DB25
mic 6 --> pin 6 MI2
gnd 3 --> pin 7 E
ptt 4 --> pin 24 (External PTT (Voice)) - Low Active - Mic = Disconnect, MI2 = Connect, DI = Disconnect
me 5 --> pin 25 ME

When the radio powered up, the PTT is constant and there is no modulation going over the air.
I tried playing around with the Mic, MI2, and DI settings to no avail. Using the KMC-35 from the front face works, but the modulation is really soft and there is a big hum in the background.

Next, I tried the KMC-28 DMTF mic and wired it per the specs above with BLC set to pin 4 Light Sense and DM to pin 5 DI. The PTT worked, but no audio came over the air and the display dimmed when keyed. I then moved DM to pin 2 RXD2, as I realized DI was likely more for CTCSS/DCS data; no joy again. The KMC-28 works from the front face, but there is a slight hum in the audio-not as bad as the KMC-35.

The KMC-27 non-DTMF mic had the best results. From the front face, the audio was loud and clear, but from the DB25, the PTT works and there is no hum, but there is no audio going over the air.

The KMC-35 seems the easiest to wire, but no joy, and I am beginning to think you can't power a noise cancelling mic from the DB25, such as the KMC-27 and KMC-28.

I am completely stumped...

Any suggestions?
Thanks!

 

[KB9LMJ]

I am trying to wire an external mic to the tk-5210s DB25 port

I mean TK-5710.

 

[mmckenna]

The schematics for the KMC-35/36 and the KMC-28 give the pinouts as:

1 - BLC
2 - SB
3 - GND
4 - PTT
5 - ME
6 - MIC
7 - HK
8 - DM

I have the KMC-27 non-DTMF, KMC-28 DTMF, and KMC-35 non-DTMF mics, and when testing them, I am getting some unusual behaviors:

First, I wired the KMC-35 as:

MIC DB25
mic 6 --> pin 6 MI2
gnd 3 --> pin 7 E
ptt 4 --> pin 24 (External PTT (Voice)) - Low Active - Mic = Disconnect, MI2 = Connect, DI = Disconnect
me 5 --> pin 25 ME

When the radio powered up, the PTT is constant and there is no modulation going over the air.
I tried playing around with the Mic, MI2, and DI settings to no avail. Using the KMC-35 from the front face works, but the modulation is really soft and there is a big hum in the background.

All that is correct, but the KMC-35 wants to see bias voltage on the Mic line.

Next, I tried the KMC-28 DMTF mic and wired it per the specs above with BLC set to pin 4 Light Sense and DM to pin 5 DI. The PTT worked, but no audio came over the air and the display dimmed when keyed. I then moved DM to pin 2 RXD2, as I realized DI was likely more for CTCSS/DCS data; no joy again. The KMC-28 works from the front face, but there is a slight hum in the audio-not as bad as the KMC-35.

Wants to see the SB 12 volts.

The KMC-27 non-DTMF mic had the best results. From the front face, the audio was loud and clear, but from the DB25, the PTT works and there is no hum, but there is no audio going over the air.

If it's a 27B, it has a dynamic mic.
If it's a 27 or 27A, it has both a dynamic "main mic" and a condenser "sub mic".

The KMC-35 seems the easiest to wire, but no joy, and I am beginning to think you can't power a noise cancelling mic from the DB25, such as the KMC-27 and KMC-28.

I am completely stumped...

Any suggestions?
Thanks!

I'd need to look at more of the service manuals, but I think you need to address the mic bias.

 

[KB9LMJ]

I have been racking my brain for the last two hours and cannot figure out what is going on...or isn't going on.

Directly from the TK-5710 service manual, the DB-25 pins are:

SB pin 14
E pins 7, 11, or 18
Mic E pin 25
MI2 pin 6

The schematic from the KMC-28 shows the pins as:

BLC pin 1
SB pin 2
E pin 3
PTT pin 4
MIC-E pin 5
MIC pin 6
HK pin 7
DM pin 8

Here is how I wired my external mic:

MIC DB25
BLC 1 --> pin 12 AUX I/O 7 | input | light sense
SB 2 --> pin 14 SB
E 3 --> 7 (I have tried 7, 11, and 18, and continuity tested those pins against each other and the radio's chassis and all grounds are common)
PTT 4 --> pin 24 | input | external PTT (voice) | modulation lines are all connected for both MIC PTT and External PTT (Voice) and Yes, Yes (I have played around with all combinations of those settings)
MIC-E 5 --> pin 25 ME
MIC 6 --> pin 6 MI2
HK 7 --> pin 13 AUX I/O 6 | input | External Hook
DM 8 --> pin 2 RXD2 (I am not sure is this is correct, but it lists it as RS-232C level data. I don't think it would go to pin 5 DI CTS or pin 10 CMOS level)

I am tying all three mics, the 27 and 28 w/secondary condenser mics (I opened them to make sure) and the 35. From the front face of the radio, the 35 works but has really low audio, the 27 is loud and clear, and the 28 works but has a hum. This is factory cabling to the 12 pin connector, not my attempt at the DB25. I am not sure why there is such a variance from the front mic connection.

From the DB25, the 35 constantly keys the PTT and no audio TXed; the PTT works on the 28 but there are no lights and no audio TXed (surprisingly, no hum); and on the 27, the PTT work but no audio and no hum.

Here are the following voltage readings from the DB25 pins to ground:

BCL 4.76 V (Why no mic lights on the 28??? It works from the front face...)
SB 13.79 V (Why no mic audio??? It works from the front face...)
Hook 4.76 V
DM big fat ZERO
MIC seems to vary from 0.08 to 1.76 V with or without the mic plugged in
PTT 4.76 V

I am using a DB25 breakout board to test all these connections so I can change them around at will.

I am not sure what I am doing wrong or why those mics perform so differently from the front face. I have also tried this on two different TK-5710s.

Thank you for your help!