I just picked up one of these T747 Mic Testers, and being disappointed with the lack of any type of instructions, decided to open it up and start poking around with an ohm meter to see what's what. So let's blow the dust off this four+ year old post and list what I found:
On the left side are 3 terminals labeled Audio, GRD, and V+.
"GRD" and "V+" are connected directly to the NEG and 13.8V+ on the back. In addition, all grounds in the tester are common and connected to the chassis.
"Audio" is connected to the input of the amplifier.
On the right side you've got 8 terminals. These are meant to be used with the Microphone/Echo Test switch.
"GND" on pin 2,6,and 7 is ground, connected to all the other grounds.
"V+" on pin 8 is a constant regulated 9VDC+ if you need that to supply power to an echo box or noise toy.
"SW" on pin 3 is wired to TX - on a Cobra 4-pin it would be Pin 3, and can be used as either an input or output. When this terminal connects to ground it tells your echo box to start sampling.
Terminal 1 and 5 only work when the Microphone/Echo Test switch is flipped, and I believe are labeled backwards on the bottom of the tester. In "Echo Test" the audio from all of the mic jacks get switched away from the amplifier and instead go to Pin 5 "Mic" which is supposed to be connected to the echo box's input. The echo box output is connected to terminal 1 "Out" which goes to the input of the audio amp.
With the Microphone/Echo Test switch flipped to "Microphone" terminals 1 & 5 are dead, but the others still work.
But what if you don't have the correct jack? For instance, I wanted to check the D104 from my old Yaesu that uses a 1/4" stereo phono plug. Easy, all you've got tip, ring, and shell. Shell is ground, and ring is audio, with the tip is connected to ground on transmit. So I run a jumper from shell to GND/GRD and ring to Audio on the left side terminal block. I don't have to activate transmit for the amp to work, but if I want to test it I run another jumper from tip over to terminal 3 "SW" on the right side. The RX LED will never light (no need for it with relay switching), but when I squeeze the lever the TX LED lights up telling me the mic switch is working.
In the future I'm probably going to drill and mount a 1/4" jack in the side of the chassis and wire it up so I can just plug these mics in and test them without resorting to jumper leads.
Well, I hope this helps clear up what all those question about how to hook up your SuperStar T747 Mic Tester!
