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 Post subject: VRM installation
PostPosted: Fri May 15, 2020 9:24 pm 
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Hi ! I start a new topic about the VRM installation (besides my other post with my regular followup/questions).
I would need some confirmation/answers to make sure how to install the VRM correctly..


Location of the VRM
Is this where it goes ? (pictures below) I cannot find another place. At first I thought it was supposed to be installed in the inside of the chassis but that's just doesn't fit inside.
Since the cabinet is long enough I guess it goes on the outside. I will need to make a special access through the cabinet.
Can you confirm me it's supposed to go on the ouside of the chassis like this ?
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How to wire the VRM
The diagram in the VRM documentation (version 3.1) locates the VRM potentiometer on the front panel. But that's where is now located the power switch (not present on the VRM layout). The tweed documentation require to connect a red wire between the right side of the standby switch to the the eyelet board (to the 4K7 resistor). Do I have to remove this wire ? Does someone would share some pictures of this version of the VRM on tweed ? I find this part so confusing between the regular Tweed build and the installation of the VRM (+with the "switch feature" which seems to be optionnal (???)). I'm sure when you know what to do it's a versy easy and fast job but I'm just lost here and don't understand what I'm supposed to do with what I've already wired and where goes thing the way I've installed the VRM... :/
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1M resistors
According to the regular Tweed layout I've installed the two 1M resistors on the Hi jacks. Do I have to remove them so as to put them on the pin 2 and 7 of the V1 as the VRM documentation seems to require ?? (I don't have any other 1M resistors). Since the two 0.1 uF opt. VRM are present on the regular Tweed layout, I excepted to have the same for the 1M resistors. But now I'm not sure and don't know which instructions to follow.
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Again, a big thanks in advance to my tweed angels, Han and Mitch.
(and sorry about the tone. I try to keep on the pleasure side of the build and not to fall in a frustrating side. But the line is thin this evening).


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 Post subject: Re: VRM installation
PostPosted: Fri May 15, 2020 9:50 pm 
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Location: Qualicum Beach, BC
The VRM does not mount on the outside of the chassis. That wouldn't be safe!

It mounts inside as shown on this drawing.

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You have to mount the VRM on the front panel instead of the power switch. The pot on the VRM board includes a switch (the black part at the back with the two terminals) and you use this instead of the regular power switch.

The drawing also shows how a red wire runs from the standby switch to HVIN on the VRM board. Another red wire runs from HVOUT on the VRM board to the eyelet on the main board where the 4k7 resistor is.

You have to remove the MOSFET from the VRM board and mount it on the side of the chassis and run wires to it from the VRM board. This is also shown on the drawing.

You have to remove the 1M resistors from the input jacks and mount them as shown on this drawing.

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 Post subject: Re: VRM installation
PostPosted: Fri May 15, 2020 11:57 pm 
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Ok, thanks. I thought that was a previous/former way to install it. There was no wire in the VRM kit I've received. That led me to think it had to be done another way, like shown in the VRM documentation... Plus I have no purple wire as I see on pictures on forum, like this download/file.php?id=1886&mode=view. Not even sure I have enough long wires to do the job. So I thought it was done differently now.

Thanks a lot for your reply Mitch. It's very appreciated. Confusion's gone now.


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 Post subject: Re: VRM installation
PostPosted: Sat May 16, 2020 12:40 am 
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No problem, Julien. Glad I could help. Hopefully you can find enough wire. Colors don't matter. The wires that run between the MOSFET and the VRM board can be any color you have.


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 Post subject: Re: VRM installation
PostPosted: Sat May 16, 2020 4:36 pm 
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Location: Shawnee, OK
Here are some pictures. Used 3 different colored wires (twisted) to prevent confusing the connections and connected wires to board first. Ran the wires down and along the chassis, over to VRM MOSFET and connected the wire to proper connections on MOSFET.
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 Post subject: Re: VRM installation
PostPosted: Sat May 16, 2020 6:00 pm 
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Yep, it's essentially the gauge of the wire that matters, not its color, that I know.. :)

Thanks Han for the pictures.

I think I'm going to have to skip the VRM. Even after removing all the solder, unattach the three legs at the same time didn't work. After being melted, the first leg hardened as soon as I took care of melting the second one and so on.. I was unable to melt the three at the same time and remove the mosfet. I had to cut the legs as short as possible. Didn't work So I simply cut them all from the other side.

As you can see on the pics the PCB seems to be damaged. So if I want to go on with this I have to order antoher kit.
I've tested the conductivity/connectivity with my multimeter. The S and D still works but I have no clue for the G. I'm not able to find a working connection anywhere on the PCB board.

So enjoy the long weekend and thanks again for your precious help !


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 Post subject: Re: VRM installation
PostPosted: Sat May 16, 2020 10:18 pm 
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Sorry, I'm stubborn... I had to try the 9V battery test (I've stacked a couple of C batteries to get just above 9v). I didn't want to solder anything and used alligators clips (I've tested the connectivity from each leg until the PCB (from Mosfet D to HVIN and from Mosfet F to the R3 5R resistor and it worked).

So, despite the apparence (pictures above), I have results...
From a total of 9.54 volts I measure 6.89 volts at HVOUT which seems to be the voltage expected in the test.
Problem is, if I turn the potentiometer one way or an other, it always stays at 6.89 volts and even if I wait some time before each move...


If someone has still some patience with me (ahah) and have any idea... (?) :)

(edit : I'm trying the mosfet testing from the troubleshooting page of the VRM)
(edit2: I'm not able to get any reading from the mosfet testing)

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 Post subject: Re: VRM installation
PostPosted: Sat May 16, 2020 10:53 pm 
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Location: Shawnee, OK
The usual advice is to get the amp up and running, then install the VRM later. Then if there's any problems, you know it's the VRM. Also, you should use clip on heat sinks on solid state devices like the MOSFET chip and the foil should come off, that's on there to prevent damage to the chip from static electricity. The MOSFET is a fairly common and reasonably priced item(at least it is in North America).

For desoldering, you should get a solder sucker (it's like a spring loaded hand vacuum).

If the MOSFET failed the test, it's probably dead :bugeye: :!:

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 Post subject: Re: VRM installation
PostPosted: Sat May 16, 2020 11:13 pm 
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Yes I agree. I emailed Stephen to get advice if I had to build the Tweed without the VRM first (and then install the VRM if everything works fine). But he replied it was easier to install it at the beginning, which is true... I think I'm going to go back to my first intention and start without, as you say..

And, yep, I've used a solder sucker (so convinient!). But it wasn't enough... :)

Good evening :)


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