NAD 3020i - /13V on Left Output/

[coojoe_213]

Hi. I repair this vinatge Nad, who was with short Left channel.
I replace with new original 2n3055/2mj2955, R453 (180om was open), Q411 (2SD669A-short), Q413(2SB649A).
After replacing short part, i connect 100 watts lamp and turn on amp. The lamp is not light /there is no short in amp/, check right channel -0V, left - 8v, 9v and up to 13 V. Please tell me, where i was wrong?

[R_J]

Re: NAD 3020i - /13V on Left Output/

Can you adjust Center voltage with R443?

[redwire]

Re: NAD 3020i - /13V on Left Output/

If R453 burned, then any one of Q415, Q417, Q409 are probably open.
You have more parts to check.

[petehall347]

Re: NAD 3020i - /13V on Left Output/

Can you adjust Center voltage with R443?

r443 is for setting idle current so it wont affect dc offset .
r411 r412 or for setting offsets .

[R_J]

Re: NAD 3020i - /13V on Left Output/

r443 is for setting idle current so it wont affect dc offset .
r411 r412 or for setting offsets .

Yes, I looked at the wrong numbers in the manual, I should have said R411

[petehall347]

Re: NAD 3020i - /13V on Left Output/

i doubt very much 13v will adjust out .. something is bad . i would pull the mains out and fix the issue first . and use 1k resistors in place of the mains . tack them in between base and emitter connections on the board .

[R_J]

Re: NAD 3020i - /13V on Left Output/

Where did I say it could be adjusted out? I asked if the adjustment made a difference being that its only +13 volts and not +43 volts
I would check for a possible open resistor like r451,445 and even r447,449 sometimes they get overlooked.

[coojoe_213]

Re: NAD 3020i - /13V on Left Output/

When i turn R411, nothing happen. I check really 80-90% from parts in this amp every parts look like is good. You can see my video. Q415, Q417, Q409 are replaced with brand new.
https://www.youtube.com/watch?v=TVC3...ature=youtu.be

[petehall347]

Re: NAD 3020i - /13V on Left Output/

check pin-outs on replacement transistors . also check value of resistors

[coojoe_213]

Re: NAD 3020i - /13V on Left Output/

also check value of resistors

Hi. Thanks for reply. Which resistors means?

[petehall347]

Re: NAD 3020i - /13V on Left Output/

i would be checking all of them comparing bad channel to good channel .. any in bad channel showing high ohms remove and test again . if low ohms something is likely shorted next to that one .

[coojoe_213]

Re: NAD 3020i - /13V on Left Output/

I measure some voltages. On B/E MJ2955/2N3055 I have 12 V?? On both side R453/180om/ I have 12V. On driver transistors 2sb649/2sd669 i have also 12V.
R445/R447, R449/R451 are good. From where come this 12v, i can't find on shceme.

[budm]

Re: NAD 3020i - /13V on Left Output/

I measure some voltages. On B/E MJ2955/2N3055 I have 12 V?? On both side R453/180om/ I have 12V. On driver transistors 2sb649/2sd669 i have also 12V.
R445/R447, R449/R451 are good. From where come this 12v, i can't find on shceme.

12V on B-E junction Voltage? If that is true then you have bad Transistor.

[petehall347]

Re: NAD 3020i - /13V on Left Output/

what voltages does it have on BCE for drivers and outputs ? 3 readings for each transistor
dont forget to say whether + or - ... and exact voltages .example 23.34 .. or if mv 600mv .
outputs cases are collectors .
all voltages reference chassis ground .

[coojoe_213]

Re: NAD 3020i - /13V on Left Output/

Hi. I see something in amp, which may be is not normal, but i don't know. I see 8 ceramic capacitors cut from main board. Is this normal or no?
6 caps 100pf/50v, 2 caps 150 pf/50v
(c229, c230, c331, c333, c335 ,c336....)

[budm]

Re: NAD 3020i - /13V on Left Output/

You need to remove those brown glues! they are corrosive and conductive.
Those caps are options depend on what the PCBA and circuit requirement are. You can have same blank PCB that can be stuffed to make many difference version of PCBA.

[petehall347]

Re: NAD 3020i - /13V on Left Output/

that glue could be causing the problem .

[coojoe_213]

Re: NAD 3020i - /13V on Left Output/

I remove this glue but problem is the same.

[budm]

Re: NAD 3020i - /13V on Left Output/

So what happen to post 12 and 13 and clarification on your method of measurement?

[coojoe_213]

Re: NAD 3020i - /13V on Left Output/

Schematic here is better : http://p10hifi.net/planet10/TLS/down..._schematic.gif

From power supply i have all correct voltages / -28v,+28v,+43, +28/+32 (4om/8om/ /

On B/E Q415/Q417 I have 12.4V /begin from 6v,...8v, 11v...etc/ -
R453 I have on both side 12.4v
On B/E Q411/413 I have 12.4V
On B/E Q409 I have 12.4V
R445 Both side 12.3v
R451 Both side 12.3v
R439 Both side 12.3v
D405 Both side 12.4v
On B/E Q407 I have 12.4V