Output has a 21VDC on BOTH channels.
The amp is playing, a sinewave on the input reproduces a sinewave on the output but clips at 5VPP.
What I did so far:
Disconnected plug 9/10/11/12 from the pre and control section
Power supply is a nice +/-38V
At R22 I measure +30.5VDC instead of +9VDC.
At collector TR06 I have +19.5VDC
The absolute weird thing is that both channels are effected.
I’ll scan the whole manual (It’s a UA-6600) for the one(s) who can help me solve this problem.
/Hugo 🙂
The amp is playing, a sinewave on the input reproduces a sinewave on the output but clips at 5VPP.
What I did so far:
Disconnected plug 9/10/11/12 from the pre and control section
Power supply is a nice +/-38V
At R22 I measure +30.5VDC instead of +9VDC.
At collector TR06 I have +19.5VDC
The absolute weird thing is that both channels are effected.
I’ll scan the whole manual (It’s a UA-6600) for the one(s) who can help me solve this problem.
/Hugo 🙂
Netlist said:
Hi Hugo
Inspect if the 9,1 volts Zener near R22 as the conection to ground...this conection to ground must be commum to both chanels...and if is missing you don't have 9 volts at this point...
Regards
Hi Netlist,
Look for the ground connection at the pcb or the other end. Tube_Dude has hit this on the head as far as I'm concerned.
An open zener solder connection would also do this. If this is the case, replace the zener and put a higher wattage unit in.
-Chris
Look for the ground connection at the pcb or the other end. Tube_Dude has hit this on the head as far as I'm concerned.
An open zener solder connection would also do this. If this is the case, replace the zener and put a higher wattage unit in.
-Chris
Can't see the other end, but you have two ground connections. Zeners are okay I think. The common connection at the other end must be the fault area.
Spot on!!
In disassembling the unit there were two ground leads detached.
You guys rock.
So if you like the manual, let me know.
/Hugo 🙂
In disassembling the unit there were two ground leads detached.
You guys rock.
So if you like the manual, let me know.
/Hugo 🙂
Ohh Ohh,I could really use the manual/schematic.
I've got a sick Sansui AU-5500 here.At first it plays fine,but after it gets warm,there will be a bit of a crackling in the left channel,then it will click the protection relay.I'm suspecting a thermal problem,maybe one of the old transistors has finally given out. (The problem is,some of them are impossible to find/get!) or maybe the bias circuit is acting up..
I still havn't figured this one out yet..I suppose I should get it up on the bench and see whats up one of these days.
Any info,or tips would be great.I'd love to get this old beast singing again!
Edit.. I looked at the PDF posted above,and it looks like the same circuit,but the P/N's of the transistors are all different. (Same PCB number..I guess they used that PCB in alot of thier amps,and just stuffed them with different parts..)
I've got a sick Sansui AU-5500 here.At first it plays fine,but after it gets warm,there will be a bit of a crackling in the left channel,then it will click the protection relay.I'm suspecting a thermal problem,maybe one of the old transistors has finally given out. (The problem is,some of them are impossible to find/get!) or maybe the bias circuit is acting up..
I still havn't figured this one out yet..I suppose I should get it up on the bench and see whats up one of these days.
Any info,or tips would be great.I'd love to get this old beast singing again!
Edit.. I looked at the PDF posted above,and it looks like the same circuit,but the P/N's of the transistors are all different. (Same PCB number..I guess they used that PCB in alot of thier amps,and just stuffed them with different parts..)
DigitalJunkie said:
When you look at the schematic in my first post, you'll see the diff pair transistors Q1/Q3 and Q2/Q4 for the other channel. Together with C27 33µF/50V in the protection circuit these are most likely the culprit.
The crackling comes almost certainly from the diff pair. You can see my handwriting, it's Dutch but describes the prob. I replaced them with BC560. Watch the pinout, it's different.
/Hugo - so happy now, will scan upon anyone’s request 🙂
I think I may have found a/the problem with the AU5500 I have here.
The bias pots seem to be dirty and intermittent.I turned them back a fourth a bit,and set them to approx. where the originaly were..and it seems to work okay now.I'm gonna dig through my box and see if I have any suitable replacements.
My question is,What should the idle bias be in the output,and how do I adjust the front end pots? What do they do? (adjust the symmetry of the front end?)
The bias pots seem to be dirty and intermittent.I turned them back a fourth a bit,and set them to approx. where the originaly were..and it seems to work okay now.I'm gonna dig through my box and see if I have any suitable replacements.
My question is,What should the idle bias be in the output,and how do I adjust the front end pots? What do they do? (adjust the symmetry of the front end?)
DigitalJunkie said:
Change the pots onto sealed multi-turn types.
The input pots probably zero the DC offset.
There should be a bias idle value in the Sansui manual. I would stick to it first and then do a listening improvements check for higher and lower values.
Carlos
Hi DigitalJunkie,
I disagree with carlmart here a bit. For replacement, use the normal single turn pots. You can put a drop of contact cleaner on the metal ring the wiper contacts and that may be just as good.
Multiturn pots get noisy too sometimes, but the wiper contact area is either smaller, or the movement is smaller. You may then be creating a problem for later.
Netlist,
Just got back from London today. The audio show was niffty. The Marantz exhibit sounded the best.
-Chris
I disagree with carlmart here a bit. For replacement, use the normal single turn pots. You can put a drop of contact cleaner on the metal ring the wiper contacts and that may be just as good.
Multiturn pots get noisy too sometimes, but the wiper contact area is either smaller, or the movement is smaller. You may then be creating a problem for later.
Netlist,
Just got back from London today. The audio show was niffty. The Marantz exhibit sounded the best.
-Chris
I didn't follow Marantz for years; do they still produce mid-fi apart from high(er) end?anatech said:
Regarding pots:
I wouldn’t spend much money on multiturns in these old amps.
Unless you recap them which also means are good amount of bucks. Simple good pots is what I usually go for.
DigitalJunkie
Do you have the manual? All settings are very well explained over there, these guys new how to write them.
/Hugo 🙂
Hi Hugo,
Apparently they do. I really didn't get a chance to hear any of that. I would be very happy to own an SC-7S1 and MA-9S1 (X2) in a system. I did walk away VERY impressed.
It is a shame the US is not supporting two channel. We are deprived over here in Canada. I sent a picture to my friend at Denon Canada (the current importer).
My current system uses a Marantz 300DC. I need to repair my SC-9 preamp.
I can't recommend multiturn pots for bias circuits. If you need the resolution for DC offset, fix the design.
-Chris
Apparently they do. I really didn't get a chance to hear any of that. I would be very happy to own an SC-7S1 and MA-9S1 (X2) in a system. I did walk away VERY impressed.
It is a shame the US is not supporting two channel. We are deprived over here in Canada. I sent a picture to my friend at Denon Canada (the current importer).
My current system uses a Marantz 300DC. I need to repair my SC-9 preamp.
I can't recommend multiturn pots for bias circuits. If you need the resolution for DC offset, fix the design.
-Chris
Netlist said:
No,I don't have it,but if you're willing to email it to me,I'm willing to let ya.. 😉
Hi Hugo,
Would it be possible to send a copy of the Sansui manual? I could use it if it's not too much trouble.
Thanks Hugo,
-Chris
Would it be possible to send a copy of the Sansui manual? I could use it if it's not too much trouble.
Thanks Hugo,
-Chris
Okay,I finally dug this beast back out of the dusty corner,and soldered in some new pots..(Yea,I'm slow...)
Now I need to go about biasing it,Anyone know the procedure?
Perhaps Hugo has it?
(Hugo,You may have already sent it to me,but I seem to have lost it,if you did. 🙄 )
Ohh,and I think it found a schematic which matches the transistors,etc. in the amp I have here.
The one Hugo posted looks like the same circuit,but the transistors are different #'s than the ones in the 5500 I've got.
Sansui AU-5500 schematic
Now I need to go about biasing it,Anyone know the procedure?
Perhaps Hugo has it?
(Hugo,You may have already sent it to me,but I seem to have lost it,if you did. 🙄 )
Ohh,and I think it found a schematic which matches the transistors,etc. in the amp I have here.
The one Hugo posted looks like the same circuit,but the transistors are different #'s than the ones in the 5500 I've got.
Sansui AU-5500 schematic
Hi DigitalJunkie,
As a rough guess, I would measure across the two emitter resistors and set the bias control to read about 20 mV. Continue to monitor this voltage as the set stabilizes. This current should be both perfectly safe and also run close to the design level.
Before replacing the controls, measure the old bias level on both channels. Just as a check point. The new controls should be placed in approximately the same mechanical position that the old ones where in. If that isn't known, turn the wiper until the pot is at maximum resistance. One end and the wiper should be shorted by the foil track on the PC Board.
First power up should be done with a variac, monitoring both channels for bias current. Make sure the DC output isn't railed either.
-Chris
As a rough guess, I would measure across the two emitter resistors and set the bias control to read about 20 mV. Continue to monitor this voltage as the set stabilizes. This current should be both perfectly safe and also run close to the design level.
Before replacing the controls, measure the old bias level on both channels. Just as a check point. The new controls should be placed in approximately the same mechanical position that the old ones where in. If that isn't known, turn the wiper until the pot is at maximum resistance. One end and the wiper should be shorted by the foil track on the PC Board.
First power up should be done with a variac, monitoring both channels for bias current. Make sure the DC output isn't railed either.
-Chris
Thanks Chris!
I set the new pots to approx. the same position and resistance of the old ones,and it seems they were set a bit low (~5mv across each emitter resistor.) so I've now got them set to approx 10mv across each resistor.. (or ~20mv across both resistors.)
I let it sit and "cook" on the bench for about a half hour,and the bias seems nice and stable. The output transistors and heatsink didn't even get lukewarm though,they were cold to the touch the whole time.
(Seems like they should have gotten atleast a little warm? Maybe I should let it 'cook' longer?)
I tried to minimise the DC offset on the output (replaced those pots too),but it bounces around a bit and doesn't seem too stable.
(All done with no input signal,and no load connected to the output.)
Any thoughts on the 'drifty' offset?
I set the new pots to approx. the same position and resistance of the old ones,and it seems they were set a bit low (~5mv across each emitter resistor.) so I've now got them set to approx 10mv across each resistor.. (or ~20mv across both resistors.)
I let it sit and "cook" on the bench for about a half hour,and the bias seems nice and stable. The output transistors and heatsink didn't even get lukewarm though,they were cold to the touch the whole time.
(Seems like they should have gotten atleast a little warm? Maybe I should let it 'cook' longer?)
I tried to minimise the DC offset on the output (replaced those pots too),but it bounces around a bit and doesn't seem too stable.
(All done with no input signal,and no load connected to the output.)
Any thoughts on the 'drifty' offset?
On the AU-6600 the bias is set by removing F01 and measure the current flowing trough the circuit.
It should read between 20 and 30mA.
Same procedure for the other channel by removing F02.
How much does the DC vary at the output?
/Hugo
It should read between 20 and 30mA.
Same procedure for the other channel by removing F02.
How much does the DC vary at the output?
/Hugo
Hey Hugo,
The DC offset varies by ~10mV on average,But I discovered that it's *very* sensitive to AC line fluctuations.Like,If I turn on my soldering station while looking at the amp's offest on the O-scope,it will jump by large amounts (250mV or more),sometimes the scope trace jumps off the screen,and then returns a moment later.
I also discovered that one of the 100uf/50V caps (C-05,IIRC) on the amp board runs a bit warm if you run a signal through the amp.
Perhaps it's time for some new caps.
Other than that,it seems to be working okay. 🙂
The DC offset varies by ~10mV on average,But I discovered that it's *very* sensitive to AC line fluctuations.Like,If I turn on my soldering station while looking at the amp's offest on the O-scope,it will jump by large amounts (250mV or more),sometimes the scope trace jumps off the screen,and then returns a moment later.
I also discovered that one of the 100uf/50V caps (C-05,IIRC) on the amp board runs a bit warm if you run a signal through the amp.
Perhaps it's time for some new caps.
Other than that,it seems to be working okay. 🙂
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