HMN1032A DTMF Mic, anyone got the schematics?

[kb0nly]

I got another DTMF mic here, thought it was the same problem as my other ones that i fought a while back, but it doesn't appear to be the same problem.

The problem is the mic works perfectly except the DTMF tones don't work, push a button and nothing happens. And its not just missing the tones, when you push a button it doesn't even go into transmit. I had one that would transmit but no tone, and one that would sound the beeper and send a tone but wouldn't transmit. Both of those were fixed by cleaning the pins and connector that mate the seperate boards.

Tried it on this one and no dice. Also, i took the keypad and front board from a known working DTMF mic and plugged them into the rear board from the non-working one and still nothing. And i took the front board and keypad from the non-working mic and plugged them into the known working mic and they work fine.

So, it has to be a problem on the rear board, the one that has the pins for the mic cable. Anyone have a schematic of that board, or the info on model differences from the manual. I know that JU1, R4, R18, R19, and CR9 vary on these DTMF mics, and perhaps this one was originally intended for an application thats different. I have the mic on a Syntor X9000, and also tried it on a Maratrac A7 that the known good DTMF mic came from, but no transmit or DTMF tone on button presses.

The audio and PTT work fine however. Any other common failures with these units?

[kcbooboo]

I was fortunate enough to buy a DTMF manual, p/n 68P81114E07-C some time ago. It covers a plethora of models, including your HMN1032B, which it claims is for a Syntor X 9000 Private Line. The only real differences among them are the cord. The jumper and component options are well documented. The boards inside are the same for all the models covered in this manual. There IS a troubleshooting guide in it.

The papers are glued into the cover, but they're only stapled together, so taking it apart to make good copies or scans would not be difficult. Several sheets are fold-outs and in color. I could try to reproduce parts of it, or offer verbal assistance via e-mail/PM.

There are schematics of both boards on the BatLabs site, although they're big. Better than nothing. Contact me if you need more info.

Bob M.

[kb0nly]

Ya know, i have been told that twice now about the schematics on the batlabs site. But i can't find em! What are the hidden under?

If you could scan that manual or at least some of the more important parts that would be a big help! Email sent...

[kcbooboo]

There's a quite generic section on DTMF mikes at

http://www.batlabs.com/dtmf.html

and down near the bottom are links to images of the two board schematics which should be "close enough" for most people to figure out.

Bob M.

[kb0nly]

Ahh, there they are. I missed that dtmf link, must have been looking too fast.

Those schematics should be a huge help. I spent some with the VOM and a working mic and traced out the voltages on the pins to the front boards and found out the non-working mic is missing the supply voltage on J3-5.

By the schematic that is supplied through one side of S1, perhaps just a bad switch! I'm going to desolder the switch and try a different one from the junk box.

[kcbooboo]

Ah yes. When the PTT switch is pushed, it removes power from the DTMF circuitry and powers the mike preamp, and vice versa. It was a major revelation when I figured out that one can NOT push the PTT button and expect DTMF tones to also come out when those buttons are pressed. I almost wish it worked that way, so I couldn't inadvertently drop the mike and have it key up and send a digit out.

Bob M.

[kb0nly]

Well the mic is fixed, it wasn't the switch though, it was the trace between the switch and J3-5, the circuit board trace was broken under the switch.

Looks as if the switch was redone before and when the switch was pulled off the board the trace was broken. So i just soldered the trace back down and re-soldered the switch.

FYI- You can setup the mic like that! It's easy to do, but, you lose the little beeper to know when a button has been pushed. If you leave the piezo element connected the mic will pick up the beep with each button press.

I have one on my UHF that i modified to function this way cause i kept bumping the buttons on it and sending tones, but i also still wanted the dtmf for remote control. I did that mod back when i had an actual mic manual, i think someone borrowed but didn't bring it back.

Its simple, with the backside of the mic facing you and the cord hanging down its the bottom PTT switch contacts. Just solder a jumper from the center contact to the right contact, this will keep power applied to the front dtmf board through J3-5 when the PTT is pressed. This makes the mic element and the DTMF board active at the same time though, so disable the little piezo beeper. I just desolder one of the leads to it and put a piece of heat shrink tubing on the wire end to keep it from shorting anything out.

Then, remove R18, its the top of the two resistors next to the piezo that are standing up proud of the pcb. R18 supplies power to Q4 which is used to switch Q5. Q5 is in parallel with the PTT switch, this is how the DTMF board switches the PTT by switching Q4 and then Q5.

[kcbooboo]

Glad it was a simple repair. I wonder if that was why the switch was pulled in the first place?

Yes, that piezo beeper is most annoying, but once you realize its purpose, it makes more sense. I would do exactly what you suggest if it weren't for the fact that the mike audio in these mikes sounds horrible, compared to the smaller palm-sized mike for MaxTracs. If they had made a mike with a normal sized element in it, and the TT pad on the back, I'd buy three.

Bob M.

[kb0nly]

I guess i haven't had any problem with audio in them. I get nothing but good comments on the audio from my X9000's. Though they are just sitting on the bench and not mobile yet.

[wa6kbl]

I have a HMN1032A and wanted to modify it so that the keypad worked when the PTT button was pressed. I printed the schematics at http://www.batlabs.com/dtmf.html but they are not for this model microphone. The instructions given in an email on this thread about modifying it were not quite correct for my microphone. I found that the schematic did not correspond to my mic and I had to ultimately remove Q5 in order to keep the keypad from keying the PTT line. R18 on my 1032A is not at all what is shown in the schematic. It is the resistor biasing the emitter of the mic preamp so it is absolutely necessary for audio.