Salas hotrodded blue DCB1 build

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mrWagner

Member
Joined 2006
Got 20 2sk170 measured them through 500 ohm. 9V batt.
Results(mA):
7.345;7.545;7.545;7.565;7.864;8.224;8.244;8.323;8.762;8.603;8.623;8.802;8.842;8.962;9.062;9.301;9.461;10.28;10;14(probably dead?)
Any pairs I should use?

The leds I got measured with 1kohm between 1.94-1.95V but most 1.943-1.945V.
 
F

freeman

Member
Joined 2010
freeman said:
Hi all, just completed my dcb1 and everything seemed fine until I hooked up the output connector. Voltage readings are very good 10.36 and -10.42 and offset readings are 2.4/1.5mV. All leds light normally. Hooked up I/O connectors and fuse blew. I notice that there is continuity between left, right, and ground terminals on output. Has anyone experienced this? The relay clicks normally but I wonder if it is damaged. There doesn't seem to be excessive heat anywhere.

Components seem to be installed correctly and there appear to be no solder bridges. My rca connectors are isolated from chassis and installed correctly. I will try to post photos shortly. I would appreciate your advice. Thanks so much.
Click to expand...

the fuse is rated at 1 amp 250v. I tested first without I/o connected. then I connected the molex connectors to rca's only. no external inputs or outputs were connected. the dcb1 seems to idle happily until I connect the molex output. :confused: the transformer is antek 15v 50va.
 

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Salas

Salas

diyAudio Chief Moderator
Joined 2002
Paid Member
freeman said:
the fuse is rated at 1 amp 250v. I tested first without I/o connected. then I connected the molex connectors to rca's only. no external inputs or outputs were connected. the dcb1 seems to idle happily until I connect the molex output. :confused: the transformer is antek 15v 50va.
Click to expand...

Check there is no continuity between MOSFET tabs to chassis first. Maybe something contacts as you press down to fit the molex, either at the MOSFETs or blob of excess solder on board. Should be mechanical. Use all screws, do continuity checks, see for wire strands at the Tx connector. Its the first time we see that so its old Murphy got you.
 
Salas

Salas

diyAudio Chief Moderator
Joined 2002
Paid Member
mrWagner said:
Got 20 2sk170 measured them through 500 ohm. 9V batt.
Results(mA):
7.345;7.545;7.545;7.565;7.864;8.224;8.244;8.323;8.762;8.603;8.623;8.802;8.842;8.962;9.062;9.301;9.461;10.28;10;14(probably dead?)
Any pairs I should use?

The leds I got measured with 1kohm between 1.94-1.95V but most 1.943-1.945V.
Click to expand...

Use the 7.545 pair and the 8.244 pair per channel for the audio signal inline quad. Transconductance won't be much different while the offset will be fine. The little current gain diff will be swamped by the 100% local feedback and the THD will be practically the same between channels.
 
D

davym

Member
Joined 2013
RE Freemans build. Is it a slow blow fuse which blew?

What I can see of the build looks ok to me, except for the MOSFET next to the power on LED, it looks like it's been partially scorched.

Can you do a comparison test between it and it's opposite on the other channel?

Also some pictures of the underside of the board might help pin this down.

EDIT should you not have a heatsink bolted to that regulator?
 
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freeman

Member
Joined 2010
davym said:
RE Freemans build. Is it a slow blow fuse which blew?

What I can see of the build looks ok to me, except for the MOSFET next to the power on LED, it looks like it's been partially scorched.

Can you do a comparison test between it and it's opposite on the other channel?

Also some pictures of the underside of the board might help pin this down.

EDIT should you not have a heatsink bolted to that regulator?
Click to expand...

Hi Davym. It's a fast blow 1amp fuse. The fet doesn't seem scorched to me. Perhaps it is just reflected yellowish light. I did some continuity checking between mosfets and they seem to behave the same. Could you recommend some tests? I could find no connection between board and chassis. I removed the regulator heatsink to trouble shoot. It doesn't get very warm. I'm reading 11.8 volts at first right position of the relay.

I'm getting continuity between all three pins on the output Molex, but indirect continuity (one short beep) when I power up. Does that seem normal? Can you recommend tests for the relay? Thanks so much. Regards.
 
F

freeman

Member
Joined 2010
Salas said:
When the pre is off the relay normally shorts each channel output to ground to get them muted. When on, after the click there should be no continuity between tip and ring on the output RCAs.
Click to expand...

Thanks Salas. I cleaned board again. I think it's working now. At least fuses have stopped blowing. One more question if you don't mind. I'm getting continuity between rca outside barrels when powered up between input and output. No continuity between rca centers only grounds. Does that seem ok? Thank you. Kind regards.:)
 
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