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NAD 216: In Protection w/ Power Supply Issues

Johnny_Law

Johnny_Law

o.O
Subscriber
Edit 1/4/20: Power Supply solved. Right amp issues now. Jump to https://audiokarma.org/forums/index...wer-supply-issues.871337/page-6#post-13374657.

Research done thus far:
https://www.diyaudio.com/forums/solid-state/330113-nad-216-help.html
https://www.diyaudio.com/forums/solid-state/318916-nad-216-worth-restoring-saving-2.html
https://www.diyaudio.com/forums/solid-state/330475-nad-216-red-protection.html

Symptoms:
(A) -67V power supply bad (I want to get this working first)
(B) Stuck in protection (will deal with protection after I get the power supply back, maybe the bad power supply is the cause?)

Related work done thus far:

Q201 2SD600 replaced with MJE15030G
Q204 2SB631 replaced with MJE15031G
Q202 2SC2240 replaced with KSC1845FTA
R203, R204 (330ohm / 1W fusistors) replaced with 300ohm / 1W metal film resistors
R205, R206 verified good
Electrolytic caps replaced w/ new

Diagnostics done thus far:

Verified +/- 60V power supply from C901/C902 good
Removed both amp boards to isolate power supply / protection circuit alone
Swapped C214/C215
Swapped R206/R209
Swapped R205/R208
Measured R207/R210, both 1.5kohms.

Measurements as follows:

bkKe1Gc - Imgur.jpg

The numbers start going bad around R205/R206/R207, but I've swapped R205 and R026 to the other channel with the same result, and R207 measures good. Starting to pull my hair out. Would love any thoughts. Thanks!

Pics for fun ...

Zw4r4WE - Imgur.jpg

DD2vfKr - Imgur.jpg

XiV3O8d - Imgur.jpg
 
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Thanks guys - I admit I posted this on the way out for the evening. Will check on the above and post up tomorrow.
 
Might have and issue with those two 33v zeners. I believe the positive side is controlled by the negative side.
 
Got the power supply back (although it's at +/- 48V instead of the 67V specified in the manual ... sign of further issues? Edit: I don't like it. Looking into why it's not closer to 67V. Maybe because I put in 300 ohm resistors at R203/R204)

Edit2: When measuring, the multimeter briefly displays 67V, then jumps down to 48V and holds it. What the heck.

Had a solder bridge underneath, bridging both sides of C218 (and R212, R213, etc). It's a mess under there, the result of many destroyed solder pads compliments of previous technician.

Edit: Will hold off on moving to protection circuit until I get 67V from the power supply. Still in protection (with amp boards still out - I am assuming the lack of amp boards shouldn't affect the protection circuit - e.g., JP201, JP202). First measurements are good +/- 15V at R243/R244.
 
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Findings:

R201 and R202 are each seeing about 45.5VAC (each resistor is dropping ~0.1VAC).

D206 cathode: 121V DC
D207 anode: -121V DC

R205: -118.7V both sides
R208: -118.8V both sides

Q204 B: -48.7V; C: -121.2V; E: -61.5V
Q201 B: 48.7V; C: 120.1V; E: 58.6V

(From other posts I've read, this Base reading could be too low? E.g., -68.7 - this might explain the missing voltage at the emitter?)

Q203B: ~0V
Q202B: 0.56V

avionic said:
Might have and issue with those two 33v zeners. I believe the positive side is controlled by the negative side.
Click to expand...

D208, D209: each has ~16V across. Should they each have 33V across?

(R216: No voltage either side)
 
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need to look closer at these .
Q203B: ~0V
Q202B: 0.56V

r216 voltage needs checking again make sure its connected to d208
 
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Hmm. R211, R214, and R215 all appear good at 1.18k; R216 appears good at 218ohms.

I verified R212 and R213 are good when I was chasing down the short earlier. R217 appears good.

C218 and C219 are new (and installed correctly).

So there's the zener diode question (should each have 33V across?) and the fact that Q202 is a new KSC1845 while Q203 is the original 2SA970.
 
bingo as we say over here ... Q202 is a new KSC1845 while Q203 is the original 2SA970.
KSC1845 NPN
2SA970 PNP
 
Ah ok, phew. I'm trying to search for other threads with reference voltages for Q202, Q203, and the zener diodes.
 
D209 anode is -48V (still so strange, shows me -67V for a split second first), down to -16V at the cathode. D208 cathode is 0V into R216.

(But, when measured directly across it, D209 shows a 16V voltage drop, despite -48V at the anode and -16V at the cathode against chassis ground.)
 
petehall347 said:
is the star ground actually chassis ground ?
Click to expand...

Yeah, there's a jumper from the star ground to the input terminal grounds which are grounded to the chassis via the input terminal screw.

If I measure directly to the star ground without that screw in place, on the underside of the board, same measurements. It reads +/- 67V for a split second, then reads +/- 48V.
 
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