Recently acquired sx-1080 is a mess inside/ need a lot of help on this one

So if this is the style/case I’m working with, can I order the replacement transistors thru Mouser???
NOT YET, the transistors pete posted about will probably not fit flat between the heat sink "fins"
I was trying to show WHY NOT.

You need to measure how much flat mounting space is OUTSIDE of the screws.
It looks to me that the TO-247 transistor case will fit between the screws,
I showed the RM60 case because it was used in the SX-3900, where I have successfully swapped the TO-247 transistors (from mouser or digikey) in.

Here's what I did:

original transistors (RM60) on an SX-3900 / D7000 with Phoenix socket replacement
d7000_transistor_phoenix_socket.JPG


TO-247 replacement transistors on the SX-3900 / SX-D7000 with Phoenix socket replacement
Notice the aluminum hold down bar with 24.4mm screw spacing holding down the replacement transistors.
aluminum.jpg
 
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TO-264 is 20mm wide
TO-3P is 15.6mm wide
TO-247 is 16 mm wide, I think these are the one to use, Onsemi MJW3281A/MJW1302A (200W/230V/15A)
make up that hold down plate(s) that Mark shows. Probably have to use longer screws, not sure what size it is (5mm?). new mica or sil pad, thermal compound (if using mica), do not over torque, check for continuity between the flange(collector) and HS (ground). See if they bias up to spec.
test(diode test) out all the bjts/R's in the power amp. could check out DCV from the PS too.
 
I have a solid 1/4 inch (7mm) of flat clearance from the outside edge of the bolt holes. I have 3/4 inch (20mm) of clearence in between the bolt holes.
 
Hello All, I tried to locate the parts TO-247 that RSC16 recommended, Mouser says both are obsolete?? Does anybody have any recommendations for some replacements?? Sounds like I will be needing some mica pads also? The originals were mounted directly to the heat sink with thermal compound. Any help and recommendations would be very helpful. I am totally lost with this rework task. Thanks for any and all help with this one..
 
Onsemi MJW3281AG and MJW1302AG ( note G at the end ) both show as active on Onsemi site, without G show as obsolete.
Mouser shows 674 of MJW3281AG and 229 of MJW1302AG in stock as of 3/21/18.
Mouser PN# 863-MJW3281AG and 863-MJW1302AG

You must use thermal compound, even if you don't need/use a mica insulator.

EDIT: more info
 
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I have one prototype clamp done with the new mjw1302ac. I have the original plastic insulator in there ( no heat grease yet) let me know what what you think??? Looks like it will work to me, but I don't know crap. Lol. Please commentIMG_0003.JPG
 
Just be careful with that insulator, do not torque the screws with no thermal paste, they can crack and cause shorts of the live tab to the heatsink which will be at ground potential.
Also not over torque the screws once paste is applied. Always double check after assembly.
 
Thanks for the replies fellas, I will finish the hold down brackets and install on heatsink and reinstall in chassis. I will need some guidence for start up procedure. Should I replace the trimmers on the amp boards, if so with what model numbers?? I have 652-3296p-1-204lf. And. 652-3386h-1-101lf. Mouser part numbers. Have 2 each
 
IMG_0005.JPG IMG_0004.JPG Afternoon all, I finished one side of heat sink. I have to finish drilling the last four aluminum clamps tonight. Here is a pic of my progress. It looks like there is no heat grease on there, but there is, I just took the time to clean up the excess with q tips. I think it came out fairly good. Comment if you like. Have a good night all.
 
looks good, measure ohms between clamp plate screws and bjt leads
what did you use for insulators?
 
I measured OHMs on all 4 trans to ground. I have no readings on any of them. So, I assume they are installed correctly? I cleaned up and reused the factory isolators. Any idea or direction for the replacement of the trimmers on the amp boards?? I have some and I listed the part numbers in a couple of posts above. I think it would be a good idea to get these replaced while apart?? (Can’t hurt) thanks again for all the help
 
image.jpg Ok, I have an update. I finished fabbing the clamps and have everything back together. I have not plugged in the amp boards yet. I was able to get the center voltage on both amps to 0 volts, the idle current is unadjustable on both amps. Do the amp boards have to be plugged in to get this to adjust 30mv with VR1??? I am not going further with this till I hear back from someone as I have too much time in this basket case. Lol. Thanks for the compliment basil13, I made the clamps out of some scrap aluminum I had in the garage.
 
Nice neat work, it's looking good.
You need all the plugs connected on the amp boards for them to operate and adjust the Idles. You have the regulated in front and the unregulated in back, powering the outputs.
Connect all the plugs on one amp board and use the DBT to power up.
Check the DC Balance and check the idle trimmer response by starting it at full CCW and adjust CW watching the readings that they move smoothly and to the trimmer movement.
If all is well. Adjust the idle trimmer back to min mV's and apply full house/line power, setting the idle to the final 30mV reading.
Then move to the other channel and repeat.
If the idle doesn't adjust or can't make the required setting, recheck your work looking for missed solder connections.
 
I CANT BELEIVEIT!!!!!!!! This thing actually is singing nicely now. I didn't think this thing would ever work again,but here it is back in service, thanks to all your help,THANKS SO MUCH. I'm speechless LOL. Gonna let it run for a bit and listen to some tunes while I clean up my bench.
 
Great to hear of success for this re-build.
I am not sure of the trimpot part numbers. The value look okay, 100 ohm for bias and 20K for offset. See if they fit and allow easy adjustment.
3296p-1-204lf. And. 652-3386h-1-101lf
If the original pot cleaning makes them operate okay, I'd leave them in.
Check idle/offset after it warms up to op temp (runs for a while), see how much it changes when it gets hot. should be set when at op temp.
 
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