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i'm on a roll... the kgsshv


kevin gilmore
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I also had an arc flash on the +15 VR. It still works but

doesnt regulate too well. So that is getting replaced also.

It was due to the cheesy, thin theramsil pad chafing through

from a sharp edge on the TO220 mounting lug. Maybe I over torqued it?

Aint gonna happen again. Bought some heavy duty insulator pad material.

Fiberglass reinforced.

I dislike the thermasil stuff for bolt-mounted hardware - particularly with the heatsinks with an oval hole - always cuts through. I now always use either good old fashioned mica, or the 2mm thick ceramic washers that Kevin found for the T2 project. Thermal resistance of all three is about the same.

The only time that thermasil works really well is when a spring clip is used to fix the transistor down, and there isn't a hole in either the washer or the heatsink.

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Almost done populating the small parts. One of the 680uf caps failed the measurement, I'm still waiting for another batch. Had to parallel/series some resistors due to the lack of values.

Still can't find #6-32 plastic screws locally :( Anyone who has some spare ones and willing to ship worldwide, please let me know.

5362474007_0c23763caf_z.jpg

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Almost done populating the small parts. One of the 680uf caps failed the measurement, I'm still waiting for another batch. Had to parallel/series some resistors due to the lack of values.

Still can't find #6-32 plastic screws locally :( Anyone who has some spare ones and willing to ship worldwide, please let me know.

5362474007_0c23763caf_z.jpg

And that is looking really good! What resistors are you using, and from where did you get them?

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MY counterfeit Nippon Chemi-con 680uF/450V from HKG:

Printed "Negative Black" on the body but no black inked on the negative terminal and original Nippon Chemi-con KMG/KMH has not printed "Negative Black" on the body.

Printed "KMG". The KMG series are the read type and up to 47uF for 450V.

Date Code is "B459" ???

When peel the shrink cover on the body, the cap has a "X" shape slit on the top. Nippon Chemi-con uses "Y" shape.

Capacitance is OK but I can't trust them to use for the high voltage applications.

http://www.chemi-con.co.jp/e/counterfeit.html

http://picasaweb.google.com/inuponken/T2#5563286571084384946

Edited by Inu
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MY counterfeit Nippon Chemi-con 680uF/450V from HKG:

Printed "Negative Black" on the body but no black inked on the negative terminal and original Nippon Chemi-con KMG/KMH has not printed "Negative Black" on the body.

Printed "KMG". The KMG series are the read type and up to 47uF for 450V.

Date Code is "B459" ???

When peel the shrink cover on the body, the cap has a "X" shape slit on the top. Nippon Chemi-con uses "Y" shape.

Capacitance is OK but I can't trust them to use for the high voltage applications.

http://www.chemi-con...ounterfeit.html

http://picasaweb.goo...286571084384946

I checked for voltage and it's still OK.

I've a big box of high voltage TCI caps but they are 1500uf 500v. I might swap for them later if the Nippons bite the dust.

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Hopefully this weekend I will have the power supply functioning again.

Havent had any time to work on it lately due to my job and family stuff.

This coming Monday I plan on biasing the amp boards.

The only info that I have found about this is on the HeadWize site.

I am assuming that the biasing method is the same as that which is

listed for the original KGSS since the circuits are similar.

Before doing this I assume that there should not be any input signal applied to the amps

nor anything connected to the outputs other than my voltmeter.

My question is does it matter if the volume attenuator is connected

while the zero volt bias(es) are performed?

If so, should the volume pot be set at zero gain while adjusting the output biases?

Secondly, there are two pots involved with the amp board biases,

RV1 (in the current source 3rd? stage) and RV2 (in the 15 volt stage).

Which of the above on board pots is adjusted for the +/- output 0V bias

and which is adjusted for the + output to ground 0V bias?

None of the above is very clear at HeadWize.

I just want to be sure before I tweak this monster.

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Adjustment is the same as with the KGSS. Insert the probes into the + and - outputs for each channel and adjust the balance for 0VDC. Then remove the - probe and ground it and adjust the offset for 0VDC. Repeat as is necessary. The RV2 sets the balance between the two sides and the RV1 sets the DC offset.

If your source doesn't output any DC (which none should do) then having it connected wouldn't have any effect on the measurements. Ditto on the volume pot.

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I'm such a jerk.

Yesterday, I soldered the new sand into the psu.

This morning I was testing it under power,

comparing the two rails because of a new voltage imbalance.

Long story short, I slipped with the test probe

and shorted the series pass regulator on the (what was the sill good) +450VDC rail.

Snap-crackle-pop, I zotched em bad.

In my own defence, I normally dont pull this kind of stuff.

Have been doing electronics for forty years now.

Maybe it's because I am getting old and this

parkinsons disease has something to do with it....<<joking>>

So it's back to Mouser, I'll update in a week or so. :(

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Snap-crackle-pop, I zotched em bad.

At least you got a good show out of it. I'll have to second the recommendation to buy ez-clip probes. I hope your luck gets a bit better soon.

I was mid-kgss build when coming across this thread. It's too late to order a larger power transformer and run with the higher voltage transistors at ~400V with the BH supply. Although I can probably still replace the one resistor per channel with the 2sa1968 current source once everything is up and running.

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you do know that it's possible to clip test probes to things, you don't have to hold them. It's a relatively new invention...

Yeah, I used to have some of those clip probes with my scope which I sold off years ago.

I'll be picking some up in the near future, the needle probes are less time consuming

as long as one doesn't make a mistake and slip as I did.

Speaking of time drains, getting those large heatsinks off of the psu pcb is a lot of work.

Due to the tight fit of the soldered-in pins to the plated thru-holes in the pcb,

no amount of solder sucking or wicking is gonna get them loose.

(it is possible with two large soldering irons and two people, one to pull on the heatsink while heated)

I only had to remove the two large sinks in the front and left the two in *back in place.(*along the pcb edge)

This was necessary to get access to the fried pass fets and their related hardware.

So for those unfortunate souls who may be heading down this slippery slope in the future,

this is what I did:

1) First, remove as much solder as possible from the pins/pads of the heatsinks and affected fets.

(on the underside of the pcb)

2) Then, with a dremel tool grind the pins flush with the solder pad/pcb surface.(pcb underside)

3) Clean the grinding dust off of both sides of the pcb with compressed air or spray contact cleaner.

4) Use a centerpunch to mark the center of the pin. (prep for drilling)

5) Drill the pin out to a depth of ~.062 (the thickness of the pcb)

Use a drill that is the same diameter of the pins. This can be verified by

checking drill sizing in the pin channel holes at the top of the heatsinks.

6) Repeat step three.

7) Pull (wiggle) the heatsinks and transistors off of the pcb.

8) Use a small drift punch (or drill bit if no punch is handy)

to tap the remainder of the pins out of the heatsink body.

9) The holes in the heatsink where the pins used to be can now be tapped with a 4-40 tap.

No additional drilling is needed, as the existing holes are the correct diameter to accept the tap.

10) Inspect the pcb surfaces thoroughly for grinding / drilling debris that may cause a short circuit.

A magnifying glass is helpful to look for metal chips that may be stuck under parts or between

terminals and traces.

11) Use 4-40 screws to re-attach the old heatsinks to the pcb, or buy new heatsinks and solder -

- providing that the solder pads on the underside of the pcb are still intact after drilling.

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meh, here's what I've done when people have sent me boards like this:

0.) remove the device

1.) use a heat gun and heat up the heat sink. Use a heat shield to avoid the PCB. Get 'em hot

2.) thread a piece of string through the hole so you have something to pull

3.) Use Chip Quik

4.) pull

They pop right off, even on the beta22 boards where the holes are too small and pads too lame.

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Point well taken, that was part of the problem with the sand in front.

The rear-most sand is occluded by the heatsinks.

Looks like it is down inside of a chimney stack.

I imagine one could manuever a replacement part and screw

down inside of there with some forceps or tweezers.

Edited by livewire
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meh, here's what I've done when people have sent me boards like this:

0.) remove the device

1.) use a heat gun and heat up the heat sink. Use a heat shield to avoid the PCB. Get 'em hot

2.) thread a piece of string through the hole so you have something to pull

3.) Use Chip Quik

4.) pull

They pop right off, even on the beta22 boards where the holes are too small and pads too lame.

Marc,

Thanks for adding that!

I always listen to the voice of experience.

Makes sense from a standpoint of the thermal mass of the heatsink.

Ima gonna file that in my "tips & tricks" memory bank.

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