SX-939 & SX-9930 Summer Project

[DrTim]

I needed a project to do that can be done inside so I can avoid the Florida summer heat and keep me off the couch. Believe me, the heat requires respect. Remembered that I had a SX-939 (Jan, 1974) and its European cousin, the SX-9930 (Oct, 1975) under a blanket in the carport. These have been out there for about 4 years. Don’t remember exactly how I acquired them but I do remember it was at different times. The 9930 was in better shape both cosmetically and internally than the 939. The 939 had the rice krispy sound and never got put into the rack. I had the 9930 set up for a couple months but it was lacking. Sounded labored and muddy. That’s why it ended up under the blanket in the carport.

Four years ago, I looked at the interior of the 939 thinking about doing a recap. I was overwhelmed. After years of reading the threads here and the recent recap threads, I feel confident that I have the desire, tools and ability to at least follow instructions enough to get both these units back to working condition. I plan on doing this slow as I have all summer to work on it. No hurry here.

The plan is to work both units one step at a time on separate tables. I will start with the power supply board on the 939 and when that is fully done and tested, then the power supply for the 9930 will be done and tested before moving on to the next section.

The other threads will give me guidance and info, but I will have questions along the way which I hope someone can help me along. Hopefully, I will not become a thorn in the side with some of my questions.

Starting with the power supply board AWR-052-0. The board for the 939 got very hot and burnt. I did a voltage check on the pins for both units and the 9930 checked out fine. However, the voltage for the 939 board was all pretty close except for Pin 4 which would run away with its voltage starting at +12 dcv and keep climbing past +60dcv. I’m wondering if that would be an indication that a couple of the resistors (like maybe R15 or R16) have failed? Should I find the problem of the voltage at Pin 4 before recapping and replacing the 3 transistors? I will test several of the resistors nearest the heat sinks to see where they stand during the recap and replace any that are not within 5 to 10% of specs. Am I on the right track? Resistors that you would replace because of the past heat? I know about raising them off the board. Suggestions appreciated and welcomed.

 

[rcs16]

However, the voltage for the 939 board was all pretty close except for Pin 4 which would run away with its voltage starting at +12 dcv and keep climbing past +60dcv.

For this to happen the Q1 regulator must not be working properly, and zener D14 must be open.
It is supposed to be 47.5VDC at terminal 6. IF it is not just re-build that section.
R20,D14 are to make the base of Q6 around 14V. There will be a diode drop at the Q6 emitter, to make the 13.XVDC at terminal 4. check all of these.

 

[larryderouin]

I've seen worse 939 P.S. boards. Best bet is to do what Rick recommends then after voltages are ok, recap and re-transistor it with the list, but get it vetted 1st. There are some differences between the 939 and the 9930. Do one of them completely, then do the other. Running back and forth between them will confuse you and you may end up making things worse in the long run. If you need schematics for the 9930 I have them. PM me with your email and I'll send you what I have. I'll see if I can dig up the latest 9930 thread.

 

[DrTim]

rcs16 and larry, thanks for taking the time to give me a hand in this project.

rcs … You were right about Q1 being the source of the problem. I replaced the transistor and Pin 4 now has a steady +13.3 dcv. I pulled a leg on the D14 and got a 700 reading which I guess is a little high but seems not to be a problem. Pin 6 was and still is reading +47.5 dcv. I have created other problems which I need to chase down but I really need to double check what I did to cause these changes in the voltage readings. I got something backwards somewhere as Pin 8 voltage changed from a + to a negative. I checked several resistors around the burn area and they tested ok. I replaced Q1, Q4 and Q6. I made the mistake of pushing down on the top of a cap and pushing the solder pad off the board. Fixed that this morning. Live and learn.

Larry … Thanks for the offer on the 9930 schematics. I will send you a PM soon. I have a copy of the 939 service manual but between the light/hazy print and my aging eyesight, a magnifying glass is always close at hand. I also took your advice elsewhere and got the hi-res copy online from kallhovde.com.

I followed the Spenser SX-939 thread closely. ( http://audiokarma.org/forums/index.php?threads/pioneer-sx-939-repair-and-restore.824334/ ) There has been no difference from his board and mine. I'm trying not to repeat information that has been already covered in that thread. Your Info posted there has gone a long way to getting me to understand a path to success. After getting into the 939 and starting this project, I have come to agree with you that doing one unit first and complete before doing the other. It will be a great help to have the unmolested 9930 around so I can look at what it is supposed to look like when I put the 939 back together.

I recapped AWR-052-0 from the Spenser list after checking each cap on the board against his list which were the same. I can see where having the list posted here for vetting and knowing what actually went into my project will help in trouble shooting my mistakes. I will post what went into my AWR-052-0 and post anything going forward. (A copy and paste, with slight changes, from Spenser's thread. Thanks Spenser for all your work putting most of this together.)


AWR-052-0 Power Supply

AWR-052 C11 47uf 63v cea up it to 100V 647-UPW2A470MPD6
AWR-052 C12 47uf 50v cea up it to 100V 647-UPW2A470MPD6
AWR-052 C13 470uf 80v ach-038 up it to100V 647-UPW2A471MHD
AWR-052 C14 470uf 80v ach-038 up it to 100V 647-UPW2A471MHD
AWR-052 C15 100uf 63v cea up it to 80V 647-UPM1K101MPD
AWR-052 C16 100uf 63v cea up it to 80V 647-UPM1K101MPD
AWR-052 C17 47uf 16v cea up it to 25V 647-UPW1E470MDD
AWR-052 C18 47uf 16v cea up it to 25V 647-UPW1E470MDD
AWR-052 C21 47uf 50v cea up it to 100V 647-UPW2A470MPD6
AWR-052 C22 2200uf 10v cea * 647-UPW1A222MHD
AWR-052 C23 220uf 16v cea * 647-UKL1C221KPDANA
AWR-052 C24 1000uf 35v ach-039 647-UPW1V102MHD


Q1 512-KSC2073H2TU
Q4 512-KSA940TU
Q6 512-KSC2073H2TU


Filter Caps look good and won’t be changed at this time.

* C22 &C23 are different than Spensers list as the voltage was not increased and are the same voltage as what was pulled from the board. His list had them increased to 25V each per Larry’s suggestion. Am I ok with the 10v &16v at these caps?

 

[larryderouin]

C22 & C23. The main reason these were bumped to 25v was for 2 reasons. 1.) availability (10 and 16V caps are getting harder to find), & 2.) to give them a bit of voltage headroom between the actual surge & operating voltage and their max rating. For example C-22 is running within 2.5V of it's max rating for voltage on the schematic, and that's at 1974 input voltages of 117-120VAC. Todays slightly higher voltages will cause a corresponding increase in the voltages from the transformer, stressing an already marginal situation. So in the case of C22 & C23 an increase to a 25v rating is a win-win for the power supply. They will have a voltage headroom that should (and does) handle voltage surges at turn on without stressing the caps, and they can handle an input voltage on their circuit that is slightly higher due to todays line voltages.

Double check your voltages on pin 6 against pin 8. If pin 6 is a + polarity so should pin 8 as they feed off the same supply. These are both DCV so Red probe on the pin and black on a clean part of the chassis for grounding. (I'm probably preaching to the choir, but a little reinforcement never hurts).

You should have the 9930 info @ your email inbox. Suggest taking the full schematic to Office depot on a flash drive, and having it printed @ as large as you can get on 24"x36" paper. The cost is a couple bucks, but like you, it makes for easier reading for these old abused eyes.

 

[DrTim]

Thanks for the files Larry. I will have them printed out when I move on to the 9930. I did have the SX-939 schematic plotted to 2x3 and had the different board pages from the service manual enlarged to 11x17 inches. It helps a lot.

I'm glad I allowed all summer to do this project because I have a feeling I won't be finishing this project up until the fall. Maybe it will get easier as I dig deeper and get a better understanding of the workings of the unit. The larger schematics help to see where it is going.

I checked my reading on Pin 8 at least 4 different times and it always came back negative. Checked all the caps and triple checked the transistors. I used ancient technology to find the fault. Appling light pressure on the caps, transistors and resistors with a chop stick, I found that R11, when pressed right, would cause the relay to click in and out of protection. With the pressure applied, Pin 8 would read positive. This is one of the resistors I had not checked previously. I touched up the solder at R11 and Pin 8 stayed in the positive. Every Pin reading now was within 2v or closer of what they should be. Except that the readings on Pins 8 and 11 would not stay steady, fluctuating up and down about 3.5volts continuously over a three second time period. Pin 8 and Pin 11 both have a 820 ohm resistor (R11 & R12) as the nearest component to the Pins. Pulled both but they checked out at 835 ohm */-.

Going into the city today to try to find replacement resistors (R11, R12, also R20) since I have two of them out and I can remount them higher. I will also try to get a new zener diode for D14 and replacement caps for C22 &C23 @ 25v. I will report back.

 

[Oldsansui441]

All the best with your overhaul on the SX-939, they are a fairly big job but well worth it when you hear the difference it makes . Nice find on R11 soldered joint.

 

[DrTim]

Thanks for the encouragement 441. It is needed right now. I keep scratching my head over this power supply. I got what I needed yesterday and soldered them into place. These include replacing C22 & C23 with 25v rated caps, the D14 Zener diode, and R11,R12 &R20 resistors. The relay comes out of protection in 4 seconds. I still have the unsteady readings on the Pins 8 & 11.

AWR-052-0
Pin
+ 25v 8 +26 to 29.50v *
+47.5v 6 +47.65v
+35v 5 +35.20v
-25v 11 -25 to 29v*
-43v 9 -44.6v
-13v 10 -13.36
+13v 4 +13.2
+ 7.5v 2 +7.5

I have stared at this board way to long and am fighting the urge to move on to the next board before finding out why I get the unsteady readings at Pin 8 &11. Its just a urge. I'm thinking its a weak trace or solder pad somewhere, a faulty 2sa or 2sc transistor or the spirit of one of my ex's coming back to mess with me. I know the demon spirit thing is on me, but can someone chime in with some suggestions on where to look to solve the unsteady voltage?

I did leave the power on for about 4 hours last night playing AM at low volume through headphones. The heat sink area ran about 90 degrees with an ambient temperature of about 74 degrees. I was switching between functions to see if it had an effect on the unsteady voltage, no change. But I did find out that if I turn the 100hz bass knob to around +8 it kicks the relay. Back off on the knob and it comes out of protection. Something I need to be aware of down the line.

After I get the power supply circuit board done, it looks like boards AWM-062-0 (protection) and AWF-013-0 (equalizer) would be the easier to do next unless I get pointed in another direction. I have gone over these two boards and have what I need to get these done. Which ever board is next I will list for vetting. I have been turning a blind eye towards the tuner board.

 

[larryderouin]

Check the input and output voltages of the Zeners (D12,D13) which are 13V 1/2W. They may be overly heat stressed and on the way out although your voltage on D14 is good for now, I'd go ahead and just replace it for peace of mind. Recap the whole thing, and replace the trouble prone transistors as per the list.

4 to 6 seconds on the protection board is fine. Cranking the bass up and sending it into protection, sounds like distortion either in the control board, or a flaky transistor(2sc1451 or 2sa725,2sa726) or cap in the amp board leaking. Do the AMP and Protection boards 1st, then work back to the inputs from there.

Leave the Tuner for Last. It's a Royal PITA to work on and slack in the wiring harness isn't enough to give you 90 degrees of rotation of the board. So you'll have to desolder the pins, Mark them and remove the board for cap replacement.

 

[DrTim]

Thanks Larry for the help. I don’t have a way to check the output and input voltage breakdown of the Zener diodes D12 ,D13 so I just replaced them. I also cleaned up some iffy soldering. Made no difference with the unsteady voltage at Pins 8 & 11. I had already recapped and replaced Q1, Q4 & Q6 before this problem showed up using what was listed above. Prior to the recap, Pin 8 and 11 were steady. I have checked and rechecked the position and polarity of the caps against the schematic, the board and referencing the AWR-052-0 board of the unmolested 9930. I will spend this morning tracing back from Pin 8 and 11 to see if anything looks hinky. This problem is a good lesson for me. Teaches patience and attention to detail.

In anticipation of finding the problem with the power supply circuit board, I need to look towards making sure I have the right caps and transistors for the protection board and the power AMP board.

Here is the list that I plan of using. It is, in part, the list that Markthefixer posted on Larrys rebuild thread from 5 years ago. I will underline and bold the parts that were changed because of availability and need more scrutiny.



AWH-030 Power Amplifier


AWH-030 C1 .47uf 25v cssa 647-QYX1H474KTP
AWH-030 C2 .47uf 25v cssa 647-QYX1H474KTP
AWH-030 C3 1uf 25v cssa 647-UKL1H010MDDANATD
AWH-030 C4 1uf 25v cssa 647-UKL1H010MDDANATD
AWH-030 C5 33uf 16v cea 647-UPW1C330MDD
AWH-030 C6 33uf 16v cea 647-UPW1C330MDD
AWH-030 C11 330uf 10v cea 647-UPW1A331MPD
AWH-030 C12 330uf 10v cea 647-UPW1A331MPD


Q1,Q2,Q3,Q4 2sa726 replace with KSA992FBU

Q7, Q8 2sc1451 replace with KSC3503DSTU

* C1 & C2 - 647-QYX1H474KTP instead of 598-DSF050J474 667-ECQ-V1H474JL

* C3 & C4 647-UKL1H010MDDANATD instead of 647-UKL1H010KDDANATD



AWM-062-0 Protection Circuit


AWM-062 C1 .22uf 10v cssa 539-168224J50C-F
AWM-062 C2 .22uf 10v cssa 539-168224J50C-F
AWM-062 C3 330uf 6v cea 647-UPW1A331MPD
AWM-062 C4 330uf 6v cea 647-UPW1A331MPD
AWM-062 C5 4.7uf 25v cea 647-UPW1V4R7MDD
AWM-062 C6 100uf 16v cea 647-UPW1E101MED

Q6 2sc945 replace with KSD1616AGBU

Flyback diode 821-1n4007G-KROG


* C1, C2 539-168224J50C-F instead of 598-DSF050J224 667-ECQ-V1H224JL


Any help is appreciated.

 

[larryderouin]

Parts replacement;
Amp
C1 & C2 OK
C3 & C4 OK You just went from 10% to 20% Tolerance. That's acceptable.

Protection Circuit
C1 & C2 OK No problem with the choice.

The only thing I could think of now is one of Q1 Q4 Q6 might be installed wrong BUT they are TO-220's and only go in one way. The fact you are getting fluctuations tells me that they are working. Something else is causing the fluctuations. Did you replace the 2sa720 and 2sc1318? Q3 & Q5. Do them as they don't have any heatsinking and are TO-92 cases (small and susceptable to heat stress). Make real sure of your leg/pin orientation with these as they could be different (download data sheets)from the originals. I'd take another look at the Zeners. Measure the voltage on either side of the zener's. Look for fluctuations on the downward side(output).
I can open up my 939 and shoot the Power supply. It might be a better choice for comparison than the Multi Voltage 9930.

 

[rcs16]

647-QYX1H474KTP
selling Nichicon films now, cool, more parts to choose from

the spirit of one of my ex's coming back to mess with me. I know the demon spirit thing is on me, but can someone chime in with some suggestions on where to look to solve the unsteady voltage?

Cute.
Every regulator needs a stable reference, so I'd suggest to start there. You can measure ACV(mV) on your DC supply to check for instability and noise.

 

[larryderouin]

You could get a priest to perform an exorcism. But watch out for pea green soup. I think my late wife is playing games in the house. Stuff gets moved overnight, odd noises now...crap like that. It's got the dog cowering under the bed if I'm not in the house. Or maybe it's just an over active imagination on my part. Who knows.

 

[DrTim]

I don't have the two transistors (2sa720 and 2sc1318) on hand to replace and can't source them locally. I did pull them and they tested ok and I put them back in the board. I also rigged a Zener tester using three 9v batteries, a inline resister and a 10 k pot to vary the power through the Zener diodes. They tested ok and I put them back in circuit. The three resisters near the heat sink that I replaced earlier seem to be ok.

My local source for electronic components is a place called Skycraft that has been in town since 1974. They are a surplus provider which used to get a lot of their stuff from NASA over on the coast. They have rows and rows of labeled boxes where you have to dig around find what you are looking for. It will do in a pinch, but being surplus and being in my early learning stage, I think it is safer for me to get the right parts by ordering online. I will add the transistors, diodes and resisters for AWR-052-0 to my next order which will be for the control amp, equalizer, muting and tuner boards. Once I get those power supply parts put in, I will see where I stand with the power supply voltages.

A question? The leads on the KSC3503DSTU transistor appear to be larger (fatter) than the leads on the 2sc1451 they will be replacing on the Power Amp. If they are larger than the through holes on the board, what are my options? ​

In the down time of waiting for online delivery, I have the covers to refinish. I will be using a paper backed walnut wood veneer. I have stripped and sanded the covers and repaired the imperfections in the finish from where I was too aggressive when removing the vinyl covering. I needed to glue and clamp some of the substrate I pulled loose where I didn't use the proper combination of heat and pulling pressure on the vinyl.

 

[Oldsansui441]

A question? The leads on the KSC3503DSTU transistor appear to be larger (fatter) than the leads on the 2sc1451 they will be replacing on the Power Amp. If they are larger than the through holes on the board, what are my options?

Use a 1mm drill to enlarge the holes in the board to suit the new KSC3503dstu's. Drill from the trace side.

n the down time of waiting for online delivery, I have the covers to refinish. I will be using a paper backed walnut wood veneer.

They will come up great in real walnut veneer, can l send mine over to you when you are finished yours .

 

[larryderouin]

Make sure you sop up ALL of the solder from the holes, this makes it easier to expand them, and DON'T use a power source on the drill bit. Finger power is sufficient to drill thru the board without damage. Take your time.

 

[DrTim]

DON'T use a power source on the drill bit. Finger power is sufficient to drill thru the board without damage. Take your time.

Got plenty of time for this project. I bought a cheap finger drill and it worked great. Took about 2 minutes a hole. Thanks.

Every regulator needs a stable reference, so I'd suggest to start there. You can measure ACV(mV) on your DC supply to check for instability and noise

This leads me to where I am now and several questions that I have to give me confidence and guidance moving forward.

I got the parts I was lacking or needed to replace for the Power Supply AWR-052-0 and installed them. These included the R10, R11 & R12. (2.7k 1w and 820 ohm 2w)
replaced Q2 Q3 Q5
replaced D8 D12 D14
replaced C12 C21 C22 C23.

This unit has been worked on before and there are soldered wire wraps with iffy connections. The wire at Pin 22 was hanging by a single thread. Stripped, tinned and reapplied. Also worked on some sloppy soldering done by yours truly.

I have steady voltage at Pin 8 and 11 now but it is running high.
AWR-052-0
Pin
8 +29v
6 +46.9v
5 +36.3v
11 -29v
9 -43.9v
10 -13.2v
4 +13.2
2 +7.3v

I did the Protection board.
AWM-062-0
Pin
2 -13.2v
11 +35.7v
12 +7.4vAC

I did the Power Amp AWH-30-0 and overall it came out good. I did put a pair of transistors in wrong which lead me to checking each and every transistor 10 or more times. I'm still looking at them for old times sake. The voltage at the Pins pretty much are in line.
AWH-030-0
Pin
7 +47v
4 +34.8v
2 -44v
22 +47v
19 +34.8v
17 -44v
14 +46.7v
15 -46.7v
29 +45.7v
30 -46.7v

The unit powers up with the dim bulb dimming and the protection relay clicks. I would like to do the DC off set and set the bias at this point but questions abound. Without touching the VR trimmers, I have 15.8mV between Pins 32 & 38. I have 21.3 between Pins 44 & 50 on house power.

DC offset is a different story. (Speakers B, no volume, tone control and balance centered, Aux) I get -50mV at Pin 10 to ground and -500mV at Pin 25 to ground. Both of those measurements range all over the place. At the speakers jacks I get negative voltage readings all over the place. I would think the relay would not click. I suspect that my VR1 &VR2 trimmers might be wonky. Can these be checked in circuit? I do have replacement Bourns trimmers but I hesitate to install them until I get a grip on where I'm at. If I have to pull the trimmers for testing, I might as well replace them. Before I start adjusting the trimmers, can someone point to a thread, or give me guidance on adjusting trimmers.

And for my clarification, as I'm facing the front faceplate of the unit, the trimmers are from right to left VR1, VR3, VR2, VR4 with VR1 and VR2 used for the DC offset?

I'm trying here guys. I am learning more every day. I spend more time reading about what I need to do then actual time doing what I need to do. Its a good thing. I appreciate the help.

They will come up great in real walnut veneer, can l send mine over to you when you are finished yours

Would be glad to wood veneer it for you. All you need to do is pay the shipping.

Might be cheaper with shipping if I just send you the supplies with instructions.​

I have been doing Pioneer PL turntables for the last year and these bonnets are a piece of cake compared to tearing down a turntable. While I was away, I veneered and finished one of the two covers. This is the one that needed repair and clamps.

 

[DrTim]

I guess I shouldn't be so afraid of my own shadow. Reading about the damage that can be done adjusting DC offset and Idle current if not done right caused me to want someone to hold my hand thru the process as I have never done it before. There are directions all over that were vague and didn't fill me with confidence. I was looking for something SX-939 specific. I found this from a 2010 thread from Markthefixer which helped. I repeat it here for anyone, like me, that needs to be led to water. http://audiokarma.org/forums/index.php?threads/sx-939-static.260039/​

with dim bulb tester connected:
page 17 of the pdf manual

1. no 8 ohm resistors in place of speakers needed. volume to zero
2. connect dmm to pins 10 and a chassis ground,
3. adjust vr1 for zero
4. connect dmm to pins 50 & 44, adjust VR3 to read 50mv on the dmm
(no sudden surges of light, maybe a little increase in brightness of dbt.)
mtf: turn down VR3 to minimum after you get 50mv..
now the other channel
2. connect dmm to pins 25 and a chassis ground,
3. adjust vr2 for zero
4. connect dmm to pins 38 & 32, adjust VR4 to read 50mv on the dmm
(no sudden surges of light, maybe a little increase in brightness of dbt.)
mtf: turn down VR4 to minimum after you get 50mv..

then if all is ok, disconnect d.b.t.

with dim bulb tester DIS-connected, and unit plugged directly into wall:
page 17 of the pdf manual

1. no 8 ohm resistors in place of speakers needed. volume to zero
2. connect dmm to pins 10 and a chassis ground,
3. adjust vr1 for zero
4. connect dmm to pins 50 & 44, adjust VR3 to read 50mv on the dmm

now the other channel
2. connect dmm to pins 25 and a chassis ground,
3. adjust vr2 for zero
4. connect dmm to pins 38 & 32, adjust VR4 to read 50mv on the dmm

redo this (check) 20 minutes later waiting for things to stabilize.

There is a picture on page 17 of the pdf with arrows pointing to the adjustments.

More from MTF:
"You can measure the offset voltages at the speaker terminals, it's usually easier... (as long as the protect relay engages, connecting the amplifier to the speaker terminals).

The two pots (offset voltage adjust) closest to the wire connections for the two bias diodes are the pots used to adjust the voltage to zero (measured in millivolts) at the speaker terminals. They should be marked with a 10K as part of their alphabet soup.

The other two (idle current adjust) pots are kinda interfered with by the connections to the power output transistors (pin 51 on one channel and pin 39 on the other) , and should be marked 100, these are the pots used to adjust to 50 millivolts (0.050 volt) between pins 50 and 44 (one dmm lead each), and for the other channel for 50 millivolts (0.050 volt) between pins 38 and 32.

Hopefully this should be clearer than mud."

Giddy up, I'm going in.

 

[Oldsansui441]

The DC offset pots are the one closest to the EDGE of the board and the third one in from that same edge. I always set the new trim pots to exactly the same resistance as the old before fitting.

Don't forget to set the BIAS to 25mV NOT 50mV as stated in the manual as it is incorrect.

In regards to the high DC offset, 500mV is usually a lot to trim out, did you replace the amplifier input differential pairs (2SA726's) with KSA992's?.

Looks like you have replaced all transistors, caps and some diodes and resistors on the power supply. If all other diodes and resistors check out ok and pins 8 and 11 are still high l wonder if the secondary voltages coming out of the transformer are slightly high also, although this should also affect your other voltages which appear to be good. Is you unit a 120v only or a multi voltage unit?

Thanks for your VERY kind offer on the case veneering, l was actually just joking in my previous post but that one you have veneered already looks absolutely terrific (super job) and l am a little jealous. Pioneer should have done this originally.

 

[DrTim]

Its a 120v unit, the SX-9930 that is next up is a multi voltage. The high readings at Pins 8 & 11 do bother me and I will revisit that problem. I was happy to get the voltage steady as it was fluctuating wildly before. I do need to ask if using KSC2690AYS is an acceptable replacement for a 2sc1318 which is the Q2 & Q3 on the Power Supply board? Just noticed that I somehow overlooked replacing Q3 when I replaced Q2. I need to get that right before I move on.

I understand what is being said about the secondary power from the transformer might be high, but I don't have a clue as to how to check it. Are there voltage checks that I can take at Pins 12 thru 23 on the power supply board that I can reference?

I did replace the transistor pairs with KSA992's on the Amp board. Those were the ones I installed wrong but found and corrected before powering up on a DBT. I didn't match the hFE of these two pairs and when, and if, I go back in to replace the trimmers, I will put in matched sets now that I have a transistor tester.

Have not set the idle or off set yet. I would like to get that 500mV under control before I do that. Power supply first, recheck Pin readings on the Protection board and then the Amp board, again.

As frustrating as the process is for me, I find it very enjoyable. Learning every step of the way. A month ago, if I had to guess, hFE would be something you went to the doctor for.