cqtsdss

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About cqtsdss

  • Birthday 06/10/1970

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  1. Dear Alain: I´ve been out of business for personal reasons. As soon as I get back to the amp and do the tests I'll let you know. Thanks for your support.
  2. Thanks again, Alain. Well, I was warned myself about the fact of the increase with the variac, you can read it on the first post. I have given a few more tries and it is a very strange thing. Maybe i didn't say it clearly, my english is maybe a bit oxidated so I may make mistakes. The Differential switch i mentioned it is called Residual Current Device in english and it cuts off when there is a difference of current between the two poles of the AC inlet of the house. This is the device I got interrupted when I first connected the amp. I thought, as many power supplies, it had some varistors on the filter to protect both phase-neutral and phase and neutral to ground. My fisrt impressión was that one of those could be responsible but my surprise was when I faced for the first time the schematics and discovered that there were no varistors at all, instead some capacitors which have been carefully checked. . Another thing I found is, mentioned on previous message, is that audio ground (on the pcb) is not tied to secondary PS ground, not even to the primary ground, but when you put the board to the chassis all these grounds become one, as the rings of the screws are connected to those different grounding points. That is why the amp switches on when out of the chassis. Once out again, I put a jumper from the audio ground to the Secondary ground of the PSU and got the protection acting again, this is, electricity off on my workshop. If a put my voltmeter from any of the grounds on the secondary side to the earth ground i can read 128 vAC, no matter if is the audio gnd or the psu. I don't pretend to say i am the smartest engineer, not at all, I believe we have to learn everyday. I have been on these job for more than 25 years but this is one of the faults that makes me want to give up (just kidding) but I am really lost with it.
  3. The voltage is set to 220 v, the one in my local area, well, in my whole country. I will check capacitors and voltages. But with special care I'll do something I have been moving in my head. The screws that fit the main pcb into the chassis are conected to different grounding areas, I mean, the audio ground is attached to one of those holes, so when you put the screw you tie this point to the same point as power ground is. Also, to other grounds that are not connected via PCB but through the chassis. As pointed in my former message, the first problem was that my electrical protections acted as soon as I switched on the amp. Using my isolator transformer and the Variac I am going to do additional tests to find out what is causing this strange problem because all the previous test were made with the pcb out of the enclosure. Thanks for your support Alain. Any advance I will publish it here.
  4. Dear colleagues, I have a XLS1500 for service with a very rare issue and I don't know where to begin with. On a first test, according to what my customer mentioned that the amplifier could not turn on, I checked the breaker and it was ok, There wasn't any apparent damages on a first visual inspection so I plugged the amp and turn it on, inmediatelly the differential switch on my electric system jumped off. Then I dissasemble the pcb from the enclosure and began to check all the power semiconductors on the PSU primary side. As I didn't find any damaged thing, I connected the PCB (Including the processor PCB) to my VARIAC and began to increase the voltage without any strange behavoiur and, as expected, when I reached the mains voltage required the unit turned on. To follow my tests I, then, instead of doing a slow voltage increase did a normal turn on, turn off procedure for a few times and the response was the right one. The next step was to test the amp working, for that I connected both speakers plugs to my dummy load (resistive load) and also connected the signal from a generator to the phono plugs, all that was made with the amp unplugged from mains. When all was ready I switch the amp on and then the relay paralleled to the NTC on the primary (controlled by the processor) began to buzz (turning on and off very fast) and the amp wasn't able to turn on. As soon as I removed the audio in plugs the amp turned on normally. To me is a problem relative to ground, but to be honest I don't know what should I do next. Looking forward for your kind help. Yours JV
  5. I'm not sure if I'm breaking the forum rules and I hope I am not. I have four units of JBL PRX518S over my workbench for servicing and I know is a CROWN design so I dare to post here in case anybody can give me some ideas or advice. The thing is that I have found some of the final switching Qfets broken, I have removed them, and to check if there's nothing else broken, I turned it on before installing the new devices, but the power supply is generating a lot of noise as if there was already something wrong. I am getting into these new technologies but experience is at its weak, so I don't know if there could be a problem, which I can't find, by connecting the module (unloaded, of course) without the Fets. On the first repair, I mean the first module I tried to fix, after I replaced the defective Qfet I turned it on and a few seconds after the power supply literally explode, so I am very worried about going ahead or not. I know that other technicians are simply (it is not the word I'd like to use) replacing the whole thing, but I refuse to throw this away, there is a lot of technology and I believe it can be fixed. Looking for your help. Yours John
  6. Macro Tech 2400 offset trouble

    OK, well I have had this sort of trouble once with another amp of this brand, but a different model, I mean the broken track. I'll carefully check all this area and in case I succeed I'll let you know. Thank you for your important information. Saludos Juan (cqtsdss)
  7. Dear friends, I have on my bench a Macro Tech 2400 power amp with a problem I can't solve without some help. After an initial test I have discovered that CH1 has an output voltage of 0.7 V which, according to the manual is out of range. As a consecuence of this I have the green led on and the ODEP one off. I first put my eyes on U104 as adviced on the test number One, I simply replaced it but the problem remains. Then, I began to compare voltages around this IC discovering that output pin 8 (High side error amp) was completely turned to -DC voltage. I compare to the other channel and at this point (pin7 on U204) there is no dc voltage, soon after, looking at the schematic I tested the output of the previous Op Amp and the Offset is OK. Then I measured the Voltage at point J2-1 AO1 and I read - 700 mV dc when at the same point on the other channel I read 0 Vdc. I continued and open R103 to test that the dc is coming from output rail and as I did this the U104 pin 8 turned 8Vdc, non inverting input raising from 100 mV dc up and the relay switching continuously. The leds behaviour still the same and at this point I feel a bit lost. To be honest, I am not very familiar to CROWN amps simply because the very few I have received for service were to replace pots or silly things like that. These are, to my opinion, very strong amps and, talking about these series, trouble free. Then, I have not much experience and although I have read many docs and even the service manual (well, not entirely) I have the feeling that some help would be great, so here I stand for your kind replies and thank you in advance the time you dedicate to me
  8. Dear friends: After a long time not getting a Crown amp into my shop (this may mean something (goog I mean)) I have now a CTs 1200 with both channels off and in the front pannel the two "fault" led blinking. To be honest it is the first time I open one of those and before I experience a disaster I'd like to receive some help that hopefully someday I'll give in return. If anybody could give me some tech docs for this model or any testing points I'll thank you a lot. I already have all the stuff I found on the web but it is only user's manual and relative stuff which tells me few or nothing of the amp design, modules or parts. Yours Juan After a few days posted: Is there anybody out there? HA HA HA HA ...... I am in a rush Thanks again for your time and support
  9. GEODYNE II

    I have just repaired a Geodyne II amp and when I began to adjust it following the procedures indicated on the Service Manual. But when I reach to point number 4 I have a doubt. I can read that the input signal on the jack, the tip and ring should be shorted. Is that right? and then, what is N100/N200 I can't find it on the schematics nor the boards. Anyway I have to continue checking because there is an important and audible difference from the repaired channel to the good one but when I read the signal on the scope everything seems to be ok. There is an important distortion like when the speaker is broken, on low frequencies (bass kick), obviously the first thing I did was to check the other channel with the same speaker and everything was OK. Any ideas? I will keep on checking and measuring, but unfortunatelly I don't have some lab equipment like distortion meter so this will keep my hands tied for some tests. Thanks for your time.
  10. AMCRON GEODYNE II

    DEAR DAVID: THANKS A LOT FOR YOUR TIME ON MY GEODYNE PROBLEM. IT IS A REAL PLEASURE TO DEAL WITH SUCH A PROFESIONAL PEOPLE, NOT VERY EASY TO FIND NOWADAYS. I HAVE NOW THE TECHNICAL DOCS I NEEDED. JUST ONE COMMENT, THE LINK TO THE USER MANUAL DOC MUST BE MISTAKING BECAUSE ANYTIME I PRESSED IT, TAKES ME TO THE GEODYNE I SERVICE MANUAL. ONCE AGAIN THANK YOU VERY MUCH.
  11. AMCRON GEODYNE II

    Thank you for your time and helpfull answer.
  12. DEAR FRIENDS I HAVE AT MY SHOP AN AMCRON GEODYNE II POWER AMP FOR REPAIR. I TRY HARD TO FIND THE SCHEMATICS ON THE WEB BUT I CAN'T FIND IT EVEN ON DISCONTINUED MODELS. DOES ANY OF YOU KNOW WHY? IS IT THERE ANY EQUIVALENT UNDER A DIFFERENT REFERENCE? THANK FOR YOUR TIME