RM Italy KL7505v Overheating Protection problem.......H E L P!!!!

[Arizona8255]

Hi Andy, It's not anything about power from the regulator. It's that the designers don't want the amp to be used in a room with a high ambient temperature and that's what the little owner's manual says is the reason the amp will go into this mode. It's not because the amp is overheating. It's because your room is too warm. The little fan that I added isn't for the purpose of cooling anything that is excessively warm. It's only to apply ambient air to the surface mounted sensor so it can do what the designer wanted it to do. Apparently they had a design team and the person who mechanically designed the amp either overlooked or misunderstood this concept and didn't realize that the firmware needed to know the Exterior rather than the Interior temperature.
I don't remember the links where I found the schematics but I saved them as PDFs so just do lots of searches like KL7505 pdf and they'll show up. There's one called Operating manual but it's actually the schematics of the small computer card showing the Thermistor sensor (R7) that has been misplaced.

 

[9C1Driver]

Hello Juan Fernandez,

I recently bought a very lightly used KL7505 from a guy I met on the radio and found that it also had the same exact problem that you described.
I searched the Internet and was able to find a complete and accurate set of schematics for the KL7505. I found that the amp has two separate temperature sensors. One is a Si diode that is thermally tied to one of the RF Power transistors and the other is a very tiny, surface mounted Thermister R7 that's on the small PIC microcontroller PCB that's located behind the control panel. This is the sensor that is intended to monitor the ambient temperature of the amplifier's surrounding. The problem is that the designers located the sensor inside the fully enclosed interior of the box where it is not only unable to measure the temperature of the surrounding room but, it's (stupidly) measuring the much warmer interior of the box. What do you think is going to happen? That's right, the computer will think the ambient temperature in your radio room is very warm and place the amp into over-temp. shutdown mode.
The solution I arrived at was to temporarilly open the little control panel in order to expose the sensor to actual room temperature. This made the over-temp shutdowns disappear, thus proving my idea was correct.
The permanent solution was to drill a series of six small holes through the bottom metal cover plate positioned so the holes are below the small space in front of the CPU card. Then I cut a 30mm hole and mounting holes to mount a small computer 12V fan onto the bottom cover plate, located in a spot behind the CPU PCB. I tied the tine fan to a constant source of 12V inside the KL7505. This then forced exterior ambient air to flow over the small CPU PCB such that the surface mounted temperature sensor is now able to measure the actual room temperature. The shutdowns never happened again. I'm sure that if I ever tried to operate the KL7505 in a very warm room that the unit will go into shutdown because now, the surface mounted sensor is able to measure the temperature of the actual room temp. as it was intended to do by the designer. Now I use this amp all the time and I love it.

Good luck.

I don't think this guy will even see your post.

Juan Fernandez
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[Arizona8255]

That's okay. Anyone else who has one of the Rm Italy KL7505 amps has probably seen the same problem and they'll perhaps be able to benefit from what I found. My background: I'm an equipment engineer from the semiconductor industry with nearly 3 decades of Ion Implantation experience and I have operated a small business rebuilding X-ray and scanning electron microscopes for 19 years.

 

[Lorenzo]

The thing is Andy, the KL7505 isn't really overheating at all when it goes into the shutdown mode. It's because the cabinet isn't ventilated and the Ambient Room Temperature sensor, R7 is located INSIDE rather than outside of the warm cabinet. Just make sure the ambient temp. sensor is able to measure the room temp. rather than the cabinet interior and the problem will disappear. Drill some holes in the bottom plate and provide a tiny fan to force room air to flow over the CPU card (where the ambient sensor is) and the design will function as intended.

Can you please show us a picture of your mod for the 7505v.

 

[Recon]

Hi Andy, It's not anything about power from the regulator. It's that the designers don't want the amp to be used in a room with a high ambient temperature and that's what the little owner's manual says is the reason the amp will go into this mode. It's not because the amp is overheating. It's because your room is too warm. The little fan that I added isn't for the purpose of cooling anything that is excessively warm. It's only to apply ambient air to the surface mounted sensor so it can do what the designer wanted it to do. Apparently they had a design team and the person who mechanically designed the amp either overlooked or misunderstood this concept and didn't realize that the firmware needed to know the Exterior rather than the Interior temperature.
I don't remember the links where I found the schematics but I saved them as PDFs so just do lots of searches like KL7505 pdf and they'll show up. There's one called Operating manual but it's actually the schematics of the small computer card showing the Thermistor sensor, R7 that has been misplaced. I have attached that PDF in a subsequent posting. You can see how tiny R7 is and how ridiculous is was to use a surface mounted sensor because it can't measure the exterior temperature very well where it is. Someone at RM Italy sure was confused.

Wow! What a dilemma! How about relocating the amp to the nice and cool basement?

 

[Onelasttime]

Well the voltage regulator on the control face does freq. fail. So it is no wonder most would start there.

How hot is your room that it is hot enough to shut this amp off? How come this problem seems to be unique to yours? Any links to more info on this from other sources would be great! I have not heard anyone else complain of this and the 7505 and 7504 have been on the market long enough this should be HUGE news.