An illustrated guide to building an F5

[Ben Mah]

I am concerned that your left channel left the light bulb bright even though you found no shorting of the Mosfet drains to ground, and that the Mosfets tested good.

.........

Next carefully check the amplifier boards. Check that you have the Q1, Q2, Q5, and Q6 in the correct positions and oriented correctly. It may be hard to check Q1 and Q2 since that are face to face, but if you carefully separate them by bending the leads a bit, you probably will be able to see the markings.

I confirmed that Q1, 2, 5, 6 are in the correct positions on the right channel.
........

Check the left channel also for the reason stated above. Again, it failed the dim bulb test even though you tested the Mosfets and they were good, and you did not find a short of Mosfet drain to heatsink (ground). There must be a reason for the failed test. Or perhaps Q5 and/or Q6 are faulty. Or hopefully not Q1 and Q2 are faulty, as they are pricey.

Also, what about my question regarding your VDC meter reading?

 

[Chiptech]

Nothing protudes from the circuit board.

Zen Mod made a comment in one of the F5 threads about the "thermistors" touching the metal washers. If the protective covering has a scratch, current flows to the heatsinks. Maybe remove the large washers and make sure the thermistors are only touching the plastic case of the mosfet.

I'm not clear on the thermistors. Mine currently touch the metal washers. You are saying they should touch the plastic case of the mosfet?

 

[bullitt5094]

BTO? That's on an Edison Wax Cylinder. Right?

Just ribbing you. They are cool. I believe I have them on cassette actually so I have zero room to talk. Maybe I should drag out the Nakamichi sometime.

 

[A321Drvr]

F5 Troubles and an Old Guy listining to BTO

I'm not clear on the thermistors. Mine currently touch the metal washers. You are saying they should touch the plastic case of the mosfet?

Yes if the paint "red" on the Thermistor has a scratch in it, there is a path to the heatsinks . Just remove the large washers and leave the small washers. The "Thermistors" should touch the plastic case of the mosfet. When you tighten the screws on the mosfets do not crush them down with too much torque. About as tight as you can get with the shaft of the screwdriver between your thumb and index finger

 

[A321Drvr]

Lotta Smack Talk There

BTO? That's on an Edison Wax Cylinder. Right?

Just ribbing you. They are cool. I believe I have them on cassette actually so I have zero room to talk. Maybe I should drag out the Nakamichi sometime.

"Not Fragile" , Turned up to "11" don't get any better that that.


Old don't mean NOT COOL


Just Sayin

 

[Chiptech]

I am puzzled that with power to the board, you measured OL for VDC across R7. Is your meter auto-ranging? Was it set on VDC? Does your meter have "mV" and "V" positions? If yes, was it set on "mV" or "V"? I am puzzled because as far as I understand meters, OL means over range. In the case of VDC, that would mean the voltage exceeds the display or measuring range of the meter. That would take a large amount of current through a 0.47 Ohm resistor to do that, but with the light bulb in place, that should not happen.

Also, what about my question regarding your VDC meter reading?

I'm using Kaiweets digital multimeters.
It is auto-ranging.
I set it for mV DC volts.

Later today I'm going to retest the left channel with the thermisters on the plastic Mosfets instead of on the washers per suggestion of A321Drvr.

I will measure the R7 & R8 and sound out. Anything else I should measure?

 

[6L6]

Just lift the thermistor a teeny bit so it’s not actually touching the washer.

 

[Ben Mah]

I'm using Kaiweets digital multimeters.
It is auto-ranging.
I set it for mV DC volts.

Later today I'm going to retest the left channel with the thermisters on the plastic Mosfets instead of on the washers per suggestion of A321Drvr.

I will measure the R7 & R8 and sound out. Anything else I should measure?

When measuring Voltage, set to VDC first. If the voltage measures in the mV range, then change to mV.

 

[Chiptech]

First, I do not have auto ranging multimeters.

I adjusted the thermistors to be just above the washers.

And the bulb did not dim. Again.

Anyway, here are my measurements:

[attached photo so you can see what I see]

R7 -0.677 V
R8 -0.691 V

Right sound out -0.459 V

The LED does not light up either.

Appreciate any observations.

 

[Dennis Hui]

Please measure the voltage across R3, R4, R5 and R6.

 

[6L6]

First, I do not have auto ranging multimeters.

No problem. Set them to 2 or 20VDC

I adjusted the thermistors to be just above the washers.

Cool

And the bulb did not dim. Again.

Is this on initial power-up with no adjustment of the potentiometers?

Anyway, here are my measurements:

R7 -0.677 V
R8 -0.691 V

Right sound out -0.459 V

Sorry if this sounds like a broken record but,

Did you measure OHMS across R5 and turn P1 down until the ohms were at the smallest amount (very close to zero), and the same thing the other side, turning down P2 whilst measuring resistance across R6?

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

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

The LED does not light up either.

Probably just in backwards. Flip it around. Easy.

 

[A321Drvr]

Dim Bulb Tester

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

 

[Dennis Hui]

Chiptech,

Your measured voltages of -0.6x across R7 and R8 imply a current flow of near 1.5A.
This is inconsistent with the ~0.84 ohm resistances across R5 and R6 in post #1519. Since
your meter is not auto-ranging, is it possible those resistance values were
actually ~0.84K ohms?

I know we're all sounding like broken records for asking this, but we're
just trying to make sure you have proper adjustment for your initial
power up.

Cheers,
Dennis

 

[Chiptech]

Thanks. Will do in the morning.

 

[Chiptech]

9-27-2020 results: from right channel amp

R3 0.026 V

R4 0.116 V

R5 5.458 V

R6 -5.385 V

Anything pop out?

 

[Dennis Hui]

The voltages across R5 and R6 suggest P1 and P2 are not set at minimum value.
Please measure them again with power off. Make note of the resistance scale
and adjust P1 and P2 so the measured resistances across R5 and R6
and as close to zero as you can get them.

The voltages across R3 and R4 are somewhat different. Did you set your meter to mV
scale for that measurement?

Can you confirm which parts you have for Q1 and Q2 and where you sourced them
from?

 

[Chiptech]

Ok. R5 and R6 are both set at 0.00 V.

For R3 and R4 I set the reading for mV.

All parts are from the DIY kit, except for the LED and LED resistor.

Two days ago I confirmed that Q1 [2SK170] and Q2 [2SJ74] are correct.

Thanks

 

[Dennis Hui]

Sorry...did you mean resistance across R5 and R6 are now at zero ohm?
Or did you power up and measured zero volt across there?

If it's the former, please try the bulb test again.

If it's the latter, did the bulb go out after a while?

 

[Chiptech]

Sorry...did you mean resistance across R5 and R6 are now at zero ohm?

I used mV to set both to 0.00 V

Rechecking them using ohms they both read around 1.03 Ohms. And don't seem to want to go lower.


Or did you power up and measured zero volt across there?


I have not powered up.

 

[Dennis Hui]

About 1 ohm across R5 and R6 is fine.