Hi all, and thanks in advance for taking the time to read my post. I am in the process of putting together an F5M using the F5 v3.0 boards sold in the diyaudio store. I used the schematic and info provide in post #70 in the F5M kit thread that provide detailed info on values and I checked and they are absolutely correct. I thought I implemented that exactly on the F5 v3.0 boards, but each channel is failing the dim bulb test (glowing very bright, r7 and r8 hot immediately), and I am at a loss as to why. Continuity testing is not showing me any issues, but I am certain if I apply full power, I'm going to see white smoke.
Observations:
F5 v3.0 boards
R1 – 15k
R2 – 33k
R3 – 43r (1w)
R4 – 43r (1w)
R5 – 2.2k
R6 – 2.2k
R7 - .47r (3w)
R8 - .47r (3w)
R9 – 560r
R10 – 510r
R11 – 510r
R12 – 560r
R13 – link, 0r
R14 – link, 0r
Q1 – 2SK170
Q2 – 2SJ74
Q3 – IRFP240 (had on hand vs the 140)
Q4 – IRFP9240 (had on had vs the 9140)
P1 – 5k, 25 turn
P2 – 5k, 25 turn
P3 – link outer pins, 0r
All other component locations on the v3.0 boards are not populated which should result in a F5M that matches the official schematic (aside from R1 & R2).
Appreciate any thoughts on how to proceed. Thank you!
Observations:
- Power supply tests out fine with +/- 27 vdc. No issue with bulb test. I’m using the universal board from the store with an AS-4220 (had on hand)
- Jfets were purchased new from the diyaudio store
- Tested resistors before soldering and confirmed values
- Tested mosfets, and v+/-, inputs/outputs for short to ground , none found
- No solder bridges or cold joints I could find
- I am getting .57 vdc across R7 and R8 with both pots turned fully counterclockwise as soon as power applied. Exact same reading on both channels
- The LEDs on the power supply do not light when either channel is connected to power. I assume this is because of excessive current draw from channel board
F5 v3.0 boards
R1 – 15k
R2 – 33k
R3 – 43r (1w)
R4 – 43r (1w)
R5 – 2.2k
R6 – 2.2k
R7 - .47r (3w)
R8 - .47r (3w)
R9 – 560r
R10 – 510r
R11 – 510r
R12 – 560r
R13 – link, 0r
R14 – link, 0r
Q1 – 2SK170
Q2 – 2SJ74
Q3 – IRFP240 (had on hand vs the 140)
Q4 – IRFP9240 (had on had vs the 9140)
P1 – 5k, 25 turn
P2 – 5k, 25 turn
P3 – link outer pins, 0r
All other component locations on the v3.0 boards are not populated which should result in a F5M that matches the official schematic (aside from R1 & R2).
Appreciate any thoughts on how to proceed. Thank you!
Thank you for the quick replies. I will check both items. One comment on PS and rectifiers. Off the PS board outputs, I am getting +27 vdc between v++ and ground and -27 vdc between v-- and ground, so I assumed that was good, but will definitely check connections. Thank you again!
Thanks for the suggestions, but no luck on either. I took one channel, reversed both pots orientation, and same behavior .... Power supply LEDs out when channel connected and .55 vdc across R7 and R8. I also checked the power supply and rectifiers wiring. All checks out. With channel disconnected, LEDs on power supply board are both on and getting just about +28 vdc between v++ and grnd, and -28vdc between v-- and grnd. I disconnected the rectifiers and I'm getting 19v from trans on each pair of wires(blue/green), which is right for as4220. When I reconnect the channel and power supply, LEDs on powersupply go out, .55vdc on R7/R8, and things get hot fast. This is on the bulb tester. Full power would probably cook it in a millisecond. Pots are fully turned counterclockwise. I am stumped.
Make sure the two pots are installed correctly, and also both turned fully in the correct directions.
Some boards (if I recall) need different directions for two pots.
This is very important to do before powering up, these instructions are from 6L6:
With power off, set meter to ohms and place across R5, then adjust P1 until it reads minimum ohms.
Do the same with R6 and P2.
Some boards (if I recall) need different directions for two pots.
This is very important to do before powering up, these instructions are from 6L6:
With power off, set meter to ohms and place across R5, then adjust P1 until it reads minimum ohms.
Do the same with R6 and P2.
Attachments
@dlvo
Couple comments.
It’s important to look at the schematic of the version 3.0 F5 boards since a few things are different compared to version 2.0, especially if you trying to use the board to build an F5M version - in review, I believe you have done so! In addition, the orientation of the pots are different between the two boards which can make things confusing. But we should be able to tease out these differences if we look at the schematic and correlate with the board version you have.
Please verify that Q1 is indeed 2SK170 and that it is oriented properly on the board with regards to drain, gate and source. Please do the same with Q2/2SJ74. As Ben has said, please verify that Q3 is an IRFP9240 or 9140 or equivalent P-channel TO-247 transistor. Please also verify the same with Q4 that it is an IRFP240 or 140 or equivalent N-channel TO-247 transistor. With the picture you posted, we are unable to verify this.
Please make sure that all 3 transistor pins on Q3, and Q4 are not shorted to each other or shorted to the heatsink (you can use bracket screws to check this). If so, then the backs of these transistors are not electrically insulated from the heatsink. The backs of these transistors has the drain pin connected to it and it must be electrically insulated. In addition, if the transistors are damaged, please replace them.
With your DMM set to ohms please place either the red or black lead onto V+ and the other lead onto the gate of Q3 (the pin closest to R13). What is the value? Is it close to 1500 ohms or closer to 0 ohms? Please make sure R5 is 2.2K ohms.
With your DMM set to ohms please place either the red or black lead onto V- and the other lead onto the gate of Q4 (the pin closest to R14). What is the value? Is it close to 1500 ohms or closer to 0 ohms? Please make sure R6 is 2.2K ohms.
Please make 100% sure that your soldering is golden! Any cold joint in the F5M can make operation difficult since there are only a few parts! Please make sure none of the leads from the resistors or other components from the PCB are touching the heatsink.
Thanks for reading.
Best,
Anand.
Couple comments.
It’s important to look at the schematic of the version 3.0 F5 boards since a few things are different compared to version 2.0, especially if you trying to use the board to build an F5M version - in review, I believe you have done so! In addition, the orientation of the pots are different between the two boards which can make things confusing. But we should be able to tease out these differences if we look at the schematic and correlate with the board version you have.
Please verify that Q1 is indeed 2SK170 and that it is oriented properly on the board with regards to drain, gate and source. Please do the same with Q2/2SJ74. As Ben has said, please verify that Q3 is an IRFP9240 or 9140 or equivalent P-channel TO-247 transistor. Please also verify the same with Q4 that it is an IRFP240 or 140 or equivalent N-channel TO-247 transistor. With the picture you posted, we are unable to verify this.
Please make sure that all 3 transistor pins on Q3, and Q4 are not shorted to each other or shorted to the heatsink (you can use bracket screws to check this). If so, then the backs of these transistors are not electrically insulated from the heatsink. The backs of these transistors has the drain pin connected to it and it must be electrically insulated. In addition, if the transistors are damaged, please replace them.
With your DMM set to ohms please place either the red or black lead onto V+ and the other lead onto the gate of Q3 (the pin closest to R13). What is the value? Is it close to 1500 ohms or closer to 0 ohms? Please make sure R5 is 2.2K ohms.
With your DMM set to ohms please place either the red or black lead onto V- and the other lead onto the gate of Q4 (the pin closest to R14). What is the value? Is it close to 1500 ohms or closer to 0 ohms? Please make sure R6 is 2.2K ohms.
Please make 100% sure that your soldering is golden! Any cold joint in the F5M can make operation difficult since there are only a few parts! Please make sure none of the leads from the resistors or other components from the PCB are touching the heatsink.
Thanks for reading.
Best,
Anand.
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@dlvo : You've been given some excellent advice so I suggest you start with these two low hanging fruits:
1) Verify Q1/Q2/Q3/Q4 are in their correct places, specifically since your original post gave the wrong polarity parts for Q3 and Q4.
2) With the power off, measure the resistance across the R5 (resp R6) (2.2K) resistor and adjust P1 (resp P2) so that your measured value is low (a few ohms). If your initial measurement is isn't low (probably in the 1.5K range) then you had turned the pot the 'wrong way'. Measuring R5 and R6 is a foolproof way of setting the trimmers so the mosfets are 'off' for your initial power up.
Good luck.
1) Verify Q1/Q2/Q3/Q4 are in their correct places, specifically since your original post gave the wrong polarity parts for Q3 and Q4.
2) With the power off, measure the resistance across the R5 (resp R6) (2.2K) resistor and adjust P1 (resp P2) so that your measured value is low (a few ohms). If your initial measurement is isn't low (probably in the 1.5K range) then you had turned the pot the 'wrong way'. Measuring R5 and R6 is a foolproof way of setting the trimmers so the mosfets are 'off' for your initial power up.
Good luck.
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That was using the schematic for your board, not the F5m board. All these differing schematics cause real confusion.
Probably best to follow post #11 instead, so adjust both pots so there is zero ohms across the pot.
This may be your problem, with the pots being set wrong for the initial power up.
R3 and R4 (43R) in conjunction with the jumper in place of the trimmer provide the 22R to ground.
I think the big issue is the Q3/Q4 mix-up.
I think the big issue is the Q3/Q4 mix-up.
Hi, thanks again for the suggestions and feedback.
- Q1, Q2, Q3, Q4 were in correct positions and orientation. In my initial post, there was a typo with my list. I reversed Q3 and Q4 part name, but they are
in the correct positions since I stuffed boards
I also rechecked each component for short to heatsink, none found. Basic continuity testing shows placement of components matches the schematic from post 70 in the F5M kit thread. No solder bridges found and I reflowed anything that looks even remotely suspect.
One thing is certain, when I initially power up first test using dim bulb, the pots were set wrong. That has been corrected. Now when I power up for a quick test, bulb still glows bright, but I measure .22 vdc across R7/R8 vs .55 vdc previously. However, R3 and R4 get very hot fast (under 3 sec). I am sure they would last more than a few more second. The LEDs on power supply also still go dark when a channel is connected. I think I've made some very basic mistake yet cannot find it. I am now considering the possibility I damaged some parts with initial bulb test. I sure hope not the the jfets. I have some mosfets.
I added a few more pics.
Thanks again for all your help and feedback.
- Q1, Q2, Q3, Q4 were in correct positions and orientation. In my initial post, there was a typo with my list. I reversed Q3 and Q4 part name, but they are
in the correct positions since I stuffed boards
- with pots set right, 7r across R5 and R6 and both confirmed to be 2.21k
- no pins on Q3 or Q4 are shorted to heatsink or the machine screws on the board
- 7r Q3 gate to V+ and 7r Q4 gate to V-
I also rechecked each component for short to heatsink, none found. Basic continuity testing shows placement of components matches the schematic from post 70 in the F5M kit thread. No solder bridges found and I reflowed anything that looks even remotely suspect.
One thing is certain, when I initially power up first test using dim bulb, the pots were set wrong. That has been corrected. Now when I power up for a quick test, bulb still glows bright, but I measure .22 vdc across R7/R8 vs .55 vdc previously. However, R3 and R4 get very hot fast (under 3 sec). I am sure they would last more than a few more second. The LEDs on power supply also still go dark when a channel is connected. I think I've made some very basic mistake yet cannot find it. I am now considering the possibility I damaged some parts with initial bulb test. I sure hope not the the jfets. I have some mosfets.
I added a few more pics.
Thanks again for all your help and feedback.
Red wire is to V- on PSU.
Green wire is to V+ on PSU
Red wire is to V+ on Amp PCB
Green wire is to V- on Amp PCB
Top photo and bottom photo.
Green wire is to V+ on PSU
Red wire is to V+ on Amp PCB
Green wire is to V- on Amp PCB
Top photo and bottom photo.
He's saying the power supply leads are reversed to the amp boards.
See the V---- label, and the V+++ label, next to the terminals on the supply board?
They should go to the amp board V- and V+ respectively.
Maybe it's wrong to both amp boards, maybe just to one. Check both carefully.
See the V---- label, and the V+++ label, next to the terminals on the supply board?
They should go to the amp board V- and V+ respectively.
Maybe it's wrong to both amp boards, maybe just to one. Check both carefully.
I'm not saying anything of the sort... I wrote what I meant.
I can't see where the wires go... As an example, in the 2nd picture the wires are disconnected.
What I would do if I were the OP is double check my DC wiring from PSU to the board(s), but I was just stating an observation.
I can't see where the wires go... As an example, in the 2nd picture the wires are disconnected.
What I would do if I were the OP is double check my DC wiring from PSU to the board(s), but I was just stating an observation.
I think you are right, since the amp board photo in post #14 has the red wire connected as positive.
Good catch.
Good catch.
You are 100% correct! I prewired the boards for testing. I also prewired far side of case for later.... but unknowingly reversed wire color by accident from PS outputs. When I began to test, I was positioning heatsink/board next to power supply outputs in photo but was matching color to far side of case when hooking up. I totally missed it.
I just tested a channel, with correct wiring, and dim bulb is out. I'm more than a bit embarrassed, but grateful for everyone's help.
Thank you!
Donn
I just tested a channel, with correct wiring, and dim bulb is out. I'm more than a bit embarrassed, but grateful for everyone's help.
Thank you!
Donn