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crown 5002vz prob


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#1 slickrick

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Posted 27 December 2013 - 11:10 PM

Hi all

I am working on a 5002vz and can not find the problem.Ch/1 singnal stays on with no
signal applied to the input.The owener said the amp will play sometimes.On ch/1 i get
105v on the + and -  ,   On ch/2 i get 71v. Any help for troubleshooting this problem will be appreciated.

#2 joust

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Posted 07 January 2014 - 08:50 AM

Hello Rick,

We'll assume no input or output connections at this point; On power up, only the red ODEP indicators should be lit. If Signal or IOC (Input/Output Comparator) is lit, then you have a problem with the channel. The supply voltage measurements are consistant with an output problem.

First thing I do is verify the solder connections of the output devices on the output module. Once you have removed the output module from its frame, disassemble the two output boards from the output module. Verify the output devices solder connections: I believe you'll find quite a few! At this point, I would do a complete refurb of the two boards: unsolder and remove the output devices, clean them and reapply a light coat of thermal paste to the output device and heat sink, reinstall and resolder the output devices. Locate the thermal sensor and the two bias transistors and refirbish these devices. If the amp should have been in contact with fog machines (you should see contamination on the boards) I would suggest to dismattle the output boards, clean them with water and soap, and dry the boards with either an air compressor or in the oven, @ 150°F until dry. Reassemble the boards.

Of course, since you've done one side, you'll have to refurbish the other output module too. Don't forget to verify and adjust the bias levels! Important!

One other reason for the IOC fault is that the amplifier is not receiving the output signal for the current sense circuit on the termination board. Using an ohmmeter, make sure that the output 'flex bars' make contact with the amplifier's  speaker connections. The flex bar could have been torn from the termination board.

I hope this helps.

Alain

#3 slickrick

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Posted 13 February 2014 - 09:03 AM

thanks for the reply

I re-solder both output module and apply new thermal compound.
Now rail voltage is equal @71v. Ch1 is playing good audio but ch2 has distorted audio.
If i turn the volume (CH2 )all the way up the loc led comes bright and stays bright even when i turn it back down.
At that point i get 1.901mv on the output terminal.That will only happen when a signal is applied
Any idea where the problem could be?

#4 joust

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Posted 13 February 2014 - 09:29 AM

At this point, I would like to 'see' what the distortion is : take out the good ol' oscilloscope and generator, apply a 1 KHz sine signal @ 1.4VAC, flic the sens switch to 1.4V and bring up levels. Verify the output, first without load and then with load (8 ohms preferable, 4 ohms for thermal test). Check with the good side.
Beforehand, make sure that the bias settings are correct, ie. 330mV at the bias TP.
It may be possible, since you discovered problematic solder connections, that the amp is working on perhaps three or two o/p devices, hence the distortion when applying signal. Make sure that the emitter resistors are good. Make sure the sine signal passes well the input stage!
Check the output flex cables, up to the terminal board.
Note : In a refurbishment situation, if the unit passed through fog machines and the like, and the boards are dirty with *beep*, I usually will 'wash' the corrupted boards with soap and water. I elliminate the water through either an air compressor or use the oven at 120°F (40°C).
Another idea came up : The amp works on two different rail voltages 45/-45V and 90/-90V. The low rail voltage is supported for 'low' level program while the high rail is engaged (seamlessly) on heavy program. The rail switching is effected on the bi-level switch assembly (caps and fets). It is possible that the rails are stuck in low power mode, not switching to high voltge rails. Verify the fet switches.

Alain

#5 slickrick

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Posted 13 February 2014 - 10:43 AM

I forgot to say it only happens with a load.

I will carry out what u suggested and report back.