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Source for KA-6100 power rectifier diodes

J

JayWFletcher

New Member
Good morning.

I am rebuilding/repairing a KA-6100 Integrated Amplifier. I have replaced all of the electrolytic caps and verified that they are correctly oriented. When I switch on the power, I immediately blow fuses Fm2 and Fm4. I suspect from reading another thread that one or more of the rectifier diodes (Dm6, Dm8, Dm10, Dm12) has gone bad.

The schematic lists part numbers U08C and S2V20 for these diodes. I can't find anything similar to U08C, and I can only find a Shindengen S2V20 at Mouser which is special order only. Can anyone recommend a good replacement for these diodes, preferably one that has similar packaging and appearance.

Thank you,
Jay
 
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Was the amplifier working properly before the replacement of the electrolytic capacitors? The diodes can be tested with a DMM (the measurements can be compared to diodes in the working channel).
 
The diodes should be isolated from the filter caps for testing.

You can use any moderately fast power rectifier for that purpose. A 400 or 600V PRV, 4A medium-fast diode should be suitable, like the STTH4L06 or similar.
 
I suggest that until the fault is resolved, the amplifier be only powered on while on a Dim Bulb Tester (DBT); there is are a few AK threads describing how to build one. It is also posible that output transistors have shorted and this causing the fuses to blow; the output transistors can be removed for testing with a DMM.
 
Watthour said:
The diodes should be isolated from the filter caps for testing.

You can use any moderately fast power rectifier for that purpose. A 400 or 600V PRV, 4A medium-fast diode should be suitable, like the STTH4L06 or similar.
Click to expand...

I removed the power rectifier diodes and tested them using the diode test mode on my multimeter. They all read about 600mV in one direction and OL in the other. I think that means they are OK.
 
Leestereo said:
I suggest that until the fault is resolved, the amplifier be only powered on while on a Dim Bulb Tester (DBT); there is are a few AK threads describing how to build one. It is also posible that output transistors have shorted and this causing the fuses to blow; the output transistors can be removed for testing with a DMM.
Click to expand...
I removed the output transistors and tested them using the diode test mode on my digital multimeter. The voltage from base to emitter in one direction is about 600mV and OL in the other (all 4 the same). I couldn't figure out where the collector connection is withe the transistor removed.
 
JayWFletcher said:
I removed the output transistors and tested them using the diode test mode on my digital multimeter. The voltage from base to emitter in one direction is about 600mV and OL in the other (all 4 the same). I couldn't figure out where the collector connection is withe the transistor removed.
Click to expand...
the case!
 
Hi Jay,
I had a similar problem, and the fault was in Qm20. Also check Qm22.

In case you decide to change the diodes U08C, I used the SBYV28-200 as substitute.
 
Hello,

I'm still working on this amplifier and still having problems getting it to power up. I built a dim bulb tester following the instructions at https://audiokarma.org/forums/index.php?threads/dim-bulb-tester-build-and-how-to.808399/.

I'm looking for some help to troubleshoot why I keep blowing fuses when I try to power up the amp. Note that the fuses don't blow when I use the DBT, but the power relay doesn't click either.

I have replaced the following capacitors (including upgrades in the phono section based on Leestereo's article at https://audiokarma.org/forums/index.php?threads/leestereos-restoration-upgrade-of-a-ka-6100.945702/). Note that some of the electrolytic caps were part of a kit I bought on eBay and are rated at higher voltage than required and/or are not audio quality caps. I plan to replace these after I solve my fuse problems. I have learned a lot during this project.

Cd1,2 C322C151K3G5TA KEMET 150pF, ±10%, C0G Temp Coeff
Cd3,4,7,8 16SEPC220MD Panasonic 220mF, 16V, low ESR
Cd7,8 16SEPC220MD Panasonic 220mF, 16V, low ESR
Cd9,10 UVP1C471MPD Nichicon 470uF, 16V, Bi-Polar
Cd11,12 RFS-25V100MF3#5 Elna 10uF, 25V, Bi-Polar
Cd13,14 BFC237524121 Vishay 120nF, 400V, Film, Polypropylene, metalized
Cd15,16 FKP2C023301L00HSSD WIMA 33nF, 63V, Polypropylene, 2.5%
Cd17,18 C315C102F5G5TA KEMET 1nF, 50V, C0G Temp Coeff, 1%
Cd25-26 EEH-AZS1V331B Panasonic 330uF, 35V, low ESR
Cd27 C410C473Z5U5TA KEMET 0.047mF, +80%, -20%, Axial
Cm3,4 UFG1A221MPM1TD Nichicon 220 µF 10 V Aluminum Electrolytic Capacitors Radial, Can - 1000 Hrs @ 85°C
Cm5,6 RFS-25V101MH4#5 Elna 100 µF 25 V Aluminum Electrolytic Capacitors Radial, Can - 1000 Hrs @ 85°C
Cm7,8 UKT1E4R7MDD Nichicon 4.7 µF 25 V Aluminum Electrolytic Capacitors Radial, Can - 1000 Hrs @ 105°C
Cm11,12 105CKE100M Illinois Capacitor 1 µF 100 V Aluminum Electrolytic Capacitors Radial, Can 132.63Ohm @ 120Hz 2000 Hrs @ 105°C
Cm13,14 UPW1H4R7MDD Nichicon 4.7 µF 50 V Aluminum Electrolytic Capacitors Radial, Can - 2000 Hrs @ 105°C
Cm15,16 476CKR050M Nichicon 47 µF 50 V Aluminum Electrolytic Capacitors Radial, Can 2.822Ohm @ 120Hz 2000 Hrs @ 85°C
Cm21~24 105CKE100M Illinois Capacitor 1 µF 100 V Aluminum Electrolytic Capacitors Radial, Can 132.63Ohm @ 120Hz 2000 Hrs @ 105°C
Cm25,26 476CKR050M Nichicon 47 µF 50 V Aluminum Electrolytic Capacitors Radial, Can 2.822Ohm @ 120Hz 2000 Hrs @ 85°C
Cm27,28 106CKR063M Illinois Capacitor 10 µF 63 V Aluminum Electrolytic Capacitors Radial, Can 16.579Ohm @ 120Hz 2000 Hrs @ 85°C
Cm41,42 UML1H3R3MDD Nichicon 3.3 µF 50 V Aluminum Electrolytic Capacitors Radial, Can - 1000 Hrs @ 85°C
Cm45,46 UKW1H470MED Nichicon 47 µF 50 V Aluminum Electrolytic Capacitors Radial, Can - 2000 Hrs @ 85°C
Cm47,48 UKW1H470MED Nichicon 47 µF 50 V Aluminum Electrolytic Capacitors Radial, Can - 2000 Hrs @ 85°C
Cm53,54 UKW1H470MED Nichicon 47 µF 50 V Aluminum Electrolytic Capacitors Radial, Can - 2000 Hrs @ 85°C
Cm55,56 UKW1H470MED Nichicon 47 µF 50 V Aluminum Electrolytic Capacitors Radial, Can - 2000 Hrs @ 85°C
Cm61,62 UKW1H470MED Nichicon 47 µF 50 V Aluminum Electrolytic Capacitors Radial, Can - 2000 Hrs @ 85°C
Cm67~70 RPE682M50V Elna 6800mF 50WV Aluminum Electrolytic Capacitor
Cm71,72 105CKE100M Illinois Capacitor 1 µF 100 V Aluminum Electrolytic Capacitors Radial, Can 132.63Ohm @ 120Hz 2000 Hrs @ 105°C
Cm81 UES1C101MPM1TD Nichicon 100 µF 16 V Aluminum Electrolytic Capacitors Radial, Can - 1000 Hrs @ 85°C
Cm82 RFS-25V101MH4#5 Elna 100 µF 25 V Aluminum Electrolytic Capacitors Radial, Can - 1000 Hrs @ 85°C
Cm83 106CKR063M Illinois Capacitor 10 µF 63 V Aluminum Electrolytic Capacitors Radial, Can 16.579Ohm @ 120Hz 2000 Hrs @ 85°C
Cm84,85 RFS-35V221MI6#5 Elna 220 µF 35 V Aluminum Electrolytic Capacitors Radial, Can - 1000 Hrs @ 85°C
Cm86~89 RFS-25V101MH4#5 Elna 100 µF 25 V Aluminum Electrolytic Capacitors Radial, Can - 1000 Hrs @ 85°C

Following the initial startup and burn out of fuses F2 and F4, I replaced the following diodes and transistors:

Dd1~4 1N457TR Diode Standard 200 V 800mA Through Hole Axial
Dm1,2,13,14,19,20 1N457TR Diode Standard 200 V 800mA Through Hole Axial 1N4148
Dm3,4 1N34A Diode Standard 65 V 50mA Through Hole DO-7
Dm5-12 SBYV28-200 Diode Standard 200 V 3.5A Through Hole DO-201AD
Dm16,17 1N5253B-TR Zener Diode 25 V 500 mW ±5% Through Hole DO-35 (DO-204AH)

Qm19,20 KSA1381ESTU Bipolar (BJT) Transistor PNP 300 V 100 mA 150MHz 7 W Through Hole TO-126-3
Qm21,22 KSC3503DS Bipolar (BJT) Transistor NPN 300 V 100 mA 150MHz 7 W Through Hole TO-126-3
Qm23,24 MJ15015 Bipolar (BJT) Transistor NPN 120 V 15 A 6MHz 180 W Through Hole TO-3
Qm25,26 MJ15016 Bipolar (BJT) Transistor PNP 120 V 15 A 18MHz 180 W Through Hole TO-3
Qm29 MJE15032 Bipolar (BJT) Transistor NPN 250 V 8 A 30MHz 2 W Through Hole TO-220
Qm30 MJE15033 Bipolar (BJT) Transistor PNP 250 V 8 A 30MHz 2 W Through Hole TO-220

I installed the new output transistors with new mica insulators and Dowsil 340 heat sink compound.

I was pretty confident that replacing all of these diodes and transistors would eliminate the problem, but when I tried to power it up again without the DBT, fuses 1, 2, 3, and 4 all burned.

I now have the amp connected to the DBT. When I turn the power on the VU meters light up, but the relay does not click. I have about 11VDC across the rectifier diodes (Dm5~12).

I have tried to follow the troubleshooting procedure in this thread https://audiokarma.org/forums/index.php?threads/blown-fuse-on-ka-6100-upon-power-up.816919/page-2, but the voltages are different because I'm running on a DBT.

I have checked all of my solder joints and they seem solid.

Is there a procedure I can follow to isolate the problem?

Thanks for any help you can provide.
Jay
 
You will need to come out of protection on DBT.

You will notice the voltage will be lower but consistent.

I like to fix the amp before recapping.

Check power supply voltage, the rail voltages on the power amp section, rail voltages on the preamp section...

Do you know which channel is causing the problem? If you don't know how to find out, say so.
 
I just checked the schematic. Measure the voltage at Rm131 to ground. And at Rm132 to ground. Post results ( in a few words).
 
rickl said:
You will need to come out of protection on DBT.

You will notice the voltage will be lower but consistent.

I like to fix the amp before recapping.

Check power supply voltage, the rail voltages on the power amp section, rail voltages on the preamp section...

Do you know which channel is causing the problem? If you don't know how to find out, say so.
Click to expand...

I still have it hooked up to the DBT. I assume the rail voltages are the potentials across the rectifier diodes? If so, they are about 10.75VDC across Dm5,7,9,11 and 11.08VDC across Dm6,8,10,12.

On the preamp board I have the following voltages relative to pin 3 (and)

Pin 1 -10.12VDC
Pin 2 +10.05VDC
Pin 4, 5, 6 0VDC

I don't know which channel is causing the problem, and I don't know how to find out.
 
rickl said:
I just checked the schematic. Measure the voltage at Rm131 to ground. And at Rm132 to ground. Post results ( in a few words).
Click to expand...

Rm131 to GND is -0.009VDC
Rm132 to GND is -0.014VDC

These are both measured on the other side of the resistors from Dm20.
 
rickl said:
If this is correct, looks like you found the problem.

Good job!
Click to expand...
Are you saying that Rm131 and Rm132 are bad? The other sides of Dm131 and Dm132 (the Dm20 side) are essentially at ground.

The other thing that doesn't seem right is that the voltage from ground to the collectors of Qm31 and Qm28 is 10.75VDC. The schematic says it should be 0.7VDC. Scaling every thing down by about a factor of 4 due to the DBT, this voltage should be 0.175VDC. I replaced Dm15 and this did not change.
 
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