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AC4AQ

Member Since 01 Oct 2012
Offline Last Active May 21 2014 02:45 PM
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Posts I've Made

In Topic: How to troubleshoot efficiently?

07 May 2014 - 03:49 PM

IT-6000 Update: This particular amp was manufactured 12/28/2004 and is serial number 8000492671. It doesn't appear to have had previous service and does not have the BCA drive board with red capacitors for C526 and C527.

After I replaced a bad FET (Q1007) I just attempted to start the amplifier with the Front End modules removed, as in the manual. However, Q1004 exploded after a few seconds and the blast wave was such that my ears were ringing for several minutes afterward. I think it should be recommended that hearing protection be worn when an amplifier is serviced where there is a fair chance that semiconductors may detonate.

I think it is reasonable to substitute 200 ohm 25 watt resistors for the toroids while troubleshooting, as this will prevent excessive current and allow non-destructive testing.

Tnx...Jeff

In Topic: How to troubleshoot efficiently?

07 May 2014 - 10:04 AM

The answer to my question of how to troubleshoot a K-2 efficiently, at least in this case, is seek out the necessary information. It turns out there was adequate data available had I searched beyond the LAN. In the end, this K-2 needed C57, U2, U51, U52 on the output module replaced and U102 on the main module. Also both opto-isolators (U2 and U52) on the other module were damaged.

As the amplifier arrived, it is likely that the only failed components were C57 (leaky, pulling down the Vss-12 source) and possibly U52. All the other components were damaged by attempting to power-up the amplifier without the rear panel in place, which ungrounds part of the main module and isolates the speaker filter network.

So the answer is: In amplifier repair and in other things it is a goodly lesson to looke ere ye leap.

Now on to the IT-6000, which went Pop! and has a leaky FET in the output stage. This one is encouraging as it uses the familiar International Rectifier Class D audio power amplifier scheme. Time to research and not rush in where angels fear to tread...

Jeff/AC4AQ

In Topic: How to troubleshoot efficiently?

25 April 2014 - 01:30 PM

I believe the work is now progressing rapidly.

Our symptoms are: Power up, relay clicks, IOC, Clip and Enable LEDs briefly flicker follower by second click and high line current. Symptoms unchanged with either output module disconnected. With either Output module connected but P2 on Input board disconnected: Power up, click, three seconds later second click with overcurrent, no LEDs light. With both disconnected, IOC, Clip and Enable LEDs illuminate, +15 VDC and -13 VDC bus good. Triangle waveform of 7.7 Vp-p, 4 uSec, on pin 3 of Main module U101, U103, U201 and U203. Triangle waveform of 3.6 Vp-p on pin 4 of same ICs, DC is nil.  However only U101 and U201 have square-wave output, 50% duty cycle output, U103 and U203 on Main board have both outputs high, suggesting these two ICs are damaged. I am now proceeding to extract them, replacements are on hand.

I suspect this came to pass due to technician ignorance, the rear panel was not in place, leaving J8 ungrounded and this likely damaged the ICs. Previously, I found U51 bad on one of the output modules, likely this was the source of the original problem but now I have to correct the self-inflicted wounds.

Thanks again for your attention.

In Topic: How to troubleshoot efficiently?

25 April 2014 - 11:13 AM

Duh, There is extensive data after all. I forgot we're dealing with 20th Century technology here and the bulk of the service information is on paper and didn't make it to the server.

In Topic: How to troubleshoot efficiently?

25 April 2014 - 10:59 AM

Thanks for your help,  Alain.

It looks like the data I have is incomplete. It consists of eight files when unzipped:

100522M    100442C   100436D
100195C    100946F    100848B
100012B     100550A.

Each of these is a schematic scanned from the original paper into a .pdf file.

In the case of this K2, it trips the overcurrent on my bench Mains source, which prevents further damage. Both output modules appear to be good as if they are supplied with Vcc, AC, -Vcc, -Vcc+12 and a suitable drive signal to the optos they will commutate. In the case of U101/103, U201/203 one is switching, the other is over to the rail.

Until a few moments ago I suspected that -Vcc+12 was absent, resulting in shoot-through in both output modules however this seems unlikely now, perhaps Crowbar is actually causing the overcurrent.

I will look for the PM, as I somehow missed it. Also please note that none of what I wrote previously was meant as criticism of Crown, as my problem of accessing the data seems not specific to any manufacturer but perhaps to the system where I work.

Thanks again and I will post any developments.

Jeff / AC4AQ