An illustrated guide to building an F5

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Chiptech

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Joined 2005
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A321Drvr said:
Chiptech,


I have followed this thread for several days now. Lots of folks with much more knowledge than me have spoken, all with great ideas and questions. Here is my question.!!!

Are you sure your "Dim Bulb Tester" is wired correctly?
To test it; plug a clock radio into the tester and flip the switch. With a 40 watt bulb should not glow at all. Unplug the radio and plug a hand drill or something that has a high amp draw. A hand drill won't rotate at all and the bulb will glow brightly. I am one of old guys that "Test" at every stage. I want you to get this thing up and running. If you are sure your Dim Bulb Tester works as it should, then I will defer to the "Really Smart Guys"


Tonight it is "Robin Trower" Too Rolling Stoned......Loud


Good Luck
Click to expand...

I agree with you - leave no stone unturned, there is probably a better metaphor. I tested just the PSU this weekend with the dim bulb and it dimmed right away. So I think that is good. Thanks
 
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Chiptech

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Joined 2005
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Ben Mah said:
I'm not an expert, just a diyer trying to help a diyer. But if the Mosfets are removed, they can be tested to see if they are functional. That was pointed out in a prior post. I don't know whether Chiptech has tested them. It would be useful to know though; if they test bad, then they are a cause of the problem but if they test good, then there is another undetermined cause.
Click to expand...

I did test the first set of Mosfets and two of the four were bad.

I tested all four of the new ones I'm using now and they are good.
 
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Chiptech

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Joined 2005
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First off, I want to thank everyone for the support and assistance. I really appreciate it.

I powered up today. Failed dim bulb test. I kept it on for a minute or so while i checked my 3 multimeters.

R7 0.688
R8 -0.693
Sound out -211.5

Looks like I should reverse the LED as it does not light up.

Per 6L6: "If it stays lit you most likely have a short somewhere or a bad transistor."
Any suggestions on how to systematically search for a short or bad transistor?

Eric said:
Chiptech: Check your mosfet mounting sites carefully. I haven't read everything above, but if you've tapped your own holes, make sure you do not have a raised lip around the screw holes on your sinks. If so, it needs to be sanded down.

I am using pre-drilled holes.

When you mount your fets, mount them to the sink first. Then, use your ohm meter to look for connectivity between the center pin and the rest of the sink. Your meter should display no connectivity at all (open loop). If you have ANY measurable resistance at all, you have a mounting problem - this is the primary way you blow a mosfet. Remove and inspect. Once your mounting is verified, THEN solder to the PCB.
Click to expand...

Unfortunately I missed this guidance and have not tested the fets mounted to the sinks.

Should I remove them from the boards and test them as described above?

Should I follow Step 1 #106 [measuring the trimpots} from Another F5 Build on the left channel to see if I get different results from the right? I adjusted P3 per the turn until you hear a click then turn back 12.5 times method on the right channel today and did P1 and P2 adjustments on the right channel Sunday.
 
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Chiptech

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Joined 2005
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This just in...

I decided to go ahead and set P1 and P2 on the left channel [untested]. i was able to set both at 0.02 ohms. And they are holding.

So then I went back to the right channel and reset P1 and P2. They are now holding at 0.02 ohms. The settings were way off.

I conclude that the test I ran earlier today did not have the trimpots set remotely close.

Time for a retest?
 
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Chiptech

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Joined 2005
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Trouble in LED City

Well, I reversed the LED that wouldn't work in the right channel. Still doesn't work. I can't tell if I oriented it correctly [long lead to the square box] the first time, but reversing it didn't change anything.

This is the LED I'm using TLHR6400 LED RED DIFFUSED 5MM T/H:
Blocked

And this is the resistor paired with it, 71-CMF6015K000FKEK 1W 15K:

https://www.mouser.com/ProductDetai...WXXwTmlLT53I74jd/80PGDQzHnod5tJAQZr2UNUHAVA==

Is this pairing ill considered?

If the above doesn't work, can I use the same LED and resistor combination I'm using on the PSU?

LED NTE3186:
Item number NTE3186

Resistor CFM14JT10K0 10K OHM 1/4W 5%
Blocked

thanks for the assistance.
 
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