No Talkback

[Mirage Music]

Hi
I can't seem to get any talkback working. When I press the talkback button I can hear hiss indicating that the channel is open but I hear nothing from the console mic. Any Idea's?

John

[Crash]

There is a talkback level. Have you checked out what you have that set too?

[Mirage Music]

Hi
Thanks for the reply. I realise there's a volume control and its clearly working. When I press the talkback button and turn the talkback level control up, I can hear the hiss getting louder.

John

[anyhorizon]

Sounds like the TB mic amp is rooted. Check the schematics and replace the necessary parts. Either that or the mic is a gonner. Mackie may have a few spares lying around. Otherwise, you may have to get creative.

Peter

[Mirage Music]

Hi Peter
Thanks for the reply. How do I go about checking the schematics? Is the mic easy to get to?

John

[synthjoe]

If it is a more or less faint white noise, hiss, rather than some digital noise, then it means that the A/D converter is delivering some meaningful digital data stream to the engine. In which case you'd need to look for the problem before the A/D converter, i.e. in the analogue part, as anyhorizon pointed out.

My first guess would be to check the cable, which is a thin grey shielded 'wire' with white 3 pin connectors on both ends. It runs between the line control card - the one with the V-pots and buttons - of the 9 fader unit and the DCA board. The DCA board is the one right behind the input connector board on the back (and a shielding plate). Of course it is nearly impossible to reach the cable without taking the whole thing apart... See picture below.

If you can unplug the cable on the line control board end, you might want to inject some faint signal (a couple of 100 mV) using the pins on the cable connector (pins 1 & 2 are carrying the differential signal according to the schematic) for a check. If the opamp preceeding the A/D converter and the A/D itself works correctly, then you'll need to look for the problem on the line controller board, all TB mic related electronics are located in the vicinity of the mic. Alternatively, you can check the relevant pins on the line controller card (e.g. hooking it to a headphone amp), microphone signal should be continuously output on these terminals (the TB switch works in the digital domain).

Thin grey shielded cable carrying TB signal at the far bottom end (near the level display) of the case.

07042011377a.JPG (Array KiB) Viewed 1685 times

Edits: typos, improved readability

[Crash]

Make sure the cable that synthjoe has circled in his picture is plugged in on both sides. If the console has been worked on before it might have been left unplugged. This is not uncommon. I can't remember the plug designator something like j45 or J38... Give it a look and see.

[synthjoe]

J60

[Mirage Music]

Hey Guys
Thanks for the help. Opened her up and guess what was hanging there not plugged in to anything? Yep thats right, a white 3 pin connector. I removed the shielding plate and managed to get my fingers under the board. Hey presto! It went in first time. All back together now and working A1.

Again many thanks

J

[anyhorizon]

Nice catch there, Crash... and synthjoe, well done! You've obviously been around the d8b for a while. What was your moniker on the old forum?

Peter