stereomour b+ is now negative

howardnair · 2883

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Offline howardnair

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on: November 16, 2011, 01:55:42 PM
this  is in my daughter's stereomour which resides in pa. it is here in nantucket  now- she has informed me j that the power went out overnite prior to the unit not working-the resistance cks are fine-but hv+ is negative-in circuit the diodes ck fine-high resistance one way zero load the other-there appears to be no visible damage-after i eat i am going to ck the power supply caps-out of circuit--any other thoughts would be appreciated-by the way it was on a surge protector but said child informed it was not tripped-not good--howie
« Last Edit: November 16, 2011, 02:03:44 PM by howardnair »


Offline Doc B.

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Reply #1 on: November 16, 2011, 02:04:49 PM
Quote from: howardnair on November 16, 2011, 01:55:42 PM
high resistance one way zero load the other-

That is an indication the rectifiers could be blown. They should read something in the 500 to 1500 ohm range in the low direction if it was still good, but zero ohms could mean it is now a dead short. Rectifiers being taken out by a power spike is not uncommon. It's quite possible that replacing them will fix the problem.

Dan "Doc B." Schmalle
President For Life
Bottlehead Corp.

Offline howardnair

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Reply #2 on: November 16, 2011, 04:13:55 PM
it most likely was  the diodes as they read 6million ohms one way and 0 the other - changed them and still a nice 2.78 negative reading both sides-- it is also the 220 uf caps -they read 2.something nf -the 100uf seem fine reading out of circuit 91uf- but i am going to replace all 4-- is there a optimum value other than 220 uf/250v [which i have] and 100 uf/450v which i need to order-thanks howie
« Last Edit: November 16, 2011, 04:48:53 PM by howardnair »


Offline Doc B.

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Reply #3 on: November 17, 2011, 06:00:15 AM
Have you checked to make sure the high voltage secondary is intact and that the rectifiers are actually getting AC voltage from the power transformer?

Dan "Doc B." Schmalle
President For Life
Bottlehead Corp.

Offline howardnair

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Reply #4 on: November 17, 2011, 09:46:03 AM
doc yes i just did that-have 224 --i cked the 270 ohm resistors-on this amp i did not set it up for 45 and 2a3-just 2a3-so anyway those resistors were reading zero so i put in some 330-those and some new power supply caps -up and running voltages are a little high-- but i have 126 volts in that outlet?????--playing brubeck/take five-- reel to reel through it --how nice tape is-thank you very much for your help-and  thanks for bottlehead and all it is
i ordered anew surge protector-the diodes cked ok on my digital meter but i put new ones in --
not a expensive fix --about 10 bucks but the shipping/packing was 125.00 ouch!!!!!!


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