Bad output device? |
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AJordan
Young Croc Joined: 06 July 2007 Status: Offline Points: 1013 |
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OK, so I did all that and powered it up. Got about five seconds of loud hum then it started to crackle so I turned it off. The fuses are still intact.
That cable must have been loose for quite a while, it didn't reach to the HF driver terminal. I had to take out the LF and rotate it to make the cable reach. Anyway here are some pics. https://www.dropbox.com/s/5h1mdeo2xcxddyn/IMG_6017.JPG?dl=0 https://www.dropbox.com/s/fwndzw6xe9yxyv8/IMG_6018.JPG?dl=0 https://www.dropbox.com/s/cauk27wmm48hsek/IMG_6023.JPG?dl=0 |
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Hemisphere
Old Croc Joined: 21 April 2008 Status: Offline Points: 2272 |
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Guitar monitor has tweeter unplugged, musician doesn't notice shock!
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jbl_man
Moderator Group Joined: 12 January 2005 Location: London. Status: Offline Points: 11154 |
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Disconnect the speaker, put your voltmeter accross the output terminals,DC setting,what does it read?
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Be seeing you.
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AJordan
Young Croc Joined: 06 July 2007 Status: Offline Points: 1013 |
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LOL to be fair it was a bass. |
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AJordan
Young Croc Joined: 06 July 2007 Status: Offline Points: 1013 |
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27.2 and still not blowing the fuses. |
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Muckerbarnes1
Old Croc Joined: 20 March 2010 Location: Stroud Status: Offline Points: 2654 |
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If you have 27V on LS o/p don't put speaker back in circuit. The crackling and hum you describe and assuming your check of o/p devices is correct, suggests to me the bridge rec is duff. As previous, take it out and test it.
Check as before with your DVM, also check it in high resistance setting for reverse reading, often a diode can read ok on those gadgets, but show it's fault with a resistance in reverse, where there should be none at all. If there is a cracking from the PCB, something will be getting hot. I would of thought you'd have found this easily. Oh, and pictures...
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Billy Dawg.
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AJordan
Young Croc Joined: 06 July 2007 Status: Offline Points: 1013 |
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Cheers Muckerbarnes1! No I won't reconnect speaker, I know DC aint good for voice coils. Crackling sound was from speaker. Funilly enough, the bridge rec was one of the first things I tested because it looked as though the heatsink paste had been melting. But, I tested it in circuit and as I am learning from testing the transistors that is not always an accurate test. Will pull it out tomorrow and try the tests you suggested. Cheers!
Oh, and pics should be a few posts back up. Edited by AJordan - 05 April 2018 at 10:32pm |
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AJordan
Young Croc Joined: 06 July 2007 Status: Offline Points: 1013 |
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Rectifier is out and tested. In diode test I'm getting between 700 and 720. Testing resistance I am on the 2000K scale and getting between 1300 and 1950 forewards. and open circuit reverse. Does that sound good or bad?
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simonp1100
Young Croc Joined: 01 September 2008 Location: Bristol Status: Offline Points: 1103 |
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Try the below things:
1. Have you check transistor isolation between the metal heatsink and the collector (can / case) of each transistor after you fitted them back in, these should be isolated. 2. The voltage that you are getting on the speaker output, is it a positive reading or a negative reading (with negative of your meter going to the ground) & also what is the voltage across each main power supply cap ???. 3. Check each output transistor emitter resistor (R22 ohms). Check ALL diodes on BOTH boards 4. They is also a +15 & -15 volt supply that is going from the main board to a small daughter board via two 1K wirewound resistors to supply a op-amp, is this voltage there ??? (measure across each zener diode (15V approx) or if not each 1K wirewound resistor on one end should have 15V approx 5. What is the chip number ???. Edited by simonp1100 - 06 April 2018 at 10:11pm |
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AJordan
Young Croc Joined: 06 July 2007 Status: Offline Points: 1013 |
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Will try all those after work tomorrow and report back
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MattStolton
Old Croc Joined: 04 September 2010 Location: Walthamstow Status: Offline Points: 4234 |
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When reinstalling the O/P mossies, did you put the right one in the right place. PNP Vs NPN (mossies gates drains mewh, but you get my point)
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Matt Stolton - Technical Director (!!!) - Wilding Sound Ltd
"Sparkius metiretur vestra" - "Meter Your Mains" |
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Muckerbarnes1
Old Croc Joined: 20 March 2010 Location: Stroud Status: Offline Points: 2654 |
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It's 2x NPN bipolar as in the OP. No FETs.
The fwd test on the BR of 0.7 and nowt in reverse; Was this the same on all 4 diodes in the BR?
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Billy Dawg.
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