Batboard

This card modulates the PL onto the voice audio before transmission on our old simulcast system. We have three cards with the same fault, no PL passed. The cards look fairly simple but we would love to get our hands on some prints so we can trace the signalling logically.

The board has the following nomenclature on it. On the back it has the number 8406408N02 Issue A. It has one of those yellow motorola stickers with the info QRN4878A1503D on it. The card has a single IC on board, a four amp JFet TL074MJ. There is also a Motorola date stamped as 1990.

Basically we would just like to troubleshoot the PL encode issue on these cards. We don't have extender cards so we are going to have to be creative. If anyone has any info that can help us troubleshoot these we would greatly appreciate it.

QRN4878A is an SDA board [Simulcast Distribution Amplifier] It splits 600 ohm audio to ten outputs each destined for a different simulcast transmitter.

It gets the 600 ohm audio from either a USCI [Universal Simulcast Controller Interface] or from a CSCI [Conventional Simulcast Controller Interface]

In a conventional system the CSCI actually generates the PL or DPL and sums it with the transmit audio. The CSCI also preemphasizes and limits the transmit audio.

The USCI, CSCI, and SDA are documented in 6881098E65.

You are correct. Our tone generator cards send the tone to our USCI which then sums the audio. At first we used a scope we have setup for our phasing to determine that PL was not being emitted on channels that used these bad SDA cards. But after thinking about it you are correct, we don't have audio out at all, not just the loss of PL as I stated before.

We have a handful of SDA boards that produce the same result. They will not pass audio. We can move them to different channel locations and the fault indication moves with them. We originally believed we had a number of these cards as good reserves but obviously people have changed them out in the past for this condition and failed to follow through with correcting them.

We know that the condition is common since we have about nine of these with the same error. We have good ones to compare against but since we don't have extender cards we don't have an easy way to test them in circuit. We are hoping someone out there has a print of the board so we can narrow down where it is lost. We have found information on the JFET so I guess a good starting point is to see if it even makes it there.

If anyone has a schematic please let us know.

Just order the manual - the schematics are in there. 1-800-422-4210