XPR8300 Fan Speed - again

[w0en]

I had the local Moto tech down for some service work today. While he was there we broke open one of several XPR8300s looking for a fan speed adjust switch or switchable jumper as would seemed to be indicated in the Moto literature and recently discussed here in another thread. We found nothing on small green fan control board that the fan harness plugs in to or wiring that looked anything like a "switch", just some surface mount parts. These XPRs are circa 2008 vintage. Does anyone know for sure that this feature was available back then? Again, it wasn't just my eyes that didn't see anything that looked switchable but a guy that has worked on Moto equipment for 20+ years. My main concern is dust, looking at an RKR1225 from same rack where the temp switch was "in" and the fan never runs, it was clean as a whistle but the 8300s were filled with dust in the RF cage area and internally in the PS.

[escomm]

Pretty sure one of the wires needs to be cut

[gopher]

Pretty sure one of the wires needs to be cut

If you cut or disconnect the brown wire the fan will run at 100%. with the exception of disconnecting, no idea how to slow it down. prob a bad idea

[escomm]

You don't want to slow down the fan on an 8300 unless you want to pay for a flat rate. PAs are bad juju in those units

[d119]

You don't want to slow down the fan on an 8300 unless you want to pay for a flat rate. PAs are bad juju in those units

Like we didn't see that coming from day one. I remember looking at our demo unit with the lid off, and saying to myself "There's no f___ing way this thing is continuous duty. NO WAY."

[JRayfield]

Actually, the XPR8300 was very much tested and proven to run 100% continuous duty. I personally know one of the engineers that was involved in this testing and what they did to that model should have quickly destroyed it, but it didn't. That's why it was released - it passed 100% duty cycle tests with 'flying colors'.

The problem wasn't the 'duty cycle', in itself. It has a lot to do with changes in temperature in the PA. Anytime that there is a change in temperature, there is 'stress' on the metal parts (metal fatigue - and there's metal inside those transistors). In situations where the repeater would run cool (low use) for a while, and then get high use (increasing temperature), and then low use, etc., and the fan didn't keep the temperature at a more 'constant' level (it let the PA go from cool to quite hot, before turning on to cool it back down), this would result in an 'up, down, up, down, etc.' type of change in temperature on the finals. That resulted in failures. That's why the fan runs so fast in the XPR8400 - to keep the temperature of the finals down at a more 'constant' temperature, instead of letting it go through that 'cool, hot, cool, hot, cool, etc.' cycle.

I experienced final transistor failures back in the 80's on EF Johnson 800 mhz PA's, and the solution was to put fans on the PA's (they had massive heat sinks which worked fine for 'constant continous duty') and let the fans run continous. That solved the problem. I asked Ted Henry (Henry Radio) about this, not too many years ago, and he agreed that it's best to let fans run continuous, and to try to keep the PA temperature at a more 'constant' temperature. He agreed that the change in temperature, with fans that 'cycle', will 'kill' PA transistors. He told me that he would prefer to ship his amplifiers with fans set up to run continous, but most people want them on thermostats, so that they'll 'cycle', and the thefore the fans will last longer. He said that fans as cheaper than transistors....but I guess his customers haven't figured that out yet.

John Rayfield, Jr. CETma

You don't want to slow down the fan on an 8300 unless you want to pay for a flat rate. PAs are bad juju in those units

Like we didn't see that coming from day one. I remember looking at our demo unit with the lid off, and saying to myself "There's no f___ing way this thing is continuous duty. NO WAY."

[escomm]

Actually, the XPR8300 was very much tested and proven to run 100% continuous duty. I personally know one of the engineers that was involved in this testing and what they did to that model should have quickly destroyed it, but it didn't. That's why it was released - it passed 100% duty cycle tests with 'flying colors'.

You may want to believe this because Motorola told you it was true and it appears reasonable. The fact they A) released an FSB B) extended warranties on existing units past their original warranty period and C) used this as an excuse to redesign to the XPR8400 all speak to the contrary.

Now this engineer that you know.... is it the same one that told me there was NO issue with the VHF units without having done any actual testing on them whatsoever? When I brought it to their attention and they "tested it out in the lab," he called me up the next day to say that my findings had been confirmed. Our implementation called for 100% duty, this is how it was claimed to have been tested in the lab. Not sure how they arrived at the same conclusion as me if what you say is true.

This testing was done with a VHF unit running at 25 watts into a dummy load. I went to bed and it was putting out 25 watts. I woke up the next morning and it was doing 5 watts. There was no temperature cycling that I'm aware of, the PTT pin was jumped on the back and the fan was at the same speed it was at when I set it to PTT-- Full Blast.

[RFguy]

The fact they A) released an FSB

What's the FSB number? I don't see one listed.

Thanks

[ard099]

I found it funny that Motorola called that repeater continuous duty also. We had one fail 3 times in a 2 month period and the repeater was brand new. I don't mean to knock Motorola but if you turn the fan around and blow air across the heat sink to remove the heat it works so much better, they just can't figure that out. The 1225same repeater was the same way. Anyhow after turning the fan around the repeater has been running for 2 years trouble free.

[KI4M]

Actually, the XPR8300 was very much tested and proven to run 100% continuous duty. I personally know one of the engineers that was involved in this testing and what they did to that model should have quickly destroyed it, but it didn't. That's why it was released - it passed 100% duty cycle tests with 'flying colors'.

The problem wasn't the 'duty cycle', in itself. It has a lot to do with changes in temperature in the PA. Anytime that there is a change in temperature, there is 'stress' on the metal parts (metal fatigue - and there's metal inside those transistors). In situations where the repeater would run cool (low use) for a while, and then get high use (increasing temperature), and then low use, etc., and the fan didn't keep the temperature at a more 'constant' level (it let the PA go from cool to quite hot, before turning on to cool it back down), this would result in an 'up, down, up, down, etc.' type of change in temperature on the finals. That resulted in failures. That's why the fan runs so fast in the XPR8400 - to keep the temperature of the finals down at a more 'constant' temperature, instead of letting it go through that 'cool, hot, cool, hot, cool, etc.' cycle.

I experienced final transistor failures back in the 80's on EF Johnson 800 mhz PA's, and the solution was to put fans on the PA's (they had massive heat sinks which worked fine for 'constant continous duty') and let the fans run continous. That solved the problem. I asked Ted Henry (Henry Radio) about this, not too many years ago, and he agreed that it's best to let fans run continuous, and to try to keep the PA temperature at a more 'constant' temperature. He agreed that the change in temperature, with fans that 'cycle', will 'kill' PA transistors. He told me that he would prefer to ship his amplifiers with fans set up to run continous, but most people want them on thermostats, so that they'll 'cycle', and the thefore the fans will last longer. He said that fans as cheaper than transistors....but I guess his customers haven't figured that out yet.

John Rayfield, Jr. CETma

You don't want to slow down the fan on an 8300 unless you want to pay for a flat rate. PAs are bad juju in those units

Like we didn't see that coming from day one. I remember looking at our demo unit with the lid off, and saying to myself "There's no f___ing way this thing is continuous duty. NO WAY."

I have noticed in some of the FRU 800 Quantar PA's we have been getting back for the past year or so that the fans run continuously. We have noticed what would appear to be less failures since then. We always thought we should modify the fans to run constantly on those. What brought us to that conclusion is that we were constantly changing PA's in the voice channels yet never having a failure on the control channel station. The Quantar fans do not come on until the thermistor voltage drops below 2.000V and that thing is toasty when that happens.

[JRayfield]

If you called up the 800 number and spoke with someone on the phone about this problem, then you would not have spoken with any of the engineers with whom I've discussed this. The engineers that I know, are the ones that design and test the equipment. They don't answer the phones. But, your experience is interesting. On the other hand, I've got a customer with 3 UHF XPR8300 repeaters which have run as long as 8 hours a day, at almost 100% transmit for that 8 hours. They're still running just fine with no problems.

John Rayfield, Jr. CETma

Actually, the XPR8300 was very much tested and proven to run 100% continuous duty. I personally know one of the engineers that was involved in this testing and what they did to that model should have quickly destroyed it, but it didn't. That's why it was released - it passed 100% duty cycle tests with 'flying colors'.

You may want to believe this because Motorola told you it was true and it appears reasonable. The fact they A) released an FSB B) extended warranties on existing units past their original warranty period and C) used this as an excuse to redesign to the XPR8400 all speak to the contrary.

Now this engineer that you know.... is it the same one that told me there was NO issue with the VHF units without having done any actual testing on them whatsoever? When I brought it to their attention and they "tested it out in the lab," he called me up the next day to say that my findings had been confirmed. Our implementation called for 100% duty, this is how it was claimed to have been tested in the lab. Not sure how they arrived at the same conclusion as me if what you say is true.

This testing was done with a VHF unit running at 25 watts into a dummy load. I went to bed and it was putting out 25 watts. I woke up the next morning and it was doing 5 watts. There was no temperature cycling that I'm aware of, the PTT pin was jumped on the back and the fan was at the same speed it was at when I set it to PTT-- Full Blast.

[Dorf411]

Quite interestingly we have a UHF repeater from around 2007 that is connected to a IP site connect system that has never failed but we also have two repeaters on the same system from later 2008/9 that have each been back for repair at least 3x each. Clearly there is a problem and I sure hope Motorola gets there :o together because I sure ain't confident is selling this :o.

[escomm]

If you called up the 800 number and spoke with someone on the phone about this problem, then you would not have spoken with any of the engineers with whom I've discussed this. The engineers that I know, are the ones that design and test the equipment. They don't answer the phones. But, your experience is interesting. On the other hand, I've got a customer with 3 UHF XPR8300 repeaters which have run as long as 8 hours a day, at almost 100% transmit for that 8 hours. They're still running just fine with no problems.

John Rayfield, Jr. CETma

I think it's safe to say they are on the same team, unless Motorola has two engineering departments: one for responding to quality & design issues and one for sharing information with special people such as yourself and nobody else. Given their drive to go lean (and the fact that most of the TRBO engineers that actually developed many of these products years ago were in China and are now employed by Hytera) I'll go with the former.

[JRayfield]

I wouldn't say that it's 'safe to say' anything, if you don't know 100% for sure.

By the way, I am a member of the MOTOTRBO Application Developer's Program. And that does give me a lot of detailed information about MOTOTRBO as well as access to engineers, to which dealers don't have access.

John Rayfield, Jr. CETma

If you called up the 800 number and spoke with someone on the phone about this problem, then you would not have spoken with any of the engineers with whom I've discussed this. The engineers that I know, are the ones that design and test the equipment. They don't answer the phones. But, your experience is interesting. On the other hand, I've got a customer with 3 UHF XPR8300 repeaters which have run as long as 8 hours a day, at almost 100% transmit for that 8 hours. They're still running just fine with no problems.

John Rayfield, Jr. CETma

I think it's safe to say they are on the same team, unless Motorola has two engineering departments: one for responding to quality & design issues and one for sharing information with special people such as yourself and nobody else. Given their drive to go lean (and the fact that most of the TRBO engineers that actually developed many of these products years ago were in China and are now employed by Hytera) I'll go with the former.

[JRayfield]

I agree that this can make a person a bit 'nervous' about selling the XPR8300 or XPR8400 into a system that runs at or near 100% duty cycle. My personal feeling is that they've got the problem resolved. Along with the higher/full-time fan speed, they made some other changes that result in better heat transfer to the heat sink. All of this results in lower (which is always better) and more constant (which is very critical) temperature on the final transistors.

John Rayfield, Jr. CETma

Quite interestingly we have a UHF repeater from around 2007 that is connected to a IP site connect system that has never failed but we also have two repeaters on the same system from later 2008/9 that have each been back for repair at least 3x each. Clearly there is a problem and I sure hope Motorola gets there together because I sure ain't confident is selling this .