Quad Sansui problem; help???

Sorry for my dumb question, but what ground do I use? And what do I look for in the DC rails?

I should also note that when I take the big caps out and touch the metal surrounding the big cap's own metal bracket it sparks a little... I dont think this happened before..
 
Ok well I just went from collector to the metal bracket of the big caps... I got readings (using continuity function) of 400+ in all but one. That one gave me no reading at all.. Its the TR all the wa to the right on the left heatsink.
 
So I got the TR out and tested it, and it was fine. I put in one of the spares, tried the collector to ground and got nothing still. Put in an original working tr and same thing. It is "TR703" on the PS board. All other collector to ground test fine (start low and build up to about 570.. although one keeps going to about 1700?)

What could be the problem? Bad connection? Bad cable?
 
Hi Betomon,
As I said before, I am not an expert, or have any experience at all using a dim bulb tester. I would take a different tack with bringing the amplifiers up, but I may not be as effective.

Why don't you give me a rundown of where you are now with this project? Let's see where we could go from here.
 
Well right now I am still stuck :( :

* I replaced the 3.9 resistors that were causing the problem. The new ones are rated at 3.9 but read at around 5

* In circuit, the resistors measure 2.5.. Although I've noticed sometimes it reads different (higher, but never higher than around 14).. but maybe its just that my meter is low on battery.

* I checked the output transistors again and they are all good, and in correct polarity. 93 PNP, 94 NPN.



I also examined the solder joints on the power supply board very closely and found that one of the capacitors I changed (80v bipolar 4.7uf) had a bad solder joint because the lead was coming off. I also noticed a little bit of black on the lead.. I think its too fine for my phone' camera to show. I'll be redoing that in a bit.

Aside from all this, TR703, which is an NPN all the way to the right, on the left heatsink if looking at the quad from behind, is still not giving me a reading when I go from collector to ground. I checked continuity on the cable itself and it is good. Now I'll be testing other connections following it's path... because other than that I dont know how else to find out why its not giving me a reading.
 
Aside from all this, TR703, which is an NPN all the way to the right, on the left heatsink if looking at the quad from behind, is still not giving me a reading when I go from collector to ground. I checked continuity on the cable itself and it is good. Now I'll be testing other connections following it's path... because other than that I dont know how else to find out why its not giving me a reading.

Why are you trying to get a reading from collector to ground on this transistor??
What reading are you trying to get.....I cant think why you would want to do this......
Can you try to explain your logic??
Maybe we can help you take some measurements which will be helpful......

All you will get doing this measurement is something quite high and rising as the multimeter charges the 80V 4.7uF cap up........
 
Let me address the power up issue. If you look at the schematic, one of the leads is going from the AC line, to the power supply board, through the two 3.9 resistors in parallel. The relay is also there, and after the big caps have charged up, so that the power transformer starts to come up to voltage, eventually enough voltage is applied across the relay and it energizes, shorting out the two 3.9 resistors. This is the sequence. Anything that interrupts this process will prevent power up.

I recently helped another guy with a power up problem who contacted me on my web site. Hi problem was the AC power switch, which is evidently a pretty common problem also. So that is the other thing you can check. some units were sent out in the beginning that only used one side of the DP switch. Check it out, and you can use both sides.
 
Why are you trying to get a reading from collector to ground on this transistor??
What reading are you trying to get.....I cant think why you would want to do this......
Can you try to explain your logic??
Maybe we can help you take some measurements which will be helpful......

All you will get doing this measurement is something quite high and rising as the multimeter charges the 80V 4.7uF cap up........

Well I was just trying to do what you told me before I guess :dunno:

kevzep said:
Measure from the base of the ouptuts to ground, and the collectors to ground, and see what you get......it should be a high reading.......

Also, I didn't mean that I was going to test the capacitor, I meant the path from the collector cable through the power supply board... I guess I'm just running out of ideas.
 
Let me address the power up issue. If you look at the schematic, one of the leads is going from the AC line, to the power supply board, through the two 3.9 resistors in parallel. The relay is also there, and after the big caps have charged up, so that the power transformer starts to come up to voltage, eventually enough voltage is applied across the relay and it energizes, shorting out the two 3.9 resistors. This is the sequence. Anything that interrupts this process will prevent power up.

I recently helped another guy with a power up problem who contacted me on my web site. Hi problem was the AC power switch, which is evidently a pretty common problem also. So that is the other thing you can check. some units were sent out in the beginning that only used one side of the DP switch. Check it out, and you can use both sides.

Ok cool, thanks for this info Jim. So how do I go about testing the AC power switch? And it has little jumper cables connecting the 4 contacts, so does this mean both sides are connected?
 
Well I was just trying to do what you told me before I guess :dunno:



Also, I didn't mean that I was going to test the capacitor, I meant the path from the collector cable through the power supply board... I guess I'm just running out of ideas.

Okay, I misunderstood your point.....what you are trying to do, is make sure there are no short circuits between the base and ground, and collector and ground.....

It sounded like in your post you were trying to see why there was no continuity between collector and ground......

Well work with Jim on the power side of things and see how you go with that........then we could look at a few things in the power-amp side before you fire the amp up.....
 
Ok cool, thanks for this info Jim. So how do I go about testing the AC power switch? And it has little jumper cables connecting the 4 contacts, so does this mean both sides are connected?

Yes, both sides are being used. put your meter across it and measure resistance. It should read 0 when switched on, infinity when off.

Best
 
Hi Betomon,
And it still won't power up? Hmmmm. I think this is where you're going to have to do some troubleshooting on your own. sometimes you can get a very revealing result just by measuring the resistance at the ac plug. With the power switch on, you should read a few ohms there. My "test unit" reads 3.4 ohms. That resistance is the sum of the two 3.9ohm resistors in parallel and the DC resistance of the power transformer. If you get a high reading, trace that through with your meter.

With the unit plugged in and turned on, you should be able to trace the AC through, using the schematic diagram. It has to go away somewhere, cause if it was getting to the transformer, something would happen, either it would power up, or a fuse would blow. Be careful when troubleshooting AC, it'll make a big spark :scratch2:
 
Betomon,
I'm really not up on testing with that. It could be the best way to do it. I think you're in the condition of it not powering up. Why don't you try to figure out why, and then when you do find something, before you change it and power up, let's talk about it here.
 
I think it's definitely worth using the DBT, it let's you know when There's a problem and you need to shut it down......
Let us know how you are going, I'm watching.....
 
Okay guys, I'll let you guys know. This week will be very busy for me so I probably wont get to work on it, but I will as soon as I can. Thanks for your continuous support gentlemen :)
 
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