STK-0050 replacement for SX-780 and others

[zebulon1]

The drops look good.

I tested the hardware that now will be included in the module kits and I wanted to bring up a few points, some of which we discussed.
The heatsink should be sanded fairly smooth with 180 grit wet/dry on a flat surface, thoroughly cleaned with soap and water, before installing the pads and transistors. Mainly you want to remove the machining burs and smooth the surface to a more even plain. Don't spend to much time on it but it must be done.
The Sil pads can become contaminated with metal filings very, very easily. The metal chips will short the collectors to the heatsink, and believe me, enough to cause big problems.
After installing the transistors, make sure there is no continuity between any collector and the heatsink!
Try to minimize the removal and reinstalling of the Sil pads.
The K-10 and SOT-32-3 (Q1, Q4 and Q5) packages do not need the insulated shoulder washer but require the metal washer. Use the M3x0.5x8 screws
The two TO-220 (Q2 and Q3) packages require the insulated shoulder washer only. Use the M3x0.5x6 screws.
I included images for the correct hardware/component installation.

 

[MichaelFin]

Good to know! I will sand my heatsinks and reinstall and check for any grounding of the collectors. Hopefully everything will pass inspection and then my 780 will fire up just fine.

 

[MichaelFin]

The drops look good.

I tested the hardware that now will be included in the module kits and I wanted to bring up a few points, some of which we discussed.
The heatsink should be sanded fairly smooth with 180 grit wet/dry on a flat surface, thoroughly cleaned with soap and water, before installing the pads and transistors. Mainly you want to remove the machining burs and smooth the surface to a more even plain. Don't spend to much time on it but it must be done.
The Sil pads can become contaminated with metal filings very, very easily. The metal chips will short the collectors to the heatsink, and believe me, enough to cause big problems.
After installing the transistors, make sure there is no continuity between any collector and the heatsink!
Try to minimize the removal and reinstalling of the Sil pads.
The K-10 and SOT-32-3 (Q1, Q4 and Q5) packages do not need the insulated shoulder washer but require the metal washer. Use the M3x0.5x8 screws
The two TO-220 (Q2 and Q3) packages require the insulated shoulder washer only. Use the M3x0.5x6 screws.
I included images for the correct hardware/component installation.

View attachment 1013016

View attachment 1013017

View attachment 1013018

View attachment 1013015

Three of my transistors, Q1,Q2, and Q4, have continuity between ground and their collectors. Is this something I can fix? What is causing this? I sanded my aluminum heat sink and I'm still having the issue.

Would the best practice for populating this board be installing the BJTs to the heat sink, checking continuity issues, then installing the rest of the board?

 

[petehall347]

Three of my transistors, Q1,Q2, and Q4, have continuity between ground and their collectors. Is this something I can fix? What is causing this? I sanded my aluminum heat sink and I'm still having the issue.

Would the best practice for populating this board be installing the BJTs to the heat sink, checking continuity issues, then installing the rest of the board?

its the insulation on the transistors ..the mica or the shoulder washer .

 

[zebulon1]

The Sil pads might be contaminated. It could of happened at the first install.
Switch to the traditional mica-paste.
Or try to clean the Sil's with soap and water but once the fine metal chips embed into the material. Its hard to get them out.

 

[rcs16]

mtf has provided some explanation of ckt operation and troubleshooting tips in this thread, see post #3
http://audiokarma.org/forums/index.php?threads/another-sx-780-issue.608200/

Yes you should always check continuity from the Al plate to the device collectors after they are mounted b4 installing the pcb. Also have the leads formed to fit through the pth's in the pcb b4 doing the final soldering of them. I offered a technique earlier to determine where to do the bend. Secure the leads on both sides b4 bending, you do not want to put stress on the lead(s) as it comes out of the lead frame(plastic moulding intersection)

 

[MichaelFin]

mtf has provided some explanation of ckt operation and troubleshooting tips in this thread, see post #3
http://audiokarma.org/forums/index.php?threads/another-sx-780-issue.608200/

Yes you should always check continuity from the Al plate to the device collectors after they are mounted b4 installing the pcb. Also have the leads formed to fit through the pth's in the pcb b4 doing the final soldering of them. I offered a technique earlier to determine where to do the bend. Secure the leads on both sides b4 bending, you do not want to put stress on the lead(s) as it comes out of the lead frame(plastic moulding intersection)

Good to know. I will try that method on my other Al plate and PCB. Hopefully I will have more success.

Thank you for all of the trouble shooting!

 

[tsd71]

Thanks guys rcs, Zeb, and other’s, got my 4th unit up and running tonight with the new modules. All hail the 780!!
I do find if you torque down the MJE,s too hard you get continuity between the collector and the aluminum plate. Had to back off a little on a few of them, not sure why. Awesome fix nonetheless. Thanks.

 

[MichaelFin]

According to the MJE data sheets the 'tab' is internally connected to the collector so whenever my screw touches the tab (and the screw is touching the Al plate) I get continuity between my collector and the tab. I guess I'm still having issues getting all of my collectors to be free of the Al plate. Q1 and Q4 and Q5 are all fine but Q2 and Q3 won't have their collectors isoalted from the tab unless I don't screw them down.

I know @tsd71 above mentioned if you torque the MJEs too hard you get continuity but if I don't torque them down I'm worried they'll eventually hit the screw and short the collector to the heat sink during use.

I guess I'm confused on how to install the MJEs without getting a continuity issue between the Al plate and Q2 and Q3. Don't I need to electrically isolate the tab?

 

[sregor]

Transistor mounting. Notice item 2. It is a shoulder washer, and is plastic and isolates the screw head from the tab. It is necessary for the driver transistors. 1 is the mica (or other) insulator. Both isolate the tab from the heatsink. If you have both and still get connection to heat sink, You most likely have a bad insulating mica or sheet, or a metal particle or burr in the hole is poking through the insulating sheet. My 2 cents.

 

[MichaelFin]

Transistor mounting. Notice item 2. It is a shoulder washer, and is plastic and isolates the screw head from the tab. It is necessary for the driver transistors. 1 is the mica (or other) insulator. Both isolate the tab from the heatsink. If you have both and still get connection to heat sink, You most likely have a bad insulating mica or sheet, or a metal particle or burr in the hole is poking through the insulating sheet. My 2 cents.

This seems to be my issue. It would appear I didn't order a shoulder washer and that is causing my issue. I will hopefully find a part laying around otherwise I'll order one.

Thank you!

 

[MichaelFin]

Whoop whoop!

Works like a charm. Going to troubleshoot my other board with the collector issues, I think its just the sil pads. But the other module works like a charm!

Thanks for helping me out everyone, I appreciate it.

 

[rcs16]

It would appear I didn't order a shoulder washer and that is causing my issue.

Thanks Steve, I thought that I made it clear about installation procedure but it is always good to have more help to get the point across.

 

[toxcrusadr]

At some point in time I think that we should work on a proper set of documentation, to hopefully avoid obvious mistakes and bundle up all the pieces of important info scattered about.

+1 on this - actually while reading the last few pages to catch up, I was thinking it would be good to have a spreadsheet of parts that includes substitutions, especially the transistor pairs. It could have links to the parts (which have been posted), notes (such as "don't mix brands when making transistor pairs"), all the stuff we ham-fisted amateurs will need to know.

I would volunteer to help with this, at the same time I'm fully aware I haven't ordered a single part yet (besides acquiring two empty boards) or worked with a Mouser BOM. If it requires going through the thread and putting things together I'd be willing to do that.

 

[zebulon1]

I have a list of parts and subs in an eBay listing for the boards and plates.
The new subs are added and the list gets updated whenever Rick recommends a sub for the module.
It wouldn't be a bad idea to make sure it's complete.

 

[jeffV]

ok, do these look good so far? are the resistors facing the correct direction?

 

[rcs16]

I hope that you are kidding, I see no smiley face? that resistors have polarity, which we know is not the case, if not, now you know. Also you soldered the TO-3P devices, did you line up the flange mounting holes with the holes in the HS first? Also with the BD139(TO-126), it needs to sit flat too, on the same HS plane as the other devices that mount to the HS, otherwise you can put too much stress on the leads thus crack/fracture the plastic package which could cause long term reliability issues.
I did not zoom in to see if you used the correct resistor values, but at a glance it look okay.

 

[jeffV]

I hope that you are kidding, I see no smiley face? that resistors have polarity, which we know is not the case, if not, now you know. Also you soldered the TO-3P devices, did you line up the flange mounting holes with the holes in the HS first? Also with the BD139(TO-126), it needs to sit flat too, on the same HS plane as the other devices that mount to the HS, otherwise you can put too much stress on the leads thus crack/fracture the plastic package which could cause long term reliability issues.
I did not zoom in to see if you used the correct resistor values, but at a glance it look okay.

I used the HS as a "jig" before I soldered. The mounting holes line up perfectly. BD139 is on the same plane as the other devices.
As far as device values, everything was ordered per the supplied Mouser parts list..

 

[zebulon1]

Looking good from this perspective.
Double check your work as you go. Looking for missing solder connections.
Remember:
The PCB's are two sided, so you need a good connection on both sides of the component leg.

 

[jeffV]

installed the 0050 modules, working perfectly! sweet upgrade.
one question, where should the trimmer resistor be set? I left it dead center..?