Yamaha CA410 problem

smitty357

New Member
Hi. It will power up, but the relay won't actuate. 32v on both sides, so no current flow. Any ideas? Thanks. Mark.
 
Can you report the voltage at the collector and base of TR436, with reference to ground. This transistor is very important. It is part of the low voltage regulated supply for the tone control amplifier, the differential input stage on the power amplifier and the first stage of the protection circuit.

When you say 32V on each side of the relay, can you be more specific? Because there is 6 pins on the relay...

BTW, Welcome to AK!
 
410

The voltage across the coil is near 0 V, the voltage across the NO contact and the coil is about 32v, on either side. There has to be a leak across the coil somewhere.
 
Connect the negative probe of your voltmeter to the negative terminal of a speaker output, this is the ground. Don't move this wire.

Measure the voltage with your red (+) probe, your meter in DC Volt mode, at these points:

Emitter of TR436
Collector of TR435
Base of TR434
Terminal L4 for the R/L meter lamps
TP2 on the amplifier board, near the big square 0.47 Ohm resistors
TP4 on the amplifier board, near the big square 0.47 Ohm resistors
 
The negative terminal of the speakers is connected to ground, no matter if the relay is open or closed. I asked to connect the negative voltage probe on the negative speaker terminal to be sure that all voltage measurements are made with respect to ground.
 
followup

Emitter of TR436 30v
Collector of TR435 21v
Base of TR434 3.1v
Terminal L4 for the R/L meter lamps 0 v
TP2 on the amplifier board, near the big square 0.47 Ohm resistors 32v
TP4 on the amplifier board, near the big square 0.47 Ohm resistors 32v

thanks.
 
Emitter of TR436 30v
Collector of TR435 21v
Base of TR434 3.1v
Terminal L4 for the R/L meter lamps 0 v
TP2 on the amplifier board, near the big square 0.47 Ohm resistors 32v
TP4 on the amplifier board, near the big square 0.47 Ohm resistors 32v

thanks.

If all measurements are true to ground (speakers' Neg terminals), DC readings this high at the TP's usually mean problems in your output stage, both channels in this case. Shorted output transistors will cause this. This DC would keep the relay from closing its contacts: it's protecting your speakers from seeing the direct DC from your amp's power supply. I had a CA610II with no relay action as well, but in it there was no DC anywhere near the protection relay, both channels were idling fine, all was good and still no sound going past the relay. It turned out to be a small cap as illustrated in the following photo.

My 2 cents.
 

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With power to Off, measure the resistance between test point TP2 and the collector (mounting screw) of TR425. Repeat for TP4 and TR426.
 
Fine, I have good reason to think that your NPN output transistors are not shorted, and the large positive voltage you have at TP2 and TP4 comes from other faulty components.

Measure the resistance of FR401 and FR402.
 
I saw that on post #11:

Collector of TR435 21v
Base of TR434 3.1v
Terminal L4 for the R/L meter lamps 0 v


but since you have a good voltage at the collector of TR435, it is possible that L1 and L4 are inverted on the schematic (vs the board). This week-end I will open my CA410 and I will check. If one lamp is bad, no light...

I did a mistake in my previous post where I asked to take the resistance between TP2 and the collector of TR425. I suggested to use the mounting screw but this screw is possibly insulated from the metal flange, which is the collector of the transistor.

Please, can you repeat the resistance measurement between the test points TP2 and TP4, and the collector of the power transistors?

When we have a large positive voltage at the output of the power transistors (like you have), there may be a few causes:

1) shorted C-E junction in the NPN power transistors (TR425), and/or NPN driver transistors (TR421). So, measure also the resistance between C and E of TR421, and TR422.

2) broken path on the base side of the PNP driver transistor, by a bad (open) voltage gain transistor TR411, or open resistors R461 or FR401. If one of these three components is bad, the base of TR421 becomes almost directly connected to the positive supply rail by R449 and R453 and both TR421 and TR425 become into saturation (low Vce).
 
ca410

resistance measurement between the test points TP2 and TP4, and the collector of the power transistors 9-10 K ohm
C and E of TR421, and TR422 10+ megaohms
transistor TR411 5+ Megaohms
R461 or FR401 10 ohm, 100 ohm

It's a puzzler
thanks.
 
Can you measure the DC voltage, with reference to ground, at B, C and E of TR405, TR407, TR409, TR411, TR421 and TR423 ?
 
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