Quantar PA fans will not run

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mogman
Posts: 126
Joined: Tue Aug 05, 2008 2:25 pm

Quantar PA fans will not run

Post by mogman »

I am bench testing a VHF Quantar and cannot get the PA fans to run, swapped PAs did the power alignment (was very close BTW) and still I can get the 300W Motorola dummy load pretty damn hot and the PA gets uncomfortably warm on the front of the amp.
I thought the fan control and alarm (no entry in the station log or status or fail of any kind) was handled within the amp itself which would surly not involve two different PAs. The fans on my 900 and 800 MHz radios seem to run all the time (relatively speaking)
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d119
Posts: 3504
Joined: Tue Mar 19, 2002 4:00 pm

Re: Quantar PA fans will not run

Post by d119 »

Do they run when you power the station on?
mogman
Posts: 126
Joined: Tue Aug 05, 2008 2:25 pm

Re: Quantar PA fans will not run

Post by mogman »

No but I can't remember ever seeing the PA fans run on startup.
mogman
Posts: 126
Joined: Tue Aug 05, 2008 2:25 pm

Re: Quantar PA fans will not run

Post by mogman »

Just powered up one of my 900MHz units and the PA fans did not run.
mogman
Posts: 126
Joined: Tue Aug 05, 2008 2:25 pm

Re: Quantar PA fans will not run

Post by mogman »

Keyed the 900MHz unit and the fans started after only 3-4 min, before I could even detect much temperature change on the front of the PA.
When I can get back to it I am going to try another SCM, but I have other fish to fry.
mogman
Posts: 126
Joined: Tue Aug 05, 2008 2:25 pm

Re: Quantar PA fans will not run

Post by mogman »

As it turns out the thermistor bias resistor was wrong from the factory on all of the PAs from this production run (of the 6 I have anyway)
Well they may not have been wrong if the factory wanted to cook the crap out of the PAs before the fans came on.
R4119 in the PA temperature circuit is listed on the schematic as 47K and in the "working" PAs it is a 47K, but on the ones in question they are 34K.
This means the PA would have to get much hotter before the SCM would turn on the fans.
Grabbed the hot air gun, popped in a 47K and all is GOOD!!
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d119
Posts: 3504
Joined: Tue Mar 19, 2002 4:00 pm

Re: Quantar PA fans will not run

Post by d119 »

Good work!
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