You asked about the slow turn on, 5 to 15 seconds, and distorted receive on Maxtrac and Radius M series radios.
I have traced the problem to a 33uf capacitor at C551 on the logic board in the detected receive audio filter stage. I found that there is a lot of leakage in the 33uf capacitor and it takes a LOOONG time to charge up so the bias on the filter amp is near where it needs to be. I found that a 4.7 uf or a 10uf capacitor works just fine here and it only takes about 2 seconds to "come on". I recomend a low leakage type here @ 25 volts rating minimum.
"Slow Warm-up & Turn On" Maxtrac/Radius
Moderator: Queue Moderator
"Slow Warm-up & Turn On" Maxtrac/Radius
Last edited by Will on Wed May 15, 2002 11:58 pm, edited 1 time in total.
Thanks. Got your message and came over here. I'll check that on my schematic later today. It's still a bit longer than I'd care to have it take, but that could most likely be fixed by decreasing the resistors (I'm assuming) to lower values but maintaining the ratio, so the cap comes up to the right voltage sooner.
Now, any ideas about the transmit audio rumbling/noise? It is very possible that the radio needs calibration and/or alignment. The manual number that I need (for the conventional Maxtrac service manual) doesn't seem to exist any more and comes back with the number for the detailed manual, which I already have and which has nothing in it about calibration and/or alignment.
Bob M.
Now, any ideas about the transmit audio rumbling/noise? It is very possible that the radio needs calibration and/or alignment. The manual number that I need (for the conventional Maxtrac service manual) doesn't seem to exist any more and comes back with the number for the detailed manual, which I already have and which has nothing in it about calibration and/or alignment.
Bob M.
kcbooboo, I will get to you on e-mail on the rest of the problems in your Maxtrac.
For the rest of the BatBoard people, the same thing, "slow warm-up", occurs on Maratracs too. Same problem. Changing the resistors in that circuit will not help this and is much harder to do. Changing the capacitor is easier and it is on the componet, top, side of the logic board and you do not even have to take the board out of the radio.
For the rest of the BatBoard people, the same thing, "slow warm-up", occurs on Maratracs too. Same problem. Changing the resistors in that circuit will not help this and is much harder to do. Changing the capacitor is easier and it is on the componet, top, side of the logic board and you do not even have to take the board out of the radio.
The radio is transmitting ordinary TPL, no DPL. The rumbling and noise on the transmitted signal is always present. It's enough to cause the PL tone deviation to vary slightly in amplitude on the meter. I have NOT disabled the PL to see how much noise is really there. I have NOT attempted to discover whether it's noise in the audio chain (i.e. modulation) or instability in the VCO (i.e. synthesizer pulling). All of these tests were done indoors on a 35a power supply with a dummy load and wattmeter.
It is noticeable by other repeater users, and sometimes seems to cause me to drop out of the repeater due to interference with the PL, although I'm not entirely sure this isn't because of excessive alternator whine.
I tried to obtain a manual that has the complete alignment and adjustment procedure for a MaxTrac but such a thing does not exist. One either has the 68-80102W84 detailed service manual that doesn't have this info, or one becomes a Motorola authorized customer, pays big bucks for RSS, and can then get the RSS manual that's supposed to have all the calibration procedures in it. To me, this still leaves all the alignment stuff undocumented, i.e. if I had to replace the VCO coil, how do I go about adjusting it? What if some previous owner tweaked all the coils in the exciter and front end? What signals do I adjust everything with? Motorola's answer, by the way, is to return the radio or RF board to their depot since only the factory does those kinds of alignments. Since I only paid $40 for the radio, these options are out of the question.
It is noticeable by other repeater users, and sometimes seems to cause me to drop out of the repeater due to interference with the PL, although I'm not entirely sure this isn't because of excessive alternator whine.
I tried to obtain a manual that has the complete alignment and adjustment procedure for a MaxTrac but such a thing does not exist. One either has the 68-80102W84 detailed service manual that doesn't have this info, or one becomes a Motorola authorized customer, pays big bucks for RSS, and can then get the RSS manual that's supposed to have all the calibration procedures in it. To me, this still leaves all the alignment stuff undocumented, i.e. if I had to replace the VCO coil, how do I go about adjusting it? What if some previous owner tweaked all the coils in the exciter and front end? What signals do I adjust everything with? Motorola's answer, by the way, is to return the radio or RF board to their depot since only the factory does those kinds of alignments. Since I only paid $40 for the radio, these options are out of the question.
Slow audio fade-up
Replacing C551 with a 10uF 35v cap did the trick beautifully. I may have lost just a bit of low frequency noise, but I don't think it's going to be a problem. Thanks.
Transmit audio rumbling/noise
I did some tests tonight. No mike, just an RIB and cable. The noise was present when keyed up via RSS on 455.005 MHz. No modulation during this test, not even PL. I scoped the RF board pins 10 and 13 and they were quiet as a mouse. Lots of signal present on both pins when the mic was plugged back in and keyed. I did some probing around the VCO but saw nothing with a noticeable low frequency jitter, down to several millivolts per division on the scope. When I touched L216, the radio went off frequency for a short time but came back on. By the way, it sounds horrible on another receiver when it first comes up transmitting via RSS software, TX power setting being used to key the radio. Like it's way off frequency and it begins to transmit before it has actually locked on the proper frequency. I think the board just needs a good going-over with the right software.
There is definatly something wrong in the Synth and or VCO section. I have fixed a lot of these and would like to look at yours due to the sevarity of the problem. As for the alignment instructions, I never saw any, even in the programming manual. There was only bits and peciecs in the RSS help and other small bits in the service manuals. I have been working on radios for so long that I did not give it a thaught, I just went to work on them and found out myself how best to do it.
Well, if there's something wrong, it must be good enough to let the radio still operate properly and be on frequency. My guess would be some bad filtering in the VCO control line, and I'm sure that just a little instability here will cause havoc with the wide frequency range it's capable of.
As soon as I find out what new, if any, Kenwood products are released at Dayton, I'll probably pick up a couple of TM-V7A rigs. I can then send you the Radius for further debugging. At least the receive problem is history. Working absolutely perfectly from my standpoint.
As soon as I find out what new, if any, Kenwood products are released at Dayton, I'll probably pick up a couple of TM-V7A rigs. I can then send you the Radius for further debugging. At least the receive problem is history. Working absolutely perfectly from my standpoint.
Hey Will, this is a great find! I have to try that on one of my Maxtracs that is really really slow warming up. And I thaught that only tube radios were warming up slow.
Thanks for your engineering knowlege and for letting the rest of know just why the problem is there and what an easy fix it is.
April
Thanks for your engineering knowlege and for letting the rest of know just why the problem is there and what an easy fix it is.
April