SX-737 Project

When using thermal grease, think about it this way...

If you take two pieces of flat metal and bolt them together you will have "voids" between them. The thermal grease is used to fill these microscopic voids so to get the maximum possible heat transfer. Too much grease can act as an insulator which is the opposite effect of what you're trying to achieve. If you keep this in mind you will always get the proper amount.

You're doing a great job and the guys above are doing a great job in this thread.

Keep up the good work!

Bob
 
I have been away. Great job so far. Yes, I did the flyback diode. Not sure on a new part number for the obsolete part tho.
 
Does anyone know if either of these diodes will work in place of 512-1N4004 as a flyback diode in the protection circuit? This is the last piece holding off my mouser order.

583-1N4004-T

625-GP10G-E3
 
With the exception of the D9 diode, which I had to order, the Power supply board is complete. I will go back and replace the last diode once it arrives in the mail. The unit tests fine on the DBT and comes out of protection after about 5 seconds.

I am going to move on to the Protection circuit next.

Here is my BOM for the Protection Circuit board.

AWM025, C1 .22 10 505-MKS2C032201BKI00
AWM025, C2 .22 10 505-MKS2C032201BKI00
AWM025, C3 330 6 647-upw1c331mpd
AWM025, C4 330 6 647-upw1c331mpd
AWM025, C5 4.7 25 647-UPW1H4R7MDD
AWM025, C6 100 16 647-UPW1E101MED
AWM025, Q1 2sc869 512-KSC1845FTA
AWM025, Q2 2sc869 512-KSC1845FTA
AWM025, Q3 2sc945 512-KSC1845FTA
AWM025, Q4 2sc945 512-KSC1845FTA
AWM025, Q5 2sa733 512-KSA992FBU
AWM025, Q6 2sc945 512-KSC2383YTA
AWM025, Q7 2sc1384 512-KSC2690AYS

Flyback diode, 583-1N4004-T

Checking the transistor data sheets, it looks like the pinout will change for Q1 and Q2, but all of the other transistors (Q3 - Q7) should swap out without any pin changes I also noticed that in the MTF BOM he lists a note for Q3, Q4, and Q5 "only if bad". Should I skip these 3? My protection circuit seems to be working fine currently.
 
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I now have the power supply board done. I went back and replaced D9 which I had missed on my initial mouser order, and I also replaced R3 with 280-CR5-180-RC. I installed the new R3 resistor up off of the board some to prevent the board from getting scorched and to help with air flow around the resistor.

I have also completed the protection circuit board. I did not replace Q3 - Q5 as my protection circuit is working, and in the MTF part list it mentions to only replace them if they are bad. I do have the replacement transistors on hand, and I can go back and replace them if you guys think that I should.

I still need to install a fly back diode as suggested in other threads. I have two parts on hand which I ordered from mouser to use for this purpose.

625-GP10G-E3

583-1N4004-T

Will one of these work as a fly back diode for the protection circuit board? The part number listed in other threads is no longer available from mouser.
 
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One thing that I have noticed so far is that after replacing a capacitor or two the DBT will glow for awhile before the protection relay triggers and everything settles down. It's still a dim glow, but not as dim as when everything is stable. Sometimes I get nervous and shut it off, and it takes a couple of on/offs before it all settles down. After the initial startup, the protection relay is back to 4-5 seconds until it triggers, and the DBT only glows for a few seconds before settling down. Do the new capacitors have to charge up or something? Is this normal behavior?

I have been using the DBT to check after replacing every few parts. I have also been keeping an eye on the bias and offset along the way. Since this is my first time I want to make sure the path to backtrack is a short one if an issue arises.
 
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Here is my BOM for the Power Amp board.

AWH033, C1 .33 25 647-QYX1H334KTP
AWH033, C2 .33 25 647-QYX1H334KTP
AWH033, C7 220 6 647-UPW1E221MPD
AWH033, C8 220 6 647-UPW1E221MPD
AWH033, C9 47 35 647-UPW1H470MED
AWH033, C10 47 35 647-UPW1H470MED
AWH033, C19 22 10 647-UPW1a220mdd
AWH033, C20 22 10 647-UPW1a220mdd
AWH033, VR1 652-3386F-1-101LF
AWH033, VR2 652-3386F-1-101LF
AWH033, VR3 3296Y-1-103
AWH033, VR4 3296Y-1-103
AWH033, Q1 2SA726 512-KSA992FBU
AWH033, Q2 2SA726 512-KSA992FBU
AWH033, Q3 2SA726 512-KSA992FBU
AWH033, Q4 2SA726 512-KSA992FBU
AWH033, Q5 2SC1451 512-KSC3503DSTU
AWH033, Q6 2SC1451 512-KSC3503DSTU
AWH033, Q7 2SD357 512-KSC2690AYS
AWH033, Q8 2SD357 512-KSC2690AYS
AWH033, Q9 2SB527 512-KSA1220AYS
AWH033, Q10 2SB527 512-KSA1220AYS
AWH033, Q11 2SD370 863-MJ21194G
AWH033, Q12 2SD370 863-MJ21194G
AWH033, Q13 2SB530 863-MJ21193G
AWH033, Q14 2SB530 863-MJ21193G

I also have four new transistor insulators, mouser part# 534-4662. Hopefully these are the correct insulators?
 
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Those will be fine. Don't forget the thermal paste.
 
For the differential pair transistors Q1-Q4, I've read it's best to gain match the set. I have a Harbor Freight multi-meter which does have a npn/pnp hFE test option. I went through the package of KSA992 transistors and found the closest four that I had.

The HF meter shows them as...
438
437
436
436

Another thread that I have read here mentioned that transistors within 10hFE of one another was ok, but within 5hFE was better. Can anyone confirm this is true?

Can anyone give me more information on gain matching the differential pair transistors?
 
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When I check for hFe I leave the transistor to be tested in the meter for a few minutes to settle down as even your body temp from your fingertips will change the reading. (Go ahead and put one in let it sit for a few minutes until it settles and then grab it with your fingers. IT WILL CHANGE!) So leave them in until they settle down and then write down the reading. I can be picky at times and only use matched within 1 or 2 digits. Put the 436's in one side and the 437-438 in the other. You won't hear the difference between 10hFe and 5Hfe, and I doubt you'll see any difference in the response in the bias/offset with those numbers. Getting them as close as possible is always a good thing tho electronically.
 
larryderouin said:
When I check for hFe I leave the transistor to be tested in the meter for a few minutes to settle down as even your body temp from your fingertips will change the reading. (Go ahead and put one in let it sit for a few minutes until it settles and then grab it with your fingers. IT WILL CHANGE!) So leave them in until they settle down and then write down the reading.
Click to expand...

Thanks for the feedback!

I noticed this while checking the transistors. I installed them in my HF meter and let them settle down before taking a reading and moving on to the next one. It took about a minute or two for each to settle down. I tried to touch them as little as possible while installing them into the meter as to not heat them up so much.
 
tsd71 said:
View attachment 978985 View attachment 978982 Dont forget the flyback diode, pins 9 and 10 on the protection board, Cathode (striped end) goes to pin 10 and the anode goes to pin 9...Use an 1N4004 for the diode. View attachment 978981
Click to expand...

I went ahead and added in the flyback diode to the protection circuit. I had to use mouser part 583-1N4004-T as the suggested diode 512-1N4004 was out of stock when I placed my most recent mouser order.

Hopefully this is okay?

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I also have the power amp board all done now. I installed the Q1-Q4 differential pair transistors exactly as larryderouin advised in his post above. Bias and offset both adjusted in fine on the DBT. They seem much more stable now, and they are much easier to adjust than before.

My next step is to replace the output transistors Q11-Q14. It looks like I will need to move the heat sink up some to be able to unscrew them. Any advice on how to go about that process without damaging anything?

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The protection relay that I ordered with my first mouser shipment 653-LY4F-DC24 was way to big, so I ordered relay 653-LY2F-DC24 with my second order from mouser. This new relay was much smaller. In fact, I was able to install the new relay guts into the original relay housing. With that figured out I went ahead and got the new protection relay installed.

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Things are moving along nicely. Next step will be to install the output transistors then I can move onto the next board. I think I'm about halfway to the finish line at this point!
 
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I was able to get the output transistors swapped out by loosening up the hold down screws on the one end, and removing the two screws on the other end. That let me tilt the entire works out enough to get to the transistors without having the entire board/heat sink flopping around.

I guess the next board in line should be the Control Amplifier board?

Here is the BOM I have for it...

AWG030, C1 1 25 647-UKL1H010KDDANA
AWG030, C2 1 25 647-UKL1H010KDDANA
AWG030, C5 100 16 647-UPW1E101MED
AWG030, C6 100 16 647-UPW1E101MED
AWG030, C9 4.7 25 647-UKL1H4R7KDDANA
AWG030, C10 4.7 25 647-UKL1H4R7KDDANA
AWG030, C17 4.7 25 647-UKL1H4R7KDDANA
AWG030, C18 4.7 25 647-UKL1H4R7KDDANA
AWG030, C19 4.7 25 647-UKL1H4R7KDDANA
AWG030, C20 4.7 25 647-UKL1H4R7KDDANA
AWG030, C21 47 10 647-UPW1H470MED
AWG030, C22 47 10 647-UPW1H470MED
AWG030, C23 2.2 25 647-UKL1H2R2MDDANA
AWG030, C24 2.2 25 647-UKL1H2R2MDDANA
AWG030, C29 100 35 647-UPW1H101MPD
AWG030, q1 2sa726 512-KSA992FBU
AWG030, q2 2sa726 512-KSA992FBU
AWG030, q3 2sc1344 512-KSC1845FTA
AWG030, q4 2sc1344 512-KSC1845FTA
AWG030, q5 2sc1344 512-KSC1845FTA
AWG030, q6 2sc1344 512-KSC1845FTA
 
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