tmsears
Active Member
This thread has gotten so confusing.
If there is anyway if cleaning it up to make it less "family circus" I would be happy to hear them for sure.
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This thread has gotten so confusing.
Well, somehow the AC coming out of the DC outputs of the (new) rectifiers is now DOUBLE what it was before I replaced them. This doesn't make any sense...
I'm thinking your AC issue is a wild goose chase..
Hilarious video, I needed that.
But what could be causing this? You don't think whatever is causing this in the power supply?
Not sure if you've gone over the boards but this particular amp was the most solder cracked piece I've ever worked on. If yours is anything like this it could very well be some of your problems.
Maybe a recap of where you are now and what symptoms you're going after would help everyone catch up. Since this is a general thread there have been a bunch of posts in between so it's a bit hard to follow.
Well, in my quest for solving my hum issue, I really screwed up.
I went ahead and tried the old "swap the main input signal cable with a input jack cable" after coming up empty handed with the hum problem. I figured if I was gentle and didn't push any components into each other I would be OK to try. I was wrong, I guess.
I plugged the tape 1 input cable into where the preamp cable normally goes into the main board, and powered it up with the DBT in circuit. The DBT, on 150 watt bulb, started to pulse so, I figured I had shorted something...again.
I checked all the components on the phono/eq board to see if I shorted anything there, as that is what happened last time. Everything checked out OK.
Unplugged the tuner cable from the main amp, checked it with nothing plugged into that socket. The DBT bulb once again pulsed, and the relay would not click on. This was expected, and I did it just to be sure, as I had not plugged the preamp out cable back in, I figured, why not check since the DBT is connected.
So I plugged everything back in the way it is supposed to be, with the unit still on the DBT. The relay takes a little while to come on, but on lower voltage, I expected as much. I turn up the volume to check for hum, and of course it is still there.
I unplug the unit from the DBT, and do a visual inspection. Everything looks good. I turn the unit back on. The Relay clicks on. Unit has volume I guess, halfway? Idling.
I start watching a you tube video since the screen is right next to the amp.
A few minutes go by, and I hear the sizzling, crackling noise. I turn my head think, "what the hell?", just in time to see a resistor, R230, Light up like a white Christmas tree light...
I turned the amp off as fast as I could. The coils (of nichrome?) that make up the resistor were pretty to watch cool down.....
The Repair Attempt:
All of the above were replaced with the correct substitutes, or uprated equivalents. I can go back into the amp and provide part numbers if necessary, but I did not think to make a replacement parts list at the time.
Also at this time I corrected a factory diode error for the 22 volt supplies on the eq board as indicated in post #206.
I got all the parts in, hooked the amp back up to the DBT, and…no click. There was a parts mismatch (see post#228). I contacted B&D and they sent me the correct parts free of charge. Swapping the correct parts in unfortunately did not remedy the problem. I then started comparing readings between both channels to see if I could find a discrepancy, but I was unsuccessful. After receiving some guidance The rail voltages were checked, with the following results:
LP+ 33.5
LP- 33.5
RP+ 49.2
RP- 33.5
D164 was suggested as a possible cause for the difference between RP+ and RP-.
Upon further instruction, AC presence was checked for at the output collectors, and this was the result:
LP+ 73.8
LP- 0
RP+ 107.9 <------The 49.2 Vdc one
RP- 0
Upon additional instruction, I checked D168,D162,D163,D164,D165,and D166, out of circuit, and they all tested good (see post#296).
Then it was suggested to test the components inside the triangle in the schematic in post #285:
View attachment 1085361
I measured these components against their counterparts in the working channel and they were identical, so I think those can be ruled out. I then checked for AC voltages as suggested in the same post (#285) and the following was the result:
AC coming out of the secondaries:
RE= 47.6V
BL= 0v (reference)
BE= 28.2
DC Rail Voltages (with ac present as noted):
HB+ 57.9Vdc and 128.2Vac
HB- 57.9Vdc
LB+ 34.3Vdc and 75Vac
LB- 34.5Vdc
DSC -30.2Vdc
LX/LP+ 33.8Vdc and 74.3Vac
LX/LP- 33.8Vdc
RX/RP+ 49.7Vdc and 109.6Vac
RX/RP- 33.9Vdc
22+ 21.5Vdc and 47.1Vac
22- 14.5Vdc
With those issues noted, I was instructed to check into the +- 22v further, by making sure there was -9V at the junction of D606 & D604, and -15V at the junction of D602 & D604. The results were:
At the junction of D606 & D604 = -4.6Vdc
At the junction of D604 & D602 = -9.2Vdc
I then verified that the diodes were correct, and correctly installed (to my knowledge) . Then I was told to measure the resistance of R759, and it was determined that it was failing (post#316). On my own volition, I replaced R759 and both bridge rectifiers. The rectifiers were both replaced with two BR62’s..which Only served to DOUBLE the AC coming out of the outputs! WUT?!
As It Stands Today:
After the repair attempt failed I put the unit away so I could get ready for the holidays and work on my main system. Having recapped and tuned up those units, I am now turning my gaze back onto the A-1000. This summary should get the thread back up to speed. Hopefully with some help, I can get this baby up and running, because my main system still had some issues that need attention.