2275 relay not engaging - Problem with left Amp section

H712b= -44Vdc is good.
Maybe check resistance of R722 (27k) incircuit, amp powered off.


Smoking R735 is a sign, 0.5W equates to 70mA. this would be driving H002 hard,
it may be damaged however not the cause. H714 may be shorting. When you have
some spare time measure H714 b/c/e voltages to GND. Measure at adjoing parts
J702 TP(e), R735(c) and R728(b)
 
H712b= -44Vdc is good.
Maybe check resistance of R722 (27k) incircuit, amp powered off.


Smoking R735 is a sign, 0.5W equates to 70mA. this would be driving H002 hard,
it may be damaged however not the cause. H714 may be shorting. When you have
some spare time measure H714 b/c/e voltages to GND. Measure at adjoing parts
J702 TP(e), R735(c) and R728(b)

Here are the H714 Voltages:-

Emitter : + 44.3 VDC
Collector : - 45 VDC (Minus)
Base : + 43.9

R722 in-circuit value is @ 27.1K
 
Here are the H714 Voltages:-

Emitter : + 44.3 VDC
Collector : - 45 VDC (Minus)
Base : + 43.9

R722 in-circuit value is @ 27.1K
H714 looks ok, Vbe is about 1V and correct polarity, Vc /=Ve or /=Vb.

I'm probably repeating myself, however these problems are a PITA to track down.
2 scenarios, a short on the positive half of the amp causing high pos voltage to flood the amp. or an open circuit on the neg half
of the amp, so missing neg voltage to counter the positive voltage. Need to step out, give me a few hours to think about it.
 
H714 looks ok, Vbe is about 1V and correct polarity, Vc /=Ve or /=Vb.

I'm probably repeating myself, however these problems are a PITA to track down.
2 scenarios, a short on the positive half of the amp causing high pos voltage to flood the amp. or an open circuit on the neg half
of the amp, so missing neg voltage to counter the positive voltage. Need to step out, give me a few hours to think about it.

Sure thank you.

I'm not an electronic engineers and have absolute no electronic background but I looked at the schematic and if I understand the basics of circuit design, I think there is something wrong with H713.

Please see attached picture. Red is + supply and Blue is negative. The negative 47 VDC after entering the board is connected via R735 to collector of H714 and I'm rightly getting -45 VDC there.

The positive 47 VDC entering the board is connected to collector of H713 via R734. On checking I'm rightly getting +46.6 VDC on collector of H713. but i'm also getting + 45.5 on emitter and + 46.1 on base of H713 which mean that there is a short on H713 EC. And if this indeed is a short and emitter of H713 is showing +45.5 VDC, the same + voltage is flowing via R740 to emitter of H714 and H714 emitter is showing + 44.3 VDC instead of -.005V.

Not sure if above makes sense or just laughable.....Sorry I'm with mechanical background......

Untitled.jpg
 
First up, I'm not an electronics anything (engineer, tech,,,). I'm just trying to learn.

Your logic is very good, the same thought crossed my mind on H713 (post #34).
I'd encourage you to spend more time developing your skills, a lot of people
can't read a schematic.

Regarding H713
c +46.6Vdc
e +45.5Vdc
b +46.1Vdc
The Vbe is +0.6V also Vb > Ve so it looks ok
Maybe the c-b junction is breaking down?

I would now rule out H711, H712(44v/44.7V) since +45.5V at H713e
That leaves H713, H714, H001 and H002 as candidates.

A question to the marantz guru's, Can the amp be safely powered up
with the outputs H001, H002 removed? Looks ok to me. Next step would
then be remove H001,2, DBT power up and check H713e voltage.
 
Is the emitter resistor R740 okay?
I had actually checked R740 yesterday. I removed R740 which is actually set of two big 5 watt resistors and checked both the resistors. Although the resistor value mentioned is 0.2+0.2 Ohms. the actual value measured is 0.9+0.9 Ohms
 
I'd prefer to wait for the guru's. It should be safe to remove H001,002 then you can test for the high Vdc. Basically preferring to identify problematic part then
replace, however it's your amp and if you are keen... There is a chance that the problem will remain, but I can't see other causes.
 
I'd prefer to wait for the guru's. It should be safe to remove H001,002 then you can test for the high Vdc. Basically preferring to identify problematic part then
replace, however it's your amp and if you are keen... There is a chance that the problem will remain, but I can't see other causes.

OK I'll wait for Marantz Gurus....
 
When in doubt as to whether you can test a power amp with the outputs removed, one can usually install a silicon diode such as the 1N400X series in place of the base-emitter junction of the output transistors, observing polarity, of course.

Tom
 
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Many times when you have voltages that make no sense, + in this case, it could mean that there's a problem with the - side and the circuit is out of balance because of it. Try checking some things on the - side to see if they make sense or not. Also the high voltage on the base of H713 may coming from further upstream, check the voltages around H711/712.
 
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In post #46 I "ruled out" H711, H712, maybe this was a mistake. The thought being the voltages at these tr's is about 44V and H713e is at 45.xV.
 
Many times when you have voltages that make no sense, + in this case, it could mean that there's a problem with the - side and the circuit is out of balance because of it. Try checking some things on the - side to see if they make sense or not. Also the high voltage on the base of H713 may coming from further upstream, check the voltages around H711/712.

Here are H711 and H712 Voltages

H712
e : -44.8 (minus)
c : +43.5
b: - 44.1 (minus)

H711
e: +45
c: +44.5
b: +44
 
OK, the collectors are wrong AND both +, let's see how a + voltage can get on the collector of H712. Which xsistors have you tested and eliminated?
 
OK, the collectors are wrong AND both +, let's see how a + voltage can get on the collector of H712. Which xsistors have tested and eliminated?

R726, R722, R719, R717, R714, R 713, R707 & R705 are tested and are OK.

I removed R740 which is actually set of two big 5 watt resistors and checked both the resistors. Although the resistor value mentioned is 0.2+0.2 Ohms, the actual value measured is 0.9+0.9 Ohms

I had replaced R735 earlier but after replacing I noticed smoke coming out of it so I put the original back and no smoke now. R735 is also ok.
 
It sure looks like H711 is bad, an E-C short would put the high voltage on H713 and then thru H710 to the collector of H712. The collector of H711 is about 1 Volt higher than the collector of H712 so it's not a direct short but possibly thru H710.

Another thought, what if H712 is open and not balancing the circuit?

Xsistor means transistor.
 
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