Discussion in 'Exclusively Sansui' started by G Heiman, Feb 28, 2018.
Where are you placing your probes when you check this? You should have the black probe touching the metal chassis and the red probe on 9, note the reading and then move the red probe to 12 and note that reading.
If the relay is not turning on, you should not have any voltage at 5 and 8. Even if the relay is on, that voltage shouln't be higher than 9 and 12.
I just double checked everything. My multimeter is set to Vdc with the neg. to chassis and positive to positions indicated on drwg. I am using a DBT .
9=4.1 Vdc 12=4.1 Vdc 5=-7.6 Vdc 8= started at -4.1 Vdc dropped to +/- 0 (-.6 to +.5) I do not hear or see any relay clicking.
Something is not making sense here. If you have 4v at 9 and 12, the protection circuit will prevent the relay from turning on. Then there should be no voltage at 5 and 8 if that diagram follows schematic conventions and shows the relay in the rest position. That said, you may be misidentifying the pins. To avoid the possibility of misidentifying the pins, please do the same check at resistors R21 and R22 on the power supply board F-2625. They are 1/2 w resistors located next the the coils near where the driver board mounts to the PS board. For this test, it doesn't matter which side of the resistor you check but if you have a choice, check the side facing away from the driver board.
If you are seeing voltages around 4 volts there, see if you can adjust them down using the DC offset trimmers on the driver board. These are the inner two trimmers located closest to the center line of that board. Pay attention to the position of the trimmers before you turn them so you can set them back to their original position if you can't change the voltages at R21 and R22.
Ok, today I replaced all of the electrolytic capacitors and transistors 1,2,3,4,5,6,11,12,13 and 14 on board F2624. I read 4.1Vdc at 9 and 12 but read -.1Vdc at 5 and 8. I read the same voltage (-.1 Vdc) at R21 and R22. I can set the bias current but not the offset voltage. On the F-2624 board I read 19.1Vdc after R33 and R34, -42.6 Vdc at the collector leg of TR13 and TR14, and -32.1 Vdc after R31 and R32.
I don't know what to tell you. I wish I was good enough to walk you through this but I'm not. With all of the parts you have replaced on this board, there are too many opportunities to introduce new faults. My best advice at this point is to very very carefully recheck your work. Look at every solder joint with a magnifying glass to ensure a clean solder joint with no solder bridges to adjacent traces. Also be very sure that your new transistors are installed correctly. Modern transistors can have different pin outs than the originals. Be equally sure your caps are installed correctly.
Here is a hint, shotgunning rarely works out. If you suspect a transistor, test it. Then put it back or replace if bad. Re-check to see if the problem persists or has changed. I like to look at the schematic and check every single voltage they provide me.
It is extremely difficult for someone to guide you online with this, as I think you would agree you have limited electronics skills. You have an issue which affects both channels, and in post #9 I suggested you should check all the PSU voltages - and by implication all the associated branches of voltage regulation (i.e. those with zeners & resistors). This is the first principle of electronics fault finding - 'ensure all PSU voltages are within specification' it doesn't seem like this has been done.
From your first post - and as it affects both channels, this suggests to me that you have a problem with the PSU itself, or something interfering with the output from the PSU.
In mitigation, the quality of the generally available schematic for this unit is very poor indeed, with the original balloon highlights turned to black, thus obscuring important information, which hasn't helped any of us. People have been trying hard to help you, however this doesn't seem to have produced the results we all would have expected or hoped for.
Thanks guys. I replaced a lot of parts, but not all at once. First the caps and resistors, no change. Next transistors 1-4 which reduced the voltage at R21 and 22 to -.1Vdc. Replacing transistor 5 and 6, no change. Replacing transistors 11,12,13,1nd 14, no change. I'm thing the voltages at R31 and 32 are too low. They are also too low at R33 and 34.
I have limited electronics knowledge, but have assembled amplifier kits and successfully restored a Mcintosh mc240. As you say the schematics are less than stellar.
By the way, I checked the parts I took out, and they seemed fine.
This may or may not be helpful ---
If the relay is not engaging there should be no voltage at the speaker terminals
If there IS voltage at the terminals you may have a missing or floating ground giving you that voltage reading
If you have a 1 watt 10 ohm resistor put that in series with your multimeter positive lead (set to ma reading of course, some meters require you to change probe location) and see if you can get a milliamp reading across the positive and negative speaker terminals with volume at zero, speaker switch on and on a dim bulb tester just in case. There should be almost no milliamps with volume at zero (other than spurious grounding voltage floating around which is another whole discussion. This will help verify the unit has not lost ground integrity somewhere which will drive everyone crazy trying to figure out.
If you can actually get to the bottom side of the rl01 relay we need voltage measurements on the pins to chassis ground, if you cannot get to the relay you will need to remove it before continuing on to the next step.
As others have noted the available schematic is downright awful so lets try old school sleuthing instead.
Second route to persue---
If you are able to get a mini grabber probe on to r09 and then r07 that come off of vr01 can you post voltages and note if the value changes when you turn vr01?
Again, this all needs to be done while the unit is on a dim bulb tester with no more than a 60w bulb, any probe slips in this area will cause mushroom cloud effects if you are on mains voltage.
Thanks for your input. I don't have a 10 ohm 1 watt resistor, but, I do have a pair of 100 watt 8 ohm resistors I used as a dummy speaker load for a McIntosh MC240 restoration. Would they work? If not I'll order the 10 ohm 1 watt resistor. I posted the readings I read off the bottom of the relay and referenced a drawing that Mattsd provided (post 13) and my post 25. I'm leaving for a week tomorrow early a.m. but will check the other measurements you asked for when I get back. Don't give up on me! I want to figure this thing out.
Earlier this month I uploaded a clean scan of the 7070 schematic to digital docs. You can read the the test voltages in this version.
Thanks for the clean schematic! It will certainly help.
It's been a while, but I have voltages to report. My readings are in green. Everything is low.
The voltages will be low if it's on a DBT but it looks like your supply voltages are low. Is the input voltage selector set for 110V?
The voltage selector is set for 110v. It has never been touched. At 123 V at wall plug, the current draw is 24 watts.
Looks like power supply, how about collector voltage at TR02 board F2626. Then check voltage to ground both sides of the vd1212. Then check both sides to ground the zd01 diode.
As a side thought looks like you lost one of the bridge rectifier diodes but start with the above checks first.
Took the measurements per your request. Voltages noted in red.
Well, after many component checks, the problem was capacitor C07 (1000uf 80V) on F-2625. Thanks to all for your advise.
Glad you got it sorted out.
Separate names with a comma.