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"Gareth Magennis" <soundserviceleeds@outlook.com>: Nov 06 08:31PM "Phil Allison" wrote in message news:627b9c70-b14a-4cc4-8288-8bffe6c3752f@googlegroups.com...   N_Cook wrote: > actual circuit nodes on this amp and modelling the schematic I don't > know how much current is actually now or should be taken by the MJE340, > but something is not hunkey dorey.   ** I had a look at that schem and could see no sign of current sensing for the fan. The MJE340 is there to increase fan speed as the heatsink gets hotter.   IIRC, the 2W resistors are carbon composition types, which are notorious for increasing their value over time - but I have seen them do the reverse when subjected to excessive temps.   Famously in the ridiculously heavy Bose 1800 amplifer, where two 3kohm 2W composition types supplied current to the op-amp input stage.   http://i.imgur.com/ETpss.jpg   These resistors ran hot ( 1.6watts each) and the amp had no internal fan, so the insides got hot too. They steadily dropped value until one of the 16V zeners fried and went short. The amp then went full rail DC sending 80V into the speakers.                 Back in the day I had an unfortunate experience buying an HH S500D amp cheap as it was "faulty". http://medias.audiofanzine.com/images/normal/hh-s500-d-970073.jpg   Plugged it into a friends 2 x 12 cab to have a listen, and both speaker cones immediately vomited out of the cabinet.   Because of one shorted Zener on the op-amp supply.     That taught me a lot that I still use every time I have an amp to repair.     Gareth.

Phil Allison <pallison49@gmail.com>: Nov 06 09:00PM -0800 Gareth Magennis wrote:   > Plugged it into a friends 2 x 12 cab to have a listen, and both speaker > cones immediately vomited out of the cabinet.   > Because of one shorted Zener on the op-amp supply.   ** I remember the HH S500D - it used a driver module for the output stage which in the early versions was fully potted in black resin, fitted into a plastic tray.   Since the was no way to access the module without wrecking it, I was forced to buy a new one from the local HH agent even for the simplest fault.   The new one came as a normal PCB assembly fitted in a similar tray but with no potting. What on earth were HH thinking??     .... Phil

captainvideo462009@gmail.com: Nov 06 04:40PM -0800 I tried posting something about this in the past but got no response. I'm holing that this time someone might read it who may have a theory as to what could be going on.   I live in southern New Hampshire and watch OTA TV out of Boston, which is about 60 miles from here. Lately I as well as several other people I know have been experiencing intermittent problems with channel four. While most other channels are presently operating fine, for the past 10 days or so channel 4's signal has been in the toilet. This station, WBZ TV operates on UHF channel 30, runs 825KW, and has an antenna height of 390 meters. By contrast Channel 5, WCVB, operates on UHF channel 20, runs 625 KW, and shares the same tower and has it's antenna at the same height as channel 4's, and we never have any problems with that channel. Could propagation be that much different 60 MHZ apart? What is really weird is that the signal just drops to almost nothing.   I discussed this with the chief engineer at Channel four and he had no explanation for this. Does anyone have any theories about this? Thanks, Lenny

mike <ham789@netzero.net>: Nov 06 07:56PM -0800 > I tried posting something about this in the past but got no response. I'm holing that this time someone might read it who may have a theory as to what could be going on.   > I live in southern New Hampshire and watch OTA TV out of Boston, which is about 60 miles from here. Lately I as well as several other people I know have been experiencing intermittent problems with channel four. While most other channels are presently operating fine, for the past 10 days or so channel 4's signal has been in the toilet. This station, WBZ TV operates on UHF channel 30, runs 825KW, and has an antenna height of 390 meters. By contrast Channel 5, WCVB, operates on UHF channel 20, runs 625 KW, and shares the same tower and has it's antenna at the same height as channel 4's, and we never have any problems with that channel. Could propagation be that much different 60 MHZ apart? What is really weird is that the signal just drops to almost nothing.   > I discussed this with the chief engineer at Channel four and he had no explanation for this. Does anyone have any theories about this? Thanks, Lenny   There's signal strength, signal quality/modulation, interference and tuner quality.   Having two stations on the same tower reduces the number of variables.   I'm only about 10 miles from the tower, but there are hills all around. Signal strength is high, but there are a lot of reflections. I did many experiments varying the antenna direction and changing signal strength into the tuners. Best picture stability was not always consistent with best signal strength. When trying to use one tuner and one antenna for multiple stations, I found that I had to attenuate the signal to get a picture on some stations.   My neighbor has a metal pole building. I found moving the antenna to the other end of the house made a dramatic improvement. Doesn't take much a reflection that might be from far away to wreak havoc on your signal due to multipath. Did Trump put up a new tower in your vicinity?   Currently, I have a win7 computer with 4 tuners. A single antenna and distribution amplifier with an output for each tuner. Over the years, I've upgraded the tuners so I no longer have to vary the signal strength to fit a particular tuner. I find that some tuners don't like specific channels. Luckily, media center will let me blacklist tuners on various channels.   Interference can come from unexpected sources. Your neighbor's wifi might be mixing in a corroded gutter junction with some other radio signal. The result trashes the signal quality of your TV station.   I once had a towing company radio mix with my radio repeater output that landed exactly at the IF frequency of my other radio.   If you have access to a spectrum analyzer, you can hook it to your antenna and look at the relative signal strengths. Look at the modulation for each channel. I found that signals were good when the "bart's head" display was flat on top. Didn't take much noise or tilt to render the channel unwatchable, even on very strong signals.   ATSC is not very forgiving.

Michael Black <et472@ncf.ca>: Nov 06 01:36PM -0500

mike <ham789@netzero.net>: Nov 06 03:19PM -0800 On 11/6/2016 10:36 AM, Michael Black wrote:   > But I know back when I got it, I was able to download a service manual > for it, so at least do a search now. Maybe that gives hints.   > Michael You really have to read the whole thread. By the time the mad snippers get through with the initial question, you miss the part that says I referred to the manual. The input so far is discussed in the original question that I spent hours to carefully configure for maximum communication... only to have it snipped and ignored. Recommending I do a search is not very helpful. It's not like we don't search before posting. What WOULD be helpful is a recommendation for keywords to search. If we search for the wrong keywords, we won't find it. A quick look at the google hit page is misleading. Many of the "hits" found by google don't exist. And many of those that do exist link to "information" on other pages that no longer exist. End of rant...   These are the current image references for the test pages and the two toner cartridge voltages for the precharge roller and developer roller.   http://imgur.com/dcuRRlW http://imgur.com/E1BSKZc http://imgur.com/sRf3DfH   Just realized that the image links aren't permanent... Voltage on the developer cylinder is about 1300V P-P with an offset of about -450V. Sorta square wave with ~550uS period. Voltage on the precharge cylinder is about 2100V P-P sine wave about 4.2 mS period. Starts out at 0V offset, then shifts to -400V offset before the paper gets there.   These voltages are for a WORKING system, see below. I thought about putting the "wired up" cartridge in a different working printer, but I have a long history of using one good system to try to fix a bad one and ending up with two bad ones.   I verified that the printer elements that are supposed to be grounded actually seem to be grounded. The resistance to ground for the precharge power supply in the Laserjet 4MP was 2.5Meg compared to 5Meg in a Laserjet 4P. You'd think the power supplies were the same, but dunno... I attached wires to the toner cartridge contacts and scoped the signals during printing.   I was very surprised to learn that the AC component of the signal was several times as big as the DC offset.   I was also very surprised to see that ALL the banding had disappeared. Both cartridges that had severe banding were now free from that banding. I had cleaned the contacts and swapped cartridges dozens of time. Now, it's all good! I didn't actually fix anything, so I'm expecting it to fail again.   Both my test cartridges were old and had vertical stripes due to the wiper blade not cleaning properly. I stuck in a NOS refilled cartridge. At power on, it made a loud "snap" and dumped toner. I can't catch a break...   I cleaned all that up and tried a NOS genuine HP toner cart. Before I installed it, I gently rocked the drum back and forth to make sure that it wasn't stuck to any of the wiper blades. That cartridge seems to work and the printer is now back in service.   I spent a week messing with this. I learned a lot, but still have no idea what caused the banding. Maybe my saga can help someone else in the future.   I'd still be interested in an explanation of how the banding shown in the picture could possibly happen. I can't come up with a failure mode that would produce such a varied banding pattern on successive printouts of the same page.

marko.cizmesinkin@gmail.com: Nov 06 02:29PM -0800 Hi Joy! I'm still looking... Marko

marko.cizmesinkin@gmail.com: Nov 06 02:32PM -0800 Hi Joy! I'm still looking... Maybe you have it? Marko

Bob Engelhardt <BobEngelhardt@comcast.net>: Nov 06 03:43PM -0500 I have a cheap Chinese capacitance meter with 3 lead sockets: "CX-" & 2 "CX+". One CX+ is labeled "200mA fused" and the other "MAX 36VDC". Neither of these labels make any sense to me & I don't understand when I would use which socket. I did check the web, without finding an answer. Can anybody help?   Thanks, Bob

N_Cook <diverse@tcp.co.uk>: Nov 06 09:41PM On 06/11/2016 20:43, Bob Engelhardt wrote: > Can anybody help?   > Thanks, > Bob   Is one at equipt ground ?

Clifford Heath <no.spam@please.net>: Nov 07 05:40AM +1100 On 07/11/16 07:43, Bob Engelhardt wrote: > Neither of these labels make any sense to me & I don't understand when I > would use which socket. I did check the web, without finding an answer. > Can anybody help?   I suspect the "MAX 36VDC" is AC coupled, perhaps with a bipolar/ceramic parallel combo, so you can test capacitance (approximately) in-circuit while it's powered up. The other one is DC coupled with a fuse.

Adrian Caspersz <email@here.invalid>: Nov 06 09:13PM On 06/11/16 12:19, N_Cook wrote: > cannot think of anything off the shelf. Using a pair of Q or Trident > type sockets and pins, offset axially , to give the polarisation. > Cosmetic appearance does not matter.   3-pin Din connector?   http://www.ebay.co.uk/itm/like/401159837174   or mini XLR?   http://www.switchcraft.com/Documents/npb_624_sealed_mini_xlr.pdf   -- Adrian C

N_Cook <diverse@tcp.co.uk>: Nov 06 09:48PM On 06/11/2016 21:13, Adrian Caspersz wrote:   > http://www.ebay.co.uk/itm/like/401159837174   > or mini XLR?   > http://www.switchcraft.com/Documents/npb_624_sealed_mini_xlr.pdf   I like the idea of mini XLR. I don't like the idea of locking connection as leaves little chance of a tripped over lead not trashing the pc. It reminded me I've some nice expensive NOS surplus line-LEMO connectors, I'll investigate how easy it is to butcher the latch function on them

"Gareth Magennis" <soundserviceleeds@outlook.com>: Nov 06 10:09PM "N_Cook" wrote in message news:nvo8ev$jlj$1@dont-email.me...   On 06/11/2016 21:13, Adrian Caspersz wrote:   > http://www.ebay.co.uk/itm/like/401159837174   > or mini XLR?   > http://www.switchcraft.com/Documents/npb_624_sealed_mini_xlr.pdf   I like the idea of mini XLR. I don't like the idea of locking connection as leaves little chance of a tripped over lead not trashing the pc. It reminded me I've some nice expensive NOS surplus line-LEMO connectors, I'll investigate how easy it is to butcher the latch function on them           https://www.youtube.com/watch?v=I8ntUVj-sqM       Maybe scale them smaller using Hard Drive magnets?     Gareth.

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