kevvywevvywoo

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About kevvywevvywoo

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  • Birthday 02/04/1975

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  1. JUst thought I'd mention I've had another MA with a faulty resistor network.
  2. Ah, never seen any with long pins. Any amps I've seen with this problem are usually rather old by then. I always check the joints even if the fault is not ostensibly on the output modules.
  3. I already changed the MOC opto. Scoping the drive waveform, its fine. When the fault occurs, the amp takes a steady 2A mains current until the bypass relays operate, then the current falls to normal idle level.
  4. can you swap the VZ modules over to prove they're ok?
  5. I have another odd one here, a repair that came in for one fault but is displaying another. While testing, I found the amplifier was not soft-starting on ChB (I found out by lifting each main transformer fuse). I found the 5R thermistor blown and scorched. I replaced it and checked the pwm pulses on the opto-triac were ok. When I switched on, the amp soft-started properly and didn't trip any breakers. However, occasionally, maybe one in 10 starts, the soft start triac operates in half-wave. This causes excessive current at startup until the relay closes, a loud buzzing from the transformer, and a strobing desk lamp. The amp works fine apart from that. I have changed the triac, snubber capacitor, checked the snubber resistor and scoped the pwm waveform, all ok. Any ideas?
  6. I agree, me neither. I was so glad to find it. On your last point, I have spent today resoldering the output devices on 2 MA5000 amps. Brittle, crystallised solder and loose connections on the end transistors causing the pcb to become loose. Sometimes this causes the transistors to fail.
  7. Hello Alain, yes the previous amplifier had the same symptoms, but this is a different amplifier and it isn't the flat ribbon..it was the first thing I checked!! This was a difficult one. I discovered that the +ODEP voltage was perfect at 12.6V...however I spotted today that the voltage was positive with respect to 0V...it should be negative -12.6V !! So we had a hard odep fault on Ch1. After 3 long days of testing, swapping chips, testing for leaky capacitors etc., I finally found the fault. The Thick Film resistor network RN101 had an out-of-tolerance section (pins 3-5). I found out by exchanging the network for the one in Ch2 and the fault transferred over. I now just need to make & fit a new ribbon cable to replace the one damaged by a previous engineer.
  8. Ok, sorted the soft start issue. It was C282 leaky. I've also sorted the fan issue, someone had cut the ODEP lines where they meet the control board. However I still have the Ch2 in IOC protect. Measuring the +/- dc bus gives uneven readings..39V on one and 48V on the other. I've fitted a new ;'main' back card and that fixes it..so the fault's on there somewhere.
  9. I have another interesting one here. MA5000VZ. The fans run flat-out fast at switch-on when cold. Channel 1 does not work and has the IOC bright and ODEP on. I've checked the thermal trip in the transformer. There's no diagnostic lights on internally. Output modules test ok. ODEP -/+ voltages are fine, temp IC sensor volts is fine. Ch2 also has a small fault, though i don't think its related. The soft-start precharge doesn't work. The amp powers up and when the soft-start time has run out the main relay comes in, dimming the lights and sometimes blowing the breaker because the capacitors are empty. Any clues?!
  10. Well, it was the flat cable sheared on the terminator end. But no cigar for you...I found out this morning after more or less eliminating everything else! The amp had been repaired elsewhere some time ago and I guess they were none too careful with the strips.
  11. Hi, got an MA5000VZ (internally same as 5002 late model) with a fault. It shows IOC (bright led) on Ch1 on switch on. The ODEP light comes on fine at the same time as the good channel. The output is muted. I've swapped the output modules over, fault is still on Ch1. Voltage checks show normal ODEP voltages and temperature. There's no DC offset at power up, bias is all zeroes suggesting the drive has been removed. The mains relay is in, there's power on the DC caps +/- balanced. If VZ-Auto is switched in, the VZ goes straight into high voltage mode. In lock low, it locks into low fine. Volt checks around the IOC warnings show the LED is being brought on by the 'ES1' line. Checks on the error amp show it is driving hard to +14V. I've swapped the error amp. I'm wondering where to probe next?
  12. Got an XTi here that will randomly turn itself off. I assume the SMPSU is being commanded off due to an intermittent detected fault such as DC/LF etc. The question is, might there be a way to find out the cause of the trip? Once the power goes off, live fault tracing is impossible..and when the power's on, it all works ok! The amp might be idling a few hours when it decides to power down.
  13. No issue, I am just asking in the interest of good customer service. I think the last update I have seen was the front panel replacement.
  14. Hello, does anyone have an up-to-date copy of these? Thanks
  15. A bright signal/ioc light just means it has detected a fault on that channel. Without further tests it's impossible to say what the fault is.