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About AC4AQ

  1. 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
  2. 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
  3. 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.
  4. 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.
  5. 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
  6. Hello to our fellow techs. I'm wondering if there is a audio technician out there who has developed a method for rapidly locating the faulty circuit area, but not necessarily the failed components in Crown audio power amplifiers. I've been trying to do this for two years now and am still having to create a technique for locating the trouble area when I encounter a particular Crown model for the first time. I am a technician who has had 20+ years experience in component-level work in RF power amplifiers, servo-controlled devices and off-line converters. In the case of the servos, a failure anywhere causes symptoms everywhere, so it is necessary to 'open the loop' to troubleshoot. Inasmuch as as Crown doesn't really sell "amplifiers" such much as "speaker servos", the similarity is obvious. However, I am now facing a K-2, with symptoms everywhere. It draws excessive line current unless both output modules are disconnected. No failed FETs, only fault found on either module was U51 (low side 12 VDC reg). Both high and low sides toggle if I feed them 12VDC, Vcc and drive the LEDs. Looking at the drive board , we have a nice sawtooth but IC 101 & 103, 201 & 203 are all locked. Going farther back, there are many pathways that can induce this failure mode. I am not looking for the answer to this problem, but a better way to find it. The schematic tells all, too much in fact, it takes a long time to find where a bus like -LVA might go to. And there are multiple closed loops, so you can't open the loop, at least not all of them. What would be ideal is either a block diagram, with the test points shown so that it not necessary to waste hours looking where the fault is not. Or maybe a Truth Table for the protection circuit, to identify quickly which failure is present. Or, a flow chart. Right now, it is the K-2. But there is an IT-6000 waiting for me next, and a smoked IT-6000 will make the K-2 look like child's play. Thanks for any thoughts on this. Jeff. 73 de AC4AQ
  7. Thanks, Alain,for your response. Ultimately the problem was C524: Among the original faults in this amplifier was leakage in C524, I substituted a 270 pF, 400 WVDC cap and this was a mistake. The extra 70 pF was enough to introduce an instability, though what mode I haven't and needn't determine. Now I need to figure why I now have a 185 mVDC offset in one channel, in Stereo mode only...
  8. Hello, Crown folks! Right now I'm trying to wrap up the repair on a MacroTech 5002VZ but the last little gremlin is stubborn. It has oscillation (actually vibration) in one output channel, causing a squarish/sineish waves of about 600 mV, 300 kHz to appear at the speaker terminals. Anyway, while applying a signal to the unloaded amplifier and as I increased the amplitude, I heard something go Pop! Nothing burned on the output module, it appears Z1 on the speaker terminal ("Terminator") board ignited. The trouble is there is nothing identified on the schematic as Z1, nor can I find a Z1 in any of the parts lists in that enchanted forest of a service manual. If anyone has some thoughts on this mystery component, please share them. Thanks, Jeff / AC4AQ
  9. I had an early XTi2000 on my bench today, customer said "fan doesn't work". It took less than five minutes to identify that it needed the software correction but it took an hour to get CLoader V.2.19 installed and reload the firmware, then another two hours to install System Architect, debug it and update the amp software. Then, knowing I can best prevent a recall by setting the fan to the Hi programmed mode, it took another 90 minutes to find out how by stumbling upon the above text, by looking at every XTi2000 post, one by one. The primary time-waster was the restriction on the Crown Forum search engine, which won't allow you to search for 3-character strings, such as "XTi" or "fan". Here's hoping to not spend five hours doing a fifteen minute job next time. jHh