SANSUII BA-3000 PROBLEMS

[vigman]

All sounds like great prep work, cept that falling down bit.... The other helpful mod IMHO.. is making external bias test points, that you can hook on to and not be afraid of shorting stuff out... here http://audiokarma.org/forums/index.php?threads/ba-3k-poof-back-under-the-hood-again.783735/ post 22

 

[pppoffice]

Here is an update and by the way, I am Mike. I started my day off bad besides not getting up until almost noon. I was moving the DBT from where I assembled it using my walker and it fell off of the walker and shattered 2 out of 3 of the bulb bases. My wife was going into town anyway so I had her pick me up 3 new bulb bases out of plastic so they won't break as easy. I got the DBT back together this evening and got a chance to use it. I put the 2508 board in this time to see if I would get the +-60 volts and the +-35 volts. I plugged the DBT into my Variac and the amp into the DBT. When I turned the amp on the 55W bulb I had in the DBT lit up pretty bright and then dimmed very fast to where I couldn't even see the filliment in the bulb. I did have the +-60 volts where it is suppose to be but did not have anything where the +-35 volts is suppose to be. I stopped there until we can find the +-35 volts. I then split the Right Channel brick and marked the transistors in it and where they came out of. I also made a little tester for the Power Transistors which is basically a Power Transistor plug with leads off of all 3 contact places so it could then be plugged into the little transistor checker I got off of ebay. I have attached pictures of the transistor tester checking one of the Power transistors for you to see.

 

[pppoffice]

Also, as per your request, here are pictures of the Right Channel Brick split open so you can see the resistor board inside. As I was sure the case would be, the C1364 in it has DARK BLACK LEADS. It is late this evening so I am going to get to bed but in the morning my plans are to split the Left Channel too, install new longer wires in it and test and record for you to see all of the readings I get on all of the Power transistors and the c1364 transistors. I will be waiting after that for you to let me know what you want to do next in regards to not having the +-35 volts.

 

[pppoffice]

All sounds like great prep work, cept that falling down bit.... The other helpful mod IMHO.. is making external bias test points, that you can hook on to and not be afraid of shorting stuff out... here http://audiokarma.org/forums/index.php?threads/ba-3k-poof-back-under-the-hood-again.783735/ post 22

I am way ahead of you about the bias test points. I took a project box and mounted 4 digital DC MV meters in it. I then made a pigtail lead up that I can solder in to the bias test points. Then I have 4 sets of leads that go to the 4 DC meters in the project box and I can monitor and set the bias voltages and zero out the speakers while looking at this project box I made up. I got tired of trying to get my meter probes in to different spots and try to figure out how to hold them on these test spots while adjusting bias and speaker outputs.

 

[vigman]

Ah the Ol WING-WANG-WONG transistor tester... I do like your quick test adaptor.....The DBT did exactly what it needed to do... your measured voltages now will be CLOSER to spec since there is no load on the supplies, If you have the +/- 60 GREAT..... +/- 35 goes to the meter driver boards & the 2513 input board. BUT it needs to be on the 2512 ( bottom side ) this is the closest output of the 2508 Off TM-05. We must be careful here there is the +/-68 volt supply ( final amps & Drivers ) BUT the drivers ALSO are powered by the 2508 +/- 65.... So considering you have a DBT AND a variac AND there is ~ 3 volt difference between the 2 " big " supplies it might be note worthy to measure what is on the BIG CAPS to assist sorting that out. OH and use voltages from the schematics not the silk screen.... For a TEST ( if you do NOT have the +/- 35 ) tack test wires on the + of C-17 and the - of C-18 on 2508 and report back..... GREAT PROGRESS Mike !! Oh how did all the Brick transistors test out and are the HFE's close ??

 

[vigman]

AHH your posting now, As far as the black leads, pull the device and clean em, I straighten the leads & use a razor & xacto knife. Pay close attention where the leads go into the plastic case.Test all .47 emitter resistors & check all the solder joints

 

[vigman]

2508 testing cont : fill in the blanks all ref to ground
TR-11 Collector voltage ( +........... )
TR-11 Emitter voltage (+..........)
TR-16 Emitter voltage (NEG...........)
TR-16 Collector voltage ( NEG......... )
Verify the 330 & 10 ohm series "R's" round that area.

 

[vigman]

I will be wrenching on a buddys car tomorrow from 8 am PST till ~10 I will check back in then...

 

[vigman]

Oh just FYI there are 2 versions of the brick there was an " early " one ( I think ) that had a double sided board for the resistors, transistor, and thermocouple with rivets that joint the front to back of the PCB. Which are PROBLEMATIC if you do not run a new wire thru the rivet & solder both sides back to the traces.. you have the single sided " good" one.
Similar issues in a CA-3000 motherboard.

 

[pppoffice]

Oh just FYI there are 2 versions of the brick there was an " early " one ( I think ) that had a double sided board for the resistors, transistor, and thermocouple with rivets that joint the front to back of the PCB. Which are PROBLEMATIC if you do not run a new wire thru the rivet & solder both sides back to the traces.. you have the single sided " good" one.
Similar issues in a CA-3000 motherboard.

Both of my amps have the single sided boards.

 

[pppoffice]

I will be wrenching on a buddys car tomorrow from 8 am PST till ~10 I will check back in then...

No problem at all with that. I'm not getting around too good this morning so I will be taking it slow and easy. I will try to get all the Power transistor reading taken to see how close they are to each other and let you know the results.

 

[vigman]

Standing by...... all done with my " stuff " for a while.....

 

[pppoffice]

Well, I worked on the amp last night fairly late. I got the Left channel also broken down and the C1364 wires scrapped and reinstalled. I also extended all the wires on the Left channel. I took readings on all of the power transistors in both bricks and also readings on the C1364's. All of the readings on the power transistors were pretty close except one where the hFE was a bit lower than the rest of the power transistors. Both of the C1364's checked out to be just fine with high readings. I had already planned on replacing all the power transistors in both amps while they are being worked on. I bought enough new power transistors for 4 complete sets. I got the new MJ21195G and the MJ21196G power transistors and planned on going thru all of them with my little transistor tester and making up sets. What are your thoughts on this? I am getting ready now to go over to my shop and get all the readings you asked for and reporting back to you this afternoon with them. That way if your near your computer you can let me know what next you want me to do.

 

[pppoffice]

Standing by...... all done with my " stuff " for a while.....

OK, here is what I came up with for the voltages you asked for. Now, the voltages on the large caps with the Variac zeroed in at exactly 100 volts AC are +68.5 VDC and -68.5 VDC. The positive side of C17 reads +2.278 VDC and the negative side of C18 reads -.887 VDC. TR-11 Collector Voltage is +79.9 VDC and Emitter voltage reads +2.2 VDC. TR-16 Collector voltage reads -79.5 VDC and Emitter voltage reads -80.2 VDC. I think that is all the voltages you asked for so I am not waiting for your next instructions. Mike

 

[vigman]

Big Caps +68.5 VDC and -68.5 GREAT

TR-11 Collector voltage ( +80 )
TR-11 Emitter voltage (+2.2 )<<<< OVER regulating
TR-16 Emitter voltage (NEG.80.2
TR-16 Collector voltage ( NEG 79.5 ) <<< Bad dog no biscuit

Sumtin VERY fishy here......
The positive side of C17 reads +2.278 VDC Hmmmm ok something in the positive regulator is broke
The negative side of C18 reads -.887 VDC Should be same as TR-16 collector ( I think that one has gone POOF )
So this reg board is POOFED BIG TIME.. and should be our next all out focus.
Did you check the 330 & 10 ohm resistors around these two? Bet R 18 is blown wide open ?

Next tests ( besides the resistors )
TR-3 collector should be close to +50 volts
TR-4 collector should be close to NEG 50 volts

Tell be what the base voltages are on TR-12 & 14

The +/- 65 ( 60 ) is OK ??

 

[pppoffice]

Big Caps +68.5 VDC and -68.5 GREAT

TR-11 Collector voltage ( +80 )
TR-11 Emitter voltage (+2.2 )<<<< OVER regulating
TR-16 Emitter voltage (NEG.80.2
TR-16 Collector voltage ( NEG 79.5 ) <<< Bad dog no biscuit

Sumtin VERY fishy here......
The positive side of C17 reads +2.278 VDC Hmmmm ok something in the positive regulator is broke
The negative side of C18 reads -.887 VDC Should be same as TR-16 collector ( I think that one has gone POOF )
So this reg board is POOFED BIG TIME.. and should be our next all out focus.
Did you check the 330 & 10 ohm resistors around these two? Bet R 18 is blown wide open ?

Next tests ( besides the resistors )
TR-3 collector should be close to +50 volts
TR-4 collector should be close to NEG 50 volts

Tell be what the base voltages are on TR-12 & 14

The +/- 65 ( 60 ) is OK ??

I am pretty sure that I tested the resistors and they are good but I will test again after dinner. I am headed home for dinner but will be working late again tonight. I will get this information after dinner and let you know the results.

 

[vigman]

OK!

 

[pppoffice]

I am pretty sure that I tested the resistors and they are good but I will test again after dinner. I am headed home for dinner but will be working late again tonight. I will get this information after dinner and let you know the results.

OK, here we go. YES, R18 (10 ohm) resistor looked like an over fried piece of bacon all hid down inside the power supply board. The voltage on collector of TR-3 was +18 VDC BEFORE I replaced R18 and was +32.9 VDC AFTER I replaced R18. The voltage on collector of TR-4 was -85 VDC BEFORE I replaced R18 and was -30.5 VDC AFTER I replaced R18. The voltage on the Base of TR12 is -.147 vollts after replacing R18 and the Base voltage on TR-14 is +.621 VDC after replacing R18 . I thnk that was all of the latest questions. I am going to work for at least another 2-3 hours this evening so if you have anything else for tonight I will try and get the answers and report back in the morning with the results.

 

[vigman]

If I understand correctly on the OUTS we have +33 and - 31. This regulator at this age will not be perfect due to resistor & cap drift.... at this point I would verify 100 VAC in and re measure the outs on the 2512 side of life. R-33. 35 & 24 make a voltage divider.. if the values are a bit drifty on the R it will effect the V out. Also check R 05 & 06 for a close match. If you REALLY want to get OCD change all R's out to 1% 1/2 watt. today's metal films 1/2 are smaller then most carbon 1/4 watts... Has this board be re capped??

 

[vigman]

Great work Mike.. we get the reg board issues sussed out and we are SO on our way to AUDIO.... BUT I will be VERY OCD about the driver boards, because if that fails , things get UGLY