maratrac question

[kb2crk]

i now have two maratrac drawers. one is vhf hi and one is vhf low. my question is can i use the same head to program both of them?
can i switch the head from one to the other without having to reprogram every time? thanks for the help.

[Bill_G]

As far as I know yeah. The display heads were not that sophisticated.

[wx4cbh]

With only a few exceptions, the heads shouldn't make any difference, especially if you're just using different versions of the A7 head. In fact, in a pinch, you can power up the radios for programming without the head or control cable by making two +12V and two 12V Neg connections to the proper pins on the large power/control connector on the drawer. As long as the radio will power up and sit idle without doing weird things, it will allow programming regardless of which head is attached or set in the RSS. What it does after you program it is determined by the combo of head and cable and what you just programmed it to expect.

If your low band is the later type that has the squelch control on the control head, putting the standard head on it will make no difference in operation so long as the internal squelch control is adjusted properly. Putting the squelch control equipped head on a MaraTrac that doesn't have the audio squelch board that's designed to use the external squelch pot will make no difference to the MaraTrac at all because the wires used for the adjustable squelch circuit aren't used in those versions, and the radio just doesn't see the external control. The later low bands were the only ones manufactured with the squelch pot on the heads.

[kb2crk]

thank you for the info. now i am having an issue with the vhf hi receive audio cutting out with strong signals. this is something that just started and i am not sure why. will the radios do this with a very strong signal? or do i have something set wrong?
thanks paul

[Jim202]

I would take a look at the radio to make sure that your TX is on frequency. If the modulation is high and the RX is slightly off frequency, the RX audio will probably
start to chop up. The way to prove this is to have the TX end station back away from the mic and see if the audio sound better.

Many of the ham repeaters have the TX audio deviation set too high and as such will walk out of the band pass of some of the commercial radios. My Motorola
Astro Spectra receiver is hard on these 2 meter repeaters. It breaks up on a number of the local 2 meter repeaters.

Jim

thank you for the info. now i am having an issue with the vhf hi receive audio cutting out with strong signals. this is something that just started and i am not sure why. will the radios do this with a very strong signal? or do i have something set wrong?
thanks paul

[kb2crk]

there are 2 2 meter repeaters that i have issue with doing this one is about three miles away and the other is only about 5. that may be the issue. the sheriffs repeater is only 2 miles away and i have had no issue with it. the deviation is probably the problem. i will see if i can find a way to test for it. it is not an all the time problem

[wx4cbh]

Does this problem occur since it got cooler? Is the serial number between 776TXWxxxx (Nov 1, 1997) through 776TZBxxxx (Jan 8, 1999)? Is the channel a CSQ receive channel or is the Channel Unmute condition in the RSS set to anything but STANDARD? If so, it's possible that the op amp U1101 on the Audio Amp Board (HLN5342E/SP01) in VHF high band and UHF models is failing under cooler temps. In STANDARD Unmuting, the squelch setting has no effect and the audio Unmutes based on proper PL only, not the relative squelch setting, so the op amp doesn't have the same effect on the Unmuting as it does in the AND setting. The AND setting requires the system to look at both the PL AND the squelch setting before Unmuting, and the op amp is the king pin in this phase of the squelch circuit in the AND and CSQ Unmuting thingie.

There was a service bulletin (SRN-1274) regarding this receive audio chopping and/or quitting, mostly on strong signals in cool weather when the Unmuting is AND or CSQ dependent. The bulletin says the symptom occurs around freezing temps, but I worked on several that would begin failing at the freezing mark and gradually get worse and fail around 45-50 degrees F.

The op amp marking for the ones that fail is RC4136. The newer op amp that reduces this problem is marked RV4136. The part number for the revised part from MotherMoto didn't change and was 51-80067C04. Don't know if it's still available or if there's a substitute.

Check your PM.

[kb2crk]

so if i were to check and make sure it was in standard setting i should not have an issue? i am going to check the serial number now.
thanks paul

[kb2crk]

i checked the serial number and it is 776tae****. i believe it is a little earlier. i will when i get a chance hook back up and check the settings.

thanks again
paul

[wx4cbh]

There's more:
First, make sure the squelch is set properly, and it's best to do that with the radio fully at room temps.

For the uninitiated, the squelch pot is easy to locate. With the drawer handle facing you, look inside toward the front about 3 inches behind the drawer handle for the ~4.5 X 7 inch module with the rectangular cover with the pull handle. At the left front of that module is a ~5/8 inch black pot with a little arrow shaped center. The center has a slot you can apply a tuning stick (highly recommended) or small jeweler's screwdriver to it and turning . Put the receiver in a carrier squelch mode. Turn the pot CCW to open the audio, and CW to close it. Set it to a position just inside the closed audio range, but far enough to keep it from "falsing" at squelch threshold. I would do this at the lowest, middle, and highest frequencies in the radio to see if the settings are different. If it does make a slight difference, good deal, but if there's much more than a 16th turn or so between the thresholds, a trip to the bench may be in order. That doesn't at all mean there's something wrong, most likely just a minor alignment thing.

DO NOT GO TURNING OTHER "SCREWS" IN THE RADIO. The radio won't like it and the shop techs you'll have to take it to will have a laugh at your expense, literally.

Look in the RSS and make sure there aren't any Signalling parameters causing the problems, and check the Scan Configuration to make sure that Minimum Hole Size is not enabled. That setting requires the scanned channels to be 5 MHz or less apart. That reduces the scan channel sample time, and as a result, the audio hole that results as it checks the Priority Channel isn't nearly as pronounced, but it will cause the scan to miss some traffic on lower level signals on freqs that are outside the 5MHz spread. I would also Enable the CODED SQUELCH SCAN parameter so that on channels with subtone you don't have to hear the noises of distant stations on the same channels or put up with the noises found at nearby ATMs, gas pumps, and other electronic devices.

On all analog MotherMoto radios, setting the Unmuting to STANDARD only applies to channels with PL/DPL on receive and works only when the receiver is not scanning. Unmuting on Carrier Squelch audio channels is always governed by the squelch setting. In the scan mode, the Unmuting automatically defaults to AND because the PL/DPL determines if it's the desired selection on that frequency, and the squelch level setting determines the desired signal strength and controls the activation of the scan resume delay. When the squelch setting is exceeded and any other channel parameters are met, the receiver stops on that channel, the delay timer is activated in the "hold off" mode, and the audio opens. The timer begins its countdown when the signal level drops below the squelch setting and the audio mutes.

Another question or two: is the label on the drawer a white label with a bar code or is it an older sort of silver and black foil type label? When you read the radio in RSS, does it display the freq range as 150.8 - 174 MHz or 144 - 174 MHz? Even though the radio may say it's a 150.8 - 174 MHz model, it should still accept the frequencies below 150, but it may not readily receive them and the transmitter may run wild somewhere below about 146 to 148 MHz. This is probably not the case with yours since the intermittent audio is a new problem, but I can't speak to the transmitter running wild as it mostly displays no symptoms to the user until it's too late.

Hope some of this helps.

[kb2crk]

the rss reads 144 to 172. the label i believe is the white one with the bar code. the symptom is not the loss of audio but loss of carrier as well and only on the 2 closest repeaters when it is cold. the problem goes away once it warms up. the transmitter seem to be doing fine at about 99 watts when keyed. the local police repeater which is closer to me than the ham ones does not exhibit the same problem. i am not big on tweaking screws unless i know exactly what the outcome will be. it is almost like the squelch is cutting the signals out. i will check the squelch setting as soon as i get a chance.
thanks again for all the help.
paul

[wx4cbh]

That line about turning screws was for the aforementioned uninitiated, not you.

It could very well be losing the carrier if the RX sensitivity in the ham band is poor, but whether the op amp is bad or the sensitivity is poor, the effect is the same. Once the circuit causes the audio to mute, the busy light goes out and the radio shows the same indication as if the carrier is lost. The only remaining indicator in either case would be the non-priority or priority light which will stay lit for the duration of the scan resume delay setting, then go out.

If someone has re-aligned the radio at some point for performance in the 150 - 165 MHz (not unusual I have found), the lower and upper ends of the 144 - 174 spread can become compromised as far as RF amplification goes. The effect is that the receiver quieting at 146 Mhz and 154 MHz at ~0.8 - 1.0 microvolt signal levels remains pretty much the same, but at 0.4 microvolt signal level, the 154 MHz response is better than specs, but there's no response at all at 146 MHz. In other words, it takes very little drop in signal level to chop or completely lose the signal. What you describe sounds pretty close to what the receiver's performance would be in that situation. Throw in a temp sensitive op amp and you've got a really frustrating listening experience.

The reason for narrowing the frequency range by alignment is usually an attempt to solve some receiver intermod/adjacent channel interference problems. While the attempt does improve the receiver intermod problems in some cases, the jury is still out on the adjacent channel rejection improvements. As mentioned by Jim202, this sensitivity thing can be caused by the radio being a bit off frequency. The above mentioned effects of attenuation by realignment are even more enhanced if the radio is off frequency.

I'm in and out of your area for the next few weeks and have a couple of white label MaraTracs you could swap in to see if there's a problem in the radio or there's something else going on. Email or PM me.

[kb2crk]

ok here we go. the last couple days have been warm and the radio works fine. the nights have been cold and that is the only time there is an issue. the issue only happens on the nearby strong signals and not just ham repeaters. 35 outside now and the sheriffs repeater and the 2 nearest ham repeaters drop out. checked the local weather service freq and the same thing. tuned in ham repeaters and sheriffs repeater further out and no problem. this includes the the weather service freqs. the weaker signals are no prob but the nearby ones either dont break the squelch or drop in and out and only when cold. the receive is set to standard in the rss. i have carrier receive set on all freqs.
is this a common problem. is the the op amp problem happening in what appears to be an earlier radio? how can i fix it? at least i know why it was taken out of service in upstate ny before being sold on the bay..
thanks again
paul

[Bill_G]

Time for a can of cold spray, and a little bench tlc.

[chartofmaryland]

When you first power on the radio, work the volume from all of the way down and back up.

You should immediatly hear a response from the radio when doing this, if you cannot hear the audio coming up as you push the volume up button then your capacitors on the audio squelch board are failing.

During the weak signal reception the audio associated with these is normally low unless you enjoy listening to white noise at +25 db . . .

Low audio will work and not swamp the audio circuit, clean loud audio will draw more current and the lack of available current from what could be your dried up caps will not allow the audio to come through the speaker.

On the other hand, if you can ramp your volume indicator tone up and down during times the audio problem is present and can hear the tone clearly then this is not your issue and is more involved.

Just the simple stuff of the top,

CoM

[kb2crk]

i will give it a try when i leave for work this afternoon. it is in the low 40's here today and the radio was acting up while i was mounting the uhf maxtrac today.
thanks
paul

[Will]

Look for the "Maxtrac slow warm up" article. You may have a leaking audio coupling cap, C521, on the logic board. It is the only 33uF 25 volt cap on the logic board. This will affect the receiver audio but NOT the volume set tone(s).

All Maratracs going thru the shop get this cap replaced.

[kb2crk]

tried it out today with the vol tone and a busy channel. there was no issue with it cutting out.
the repeaters that were close and had strong signals were still cutting out. once i was a few miles down the road it worked fine.

[arlojanis]

I have had the choppy or muted audio during cold weather on several VHF MaraTracs, and setting the channel unmute condition to standard via RSS cured the problem.

[wx4cbh]

The symptoms you're describing are the typical op amp problem symptoms. MaraTracs have always displayed some quirks when in anything but Standard unmuting, and the severity of those quirks varies from radio to radio and how the squelch is set and the age of the radio. As stated by some of the other people here, cap problems aren't limited to the Spectras. MaraTracs can be susceptible, too, but in Max and MaraTrac cases, it's usually dried out caps instead of leaking ones.

Check yer PM

[kb2crk]

it is alive and running well. a swap of the squelch board and the radio is working as it should. thanks for all the help.

[wx4cbh]

Did you rob the donor radio for the audio/squelch board? Just curious.

[kb2crk]

that is exactly what i did. it pretty much points right at the op amp. the radio is working very well but i do need to adjust the squelch just a hair as it is a little too sensitive. still working well even in the cold weather.
thanks again

[wx4cbh]

You're very welcome. And just think, replace the opamp and you'll have another hammerdown 110 watter.