Samuel STEIN
Member
The 18V (P525,P524) are coming up at -27 and 22 though.
NAD 7100 Troubleshooting
- Thread starter Samuel STEIN
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Ylli
Super Member
That should be enough for the regulator to be fully functional. Are you seeing +24.5 on Q501 emitter and -24.5 on Q502 emitter?
OK, didn't see your second post at first...
Do check for +/- 24.5 volts. Then let's see the voltage at the base of Q507 and board point P524. Are any of the larger (TO-22) transistors getting hot?
OK, didn't see your second post at first...
Do check for +/- 24.5 volts. Then let's see the voltage at the base of Q507 and board point P524. Are any of the larger (TO-22) transistors getting hot?
Samuel STEIN
Member
I'm getting 4.75 for the base of Q507, the emitters are -29.5 and 28.5
The transistors are getting warm, I wouldn't say hot, but the heat sink on Q502 sent some surprise current to me when I touched it.
The transistors are getting warm, I wouldn't say hot, but the heat sink on Q502 sent some surprise current to me when I touched it.
Samuel STEIN
Member
*The emitters of Q501 and Q502 are 28.5 and - 29.5 respectively.
Q505 was the warmest, but I wouldn't say hot.
the Q501 and 502 heat sinks were getting a reading of up to .2 V, which is weird b/c they are very grounded
Q505 was the warmest, but I wouldn't say hot.
the Q501 and 502 heat sinks were getting a reading of up to .2 V, which is weird b/c they are very grounded
Ylli
Super Member
If you have -29.5 volts on the emitter of Q502, then you should have -5.5 volts across R514. Can you confirm that? If you do see -5.5 volts across R514, then measure the voltage at the base of Q504. Perhaps you still have the Q504 leads in the wrong holes or it may have blown from being installed incorrectly.
Samuel STEIN
Member
fuses blew, and I'm out of fuses for the night. Will pick up more tomorrow :'(
Samuel STEIN
Member
I have bought Austin out of fast acting 5x20mm 500 mA fuses 
Tried some 400mA, and as you could probably guess, they blew immediately. Going on a Mouser order. Do you have any recommendations for while I'm paying for shipping? (Like the 6.3A ones? the A1015's or the C1815 replacements?)
Tried some 400mA, and as you could probably guess, they blew immediately. Going on a Mouser order. Do you have any recommendations for while I'm paying for shipping? (Like the 6.3A ones? the A1015's or the C1815 replacements?)
Samuel STEIN
Member
Also, on Q502 (because I was shocked on it's heat sink), I am measuring between the collector and sometimes the base legs and ground,I get a beep on my resistance-ground mode, but the resistance then climbs. Is it because I am playing around with a receiver thats off where everything is grounded, or because it is grounded? (I visually inspected and saw no obvious ground.)
Ylli
Super Member
That thing should not be drawing enough current from that transformer secondary to blow the fuses. With the 18 volt regulators disconnected (Q505 & Q506 removed) there should only be the 24 volt regulator and its load - the phono preamps. That should come no where near blowing fuses.
The only load on the +35 volt line on the power amplifier board are the speaker relays, and those have series resistors that would smoke before blowing fuses. Could have a bad bridge rectifier D503, or electrically leaky filter caps C513 or C514. All three of these items should be removed from the board and tested. Its also possible that C503 is bad, better pull that and check it for leakage. If you need directions on how to test, let me know.
If you are ordering from Mouser, may as well get that KSP2907AC transistor https://www.mouser.com/ProductDetai...=sGAEpiMZZMshyDBzk1/Wi8oN7VHZ91OkLqsDkJCp/c8= . That way the basing will be the same as the original and can be installed without twisting leads.
The only load on the +35 volt line on the power amplifier board are the speaker relays, and those have series resistors that would smoke before blowing fuses. Could have a bad bridge rectifier D503, or electrically leaky filter caps C513 or C514. All three of these items should be removed from the board and tested. Its also possible that C503 is bad, better pull that and check it for leakage. If you need directions on how to test, let me know.
If you are ordering from Mouser, may as well get that KSP2907AC transistor https://www.mouser.com/ProductDetai...=sGAEpiMZZMshyDBzk1/Wi8oN7VHZ91OkLqsDkJCp/c8= . That way the basing will be the same as the original and can be installed without twisting leads.
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Ylli
Super Member
If I understand correctly, when you measure the resistance from the collector or base of Q502, your ohmmeter shows a low resistance at first, then creeps up. That would be normal as the ohmmeter would have to charge some pretty large capacitors. Now getting a shock off of Q502.... 35 volts is getting up there a bit. It's still considered "Low Voltage" until it reaches 50 volts. I can't feel 35 volts on dry skin, but some can.
Samuel STEIN
Member
Good to hear, I must be looking for it, and thus super aware and over/psycho-sensitive.
I took out the two capacitors C513, 514 and they're reading 1.2nF which is less than the 10K uF they should be, but I assumed it would be the opposite fail (as in it would make the voltage zero, not higher).
The ceramic capacitor was reading 22nF, which seams right
The diode is also good if it's the same as https://www.mouser.com/datasheet/2/427/woo5g-280147.pdf
Ordering the transistor and these two diodes. I feel like i should probably spot check some more capacitors or buy one of those emf testers.
I took out the two capacitors C513, 514 and they're reading 1.2nF which is less than the 10K uF they should be, but I assumed it would be the opposite fail (as in it would make the voltage zero, not higher).
The ceramic capacitor was reading 22nF, which seams right
The diode is also good if it's the same as https://www.mouser.com/datasheet/2/427/woo5g-280147.pdf
Ordering the transistor and these two diodes. I feel like i should probably spot check some more capacitors or buy one of those emf testers.
Ylli
Super Member
Did they show a large leakage or did you do an ohmmeter check on them?
Ceramics rarely fail.
If you are replacing the bridge, the W02G would be the appropriate choice.
If C513 and C514 are measuring only 1200 uF, then i would suggest you replace those too.
Samuel STEIN
Member
I went to buy the new capacitors, left for a business trip, then came back to find that they capacitors should be 1K, not 10K uF, so reordering, will update soon.
Samuel STEIN
Member
two weeks worth of logistics and UPS loosing the capacitors in their truck... the capacitors came in, and the fuse is still blowing immediately with the new capacitors. (I put in slightly larger audio grade capacitors because it was what was in stock, but their ratings were the same, I don't think this is the problem).
Ylli
Super Member
Let's review.... We are talking about fuses F501 and/or F502, right? Are they both blowing or only one?
Q505 & Q506 have been removed, so the only load on this transformer winding is the +/- 24 volt regulators.
C513 & C514 have been replaced - I assume correct polarity was observed. Did you test the bridge rectifier D503?
If only F501 is blowing, there is a possibility D603 or C605 is shorted.
You could remove Q501 & Q502 to totally remove any load from this section.
Q505 & Q506 have been removed, so the only load on this transformer winding is the +/- 24 volt regulators.
C513 & C514 have been replaced - I assume correct polarity was observed. Did you test the bridge rectifier D503?
If only F501 is blowing, there is a possibility D603 or C605 is shorted.
You could remove Q501 & Q502 to totally remove any load from this section.
Samuel STEIN
Member
It was the polarity of the capacitors! :'D.
I put Q505 and Q506 back in because I had the solder iron hot. The fuse didn't blow but there was clicking.
FYI P522: -34.8V, P521: +34.8V, P525: -21.6V, P524:+22.9V, P901: +5.78V, P902: +11.9V, Emitter Q501: 23.6V, Emitter Q502:-23.8V. Those latter seemed very stable, so I should think the Q501-Q504 area looks good, but I am going to re-remove the Q505 and Q506 to double check that, and see if we get some silence in the receiver.
I put Q505 and Q506 back in because I had the solder iron hot. The fuse didn't blow but there was clicking.
FYI P522: -34.8V, P521: +34.8V, P525: -21.6V, P524:+22.9V, P901: +5.78V, P902: +11.9V, Emitter Q501: 23.6V, Emitter Q502:-23.8V. Those latter seemed very stable, so I should think the Q501-Q504 area looks good, but I am going to re-remove the Q505 and Q506 to double check that, and see if we get some silence in the receiver.
Samuel STEIN
Member
Without Q505 and Q506, the receiver doesn't click, and P522=-37, P521=36.7, P525=.72, P524=2.78, P902=12.2, P901=5.78, I am going to follow P525 to see where those 2-3/4V are coming from.
Ylli
Super Member
P524 & P525 deem a bit high. The +18.5 volt line is not really a regulator, but rather is set by the voltage divider of R519 & R520 off of the +24.5 volt line. If you have +23.6 volts on the emitter of Q501, then you should have +18.6 volts on the base of Q506 and +18.0 volts on the emitter of Q506/P524. The -18.5 volt line should mirror the voltage on P524 through the inverting amplifier connected to R523/R524/R525.
I need to go back and review the thread, too many irons in the fire......
I need to go back and review the thread, too many irons in the fire......
Ylli
Super Member
Without doing a bunch of calculations, the above sounds reasonable. P524 is getting some voltage through the emitter follower action of Q507. The positive voltage on P525 is likely current through R523 to the base of Q508.(there should be a dot connection there that is missing) and the base voltage of Q508 is coupled though R524/R525 to P525.
Not sure what could cause P524 and P525 to be high when Q505 and Q506 are installed. Have you checked Q505 and Q506 with the diode mode of your ohmmeter? Could be R520 going high, but that does not seem likely.