Marantz 1152dc issues problems.

[dr*audio]

I tested 417/418....both very close to 3.3k ohm. Q405(ksc1845) tested good(6-way tr test). Q407(ksc2690) also tested good.

I am thoroughly 'conundrummed'!

I think I know what is going on. I think the transistors you chose are fine, but if you look at the circuit and do the math, you find that you can't get the voltage on the base of Q408 that is shown, with the resistor values for R419 and R421, and Q408 is not being turned on. You need to use a 1.1K resistor for R419. Try that and I think it will work. If you don't have a 1.1K, use 1.2K or 1.3K, but then I will want you to measure the voltage drop across R423 so I can calculate the current through Q408.

 

[anderslober]

OK....I will change r419/420(1k's) to 1.2ks.....you want me to go UP in resistance....correct?......lets see what happens.....

 

[dr*audio]

OK....I will change r419/420(1k's) to 1.2ks.....you me to go UP in resistance....correct?......lets see what happens.....

Correct, the value must go up. One way to think about this is; R419 tends to turn Q405 off, by putting a more positive voltage on the base. Raise the resistance on R419 and the voltage on the base goes down, making Q405 turn on harder.

 

[anderslober]

ok......great.....lets try it......

 

[anderslober]

Dr.audio...I changed r419/420 from 1k to 1.2k resistors.......I still have 20v on r429/430 when in AUX and 16v in PHONO.

I dunno'...............

 

[dr*audio]

Dr.audio...I changed r419/420 from 1k to 1.2k resistors.......I still have 20v on r429/430 when in AUX and 16v in PHONO.

I dunno'...............

You keep leaving off the polarity on your voltage readings and it's confusing. Do you have +20V or -20V? Before it was negative...

 

[anderslober]

Sorry its negative....-20v.....-16v....

 

[dr*audio]

Sorry its negative....-20v.....-16v....

Ok. Measure the voltage on the base of Q401 with the switch in Aux and in Phono. You will probably have to have your meter on the 200mV range to measure it. Make sure you post the polarity.

 

[anderslober]

Q401 base......AUX....-0.0302v.
Q401 base.....PHONO....-0.0303v.

The voltages do fluctuate a bit......but are VERY close.

 

[anderslober]

Q403...base...AUX...-0.0024.
Q403...base...PHONO....-0.0016v.

Slightly lower than q401.

 

[dr*audio]

Q403...base...AUX...-0.0024.
Q403...base...PHONO....-0.0016v.

Slightly lower than q401.

It's a lot lower, almost 1/10 the voltage.
Carefully short the input side of R405 to ground and read the voltage on the output (R429.)

 

[anderslober]

Ok...the input side.....is that the end towards c403? A clip there and the other end to gnd/chassis..?
And then measure voltage at r429...?
Just want to make sure i dont mess up...

 

[dr*audio]

Ok...the input side.....is that the end towards c403? A clip there and the other end to gnd/chassis..?
And then measure voltage at r429...?
Just want to make sure i dont mess up...

Correct on all counts.

 

[anderslober]

I did as you said,....shorted the input side of r405 to chassis......measured -12v at r429. Unit was in PHONO.

 

[dr*audio]

I did as you said,....shorted the input side of r405 to chassis......measured -12v at r429. Unit was in PHONO.

Do this again and measure the voltage on the collector of Q408.

 

[anderslober]

Q408.....collector.....unit in PHONO.....r405 input shorted to chassis.....-43.8v.

I have a feeling we are looking in the wrong place. Why does the voltage at r429 start at around -22/-23v and after the unit has been ON for a few minutes , the voltage drops to -8/-9v............I just don't get it..................BOTH channels.
Can I try the PHONO with a cd-player...........low volume of course........?

 

[dr*audio]

Q408.....collector.....unit in PHONO.....r405 input shorted to chassis.....-43.8v.

I have a feeling we are looking in the wrong place. Why does the voltage at r429 start at around -22/-23v and after the unit has been ON for a few minutes , the voltage drops to -8/-9v............I just don't get it..................BOTH channels.
Can I try the PHONO with a cd-player...........low volume of course........?

The voltage on R429 has a capacitor in series with it, that blocks DC. You are seeing the cap discharging. The collector of Q408 is the correct place to look.
DO NOT run a CD player into the phono stage, you will damage it. The output is way too high, even turned down it's too high.
Please measure the voltages on Q407 and Q408 ECB. You don't have to short the input, just put it in Phono mode.

 

[anderslober]

Q407.....ksc2690....ecb.....-42.8.....-42.7....-42.1.
Q408.....ksa1220....ecb.....41.3.....-42.7.....40.9.

Unit set to PHONO. No shorting.

 

[anderslober]

Can a cap 'short'? C417/418?

 

[dr*audio]

Can a cap 'short'? C417/418?

Good catch, I missed those. Yes, they could be shorted or leaky and that would explain the behavior. Remove them from the board and test using your Ohm meter on the highest rang. They should read open. Don't put your fingers on the leads or you will read the resistance of your body.