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MSF5000 RF deck getting hot

This forum is for discussions regarding System Infrastructure and Related Equipment. This includes but is not limited to repeaters, base stations, consoles, voters, Voice over IP, system design and implementation, and other related topics.

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MSF5000 RF deck getting hot

Postby kcbooboo » Sat Aug 16, 2003 3:46 am

I have an MSF5000 Limited station (C64RLB7106) UHF 75 watts, setup as a repeater, sitting in my garage on a workbench. Transmitter is connected to a 150w dummy load, receiver to an antenna. A repeater controller makes the unit send out a beacon for about 12 seconds every 30 minutes. Other than that, it sits in standby receive mode. It has been on like this for several weeks. Yes, the garage does get hot but it also cools off at night.

The front panel of the RF deck, and all the cast metal behind it, is very hot to the touch. The deck is at the very bottom of the cabinet, there is no fan inside, and the standard louvers are free and clear. The power amp is what I'd call ambient - certainly warmer than if it were sitting in a cool basement. You can actually feel the heat rising from the RF deck. I can hold on to everything, but it's not comfortable to do so. There shouldn't be too much in there to get hot, unless there are crystal ovens or heaters somewhere. The MSF5000 manual is very incomplete as some of you may realize, so I can't even look at a schematic to figure out what could even generate that much heat.

Is this normal? If not, any suggestions?

Thanks.
Bob M.

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Postby Monty » Sat Aug 16, 2003 7:40 am

Hi:

If your MSF is running @ rated power, you may only
need the fan kit.

But, I would disable the Transmitter, place a DC current
meter in line with the PA source voltage , and see if its
drawing a a lot of current.

This is to rule out leakage in the PA Transistors,
and perhaps any By-Pass Caps.

It should NOT get that hot for being on 12 Seconds
and OFF for 30 minutes.

If no / very low current is seen, chances are the
PA is OK, and the heat is being generated by the
Transmitter when turned on.

But I would suspect the Transmitter is on for
more than 12 Seconds....Maybe 12 min ?

Although the MSF's are rated a continuous duty, I still
would add a fan Kit.

The Originals are pretty expensive, but you can make
up something for about ½ of what Motorola charges.

I have one Brand New in the box, but its not cheap.

I also have one of the Depot Manuals ( not available to
the GP anymore ) so if you need a page or two, let me
know. Its about 8 " Thick.

The one in the white binder is close to being useless, but
Motorola believes the majority of persons in the field now
are technically incompetent when addressing MSF's

Wrong !

Monty
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Contact me anytime/All availible / Free Support Info !

mail to: mailto:MSisco9939@aol.com
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Postby kcbooboo » Sat Aug 16, 2003 8:39 am

I think we're talking about two different assemblies here.

The unit that's getting hot is the RF deck. That's the unit that the SCCB and TTRC boards and their plastic enclosure mount to. The thing that has the 6 receiver front end adjustments on the front of it. The unit that has the VCO locking knobs (TRANSIT/OPERATE) on it. The unit that slides out on its own rack mount slides and has two finger-latches at the bottom corners of the front panel.

The unit way at the top that hinges down and is mostly a big heat sink is what I'd call the PA (power amp). Behind that is the power supply. These two units at the top only get warm after the station has been transmitting a while, otherwise they stay at whatever ambient temperature exists in the garage.

The unit at the bottom that proudly says "MSF5000 Limited" on the front panel is getting hot. The front panel is hot. The top of the chassis, under the control enclosure, is hot. If I slide the unit out, any metal area I can touch is also hot. For example, right now it's 90 outside. The PA heatsink temp is 98. The outside of the cabinet (it's in a hot garage) is 100. The front left side of the RF deck's front panel is 110. The front right side of the same panel is 108. The front door of the cabinet (28 inch tall) is on. The temp at the bottom of the front door is warmer than the top of the front door, just by feeling it. It's my guess that the rising heat is heating the upper section, but it's obviously coming from the RF deck. There is no fan in this cabinet, although I probably will add one "just because".

There can't be that much down there capable of generating heat during standby conditions except some power supply regulators. When the unit is not transmitting, only the Rx Lock and Tx Lock LEDs on the controller are lit. As far as I can tell, the station is operating normally. The dummy load on the transmitter output is at ambient temperature, and certainly gets warmer with the transmitter turned on. The only reason the transmitter is on a dummy load and the receiver is on an antenna is that I haven't mounted my duplexer to the back of the cabinet or assembled the coax cables to connect it to the two RF jacks on the side of the unit.

If I had a schematic. it would let me know what's in the RF deck, and I probably wouldn't worry about it as much.

Bob M.

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Postby bernie » Sat Aug 16, 2003 6:03 pm

My two bits worth:

I agree with Monty.
The RF casting has the 9.6V regulator, IPA, the VCOs, and the uni-board.
I guess that the injection amp could get warm. The casting the metal panel with the "MSF5000" lettering is attached to is a receive filter. All passive components.
This does not even get warm.
The only thing that could heat up the whole casting would have to be on the IPA assembly.
Aloha, Bernie

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Postby kcbooboo » Sat Aug 16, 2003 6:11 pm

Well, 110F may not seem hot, but to the hand, it's hotter than anything else in the cabinet, and I can definitely tell you that the black panel with the MSF5000 lettering on it is just as hot as the casting behind it, and the aluminum cover under the control assembly. All the lights on the control unit indicate it's not transmitting, but those might only tell me what the big power amp is being told to do. I suppose something in the exciter could still be transmitting and making some small amount of power. However, walking around with an HT, I don't get very far before the signal is gone, like maybe 15 feet, so it isn't putting out that much power. Is there anything I can put a meter on to check if something is still transmitting even though the PA isn't? The RF deck is on the bottom of the cabinet and getting to anything underneath it is nearly impossible. If it were on the floor I'd say it IS impossible.

Still open to suggestions.

Bob M.

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Postby srefurd » Sat Aug 16, 2003 6:42 pm

Bob how long did you have it plugged in before you noticed the heat?

Reason I ask it that I have a MSF low power unit on my bench right now that I would be willing to power up and see If I get the same results.

Let me know If I need to do this. Although mine is inside I could still tell you if something similar is going.
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Postby Jim202 » Sun Aug 17, 2003 5:10 pm

As Monty recommended, you need to put an amp meter in line with the PA high current wire. When the TX is not operating, you should not see any current being pulled by the PA.

There can be a problem with the PA transistors and it could draw current. When it does this, the PA transistors will generate heat even though no RF power is being generated. This is why you need to measure the current draw with no TX power.

If you find this, the PA transistors will probably need to be replaced. Don't try to just replace just one. Do both at the same time. If one went bad, the other one has been stressed and will fail down the road. There is a chance that one of the capacitors has gone bad, but not that common.

Jim

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Postby Nand » Sun Aug 17, 2003 7:47 pm

Am I missing something in the replies?

Bob is asking why the RF deck is getting hot, not the PA. The PA apparently is cooler than the RF deck because it is only keyed up 12 second each half hour for ID.

What are you saying Bernie? You agree with Monty who talks about the PA but you correctly conclude that the problem has to be the IPA instead, which is located in the RF deck.

Nand.

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Postby srefurd » Sun Aug 17, 2003 7:57 pm

I'm glad I'm not the only one to read it that way Nand!

I have got my MSF plugged in (for about 5 hours). It doesn't transmit unless keyed. The top of the RF deck it warm to the touch. Not hot by any stretch, but I will check it again in the morning, and let ya'll know.
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Postby bernie » Sun Aug 17, 2003 11:03 pm

My two bits worth:
I have an MSF by my bench for testing boards. I will fire it up and see what gets warm. I would not think that the PA would get warm unless one or more of the PA modules was defective. These modules are very reliable. The pa is reportedly cool, anyway.

It would seem that the RF casting is getting hot. Why?
Is this normal?
The power supply naturally runs hot.
The transformer in a ferro-resonant supply runs hot by design.
It would not seem likely that hot components on the top of the station would make the RF casting hot to the touch.

Consider what is inside the RF casting:
Only the IPA/9.6V regulator is heat sinked to the casting.
Any other component that could heat the casting would be charcoal by now.
I would look for a problem with the 9.6V supply, such as a shorted cap.
Or less likely the IPA amp is drawing current.

I presume that this station is not equipped with a heater, which might be found on an un-heated site.
Aloha, Bernie

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Postby wavetar » Mon Aug 18, 2003 5:54 am

We have a lot of MSF5000's in a controlled environment, constant 70 degrees F. The RF deck is what I'd call 'warm' to the touch. In other words, it doesn't feel 'cool' to the touch like other metal objects in the site. This tells me the RF deck generates it's own heat. This is with dual fans in the units. I can easily see it getting 'hot' to the touch in 'hot' environments, especially without the fans. The garage is approx 100F, the hottest part of the deck is only 10 degrees higher. I'd say it's normal for where it's located.

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Postby srefurd » Mon Aug 18, 2003 8:57 am

I agree with wavetar. I plugged my msf up last night and it didn't take but about 30 minutes or so for the rf deck to get warm to the touch. Now about 15 hours later the deck is still about the same temp. So maybe it is going to get x above ambient no matter what temp or where it is.
Within limits of course.

Now as I said above my system doesn't auto id either. The only time it transmits is when it's keyed.
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Postby kcbooboo » Mon Aug 18, 2003 9:19 am

Thanks to all who responded. I was waiting for notification from the BBS that more people had posted, but hadn't gotten anything earlier this morning.

First, the PA is the big unit that hinges down and is mounted to the power supply. It also is 50% heatsink. This unit is ambient temperature and is only getting slightly warmer when the unit is transmitting for 30 minutes. This is expected and I'm not writing about this particular assembly.

The power supply behind the PA also is generating just a little bit of heat. This is expected and I'm not writing about this particular assembly.

The RF deck is the unit that has the receiver tuning adjustments on it, and has the control logic boards mounted above it. This is the unit that's getting hot. Even though the IR thermometer says 110, it feels hotter to the touch. Yes, the garage is not ventilated and gets up to a rather high temperature, so the entire station could get warm.

There is no heater inside that I'm aware of, at least nothing is visible.

I pulled each of the fuses in the power supply and measured the current. In standby, one supply provides 1.2 amps, the other about 0.2 amps. In transmit, one supply provides about 2.2 amps, the other remains at 0.2 amps. The voltage in standby is 15.5, in transmit it's 14.4.

The unit has been on for several weeks continuously. It's only transmitting a 12-second beacon every 30 minutes, and the antenna jack is connected to a 150w dummy load.

I removed the top cover from the RF deck and everything inside is at the same temperature. The two VCOs are mounted on their springs. I pulled the circuit board inside and the entire aluminum casting is the same temperature. However, since it was cooler outside yesterday, the front panel (black panel with MSF5000 LIMITED stenciled on it) was noticeably cooler than the top cover of the RF deck.

If someone has a similar unit that they could leave on, with the front door in place, I'd be interested to find out how hot it gets. If there are any other tests I could perform, please let me know. If someone else could measure the current at the two fuse jacks in the power supply, that would give me something to compare to.

Thanks.
Bob M.

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Postby wavetar » Mon Aug 18, 2003 11:42 am

?????
I realize you are not talking about the power amplifier, nor the power supply. I am referring to the same RF deck you are. It will become hot in a hot environment, plain & simple. It is warm even in a very cool environment. I recommend dual 4-inch fans inside for cooling, especially in your summer garage environment.

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Postby srefurd » Mon Aug 18, 2003 1:12 pm

I think he was responding to everybody further up the board. He was trying to explain it where everyone would understand.

Bob I am going to leave my system on for the next coupla of weeks I'll let you know what happens
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Postby Will » Tue Aug 19, 2003 2:05 am

One point five amps seems a bit high on receive. That is about 21 watts!. The IPA, intermeadiate power amp should not draw that much on standby, it has a shutdown lead and shuts down the clas A stage, the rest of the low level stages are class C, and only draw current when driven by the first class A stage. A note here the VCO runs at freq all the time and that feeds the class A stage, hense the need for the disable. The 9.6 volt regulator is basically in the IPA section, to the rear of the RF Tray casting. The IPA could be self oscillating and be putting out power on the cable leading to the PA.

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Postby kcbooboo » Tue Aug 19, 2003 3:35 am

The current is 1.2 amps in standby, not 1.5. And I realize that the VCO and basically the entire RF deck is operational in standby. I'll have to disconnect the RF cable going to the PA and see if anything is coming out of that connector. Unfortunately, if it is, there's not much I can do about it since Motorola was so kind not to provide full schematics of everything in the RF deck. If I knew what was in there, I could do a much better job of diagnosing what's generating all the heat.

And yes, a few of my posts were directed at the general readership, not at any one in specific, in an attempt to let people know that the RF deck (the unit that is mounted on rack slides) is the unit getting hot, not the PA or the power supply.

Sounds like a couple of fans are required no matter what I do, so that'll be the next thing to try to fit in. The site where this unit will be running is a controlled environment but I'm at the end of the room that doesn't get much air flow from the A/C system, so the temp tends to be around 75F. Considering that there's a 20kw FM transmitter, running at 11kw, six feet away, blowing out all kinds of hot air at 150F, the A/C system does quite a nice job. In fact, that's the only source of heat for the room. It would seem to me that they should have vented the transmitter outside for the summertime rather than fight all the hot air it puts out, but I just live there and don't have any decision-making powers.

Follow-up to those that have posted comments here. The entire unit is cool when the garage is cool, but the RF deck is definitely hot. I would skip the warm state entirely. I can leave my hand on the top of the RF deck but it's uncomfortable to do so for more than a minute. Everything else in the cabinet is cold, i.e. ambient temp. The transmitter comes on for such a short duty cycle that nothing gets warm because of that, yet. Once the repeater goes up to the site and starts being used, I would expect everything to get hot, and I was planning to add a fan just to move the air past the PA. While I could leave the front panel off the station to increase ventilation, I think it doesn't look as professional, and leaves it rather unsecure, by doing so.

Bob M.

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Postby srefurd » Tue Aug 19, 2003 5:48 am

Bob I am an amateur so don't jump down my throat for asking this. Do you have the VCO locking devices turned to the operate position?

This was stupid of me, but when I first plugged up I had forgot to move them from transit to operate and in the first 15 minutes the unit got a lot warmer than after I unlocked them.

Right now been running 36 hours and everthing is barely warm to the touch.
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Postby Nand » Tue Aug 19, 2003 1:43 pm

I just returned from taking the current measurements on my 35-watt UHF MSF5000 that has been running for several months now in an uncontrolled shack out in the hot sun. And yes, the RF tray is very hot. The cover over the uni-board is very uncomfortable to touch and the front of the RF tray isn’t a lot cooler.
The current through the top fuse is 1.12 Amp and the lower fuse carries .09 Amps. This repeater does not have the wire line board in it, so the current may be a bit different from Bob’s repeater.

I also finally got a real manual for this beast. It is the 68P81082E10-O, about 4.5 inches thick. I had this verified. The other manuals like the 86P81092E80 and the E05 are either incomplete or not meant for detailed repair.

As in interesting note, when NOT transmitting, the first three RF transistors in the IPA do get fully turned on (saturated) to prevent these from passing on any signal. This will account for an extra bit of heat while in standby when there is extra current drawn. Leave it to Motorola to do things different and often better at the same time.

For those wondering what IPA stands for, it means Intermediate Power Amplifier.

Nand.

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Postby kcbooboo » Thu Aug 21, 2003 10:59 am

Answer to a previous question: Oh yeah, the VCO transit locks are definitely in the OPERATE position. I had no idea they were even lockable when I moved the unit from my friend's garage to mine, then when I started investigating the insides I discovered, too late, about the transit locks. To get to the VCO adjustments one must lock these down, but once done I did unlock them. When I move the unit to my repeater's location I will make use of these locks. For something so important I would have liked to see some kind of warning label plastered in a prominent place on the RF deck.

By the way, Motorola calls it the "RF Tray". Sorry for any confusion I may have caused by calling it the "RF Deck".

Nand: You spoiled all the fun by explaining what IPA stands for !

Well, I'm glad I'm not the only one who's RF deck is getting hot. Nand's observation is right in line with mine. Add a front door to the enclosure and the front panel of the RF deck will get to be as hot as the top cover of the RF deck. The slight difference in current also would make very little difference in actual dissipated heat.

Sounds like that manual has all the missing stuff that the "service" manual should have had. If it gave you details on the IPA circuitry, that's certainly an improvement. Does it have full schematics of the RF deck, PA, and power supply? I just called /\/\ and that 68-81082E10 number (a depot service manual by the way) crosses to a 68P81092E80 which is the regular incomplete MSF5000 UHF Service Manual that I already bought for $55.12. No other detailed service manuals are available for this radio.

Bob M.

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Postby Nand » Thu Aug 21, 2003 3:22 pm

Just in case you like a peek, here it is.

http://142.46.202.89/990/MSF5000/IPA.pdf

Nand


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