An illustrated guide to building an F5

[A321Drvr]

This Info is worth a Read

Chiptech,

When I built my F5 these two posts cleared it all up for me.
#106 and#109. The entire thread is full of good Info.


Another F5 Build

 

[6L6]

Chiptech - If you are reading ~1 ohm across R5 R6, you are good to power it up again with the bulb tester. If it stays lit you most likely have a short somewhere or a bad transistor.

 

[Chiptech]

So good to fire it up...again?

 

[6L6]

Yes

 

[bullitt5094]

This is painful. I feel for you.



I would like to add I really like the "Test the tester" suggestion. Did you do that? If it was me, I always find the least possible error as the solution.

 

[Dennis Hui]

With R5 and R6 measuring at 1 ohm the power mosfets should be off.
Hopefully the bulb test will be ok.

 

[Chiptech]

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

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

 

[Chiptech]

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.

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.

 

[Chiptech]

From 1531:
Are you totally sure you have the 240 in Q4 and the 9240 in Q3?

I rechecked them today. They are correct.

Do you maybe have a short to ground through the Keratherm?

When i put in the new set of Mosfets I used new Kerathem pads.

 

[Chiptech]

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?

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.

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.

 

[Chiptech]

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?

 

[bullitt5094]

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

I'm thinking Bridge of Sighs is more appropriate for this thread. But I really need to come to your place for a listening session!

 

[Chiptech]

Bridge of Sighs. Good one.

You are welcome to Tucson any time. It may get below 100 degrees soon, end of the month, maybe.

At least I finally figured out the trimpots.

 

[6L6]

Chiptech- yes, try powering up again and see if the lightbulb goes dim.

 

[Dennis Hui]

Happy to hear you are making progress though I'm frankly quite confused
by your previous reporting of P1 and P2 adjustments showing R5 and R6 measuring
around 1 ohm.

Anyway, I hope your bulb test works now.

 

[Chiptech]

Success!

Well I've finally achieved dimmed status at last. I'm a dim bulb.

I'm going to take this as a victory and take the night off.

Tomorrow new adventures await.

Again, thanks to all.

Ah, first thing tomorrow is reversing the LED polarity.

 

[Dennis Hui]

Most excellent! The end is now in sight.

 

[Chiptech]

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.

 

[Dennis Hui]

I don't see anything wrong with either pairing.
It's possible the red led was damaged from desoldering.
If you have spare LEDs I would just use a new one. Should you
decide to use blue LED there's no need to change the resistor.

 

[Chiptech]

Do I have it right: long lead in the square box?

And thanks,