sci.electronics.repair@googlegroups.com

Google Groups

yomoyco@gmail.com: Oct 15 09:09AM -0700 El miércoles, 29 de enero de 1997, 0:00:00 (UTC-8), J Heuer escribió: > -- > Jeff Heuer > Fresno,CA   El miércoles, 29 de enero de 1997, 0:00:00 (UTC-8), J Heuer escribió: > -- > Jeff Heuer > Fresno,CA   el valor de r602 es 22 ohms a 1w

N_Cook <diverse@tcp.co.uk>: Oct 15 10:34AM +0100 Only 1 changed resistor inside in 40 years, pretty good for twice weekly use over most of that time. Heaters glow but HT and bias supply stays up and no extra current draw coming out of standby. The 2.2K 7W W/W dropper for the minor HTs gone o/c. First set went fine, switched to standby for break and then nothing there for the second set. Is that resistor most stressed in standby? No obvious overheating of the R or the whale hide or whatever "circuit board" material. Assuming no other problem , it just failed from old age/corrossion but replace with same rating or go up to 11W? No rubber insulation found , any health and safety considerations other than the usual modern considerations? 2 issues with the Bulgin plug+socket mounted on the cab but thats just a UK thing. I'll do the usual remove the red voltage selctor knob on the rear and secure inside and blank off the shaft of the switch, as too easy to drunkenly turn that knob to "repair" a fault situation in UK 240V land.

N_Cook <diverse@tcp.co.uk>: Oct 15 01:08PM +0100 Bad mains earth bond-point. Decided to autopsy the Rockwood , presumably original, 2.2K 7W dropper, the previously replaced one is elsewhere 1/2W . Stopped going in further when it looked as though asbestos was part of the construction. I'd not thought how fine the wire must be for 2.2K. Looks as though the asbestos wraps around the core , for thermal expansion give, allowing isolation of the turns at the same time, then covered in fire-cement set in a moulded ceramic body. As brown colour at one end I'll assume it was rust and failure was corrossion, the resistance wire looked fine , what I could see of it but making contact with it meant it locally broke.

neilwrites2@hotmail.com: Oct 15 02:34AM -0700 Hello,   I have an old Data Precision (USA) 1350 "3 1/2" Digit LED type Multimeter from the 70's era. It works great, except after performing a calibration the low K ohm scales are displaying readings are generally out by more then 5 percent.   So, the first step of calibration is adjusting the time base or oscillator to 40 KHZ( +/- 200Hz) for the AD7107. The next step is the Gain calibration by inputing a DC reference voltage of 1.900 volts, and adjusting a pot to this voltage on the display. The last step is balance, where a lead wire is tied back from the red banana jack to pin 36 (Hi Ref) AD7107, and is adjusted to 50 millivolts (+/- 50mv)   The multimeter readings are very good, except for the Low resistance scales.   Does anyone have any ideas on why?   Examples: 475 ohm 1% resistor it reads 430 ohms. 2K Ohm 1% resistor, it displays 1861 ohms   Thanks, Neil

N_Cook <diverse@tcp.co.uk>: Oct 15 10:39AM +0100 > 2K Ohm 1% resistor, it displays 1861 ohms   > Thanks, > Neil   Corrossion at a terminal or joint somewhere? tried different probes? tried twizzling stuff while reading a resistor ohmage under test?

Clifford Heath <no.spam@please.net>: Oct 15 08:44PM +1100 > Does anyone have any ideas on why?   > Examples: 475 ohm 1% resistor it reads 430 ohms. > 2K Ohm 1% resistor, it displays 1861 ohms   Used it to measure voltage and partly fried some of the low-value resisters, seems most likely.

"Ian Field" <gangprobing.alien@ntlworld.com>: Oct 14 06:09PM +0100 "Leonardo Capossio" <capossio.leonardo@gmail.com> wrote in message news:7cdfcf24-c1a0-4479-8006-bea580bc263d@googlegroups.com...   > The crackling sound seems to appear when strongly strumming the guitar. > The volume does not go up or down, it just never reaches a level above > lets say 20W.     For that big a drop, I'd think maybe half the push-pull is cut off and only making it intermittently on big peaks. RoHS solder can cause things like that.   It it turns out to be the low level stages, look for any discrete transistor (or JFET) stages, a high ESR emitter bypass cap can allow a lot of unintended nfb in that stage, so its gain will be a lot less than designed for.   Any electrolytics coupling one stage to the next are also a possibility - if you find any tantalum beads, study the circuit and satisfy yourself that they can't under any circumstances be subjected to reverse voltage, they can go leaky at the drop of a hat! If you find any tantalum caps in signal paths, its not a bad idea to replace them with multilayer ceramic chip types - some manufacturers offer them up to 180uF, and a few can supply resin dipped leaded types.   Generally speaking; start with the soldering, then check electrolytics (especially small ones). Resistors can go high in value or open circuit - high resistance parts are particularly prone to increasing, the lower values (especially wire wound) tend to fail open circuit, these are also slightly more likely to show a burn mark.   If you find any scorched or burned open resistors, there's a good case to start checking for leaky or shorted semiconductors.

"Gareth Magennis" <sound.service@btconnect.com>: Oct 14 07:42PM +0100 wrote in message news:b8a6f8b3-174b-47a6-add9-8d7e05c53f17@googlegroups.com...   Hello,   I was wondering if you could help repair a guitar amplifier, it is a Fender Frontman 212R, schematics are here: http://support.fender.com/schematics/guitar_amplifiers/FM212R_schematic.pdf   The problems are: -Low volume. It is a 100W amplifier and at full power is delivering something like 20W tops at max volume. -Paper crackling sound when guitar is played very hard. It is very subtle, but is annoying.   I know that: -Power supply voltages are ok (including the power amp stage) -Speakers are ok (it has two speakers of 8 ohms in parallel as load) -Nothing seems to be burnt on the PCB, or any cap seems bloated or something   It is unknown to me what the PTC (RT2) is doing, I know the NTC (RT1) is for mains thermal shutdown, but the PTC seems to be for thermal shutdown of the power stage only (because it is thermally coupled to the power transistors power dissipator with some paste).   The next time I see it I will try to see if it is a pre-amp problem or a power amp problem (because fortunately it has a pre-amp out and pwr amp in)   Thanks.         Plug a signal into the Power Amp In socket - this is switched and if the switch gets dirty it can cause your symptoms.   If you take the main board out you will find a couple of discoloured hot spots, particularly around the zener diodes providing the +- 15v for the pre-amp. These need sorting out before they become dry joints, if they haven't already.   I had one of these not so long ago that had dry joints causing one half of the push pull circuit not working, as Ian suggests.     The best solution here is to resolder EVERY joint on the mainboard. That might sound like overkill, but I bet it would take you less than 10 minutes - probably less time than in would take to track down the single (at present) dry joint.     Gareth.

Leonardo Capossio <capossio.leonardo@gmail.com>: Oct 14 01:29PM -0700 On Wednesday, October 14, 2015 at 2:09:49 PM UTC-3, Ian Field wrote: > more likely to show a burn mark.   > If you find any scorched or burned open resistors, there's a good case to > start checking for leaky or shorted semiconductors.   Hi all, thanks for all the replies. I have tested the pre-amp with another PA, and it seems to work correctly, even for the distorsion channels.   Taking out the PCB revealed that three 5W 0.22 ohm resistors were not original, but had been changed by someone (whom the owner cannot pinpoint), and this someone changed them for 22ohm resistors (one .22 ohm from the original remained, and this is probably causing the imbalance). I will replace this resistors with correct ones, and see if this fixes all the problems.

"Ian Field" <gangprobing.alien@ntlworld.com>: Oct 14 09:57PM +0100 "Leonardo Capossio" <capossio.leonardo@gmail.com> wrote in message news:c922cd09-fa98-4ccd-adf9-ea70dedd9d5f@googlegroups.com... > from the original remained, and this is probably causing the imbalance). I > will replace this resistors with correct ones, and see if this fixes all > the problems.   Those parts had probably been replaced because the originals blew. Check whether any associated semiconductors show any sign of having been replaced as well - it wouldn't hurt to test them anyway.

jurb6006@gmail.com: Oct 14 06:16PM -0700 How are you measuring this power output to be 20 watts ?   And as for what is happening here, it is EXTREMELY hard to describe sounds with words, like second harmonic distortion n shit and how it differs from third harmonic.   Know what ? I got an idea and I can do it. Put up a website with different sounds describing what they are. People do not even know the difference between a 60 cycle hum and a 120 cycle hum. I can hear the effect of an open polarity in an amp hands down and go immediately to the problem which usually was a driver (not output) transistor with an open B-E or B-C junction. I could ID the problem by the sound.   Maybe what I should do is make these sounds and put them up on the net. I know how to disconnect this or that and make it sound like that exact fault.   ^Yeah right. Bob Carver got his claim to fame mimicking the sound of super audiophile amps, well I am Cletus Carver and I am gong to have my claim to fame mimicking fucked up amps...   LOL LOL

Phil Allison <pallison49@gmail.com>: Oct 14 10:01PM -0700 Leonardo Capossio wrote:   > original remained, and this is probably causing the imbalance). I will > replace this resistors with correct ones, and see if this fixes all > the problems.   ** That is bad error to make, the repairer must have been clueless or blind.   I see four 0.22ohm, 5W resistors on the schem - two in the power amp and two ( wired in parallel) in series with the ground link for the speaker.   The only time you need to change such resistors is when output transistors have failed and caused them to burn out - so make sure they are the correct type numbers and mounted properly to the heatsink.     ... Phil

Phil Allison <pallison49@gmail.com>: Oct 14 08:11PM -0700 > OK - a few basics on speakers - at least as they were sold in the > US under FTC regulations (sit on your fingers, Phil!):     ** The are simply no FTC rules for published speaker power ratings. The rules you seem to be alluding to are for *amplifers* used in home entertainment.   > c) Low cost, low-wattage amplifiers are much more likely to cause speaker damage than large amplifiers.     ** Depends a lot who is using the amplifer - but in general the risk of speaker damage goes up with more amp power.     > What can happen with some solid-state designs is that when the > amplifier clips (called to produce more power than it can), > it may send straight DC into the speaker   ** Absurd.   Clipping does not cause DC, the main effect is to compress the dynamic range of the music so there is more average power going to the speaker - which eventually overheats the voice coil.     > This issue is far less so from a tube amp - the simplistic explanation is >that it is harder for a transformer to pass DC,   ** Impossible in fact, but clipping wave peaks is just what tube guitar amps do most of all the time and blown speakers are very common - due again to high average power levels.     ... Phil

jurb6006@gmail.com: Oct 14 06:01PM -0700 My laptop doesn't always charge the battery. I have seen it read "32 % not charging" and similar. I have read a bit on it and it seems if you never use it on the battery it might do this. However in my case it seems to be like intermittent or something.   The thing runs Vista Hoe Premium. (that is a typo I kept !) Looking in power management I see nothing that could reinitiate charging. This battery did charge in the other PC, and the battery that belongs in this one did charge and is at 92 %. so I switch it out and the other battery does not even start to boot, so it is below the threshold of operation. I doubt it is completely dead though. We used to keep it charged.   It is a Gateway P series laptop. Well laptopS. I got three. I bought four, one was defective and I lost out due to the warranty expiring before I even booted it up. One got stolen, and when that asshole gets out of jail I am going to smack him upside the head with something made of metal. So I got two of these things running, mine which I am on and just today changed the keyboard, and the other which I gave to my sister but she has no real interest in it. I ran that for a day and could not stand it, I should just clone this thing to it really and have a real solid backup. Hers has seemingly unresolvable browser issues and a few OS peculiarities that really get under my skin. She would probably rather run it the way I set it up if she ever has to. Plus I got a bunch of irreplaceable software. She would have to get used to it but now she has a new one and is getting used to Win 8. So I can pretty much do what I want with it.   Anyway, I am deathly afraid of fucking with BIOS/CMOS in this thing because that caused the one's HD to totally lock up. It is a known problem with the WD1600BEVT, easy to find on the web. I KNOW there is a fault in the mobo of that one and ??I suspect that brought it on. I cannot do the procedure to unlock it, if I could I would and use it because I could use the space. It is less trouble to just use my network. Also, the good HD is actually running, I just have to fix it up. Cloning it would be a stopgap thing, but really there is no real data on that one.   Anyway, I am not sure how to proceed here. I would prefer not to reset the CMOS or any of that because of that risk, however remote I would be F U C K E D R O Y A L.   Right now I am able to download and burn the ISO for the OS of both these machines, and actually I have another that would benefit by that maybe, have to check the version. The problem is these things have built in cameras and finding drivers might be a PITA.   Whatever advice, throw it up here. And Jeff Leiberman, the de facto expert on batteries, I want to hear what you have to say. I just do not want to change anything else, just make it at least try to charge the batteries. If it finds out they are no good OK. But I doubt they are bad. Even in view of the age. They were used some, but not alot. And I got one that is pretty damn good after all these years. They are also rather large I think compared to others.   It is like the battery and screen are the best features of these things. They are not all that fast, the built in cameras suck, the sound sucks. But you know what ? this is what I got and I cannot afford to go out and buy another one and even if I did I have no interest in a newer OS. I just now got this one tamed.   Bottom line is that I really do not use these things mobile all that much, but I want to maintain the batteries as long as possible. People have freaked out over how long my laptop will run, theirs get two years old and they have trouble getting fifteen minutes out of them. Mine out in the garage feeds the garage stereo with a concert that lasts like two hours and the thing is still reading like 70 %. And that used to be on all the batteries.   I know this is too long, just skin though the uninteresting parts I guess.   Thanks.

Bob <rgsros@notme.invalid>: Oct 14 06:23PM -0400 Hi,   Figure that someone here would know.   My TV has only 2 HDMI inputs.   I have a USB hub on my PC that allows 6 USB inputs to be ported to, and shared, by a single USB input on my home desktop PC.   Is there anything similar for TV HDMI inputs ?   Or, are there switch-boxes available as an alternate solution, where you manually can switch from one HDMI source to another one, and then feed the single TV HDMI Port ?   Or,...?   Thanks, Bob

"Dave M" <dgminala@mediacombb.net>: Oct 14 06:27PM -0500 This box will probably do what you want: http://www.newegg.com/Product/Product.aspx?Item=9SIA1KT2VT9895   If it's not what you want, you can search Google for HDMI Switcher or HDMI matrix switch   Hope that helps Dave M     Bob wrote:

Bob Horvath <bhorvath13@comcast.net>: Oct 14 07:57PM -0400 >Or,...?   >Thanks, >Bob   Go to Amazon and search for HDMI switch.

"Tom Del Rosso" <fizzbintuesday@that-google-mail-domain.com>: Oct 14 04:08PM -0400 Cursitor Doom wrote:   > The whole thing is bullshit made up for political purposes:   > http://www.infowars.com/video-of-white-guy-with-briefcase-clock- > contradicts-claim-ahmed-mohamed-was-targeted-because-he-was-muslim/   I never suspected he was targeted because he is Muslim. Considering the things that get kids suspended from U.S. schools nowadays, like drawing a picture of a gun, I never doubted that he was suspended because teachers and policemen are all idiots. When I was his age I made a bicycle odometer which certainly would have gotten me the same treatment if it was today.   --

You received this digest because you're subscribed to updates for this group. You can change your settings on the group membership page. To unsubscribe from this group and stop receiving emails from it send an email to sci.electronics.repair+unsubscribe@googlegroups.com.