Bottlehead Forum
Bottlehead Kits => Legacy Kit Products => Crack-a-two-a => Topic started by: schweigc on November 29, 2015, 01:45:38 PM
-
Hi all, I have just done the resistance checks and am getting an "Overload; Range Exceeded" reading on my DMM on the following terminals: 10, 22-24, 26, 27, and 30. Is it safe to proceed to the voltage checks?
-
Yes, those readings just need to not be anything resembling 0 Ohms.
-PB
-
Thanks for the response. I did my Voltage checks and I have some problems. First the LED on A3 does not light and none on the Low Current board and the high current board near the power switch. The Following are my Voltages:
LC Cs4:
IA: 149.5 V
OA: 75.5 V
KregA: 5.9 V
bRegA: 149.5 V
IB: -297 mV
OB: -.71 V
KregB : 1.24 V
bRegB: -294 mV
HC Cs4 (Near Selector Switch)
IA: 205.5 V
OA: 149.5 V
bA: .5 mV
IB: .5 mV
OB: 95 V
bB: 149.5 V
HC Cs4 (Near Power Switch)
IA: 1.5 V
OA: -275 mV
bA: .2 mV
IB: .2 mV
OB: .466 V
bB: - 215 mV
HJ:
Tip: 0
Ring: 48 mV
Any ideas? Thanks,
-
The high voltage just isn't available to one channel.
This starts at IA on the board where you aren't seeing ~200V.
On the lucky end of things, half your amp is working perfectly. Both IA pads wire to B+, what voltage do you measure at terminal 24 vs. terminal 30? If you have very low voltage at one of these terminals, which feeds that flaky IA, and your 270 Ohm resistor isn't smoking, then you have a flaky solder joint preventing the B+ from making it's way to that channel.
-PB
-
One of the 270 Ohm resistors is actually broken. I have some spare resistors (CP-5-3 Mexico 1038 - 270 Ω 5% Dale 5W). Could I replace the broken one with this one?
-
Sure, those ought to work just fine.
-PB
-
Thanks again, the Bottlehead crew is awesome. I'll start the surgery soon...
-
I just replaced the 270 Ohm resistor. Powered it up and the resistor promptly fried. What do I check next?
-
Do you have a backwards 220uF capacitor?
-
No, The striped sides all face the near edge of the Chassis, correct? (Striped side to terminals 25, 31, and 33)
-
Yes, that is correct.
The next step would be to check the connections and jumpers on the large C4S board with the low voltages. Somewhere, there is a jumper that isn't where it's supposed to be, or a connection has been reversed that is creating quite a short in your amplifier.
-PB
-
Ok, I'll check it over. When I find the problem and replace the 270 Ohm resistor again, I will have to clean up the 2 terminal blocks as well. If I damage a rectifier while doing this can I replace it with any UF4007 rectifier? What I have on hand is mouser # 625-UF4007 E3/54.
-
The rectifiers should be fine, you'll just need to find the wiring error that is causing that excessive current consumption.
-
Hello,
I do not know the Crackatwoa, I don't have it.
It might be a good idea to ask a friend to check your amp against the manual. He may find something that you keep missing. A fresh pair of eyes could make a difference.
Richard
-
I have checked the wiring and solder joints and don't see anything obviously wrong. Could this be a bad capcitor, rectifier or resistor? The second time the 270 Ohm resistor blew all LEDs except the one attached to A3 lit until the resistor died.
-
Could this be a bad capcitor, rectifier or resistor?
You can temporarily remove the red going to IA on the big board of the offending side, then check the voltage at the 220uF capacitor after the 270 Ohm resistor that is smoking. In my opinion, you will not find an issue with this testing, but it will eliminate the capacitors, rectifier diodes, and resistors in the power supply.
The second time the 270 Ohm resistor blew all LEDs except the one attached to A3 lit until the resistor died.
It's really important not to fixate on which LED's do and don't light up. You have a short in your amplifier that is drawing enough current to blow up a 5 Watt resistor quite quickly. This would tend to be a significant wiring error or two components touching that shouldn't be.
It can often be helpful to post some photos of your build also, in particular the high current C4S board on the offending side, as well as the small PC board in the middle (top and bottom), and the 7 pin and 8 octal socket.
-PB
-
Thanks again for the quick replies. I will be out of town for the next couple of days, I'll tackle it again with a fresh set of eyes when I get back. If I can't find anything, I'll post pictures. I love my Crack and can't wait to hear this one.
-
I swapped the high current boards and I get the same voltage readings. So I have been focusing on the low current board. I have noticed that the A & B sides are symertrical except for the outboard -reg. On the A side it is attached to 1U but is empty on the B side. Is this accurate?
-
There should be a jumper to -reg. If you didn't have this jumper, you wouldn't have the issues that you're having, but if this jumper isn't in the correct place, it could cause some issues.
Regardless, the C4S that is IA/OA should limit the current drawn from the power supply, which makes me suspicious that there is an error on that PC board.