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About Wrighty

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  1. I've had two Macro-Techs in, with faulty resistor networks... Both were a right pig to find!
  2. Ok, just done that and the problem is still there with Ch2's VZ module connected to Ch1. So... looks like main or output module fault.
  3. Yeah, could do I guess. Project for this afternoon...
  4. I've got a 3600VZ on the bench here, with an odd fault on one channel. Basically, it looks like something's going unstable and oscillating in the positive half of the cycle, resulting in this output waveform (photos were taken a while ago): With no load attached: With 4 ohm dummy load attached: I happen to be using a 200Hz sine wave input, but some kind of distortion happens at all frequencies. The trace is shifted down, so the oscillation can be seen on the positive cycle. Here are some more photos from today, with no load, at different frequencies: 100Hz: 1500Hz: 10000Hz: Any ideas?? Note the huge negative spike at the same positive voltage level on every trace... Biases are all in spec and I've swapped everything socketed on the main board to no avail. Cheers, Richard
  5. That was my first thought but having never seen it before, I was slightly surprised when I did! Thank you both for your replies
  6. Oh, really? Never noticed it before, but then again, there isn't usually another rig running in the same venue! How come the other one wasn't doing it then? And what causes this odd behaviour? Something to do with certain parts of the amp being powered down when the sleep circuit is active?
  7. I was doing a gig on Saturday night with a couple of K2s - one driving a pair of FOH speakers and the other driving a pair of wedges. There was a DJ there with his own rig too, playing his stuff between the band's sets. After the band's first set, I went over to the amp racks to make some adjustments to the crossover and noticed that the signal lights on the K2 driving the FOH speakers were lighting in time with the DJ's music. I had no signal going into the K2 at the time. The amp was in standby (because it had no signal). When I disconnected the speakers, the signal lights went out. Upon reconnecting each in turn, each signal light started flashing in time with the DJ's music again. It was as though the speakers were acting as microphones and the signal LED circuitry was somehow picking the tiny signal up. The second K2 driving the wedges was behaving normally (ie. signal lights off). The amp worked fine for the whole gig, in spite of this! Any idea what could cause that behaviour, before I dig out the service manual and start investigating? I've yet to try reproducing the fault on the bench. Cheers, Richard Wright
  8. Just to update: ODEP LED problem turned out to be both LEDs were shot - unbelievable as it may seem! I was looking for a common cause, eg. the TL072 op-amp, but that was fine. I stuck a couple of other LEDs across the existing ones and they worked fine, so replace them both and all good now. Overheating problem turned out to be due to the fan blade being on the wrong way round. This wasn't immediately apparent until I compared it to another unit. Flipped it over and all is fine now
  9. Hi, I'm looking at this one for Conrad at the moment. I solved the huge pop at power off - the suppressor cap across the power switch was faulty! I saw it was there (ie. didn't need one fitting), so went on to check C1, C2, U1, U2 on the main board which were all OK, so went on to swap the suppressor cap for another and bingo - clean as a whistle! Everything looks fine on a bench test - no DC offset, biases are fine, CMR fine, ODEP voltages all fine. It passes audio and quite happily drives dummy loads to the published specs. However, neither of the ODEP lights come on after the relays click in. Any ideas? It's time to go home now, but Monday's project is take the front panel apart and check the display board. Is there a schematic available for this, as it doesn't seem to be included in the ones downloadable in the legacy amps section. Serial number is A173535, date code 9063. EDIT: Just found display board schematic - it's "Macro-Tech 1200 Schematic-1" on your website... Cheers, Richard
  10. Well, that faulty Micro-Tech 1200LX went on the shelf for a few months and finally came out again this week to continue the repair... The biases all adjusted fine but ODEP seemed to be causing a problem. Kip - you were spot on with the open resistor - R134 was open circuit. Replacing that allowed me to adjust the ODEP voltages correctly. Thought I was on to a winner, but then I discovered the supply was still wildly unbalanced - I was measuring about +12/-73V on Ch.1 and adjustment of R132 caused the ODEP light to go from off to full on I did my favourite trick of flipping the main module round and using Ch.2 input circuitry on Ch.1 output module, which told me immediately that the problem was on the main module and definitely not the output module. Even knowing that, it still took ages to find the cause of the fault. I removed Q100 and Q103 (as suggested by Kip in another post about a faulty Macro-Tech) to remove ODEP from the signal path. Still got a problem. Checked all the resistors around Q115 and Q116 and even swapped Q115 and Q116 with Q215 and Q216. Still the same. Eventually, after a lot of head scratching and checking voltages at various points, I discovered that there was a huge difference in voltage between J600-3 and J800-3, with the main module unplugged from both output modules. I started looking at other things connected to that pin, which I hadn't already checked (purely following tracks on the PCB, as the pin number marking for J500/600/700/800 is a bit sparse on the Micro-Tech 1200 schematic J0275-8), which led me to resistor network N102. Swapped it with N202 and BINGO! There's the faulty component! I think that when R134 (18k 0.5W resistor) went open circuit, the current flowed through N102 instead. The 33k resistor connected between pins 5 and 7 (7 being connected to J600-3 [-VCC]) is actually measuring more like 330k now, so it's definitely suffered. Time to get on the phone to Harman Pro UK and order some bits... I'm learning more and more each time I fix grounded bridge Crowns - I've done small things on a couple of CSLs, a major repair and refurb on another CSL and this will be the 3rd Micro/Macro with multiple odd faults which I've done now. I like the serviceability of these amps, the commonality in design between so many models and the fact that all the schematics and service manuals are freely available for download - and this forum can be a godsend too! Keep it up, Crown! Cheers, Richard
  11. Hi, Is there a schematic available for the Micro-Tech 1200LX? I've fixed the faults on the one I've got in for service, but it would be useful for future reference. Main module PCB is D6304B2. Also, does anybody know the Crown part number and availability of the push button power switch used on this model? The part I'm talking about is just a button, spring and actuator assembly, which pushes a microswitch mounted on one of the heatsinks. The plastic actuator is broken and I don't know how long superglue will last... The only part I can see is a complete 10A SPST switch (C9091-7) in the service manual for a Macro-Tech 1200. Is that the replacement for the seperate actuator / microswitch arrangement, or is there another part? EDIT: Found the part number in the MA-2400 service manual! D7167-6 Cheers, Richard Wright
  12. Hi Kip, Thanks for your reply. Ah, PLASA, I take it...? I was hoping to go this year but I've got too much work on and London is a 3-4 hour train journey from where I am! I've checked the output bias voltages - they're done before the ODEP adjustment in the check-out procedures. They set up to 300-320mV no probs. I'll have a look for and check those 2 resistors in the ODEP circuit - thanks for that info. I've got a couple of other projects on this week so I may not get a chance to have a proper look until next week but I'll let you know how I get on. Cheers, Richard
  13. Hi, Anybody got any ideas on this one?! Cheers, Richard
  14. Hi, I've been given 3 old Crowns to sort out by a colleague, with various faults. I'm currently working on a Micro-Tech 1200LX (March 1987 vintage) which was reported as having the ODEP indicators doing odd things, although the amp seemed fine in operation. After a good clean out and complete resolder of the front panel PCB to eliminate dry joints, it's still faulty. Ch 2 is normal - ODEP light comes on quickly after power up. Ch 1 ODEP light slowly fades up after a few seconds. I've done the first few tests in the service manual, up as far as setting up the ODEP voltages. At this point, Ch 2 is fine, but R121 has very little effect and R132 has no effect on the voltages measured on U100 and U103 respectively. U100-6 measures about -12.3 to -13.2V (as you adjust R121) and U103-6 measures about +11.4V with no difference as R132 is adjusted. Some more checks around the PCB revealed that the +VCC line is at about +7.7V and -VCC is at -78V on Ch 1. Ch 2 is approx +/-43V, as it should be. Measurements taken with respect to chassis ground. If I unplug the main board from both output modules, Ch 2's rails are still stable, but on Ch 1 they gradually float down to about +27V and -60V. I've been round the output module quickly with the meter and all the output and driver transistors appear to be fine, as do all the diodes. I can't see much else on the schematic which could be pulling the reference point up. I even went as far as changing C302 and C303 to make sure I didn't have a couple of leaky caps, to no avail. Any suggestions? The main module PCB is D6304B2 and the output modules are P10115-7. Cheers, Richard Wright
  15. Hi, I've just acquired a faulty Crown 800CSL. The guy I bought it off said that it worked fine until somebody decided to give it a drink... On initial power up test, I found a 60V (approx) DC offset on Ch1 and about 32V DC offset on Ch2. When I took the amp apart, there wasn't much evidence of liquid but there was evidence of somebody disassembling things at some stage, eg. wire colour markings on heatsinks. There were some burned resistors on the output PCBs too and Ch1 seems to have suffered more than Ch2. On this basis, I completely disconnected Ch1 and set to work on trying to get Ch2 back in a working condition. I have completely rebuilt the output transistor banks on Ch2. One device only had 1 leg (the 2nd leg was completely missing - suspect it got broken off when the previous repairer had a go at it) so I have used a device from Ch1 instead. All drive and output devices pass a basic transistor test with a multimeter, so I'm happy that they're ok. I have replaced R01 and R10 (both 470 ohm) which were both burned out. The problem is, I still have about 30V DC offset on that channel after the power-on delay kicks out, when the main module is plugged into the output module. If I just run the output module up, there is no DC offset. If I use Ch1's input stages from the main module, the DC offset goes. However, there is a buzz on the output and it is impossible to adjust the biases to the correct voltage (0.3V). The high side bias won't change from 0V and the low side bias will only go down to about 0.45V. I did also notice that R30 (programs S100) has become quite hot, although still measures 102 ohms. If S100 (LM224/LM234 current source) has also been fried, could that cause the problem I'm having? Is it possible/safe to disconnect the ODEP circuitry completely, to rule that out of the equation whilst I have it on the test bench, or should I be looking somewhere else? One thing that did concern me is that the DC offset protection is obviously not kicking in. The theory in the service manual talks about "control/protection transistors" which are "tied into the voltage translator inputs", which "act as switches to totally shunt audio to ground during the turn-on delay, or during a DC/LF or fault protective action." The turn-on delay works, but the DC offset protection obviously isn't. Just thought of something: I also have fully working 460CSL and 1400CSL units. Could I borrow the main module out of either of these (the 460CSL is fitted with 43060-7 and the 800CSL has 43059-7) so that I can narrow the fault down to the output module or main module? I remember Gary at Fuzion in the UK writing that the main modules of this design of amp (Micros, Macros, CSLs, Geodynes, etc.) were largely compatible with each other - for testing purposes if nothing else. Cheers, Wrighty