merchauser

[QUOTEFrom the rest of the list, I'm guessing this is supposed to be "FULL fans", but it would be nice to know for sure.][/QUOTE]

+1

Ducman82

HA< i did.. yes full fans

Wisconsin Joe

Thank you.

I somewhat doubt I will ever need this, but it's nice to have.

It utterly amazes me the depth and breadth of the knowledge on here.

Ducman82

I built a stand along dedicated test rig at work to diag fan amps and controllers :-)

Captain_Slow

A fan doesn't need to be bad for the amp to think a fan is bad. This checking cycle behavior occurred with my fans. I replaced the fuses. Did not help. Previous owner had swapped the controller (later I did it again). Then with help from Fraggle, swapping amps between our cars...fans still worked in his car, not in mine. Theo then gave me the full education on how the system works, and still, it seemed to be the amp....and Theo sent me an amp he rebuilt. Still, the checking and cycling of the good fan continued. Then a breakthrough. Deoxit in the fuse holder brought almost a year of trouble free operation before the checking behavior returned. I pulled the fuses...and they were melted - not blown. I realized at this point the fuse contacts were acting like resistors, heating up, and reducing current. It becomes a runaway effect - as heat increases resistance. The result is the real damage is in the fuse sockets - ruining the copper fuse holders and melting the fuse block. I decided the fix was replacing the fuse block. The process is described here: https://rennlist.com/forums/928-foru...nor-block.html

This may not help this specific problem, but I'm sure many amps, controllers, fans, etc. have been wrongly accused. Total resistance increases throughout the system as contacts oxidize and degrade. The total increase in resistance can reach a point where the amp doesn't "see" the specified narrow range in current or voltage (can't remember which) and will go into "check" mode.

Alan

In normal operation: both fans should always be doing the same thing - on or off at the same time and running at the same speed. If they aren't you have a problem.

Alan

GregBBRD

Absolutely true.

merchauser

new information: pretty certain that I have an amplifier that has gone awry. but, it is an intermittent problem and
I believe is heat related. Can a MOSFET (or the amp in general) get too hot, not blow a fuse, but decide to take a nap, only to come
back to life after everything cools down??

GregBBRD

The MOSFETs are attached to their head sinks by a "staked" over tiny aluminum pin that is cast into the heat sink. Fairly common for these pins to fail, which results in a MOSFIT which is no longer attached to its heat sink.

They then overheat, which usually ruins the MOSFIT pretty quickly, but I can imagine it also being intermittent as it heats and cools.

Alan

Overheating components are rarely due to over current - its more commonly due to conditions that cause poor connections or other effects that actually limit currents to below normal but dissipate lots of heat in areas that are not supposed to get hot - thus a fuse is not likely to blow.

Alan

dr bob

Popular failure points that lead to these symptoms include connections at the battery. There are two separate feeders from the battery to two separate fuses in the CE panel, then the two circuits continue to the final stages module on the front apron. With the fans runing, you can test for voltage at each fuse via the little openings in the back of the fuse. A needle probe (looks a lot like a paper clip if you don't have a good test-leads kit...) into the openings will help you identify voltage drop upstream of the fuses. Check with fans off. Then connect the fan switch wires at the intake manifold switch to get low fan speed. Hood must be closed or hood switch clinically depressed. Check voltage at the fuses again, compare readings with fans off to find voltage drop evidence. A poor connection in either circuit will appear to be a fan failure to the monitoring system. If one is consistently different, swap the plugs at the individual fans to see if the problem moves with the plug.

merchauser

great information from all! thanks!

GregBBRD

We also are seeing a large quantity of the connections directly at the fan overheating and melting both the plastic connector and even the plastic on the fan, these days.

All sources of resistance must be repaired, before any tracing of problems can begin. We check all these connections first, whenever there is a fan issue.

Since we have a complete fan system (wiring, fans, logic controller, and fan amplifier) in the shop on a test board, we can take test system over to a car and plug it directly into the car....to check the fans, themselves. (Fan failures are very common, at his point in time.....Mary keeps 4 fans, in stock, at all times.) We can then individually test the controller and the amplifier (which we can do, if these pieces are sent to us.). Saves a whole bunch of money in diagnostic time for our clients.

Amplifier issues are still the most common problem. However, it is important to remember that the amplifiers can fail from the resistance in the actual fans getting too high.

merchauser

Since it is very difficult to properly test MOSFETs, I have decided to replace them with newer ones. the MOSFETs
are most likely, the culprits. all other components look and test fine. (diodes, connections, etc.) however, there is
a complete absence of any heat conducting paste that I have read should be inside??

is it possible that age and heat have caused the paste to "evaporate?"

could this cause the intermittent overheating that I have experienced?

GregBBRD

The heat paste sits between the heat sinks for the MOSFITS and the black chassis. There is also a piece of Mica there to insulate the heat sinks. from the chassis. There is paste on both sides of the Mica. The paste is white and does not "evaporate", although it does get pretty "crispy" between the MOSFIT heat sink and the Mica.