- Crystal Tuned TRF (I Think) FM Receiver - 9 Updates
- Alternator on DD-3-53 does not charge at idle - 2 Updates
- Denon UD-M31 CD Problem - 10 Updates
| jurb6006@gmail.com: Jun 13 05:42PM -0700 Trying to get a handle on these things. Next time you want to bitch about not being able to get parts and prints, I work for the factor and can't get shit. I do not mean an ASC, I am talking about the company. Not in manufacturing but my bosses own most of the brand, of course made in China, it seems mostly by Apex. Anyway these are wireless microphones and of course there are no prints. The receivers use the LA1140 and LA1186 chipset. They are fixed frequency so I am not sure what to do with them because some of them work just fine so I suspect there was interference at the venue. I am going to tell them to sell them locally so that people can just drop them off and pick up a different frequency set, which should cure some of the problems. This is less practical when you ship the thing to bumfuckt Egypt somewhere Thing is, the chipset appears to be hetrodyne but might not be being used that way. Reason I think that is that the frequency marked on the crystals is exactly the frequency of the mics. You would think it would be offset by the IF frequency, like 10.7 MHz or something. They must be putting the signal through or across the crystal, depending on which cut it is, series or parallel resonant. On these, if the mic is labelled 208.95 MHz, so is the crystal in the receiver. But why bother ? There are like four tuned circuits on there per channel so that should give adequate selectivity. Anyway, anyone know about these things ? |
| Jeff Liebermann <jeffl@cruzio.com>: Jun 13 07:17PM -0700 >They must be putting the signal through or across the crystal, depending >on which cut it is, series or parallel resonant. On these, if the >mic is labelled 208.95 MHz, so is the crystal in the receiver. Use a frequency counter to see what frequency the receiver crystal is oscillating. It's probably the receive frequency, plus or minus the IF frequency. It's common to label the receive crystal at the operating frequency and maybe stamp the crystal with the actual crystal frequency. Same with the transmitter, where the can might be stamped with the crystal frequency with the operating frequency being some multiple of the crystal frequency. I dunno how it's done with wireless mics, but in the bad old days of crystal controlled 2-way radios, most (not all) manufacturers crystals were labeled with the operating frequency because the various crystal suppliers were only interested in the crystal frequency and want extra money to stamp the can with the operating frequency. Some, like Motorola did both on the can. So, what problem are you trying to solve (or create)? -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
| Michael Black <et472@ncf.ca>: Jun 13 11:35PM -0400 |
| Phil Allison <pallison49@gmail.com>: Jun 13 09:05PM -0700 > Thing is, the chipset appears to be hetrodyne but might not be being used that way. Reason I think that is that the frequency marked on the crystals is exactly the frequency of the mics. You would think it would be offset by the IF frequency, like 10.7 MHz or something. They must be putting the signal through or across the crystal, depending on which cut it is, series or parallel resonant. On these, if the mic is labelled 208.95 MHz, so is the crystal in the receiver. > But why bother ? There are like four tuned circuits on there per channel so that should give adequate selectivity. > Anyway, anyone know about these things ? ** I used to regularly see fixed frequency, VHF radio mics through the 1980s and 90s until they were replaced by UHF models. Owners had plenty of problems with VHF models - but practically none were due to faults in the mics themselves. As a service tech, all you can do is check the mic is transmitting on the frequency it is labelled and operates with the receiver over a decent range, like 50 metres. You will need a counter that covers the VHF range and a short antenna fitted with a BNC plug. No direct connection is needed, the mic ought to drive the antenna hard enough to get a steady reading from a foot or two away. The crystals oscillate at a frequency that is either a 1/3 or 1/5 of the VHF frequency and multipliers are used to get to the final result. Rx and Tx crystals are different types and have different actual frequencies - often the Tx crystal is "pulled" to create FM modulation. Most mic systems use wide band FM, same as broadcast FM but a few use narrow band and their noise performance is much poorer. Practically all use audio companding to improve s/n ratios under weak signal conditions. It is possible to change the operating frequency by swapping both crystals, but the new frequency must be less than 2% away from the old to avoid the need to do a major re-tune. You mention 208.95MHz, which is covered by TV station 12 in the USA. If the mic is being used inside a venue and which is not close to a Ch12 transmitter, it will work OK. If used outdoors, it will likely have poor range. I assume the receivers are "true diversity" types with twin antennas and front ends - otherwise expect major problems with signal drop outs. A "drop out" is often not simply a loss of audio signal but a burst of white noise as the mic is moved around by even small distances. Wireless mic receivers must be located close as possible to where the mic is being used and with its antennas well clear of obstructions, especially metalwork. Many owners do no appreciate this and do the opposite - the result is lots of drop outs. Placing the receiver near a PC or any other source of VHF interference is also a big no-no. DJs may well do this if they use a PC as part of their set up. The other annoying issue is with batteries, but I figure you can work them out for yourself. ..... Phil |
| Phil Allison <pallison49@gmail.com>: Jun 13 09:12PM -0700 Michael Black wrote: > (because you already have one on that frequency, or someone in the theatre > next door is using the first frequency), it makes sense to keep a stock of > crystals and let the user change them. ** I have never come across user replaceable crystals in a radio mic. .... Phil |
| jurb6006@gmail.com: Jun 14 02:19AM -0700 >IF frequency. It's common to label the receive crystal at the >operating frequency and maybe stamp the crystal with the actual >crystal frequency." Oh boy, I can't believe I didn't figure that out. I am slipping, but I got an excuse. Not going into that right now. Doing that, printing the operating frequency on the crystals would not only facilitate service, if the friggin told us, but assembly. Another thing I found out about the construction of these marvels of (down(s)) engineering is that the frequency displays in the front are fixed. So to speak. Basic LED display and it says the frequency but what it says is marked on the side with a sharpie. When you look at the back of the board you can see that the terminals are all connected together. Obviously they had the vendor purposely burn out the segments they did not want on. This is not changeable. And I got unit that the frequency does not match either the display on the front or the sticker on the back. (which do match each other though, and the mics were changed to match) Anyway thanks for your input, you are one of the sharper people on here. OH ! I have another reason to believe these are TRFs, they are two channel, dual mics. The side with the lower frequency, some are down like 174 MHz, that channel I have noticed usually has the cores in the tuned circuits lower. As a matter of fact, the construction of those coils or whatever seems pretty stout these days. The look like they have brass cores and take flathead screwdrivers. They didn't put that money there fro nothing. Nobody does that these days. And I am pretty sure it was built by Apex, if Apex puts the money into this you now there is a reason. |
| jurb6006@gmail.com: Jun 14 02:26AM -0700 >CB crystals were often marked with the CB channel (and "T" or "R" for >transmit or receive), though of courze they only worked in a >specific set, >a receiver with a different IF wouldn't be on frequency. " https://www.youtube.com/watch?v=0evW6v69yF0 I was used to seeing a crystal of 3,579,545 Hertz and that was the damn resonant frequency. In TVs, when it said 4.000 MHz it was. This shit should be illegal. Where is the FTC ? |
| jurb6006@gmail.com: Jun 14 02:40AM -0700 >"** I used to regularly see fixed frequency, VHF radio mics through >the 1980s and 90s until they were replaced by UHF models. Owners had >plenty of problems with VHF models - but practically none were due >to faults in the mics themselves." I have labelled a bunch of them "SUSPECT INTERFERENCE IN VENUE". I don't know if you read when I spouted off about it, but though I was never a proponent of digital TV, I was of abolishing VHF. The system here was AM and a mess, and every time it rained on a power line you get hum bars in the picture from the arcing. At least in some places. I did mention the crumbling infrastructure right ? And now, about channel 12 TV (even though we do not have that here at the moment) now the TV is digital and the sidebands are like, who knows. Seriously. They should have abolished VHF TV decades ago and gave more high fidelity radio stations. Or something. In fact, that VHF range is about where RC planes are. Now can you imagine some broad singing "stand by your man" at a bar making an RC plane or copter take the wrong turn and kill someone ? |
| Jeff Liebermann <jeffl@cruzio.com>: Jun 14 08:35AM -0700 >I was used to seeing a crystal of 3,579,545 Hertz and that >was the damn resonant frequency. In TVs, when it said >4.000 MHz it was. 3.579545MHz is the color burst frequency. You'll see such crystals in TV sets, not wireless mics. >This shit should be illegal. Where is the FTC ? I think you mean the FCC. Congress cut their budget some years ago, so the FCC simply reduced the enforcement burro. <http://www.arrl.org/news/fcc-announces-enforcement-bureau-field-office-reorganization-plans> Field offices deal primarily with enforcement issues. FCC enforcement is now generally controlled by Homeland Security, <https://www.fcc.gov/public-safety-and-homeland-security> which means you will need to complain about an act of terrorism before you'll get the FCC's attention. If there's substantial potential revenue from fines "notices of apparent liability", the FCC might think about acting. <http://transition.fcc.gov/eb/> -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
| Jon Elson <jmelson@wustl.edu>: Jun 13 06:02PM -0500 Ignoramus13864 wrote: > It definitely needs to charge at idle. You MAY be able to modify the alternator to get it to charge at idle. The regulator may be dropping out at low voltage. Possibly putting a resistor across the regulator circuit might cause it to deliver a little current even at a low voltage. But, the real problem may be that the new alternator is not designed for running off this Diesel engine. Depending on the engine's idle speed and the crank pulley diameter, it may not get the alternator spinning fast enough. Possibly the original alternator (do you still have it?) had a different rotor or stator winding pattern to accomodate this. If you still have the old alternator, you might be able to replace the rotor brushes or rectifier diodes to get it to work again. 1250 RPM sounds pretty low. Most small cars have engines that idle around 800 - 1000 RPM, and with a 3:1 pulley belt ratio, the alternator would be spinning at least 2400 RPM at idle. Jon |
| Jeff Liebermann <jeffl@cruzio.com>: Jun 13 05:20PM -0700 On Mon, 13 Jun 2016 18:02:10 -0500, Jon Elson <jmelson@wustl.edu> wrote: >1250 RPM sounds pretty low. Most small cars have engines that idle around >800 - 1000 RPM, and with a 3:1 pulley belt ratio, the alternator would be >spinning at least 2400 RPM at idle. The pulley ratio is not always exactly 3:1. For example: <http://www.penntexusa.com/PulleyRatioChart.pdf> Looks like between 1.85:1 to 4.21. I would not speculate as to the alternator RPM until the OP delivers the actual pulley ratio(s) on his unspecified model forklift(s). -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
| rupert handford <rupert.handford@gmail.com>: Jun 13 10:01AM -0700 Calling all CD repair experts! This is my first in depth CD repair and I have the following questions: I have the above unit, that won't play CD's. I have replaced the laser mech and still have the same fault. The CD will 'twitch' but not run up to speed. Using service mode I am monitoring the output from pin 62 IC802 and it never seems to go low (thus powering the laser). Clock, data, CS and all Vcc lines are correct and the chip is being told to turn on from the processor. I have also checked the operation of TR806. Has anyone had experience of these IC's failing or is there another possible cause? Please let me know if I have missed anything! Regards, Rupert |
| "pfjw@aol.com" <pfjw@aol.com>: Jun 13 10:21AM -0700 Are you sure the drive motor is good? If it is 'twitching' as you suggest, it just may be bad. I expect it is a Hall Effect motor with the speed fixed by the clock. So, either the motor or the clock should be on your list of suspects. Do you get output to the motor? This is, after all, a mini-system, and so may not be as rugged or as easily serviced as a stand-alone CD player. Peter Wieck Melrose Park, PA |
| rupert handford <rupert.handford@gmail.com>: Jun 13 10:34AM -0700 > This is, after all, a mini-system, and so may not be as rugged or as easily serviced as a stand-alone CD player. > Peter Wieck > Melrose Park, PA Thanks for the reply. I have replaced the entire CD mechanism and so have replaced the motor. I believe that the sequence is as follows: 1. Laser turns on 2. Focus adjustment 3. Motor will start if focus is OK, PLL is OK and RF output is present. I have clock (from the chip). Focus is active (lens moves) but I have no RF and the APC of the chip is not going low. Can happily email schematic and datasheet is it would help. Regards, Rupert |
| dansabrservices@yahoo.com: Jun 13 11:34AM -0700 Check the motor driver IC. I have had these go bad from faulty motors. With the mechanism replacement, you now have a new motor, but not a new driver IC. Dan |
| "Gareth Magennis" <soundserviceleeds@outlook.com>: Jun 13 07:38PM +0100 "rupert handford" wrote in message news:048de354-e0a6-428e-9df1-8e9d48250e14@googlegroups.com... Calling all CD repair experts! This is my first in depth CD repair and I have the following questions: I have the above unit, that won't play CD's. I have replaced the laser mech and still have the same fault. The CD will 'twitch' but not run up to speed. Using service mode I am monitoring the output from pin 62 IC802 and it never seems to go low (thus powering the laser). Clock, data, CS and all Vcc lines are correct and the chip is being told to turn on from the processor. I have also checked the operation of TR806. Has anyone had experience of these IC's failing or is there another possible cause? Please let me know if I have missed anything! Regards, Rupert Where did you get the mech from and how much did you pay for it? I've bought many lasers from ebay that just don't work. That's why they are so cheap and on Ebay. Gareth. |
| rupert handford <rupert.handford@gmail.com>: Jun 13 01:16PM -0700 > Check the motor driver IC. I have had these go bad from faulty motors. With the mechanism replacement, you now have a new motor, but not a new driver IC. > Dan Thanks Dan, The motor is driven from the analog signal processor that I was asking about, but as the motor does move I guess that it is getting some signals? |
| rupert handford <rupert.handford@gmail.com>: Jun 13 01:19PM -0700 On Monday, 13 June 2016 19:38:25 UTC+1, Gareth Magennis wrote: > I've bought many lasers from ebay that just don't work. That's why they > are so cheap and on Ebay. > Gareth. Hi Gareth, The motor was from ebay but from a supplier that I have used before and not had any problems with. What are the chances of replacing a unit and having exactly the same fault as the origional? Thanks for the idea though I am not ruleing anything out at the moment! |
| dansabrservices@yahoo.com: Jun 13 01:52PM -0700 > The motor is driven from the analog signal processor that I was asking about, but as the motor does move I guess that it is getting some signals? Look at the BA6287F IC. This is hte motor driver IC and is separate from the signal processor. The signal processor will trigger the driver, but the driver itself may be the problem. If the driver has been weakened or damaged because of a bad motor, it may not be able to drive the new one either. The way these work is that the CD needs to spin up to a certain speed in a particular period of time, before the focus takes place and an attempt to read the TOC happens. If you are just getting a short shake of the CD, I would start with the motor driver. |
| "Gareth Magennis" <soundserviceleeds@outlook.com>: Jun 13 10:09PM +0100 "rupert handford" wrote in message news:4388f406-9b02-411a-97cc-4a5f682a3b89@googlegroups.com... On Monday, 13 June 2016 19:38:25 UTC+1, Gareth Magennis wrote: > I've bought many lasers from ebay that just don't work. That's why they > are so cheap and on Ebay. > Gareth. Hi Gareth, The motor was from ebay but from a supplier that I have used before and not had any problems with. What are the chances of replacing a unit and having exactly the same fault as the origional? Thanks for the idea though I am not ruleing anything out at the moment! Those chances are IMHO reasonable. There is a lot of fake shite out there. Think Occam's razor before suspecting pin blah blah on IC blah. Gareth. |
| "Gareth Magennis" <soundserviceleeds@outlook.com>: Jun 13 10:16PM +0100 And I assume you have removed the soldered safety short that is shipped with a new laser pickup before trying to use it? Gareth. |
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