Ok here’s an update
All the resistors test good
I replaced all the 2sa818 and 2sc1628 with ksa1381 and ksc3503 however the distortion is still present, right channel is perfect and bias holds steady on both channels
Sansui BA-2000 bias adjustment
- Thread starter quadmatrix82
- Start date
All the resistors test good
I replaced all the 2sa818 and 2sc1628 with ksa1381 and ksc3503 however the distortion is still present, right channel is perfect and bias holds steady on both channels
Well, need to check R63 & R65 (68Ω), but after those I am out of obvious candidates. You mentioned some restoration done to the driver board - I assume replacement capacitors too? - anything look different about the left side components compared to the right side?
Post a picture? - big and close enough to see detail.
Post a picture? - big and close enough to see detail.
Last edited:
Let's get some driver board voltages.
Here’s some photos I will start to test some more components…Well, need to check R63 & R65 (68Ω), but after those I am out of obvious candidates. You mentioned some restoration done to the driver board - I assume replacement capacitors too? - anything look different about the left side components compared to the right side?
Post a picture? - big and close enough to see detail.
Attachments
Sounds good where should I measure from and I can report back?
I just counted 13 voltages the schematic gives you on the amp board, let's get all of them.
They highlighted those voltages because they're a great troubleshooting tool.
Both channels look the same this was refurbed about 8 years ago and has been fine, I retired it for about a year rotating in a x1 and x911dg, bringing it back to rotation the fault was there…the 68 ohm resistors are new and test goodWell, need to check R63 & R65 (68Ω), but after those I am out of obvious candidates. You mentioned some restoration done to the driver board - I assume replacement capacitors too? - anything look different about the left side components compared to the right side?
Post a picture? - big and close enough to see detail.
Th
Thanks, the challenge is the component side faces inwards towards the heat sink with little room any suggestion how to safely take the measurements this way?
You can measure voltages on the solder side too.
I had another look this evening I reflowed some joints and things took a negative turn, the amp now stays in protection, I rechecked the board and don’t see anything a miss the bias still stays steady but I don’t see any obvious fault -using the dim bulb it doesn’t light up as it’s in protection
I think so, certainly if it gives you a better chance to measure voltages, then I say give it a try.
I removed the power supply to see if anything was suspect, I found a few dry joints which were reflowed however came across something unusual, D616 diode 10-d1 is missing from the board, it looks as if the legs were cut and ithe diode was removed - did sansui not fit this in some models? Should I put a 1n5393 back in its place? It’s worked all these years without it but perhaps someone removed before my ownership?
Attachments
That needs to go back in - it's the back EMF suppression diode for RL02 (soft start) relay coil. In this case because it is not associated with a transistor to turn the relay on, the diode isn't so important - but I think it should be there. It isn't carrying any current so you could replace it with a 1N400X series diode, 1N5393 would be overkill but ok to use in this case.
Added the diode back into circuit and reassembled the power supply, filter caps arrived and think I found a potential culprit to some issues I was having…filter caps appear to have leaked and test pretty low.
18000uf 75v screw filter caps recommended by @ivandezande will be fitted, seem a good fit just note you may need to increase the screw hole size for the metal tabs and bar that fit to the filter cap
18000uf 75v screw filter caps recommended by @ivandezande will be fitted, seem a good fit just note you may need to increase the screw hole size for the metal tabs and bar that fit to the filter cap
Attachments
After a spell of covid the past few weeks I finally had a chance to revisit the Sansui BA-2000 last night.
Upon further testing I have realised the distortion I was hearing is in BOTH channels so I moved to the power supply board.
I replaced both relays as they were still the original ones fitted they were pretty pitted on the contacts.
Also replaced 2sd356 and 2sb256 they seemed to have had some heat damaged.
Using a 100w dim bulb, both relays click in and the bulb dims very low, however distortion is still present on both channels no change from before.
Checking the power supply, I get 7.2v on pin 26 and -5.2v on pin 27, the board has been recapped and had all its fuse resistors replaced.
Any suggestions where I should look from here?
Upon further testing I have realised the distortion I was hearing is in BOTH channels so I moved to the power supply board.
I replaced both relays as they were still the original ones fitted they were pretty pitted on the contacts.
Also replaced 2sd356 and 2sb256 they seemed to have had some heat damaged.
Using a 100w dim bulb, both relays click in and the bulb dims very low, however distortion is still present on both channels no change from before.
Checking the power supply, I get 7.2v on pin 26 and -5.2v on pin 27, the board has been recapped and had all its fuse resistors replaced.
Any suggestions where I should look from here?
You still (very likely), have some failed transistors or diodes in the regulated PSU, check the incoming rectified DC voltage at TR607 collector (+70V) and the same at TR608 collector (-70V). Check the voltage across ZD602 - should be close to 13V. If that tests good remove and check all the transistors in the Negative regulator, TR604, TR612, TR616 & TR608 - replace any that are faulty. Report back with results.
Thanks Hyperion this is really helpful, I’ll check them and report back all those bits were changed about 8 years ago maybe there’s a bad joint I’ll look and report back
As you are probably aware by now power supply voltages and getting them correct is crucially important, they are the first thing you check when you have a fault, don't even think about looking at anything else until your power supply voltages are correct.
Don't worry too much about the transistors in the positive regulator, we'll get to those later, let's get the negative regulator up first.
Don't worry too much about the transistors in the positive regulator, we'll get to those later, let's get the negative regulator up first.