MSF5000 No Repeat Audio

[rdunajewsk]

I just acquired an Analog-Only UHF MSF5000 which programs via EEPROM. I fired it up, realizing that it needs the power supply capacitors replaced (clearly one of them has seen better days), but wanted to get a feel for it while I ordered the parts. Right away I notice that repeat audio does not work. The proper PL keys the repeater with dead air, but the repeater does generate a PL when keyed. If I flip the PL Disable switch, the repeater passes audio as expected but of course now it's operating in CSQ. I read up that some radios had a pin on U831 cut to allow trunking data through but not in-cabinet repeat audio. Since this is a UHF analog-only repeater, there's a different chip at U831, a 14-pin instead of the 8-pin shown by everyone else. It's fully in-tact.

So either something on the SSCB is bad; a chip, a trace, or another component, or there's a jumper or programming error. I didn't burn the EEPROM, it was done for me by a friend of a friend so I don't know for sure what the parameters were except for the frequencies and tones and timer values. There's no CWID, so I can't check if that modulates the carrier or not.

What does PL Disable do to the audio path that makes it work? What components does the audio bypass, if any?

A seemingly unrelated matter is those filter capacitors. After the station is powered up idle for several minutes, the Test LED begins to intermittently flash. Then the rate slowly speeds up over time until it's solid on and the VCO lock lights go out. Powering down the repeater only yields the same result unless I wait a good 15 minutes before connecting power again. Using a can of compressed air, I was able to verify this was due to those capacitors by hitting them with air while Test was flashing. As they cooled down, the flash rate slowed and eventually stopped until they warmed again. I don't think this has anything to due with the audio issue, but I won't put my neck on the line and say it couldn't be a side effect. Perhaps the sloppy 5V line is causing a component in the audio path to bug out, causing the failure. PL Disable might bypass that component and allow audio to pass.

So, any thoughts? Thanks!

[kcbooboo]

The references to U831 are for the digital-capable and analog-plus stations that use RSS for programming. The EPROM-programmed analog stations have a completely different station control board. About the only things that are compatible between the two boards is that they both have the same volume and squelch knobs on the front, the same two on-off-mom toggle switches on the front, and use the same 6-pin power connector. Other than that, totally different beast.

The PL DIS switch only disables the necessity for PL on the receive signal. The logic is all performed in the microprocessor.

Pressing the XMIT switch causes the transmitter to be activated WITH NO MODULATION, so if you're using that switch to transmit, you won't get PL, audio, or anything else except a quiet carrier signal.

Lots of things that could go wrong with the audio. Luckily it's fairly simple (at least when you have the schematic in front of you). There are a few front-panel adjustable pots that control repeat audio and transmit deviation. One of those could be bad. There's a TX Audio test point you can inject audio into and see if it's causing transmit deviation to occur. All you can really do is follow the receive audio through the ICs or inject your own audio at various places and find where it stops. The analog stations don't have the extensive audio testing built into the digital stations.

Leave the station off and replace the PS caps before some other damage occurs.

Bob M.

[rdunajewsk]

I understand the difference between the analog and analog-plus/digital models, no issue there. What bothers me is that it works fine with the PL disabled, but clearly it's matching the PL from the transmitting radio to key the machine. The person who gave me the repeater suggests that the receiver may need to be tuned for audio to show up, but then I would expect no repeat audio whatsoever.

Perhaps there was a programming error in the EEPROM -- I'm not familiar with the programming parameters on this repeater, so I don't know if there's a setting to control the repeat audio behavior.

When talking through the repeater with PL on, the machine keys with dead air but it does modulate with the proper PL tone, so the receiving radio unsquelches but there's just no repeat audio. Forcing it to key by using XMIT keys it without ANY modulation, but that's normal. Flipping the PL Disable switch makes the repeat audio work great, nice and loud and no distortion but now it's no longer going to match a PL. I would think that if an audio level pot were turned down or bad, there would be no or low repeat audio when PL Disable was on.

So then the microcontroller/firmware/codeplug must be bad, logically, unless there is an audio gate somewhere on the board similar to the other recent models. Something has to squelch and unsquelch the audio outside of the CPU. U831 doesn't apply to this model, so is there another chip which does the same thing at a different point in the circuit?

Again, if the receiver needed tuning, I wouldn't expect it to work with PL disable on. It decodes the incoming PL fine, so the receiver clearly is working. I'm less than 2 MHz away from the old frequency which it was on.

Replacing the caps is my next job, this was just what I noticed when I powered it up to test when I got it home. Can anyone recommend aftermarket replacement parts (non-Motorola) that are known to work? I hear the Motorola stock is old generally speaking and aftermarket parts yield the best results.

[fineshot1]

[quote="rdunajewsk"]The person who gave me the repeater suggests that the receiver may need to be tuned for audio to show up, but then I would expect no repeat audio whatsoever.[quote]

Rich - sorry for the confusion but when I mentioned this to you I ment it as a possible seperate issue(when changing frequencies).

[quote="rdunajewsk"]Perhaps there was a programming error in the EEPROM -- I'm not familiar with the programming parameters on this repeater, so I don't know if there's a setting to control the repeat audio behavior.[quote]

I am not familiar with the programing of the eproms either but do know that they only contain basic info - ie: frequency, PL/DPL, callsign, etc. etc.

Did your testing with the original eprom on the original frequency yield the same audio results?

[rdunajewsk]

No problem, i misunderstood what you were saying. I realize it may need to be tuned but 2 MHz appears to be within TX and RX specs for tuned bandwidth. Worst case I could just use an external controller.

I didn't find the input frequency, I tried +/- 5 MHz in CSQ and got nothing. So then I loaded up my EEPROM and it received fine. I guess it was set up for a non-standard split and I didn't have a frequency-agile radio handy to try different frequencies.

I guess I can load up the old codeplug but I'd rather not stress the socket/chip over and over if i don't have to. I didn't find the input frequency, I tried +/- 5 MHz in CSQ and got nothing. So then I loaded up my EEPROM and it received fine. I guess it was set up for a non-standard split and I didn't have a frequency-agile radio handy to try different frequencies.
In
I guess I can load up the old codeplug but I'd rather not stress the socket/chip over and over if i don't have to.

[d119]

Rich,

So you have or have access to the R1801 to reprogram the station? That makes life a lot easier.

Sounds like you might have had something other than a standard repeater based on your comments.

THE first thing you need to do before moving on is to replace those filter capacitors. I had two CLB series MSF 5000's that had sat in our shop powered off for ages before I decided to do something with them, and upon powering them up, neither worked properly and both behaved really screwy until I replaced the filter caps.

I could be wrong here, but by not replacing them not only will you get odd station operation (possibly including the audio issues you've mentioned), but you also run the risk of potentially damaging the 5v section of the SCB, and replacement parts for that aren't easy to come by. IIRC, they used some sort of strange triac to get the 5v... I've got a bunch of boards with burned up 5v sections in my junk pile.

The stock filter caps are a three-legged device (two pins on one end, one on the other), but you can just replace them with the same value axial component, 660uF 40V might be hard to come by, I recall having used 1000uF 25V without issue. Just make sure it's aligned properly on the SCB.

If after replacing the filter capacitors you're still encountering trouble, the best place to start would be with a known good, properly programmed codeplug EPROM, as you said.

If this is indeed an analog-only, "CLB" series station, you'll need the R1801, a UV EPROM eraser, and a known good 27C32 EPROM.

These stations have no EEPROM's in them, those are in the "CXB" "Digital-Capable" (meaning CVSD SECURENET) MSF 5000's. Likewise, CLB stations don't have an SSCB (Secure Station Control Board), they just have an "SCB" (Station Control Board), as they don't support SECURENET operation.

Just pull the EPROM straight out and push it straight back in, minding the pins, you won't stress anything out. Those EPROM's are a common product available from countless sources, so if you break it, it's not a big deal.

[rdunajewsk]

UPDATE: Still waiting on the capacitors to come in, but I powered it up briefly to see if it would ID. I looked up the callsign and pulled up the authorized frequencies. Perfect match! Punched them into my radio one by one and finally found the input. The old codeplug works normally, no need to put the repeater in PL Disable mode to get audio to pass. So this means that the new EEPROM is messed up, probably a programming issue since I took great care to install it (static-free). Can't be a PL/DPL tone issue, or the repeater shouldn't key up at all on the matching tone. Perhaps in-cabinet repeat was disabled when the programmer burned the EEPROM?

The irony is that putting the old codeplug into PL Disable didn't disable the requirement for a proper PL. I was on-frequency in CSQ and PL Disable on, but it didn't key until I found the PL of 206.5 Hz. Can this switch be reprogrammed/modified for another purpose then? It seems to defy logic.

Does anyone have the full list of programming parameters for these repeaters (CLB)? Other than the basics I don't know what options are available or what could have been mixed up at program-time.

[d119]

The PL disable switch as well as the front panel volume/squelch controls only affect the local speaker. The qualifier for repeat operation is still CSQ + PL (usually. Aka "AND" squelch).