Bottlehead Forum
Bottlehead Kits => Crack => Topic started by: jmineart on August 31, 2015, 04:48:28 PM
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After having my Crack+speedball working for several months I moved into a new place and into the basement. This room can be humid at times which I don't know if that could be a factor.
Yesterday it was working great. Using it today however, only the left channel is is working but is quiet and at louder levels become distorted. On the speedball upgrade the LEDs located on the big board near the top do not light up and the top most led on attached to the small tube does not light up. I checked the voltages and at a glance they seemed to be a fraction of what they should be. Also, the top most resistor that spans across the big power block (forgot it's name) becomes extremely hot which I do not remember if this is normal or not. I can provide pictures if needed, thank you.
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Please post your voltages.
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In process of checking voltages the resistor that spans 13 to 15 started smoking.
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In the case of the voltages, what I could read was a rising voltage on terminal 1 and 2 starting at ~100mV. No reasonable readings on any others I managed to try. Also, when turning on the crack, the top most led on the small tube lights up initially then slowly dims out.
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You should go back and do your resistance measurements again. You might also want to post pictures of the underside.
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For all values of zero. The meter starts at zero, raises to ~4 ohms and then falls to ~1 ohms eventually. When touching the probe together a similar situation occurs raising to 3 then falling to around .5 ohms so I'm assuming these values are basically zero and is the meter's fault.
Terminal Resistance
1 *
2 *
3 0 ohms
4 *
5 *
6 2.5K ohms
7 ~1 ohms
8 0 ohms
9 Overload- somtimes a number starting at 100K that raises to an overload.
10 2.51K ohms
12 0 ohms
13 starts at 1.3M ohms then drops
14 0 ohms
20 0 ohms
22 0 ohms
B3 0 ohms
B6 overload same as terminal 9
RCA jacks:
Ground lug 0 ohms
Center pin 93.1k ohms
I did install the blue capacitors on the wrong side of the board but their lead locations are in the correct place so I do not believe that it is an issue but will change if so.
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Having troubles with pictures
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only letting me post one at a time
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More
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7 ~1 ohms
This suggests an improperly mounted TIP50 transistor (check the directions in the manual, specifically regarding the fiber shoulder washer and transistor insulator).
-PB
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I can get you close up pictures on how they are secured but I can not for the life of me tell the difference from the manual. However, screwing and unscrewing results in a reading of overload before the unit is turned on. Then all of the lights turn on when the amp is powered on, however they soon go out and when I check the resistance after it is back to zero. Actually it seems like after some time it goes back to having the overload charge.
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What do you know. I loosened the screw just a tad on the uppermost TIP50 transitor and now it works like a charm. All of the voltages check out. Weird that this problem sprung out of the blew. Thank you very much for your help!
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sorry for being premature there, was just a temporary fix. If there are any ideas why it is being so finicky or any more pictures or needed just let me know. I will keep tinkering with it.
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The heat sink at the front is clearly mounted incorrectly. There are two "bumps" visible below the screw head, and there should only be one. The shoulder washer must have its ridge seated in the hole of the TIP-50—this isolates the screw (and therefore the heatsink) from the transistor. Most likely the second bump is the lock washer that should be on the other side of the sink.
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Good catch! That seems to have it working again. I will give it a day again to see if it stays working but thank you very much in the mean time!
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Good eyes, Josh!