Is there a B&K 470 doctor in the house?

Doughbroz

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Before I ship this thing off for repairs, maybe someone can point me in the right direction. It allows me to set the heater voltage and test for leaks, but that's as far as it goes. Go to set G1 voltage and the needle never moves. Power LED is not lit, but is getting 3 VAC. Input to wiper stack is 120 VAC. Output to G1 adjustment pot is 33 VAC, all legs of that pot read 33 VAC to ground regardless of pot adjustment. Reading between any combination of the pot legs is zero regardless of pot adjustment. R7 pot on board is roughly 15 VAC on both legs. Both large ceramic resistors on board are roughly 6 VAC on both ends. Every wire from the transformer is putting out AC voltage, most in the 40 to 60 volt range, one going to the board is 230 volts, which surprises me a little. Solder all looks good, no bulging caps or darkened components, this thing looks darn near new. So, any ideas appreciated as always.
 
Test the pots for resistance. Do they vary or not? It sounds like the G1 adjustment pot is shorted.

Off the top of my head I don't remember what that pot is rated for, but the schematics will give you that info.
 
The G1 pot does vary in resistance from zero to infinity, but it seems odd that the voltage through it does not vary at all with the power on. I'm also wondering if the 33 VAC it is getting from the wiper stack is correct. I don't have a schematic for it. Any source available other than the manufacturer? Thanks for the reply.
 
The G1 pot does vary in resistance from zero to infinity, but it seems odd that the voltage through it does not vary at all with the power on. I'm also wondering if the 33 VAC it is getting from the wiper stack is correct. I don't have a schematic for it. Any source available other than the manufacturer? Thanks for the reply.


The pot should not go to infinity.
 
Doughbroz, is it hard to remove the 470's guts from its case? I was thinking of checking mine over for bad solder and maybe changing caps, but I don't see how it comes out of the case. Also, if you don't mind me asking, where were you looking to send it for repair? From what I've seen at B&K's site (thanks again Ken for that link) they don't work on anything that's been discontinued for more than 7 years.
 
I *THINK* they said its like a $100 or so (maybe 125?) flat rate repair service, and they would still service it. This was several months ago, like last summer.

Making myself a note to see if I have that file when I get home.
 
Remove the screws holding the rubber feet and the unit lifts out of the case. Bought it off ebay for $48 after failing to get a 467 for twice that amount. Sounds like a new G1 pot is next on my list. Thanks for the replies, everyone.
 
I just love electronic shit that fixes itself. Yesterday I did some more checking on this thing. It has been lying untouched on a table since last week. Turned it on, checked a few voltages, turned it right side up and the power LED was lit. WTF. Hooked it up to a tube, ran it through all the tests, and it works perfectly. I did not do a single thing differently that was not done a dozen times already, went through all the steps exactly as before, and no amount of tapping and shaking will make it malfunction. I guess I'm happy it's working, but sometimes I just wonder if the electronic gremlins decided it was time to go and screw with someone else.
 
I just love electronic shit that fixes itself. Yesterday I did some more checking on this thing. It has been lying untouched on a table since last week. Turned it on, checked a few voltages, turned it right side up and the power LED was lit. WTF. Hooked it up to a tube, ran it through all the tests, and it works perfectly. I did not do a single thing differently that was not done a dozen times already, went through all the steps exactly as before, and no amount of tapping and shaking will make it malfunction. I guess I'm happy it's working, but sometimes I just wonder if the electronic gremlins decided it was time to go and screw with someone else.
It is nice when things start working out of the blue. :) Thanks everyone for also confirming how to remove the guts from the case on these things. It figures it would be something simple.
 
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