Today the power supply for my KBL went up in smoke and blew the fuse. There's a completely burnt resistor and a shorted diode on the board. The associated regulator transistors (15030 and 15031 pairs) seem to be OK (they're not open, not shorted based on testing with ohmmeter) . Unfortunately I haven't been able to find a schematic. The design seems to be dual pwr supplies with seperate transformers, each is balanced and just differ in voltage. My repair strategy is this:
Any comments would be very welcome. Thanks in advance.
- Replace the toasted parts (resistor, diode).
- Replace corresponding components on the 'mirror' side of the circuit as well
- Also replace ALL the electrolytic capacitors since the unit is about 20 years old. Since the unit is disassembled it's not that hard.
- Leave regulators alone since they seem to be ok.
Any comments would be very welcome. Thanks in advance.
I would try and find the cause of the fault first and only work on the faulty channel before touching the other side.
A complete electrolytic Recap is a good idea and not that expensive if you spend time sourcing replacements.
The Regulators if working are likely to be OK, but if cheap and from a good source, why not replace them or see if there is a better alternative?
I replaced all my Caps in an ML no380 pre amp with superior products for less than £100.
All of my caps have lower ESR and longer life than the originals, except for 4 caps, which were Vishay and were already top spec, so I put new versions of the same.
Sounds better than ever now.
Good Luck
A complete electrolytic Recap is a good idea and not that expensive if you spend time sourcing replacements.
The Regulators if working are likely to be OK, but if cheap and from a good source, why not replace them or see if there is a better alternative?
I replaced all my Caps in an ML no380 pre amp with superior products for less than £100.
All of my caps have lower ESR and longer life than the originals, except for 4 caps, which were Vishay and were already top spec, so I put new versions of the same.
Sounds better than ever now.
Good Luck
Thanks for the suggestions and advice. What I think I'll do is go ahead and replace all the caps, and the diodes/regulators on the blown channel (on both legs of the circuit so components are better 'matched'). Getting the regulators out is a bear because the heat sinks are soldered to the board so I'm not inclined to just replace them all.
I found all the components at Parts Connexion and Newark Electronics.
I'll take detailed pix of the board to trace the circuit for a schematic at some point. Unfortunately this part of the project will get added to my 'do someday' project list. I'd like the schematic too, but it will have to wait for a few cold winter nights.
I found all the components at Parts Connexion and Newark Electronics.
I'll take detailed pix of the board to trace the circuit for a schematic at some point. Unfortunately this part of the project will get added to my 'do someday' project list. I'd like the schematic too, but it will have to wait for a few cold winter nights.
@rwwear: Thanks. I can see a few of the transistors have a note of which type it is. However, the other small signal types seems to be missing. Are they the usual 2SC2240BL/2SA970BL as used in other Krell products of the same age?
@kamis: Sorry, for some reason I have either missed or not received notification that you had answered. I have the PAM3 schematic somewhere around here. I will try to find it and scan it. It might take a few days.
Cheers,
Mogens
@kamis: Sorry, for some reason I have either missed or not received notification that you had answered. I have the PAM3 schematic somewhere around here. I will try to find it and scan it. It might take a few days.
Cheers,
Mogens
Sorry Mogens for any inconvenience but this is the schematic my friend at Krell sent me. He told me it was crude but all they have. I will ask him if he can supply the information as I see there is no parts lists either. I would also like to know which diodes were used. My KBL PS released some of it's magic smoke also and he wants me to send it to him and let him evaluate it and I'll recap it myself.
Thanks for this. I since repaired everything and the KBL has been working fine ever since. But who knows what may come next? Great info.
no idea I'm afraid. But I'll open it up and have a look when I get a chance over the next week or so. I'll post what I find out.
This afternoon I opened it up to have a look. The LED indicator has grown very dim over the years so I'll be replacing that.
Anyway, I did indeed replace ALL the electrolyic caps. The brands were a grab bag, almost certainly as a result of what I could find out there. There was no special rhyme or reason to it. I do recall that in a few cases I went to higher voltage ratings. I found these brands:
- Nichicon Fine Gold,
- Nichicon Muse
- Nippon Chemi-Con
- Audio KA(M)
Thanks Raueda.
I was really interested in the diodes and regulators. Maybe none needed replacing?
For sure, I did replace someof the diodes and 2 of the regulators. But - it's very hard to see which and now I have no clear idea why. One or 2 were clearly blown but not all. As best I can recall I just replaced stuff in a more or less symetrical way. It seemed to work.
InFor sure, I did replace someof the diodes and 2 of the regulators. But - it's very hard to see which and now I have no clear idea why. One or 2 were clearly blown but not all. As best I can recall I just replaced stuff in a more or less symetrical way. It seemed to work.
Thanks a lot for taking the time to check.
Robt.
Here are the parts Krell replaced in my KBL Power Supply.
02 - TRANS,15030 PWR TO220
01 - 1N 5360 Zener Diode
14 - CAP, EL RD 470UF 20% 100V
02 - CAP, ELEC RD 100UF 100V
02 - CAP, ELC RD 1000UF 20% 25V
01 - LED, BLUE 5MM ROUND
We confirm unit will not power up due to failed FET transistors (2) and
zener diode (1) in power supply. Failure of these components caused
by worn capacitors (18) in power supply. Main power LED weak, needs
to be replaced.
02 - TRANS,15030 PWR TO220
01 - 1N 5360 Zener Diode
14 - CAP, EL RD 470UF 20% 100V
02 - CAP, ELEC RD 100UF 100V
02 - CAP, ELC RD 1000UF 20% 25V
01 - LED, BLUE 5MM ROUND
We confirm unit will not power up due to failed FET transistors (2) and
zener diode (1) in power supply. Failure of these components caused
by worn capacitors (18) in power supply. Main power LED weak, needs
to be replaced.
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