Looks fine to me - I am very pleased for you!
Sansui BA-3000 blowing mains fuse following restoration
- Thread starter BradWil
- Start date
Sanken Rectifiers
D01 SG-5TS common cathode
D1 Vf=0.572V If=4.401mA
D2 Vf=0.573V If=4.401mA
D02 SG-5TR common anode
D1 Vf=0.578V If=4.393mA
D2 Vf=0.555V If=4.416mA
Tested with Atlas DCA55
Mica seems intact
D03 C08PN (1850) common cathode
D1 Vf=0.615V If=4.358mA
D2 Vf=0.619V If=4.3545mA
D04 C08PR (1850R) common anode
D1 Vf=0.613V If=4.359mA
D2 Vf=0.607V If=4.366mA
F-2511 top and bottom photos
Transistors next
D01 SG-5TS common cathode
D1 Vf=0.572V If=4.401mA
D2 Vf=0.573V If=4.401mA
D02 SG-5TR common anode
D1 Vf=0.578V If=4.393mA
D2 Vf=0.555V If=4.416mA
Tested with Atlas DCA55
Mica seems intact
D03 C08PN (1850) common cathode
D1 Vf=0.615V If=4.358mA
D2 Vf=0.619V If=4.3545mA
D04 C08PR (1850R) common anode
D1 Vf=0.613V If=4.359mA
D2 Vf=0.607V If=4.366mA
F-2511 top and bottom photos
Transistors next
Attachments
They look OK - perhaps surprisingly - leaving only the remote possibility of 'breakdown under load'.
Next step I recommend: - connecting the secondary to the low current supply, (Yellow-Green-Yellow) and measuring voltage +ve & -ve to ground, applying power with DBT & Variac if wanted. For this test it shouldn't matter that the output of the rectifiers can 'see' the regulator circuitry. Should get a small flash from the DBT and dimming to almost nothing.
You could continue selectively reconnecting stuff one at a time, in the above fashion - 'baby steps'
Next step I recommend: - connecting the secondary to the low current supply, (Yellow-Green-Yellow) and measuring voltage +ve & -ve to ground, applying power with DBT & Variac if wanted. For this test it shouldn't matter that the output of the rectifiers can 'see' the regulator circuitry. Should get a small flash from the DBT and dimming to almost nothing.
You could continue selectively reconnecting stuff one at a time, in the above fashion - 'baby steps'
Last edited:
I just realised that even though the driver amps are isolated, pins 18, 24, 25 on F-2511 and the blue/red leads to the filter caps are connected to the output array. The outputs are all original matched Sanken and tested fine during restoration. Any outputs shorting to ground would also cause a DBT fail, even with the driver amps isolated, right?
I will remove the heatsinks and test each one next ...
I will remove the heatsinks and test each one next ...
Yes, I think so, if the short were C-E, but probably not if B-E for example.
richardpp
Well-Known Member
@Hyperion is correct, a C-E short will fail the DBT even with the driver amps isolated.
You can quick-check the output transistors for C-E shorts without removing the heatsink assemblies by probing the transistor case (C) together with the orange wire on the output board (E) shown in your last photo above. Because the transistors are in parallel you only need to test one to test all three, so test one of the NPN's on the front side of the heatsink and one PNP on the back, for each heatsink.
To properly isolate the load from the unregulated supply when testing with a DBT, disconnect terminals 7 and 8 (output stage) and 29 and 30 (driver stage) on F-2511.
Just saw your last post re: shorted outputs. Old uniwatt pre-driver transistors a common cause for shorted outputs.
You can quick-check the output transistors for C-E shorts without removing the heatsink assemblies by probing the transistor case (C) together with the orange wire on the output board (E) shown in your last photo above. Because the transistors are in parallel you only need to test one to test all three, so test one of the NPN's on the front side of the heatsink and one PNP on the back, for each heatsink.
To properly isolate the load from the unregulated supply when testing with a DBT, disconnect terminals 7 and 8 (output stage) and 29 and 30 (driver stage) on F-2511.
Just saw your last post re: shorted outputs. Old uniwatt pre-driver transistors a common cause for shorted outputs.
Last edited:
Many thanks, very helpful.
Going through the outputs now. Second one tested, TR708 2SA908 shorted on CBE.
Will replace all outputs then check and replace the pre-drivers on the driver amps. Thank goodness it's a completely straightforward fix. The lack of rail fuses really threw me and I really should have checked the outputs first! Live and learn.
The shorted ones, literally shorted all 3 (CBE) leads. The failed one registered as a diode so one side was open.
Thanks, will check those resistors, very helpful.
Appreciate the offer but I'm going to run with OnSemis as per below.
With the power amps, I plan to replace TR08 (2SC1628), TR09 (2SA818) and TR04 (2SA818), TR05 (2SC1628) - may use Toshibas TTC004B/TTA004B but need to research this.
Failed Right power amp pictured.
Attachments
Replaced the right driver transistors as per below. Passed DBT but now I'm unable to dial any BIAS, even on full mains - any ideas?
Perhaps I should reinstall the originals, which did test OK? I only changed them as it was mentioned the original pre-drivers are a potential point of failure.
Perhaps I should reinstall the originals, which did test OK? I only changed them as it was mentioned the original pre-drivers are a potential point of failure.
Something's up. Installed the left driver board, unaltered with all original semis - no BIAS either?
DBT passes fine and unit is comes out of protection.
Rails +/- 68V correctly feeding F-2512 connector board.
Any experience using the MJ21195/96 On Semis on the BA3K? Do some resistor values need to be changed on the drivers in order to BIAS? In the case of the left driver, it is only the outputs that have changed, all drivers, pre-drivers and other semis original.
DBT passes fine and unit is comes out of protection.
Rails +/- 68V correctly feeding F-2512 connector board.
Any experience using the MJ21195/96 On Semis on the BA3K? Do some resistor values need to be changed on the drivers in order to BIAS? In the case of the left driver, it is only the outputs that have changed, all drivers, pre-drivers and other semis original.
Last edited:
richardpp
Well-Known Member
Suggest you switch the meter to read resistance between the bias test points. Power off. You should see a reading of ~1.2 Ω. (0.47 +0.47 + lead resistance). If not, an emitter resister might have gone open.
You can also check whether or not the driver board is providing sufficient voltage to turn on the output transistors by measuring voltage to ground at each of the two points shown below. First remove the connector board F-2510. Start with the bias trimmer set full CCW and adjust up. If all is well, a positive or negative voltage of approximately 500mV should be achievable using the bias trimmer and any discrepancy between positive and negative readings should be able to be nulled using the dc-offset trimmer.
Edit: There shouldn't be any problems using the On-Semi transistors. Hope this helps.
You can also check whether or not the driver board is providing sufficient voltage to turn on the output transistors by measuring voltage to ground at each of the two points shown below. First remove the connector board F-2510. Start with the bias trimmer set full CCW and adjust up. If all is well, a positive or negative voltage of approximately 500mV should be achievable using the bias trimmer and any discrepancy between positive and negative readings should be able to be nulled using the dc-offset trimmer.
Edit: There shouldn't be any problems using the On-Semi transistors. Hope this helps.
Last edited:
I get 1.17Ω at left bias test points and 1.14Ω at the right.
Left arrow voltage to GND = 0
Right arrow voltage to GND = 0
Same on both channels
EDIT: With F-2510 disconnected I'm getting 0V at the bias test points regardless of whether VR02 is fully CCW or CW. Also getting 0V DC at the speaker terminals.
Last edited:
Good call.Be careful... keep the DBT in circuit, in this situation you may find the bias situation may recover without sending you a memo.