Harris Digit CD

[Lazy J]

I've got a Harris Digit CD exciter that's causing me some grief. It's giving me slightly distorted audio. You can hear very faint crackling in quiet spots and it sounds like intermod distortion in the bass and mids. I would say it sounds 95% good and 5% crappy, which is just enough to drive me up the wall.

I am running composite audio into the analog audio card. I know it's the exciter and not somewhere else in the chain because I put my standby Flexstar exciter in and it sounds great. I called Harris and they had no suggestions except to send the DIGIT in for a $1450 refurbish. I think I'll try to fix it myself for that price.

Anybody ever had anything like this? I'm well aware of the famous "DIGIT Whistle", but this is different. So... where to begin?

 

[jboyd]

You can begin by contacting Michael Patton and Associates in Baton Rogue, LA. He solved a digit problem that Harris said that they " cannot make fail" for me. I am not associated with that operation: JBI

 

[WNTIRadio]

Stupid question here, but why don't you run the Flexstar all the time and relegate the repaired Digit to backup status?

I would run something other than a Digit if I had it. FX-50, Flexstar, Nautel anything, Continental...

 

[Lazy J]

The flexstar is used in an N+1 setup where the frequency can be changed remotely. The digit has dipswitches, so it's a PITA to switch it in a rush.

 

[fm-engineer]

I've removed several Digit exciters and replaced them with Nautel boxes. I never liked the sound of the Digit, especially the digital input. The composite is much better, but it sounds like you may have an issue with the input coupler.

 

[awsherrill]

I don't know if the digital composite limiter would cause the symptom you describe, but you would want to make sure it is disabled (turned all the way down).

 

[boiseengineer]

As with all Harris products, shot-gunning the caps is needed.

Guess I'll get out the bag of capacitors and get to work on Digit #3 of 3 that needed fix'n!

 

[Dr. Bob]

Maybe I'm missing something but you repaced the Digit with the Flexstar, all inputs the same, same xmitter and the Digit had the noise but the Flexstar did not?

Have you got a known good FM modulation, stereo monitor and scope? If not, i would do what jboyd said and use Mr. Patton. If you do, then set up the Digit with the all inputs terminated into a dummy load and feed the mod monitor a sample. Looking at the output of the stereo monitor will give you clues as to where the noise might be comming from. I might exercise and clean all dip switches as these are known to be an issue in other exciters when they sit for years in the same position.

Good luck

Bob

 

[Bengalsfan]

I'm on the verge of replacing a 1995 Digit with a Continental 802A exciter. I have a classical station using the AES input and we are getting complaints of snaps and pops in the audio, distortion on the higher frequency instruments and such. I can listen to the output of the 8600 and it sounds fine. I didn't consider the exciter until seeing this message and others regarding older Digits. It's an issue the station has been dealing with for some time, but for some reason they are just now bringing it to my attention. :

 

[chriscollins]

The flexstar is used in an N+1 setup where the frequency can be changed remotely. The digit has dipswitches, so it's a PITA to switch it in a rush.

There is a box that allows you to remote change the Digit. We use one for our backup transmitter that backs up 4 FM's. One of our old engineers actually built a remote system that did this prior to the box. If I recall correctly, a Harris representative visited us, saw the potential and made their own box.

 

[TomT]

Bengalsfan:

Two things on the 802A (I've assumed a recent re-capping):

1. Put a zener across the big cap to ground. Continental will sell you a kit with zener and bracket--I just used a piece of copper strap. If memory serves me, the zener is something like 50 watts at 48 volts. Provides power supply protection in the event of surges.

2. There is a modification for both the 802A and B to ease the strain on the Darlington power controller if you will be running the exciter at low power (10 watts or so). The Darlington (originally an MJE 3001, NTE 245 replacement) acts as a voltage divider, running at lower than the 30~50 watts the unit was designed for causes it to run very hot. The mod "throttles back" the supply voltage. See instructions at:

http://mwpersons.com/tech-tips/FM/Continental-802B-Exciter.htm

 

[Bengalsfan]

Bengalsfan:

Two things on the 802A (I've assumed a recent re-capping):

Thanks for the heads up Tom. I've already made the modifications you mentioned. I keep it in my stable of stand-by exciters. I'm hoping to be replacing all three of these transmitters later this year or early next year. If it is out Digit fouling up the audio, I just want to put something on to last until the transmitter upgrades.

 

[Lazy J]

So boiseengineer, when you recap a DIGIT, do you literally replace every electrolytic in the entire unit? Or are there certain boards you focus on. Do you replace the surface mount caps too?

 

[boiseengineer]

That one C29 on the PA board.
Seven caps and modify the cover (add air holes) on the Upconverter.
Regulator bypass caps and filter caps on the power supply.

 

[bradgoehl]

Yep, just did this on one of ours to cure the noisiness.

 

[boiseengineer]

The third DIgit of three is now re-capped and cooking over night.
Found that -17 V reg supply C35 3300 mfd cap had cold solder on the + side.
Pulled right off the board when I heated up the neg side.
See if that fixes the occasional spurs that follow modulation and make the combiner and the neighbors unhappy .

 

[boiseengineer]

But then again we've never seen any proof that there's a spur.