Date
1 - 20 of 43
jobs from hell
|
Hi,
I just finished reassembling a 7A12 after replacing all the lamps. The whole thing must be completely disassembled to do this. GRRRR! I was successful yesterday in replacing the actuator tabs in a 7704A vertical mode selector switch. It must be completely desassembled again and tiny parts managed. It works! I have all the switch assemblies I need now but feel I can fix them now if spare parts are available. I would like to aquire mode selector switches that could serve as parts donors for future repairs. I now have a 7704A calibrator board that i could fix if i had a parts Horizontal Selector Switch 670-1878-00. Jerry Massengale
|
|
|
|
ditter2
--- In TekScopes@yahoogroups.com, jerry massengale <j_massengale@...> wrote:
The 7A12 was one of the first 7000 series plug-ins that was discontinued. I think you are learning first hand why. It turned out that pushbutton switching for attenuators was not reliable. Same as the invert and BW limit in the original 7A16. - Steve
|
|
|
|
On Tue, 16 Jul 2013 20:28:23 -0000, "Steve" <ditter2@yahoo.com> wrote:
--- In TekScopes@yahoogroups.com, jerry massengale <j_massengale@...> wrote:Was it the pushbutton switches which they kept in later plug-ins orThe 7A12 was one of the first 7000 series plug-ins that was discontinued. I think you are learning first hand why. the relays? I imagine those relays were expensive which would be another reason to get rid of them. I have had more problems with the Tektronix relays than the switches and made a list of which plug-ins have the relays so I can keep a watch out for spares.
|
|
|
|
David DiGiacomo
Was it the pushbutton switches which they kept in later plug-ins orI'm not sure what you are saying, but the white relays were used in the 7A13 for a long time after the 7A12 was gone. Also, there are lots of other plugins (and mainframes) where changing the lamps is no fun at all. Soldering incandescent lamps just seems like a bad idea.
|
|
|
|
On Tue, 16 Jul 2013 17:50:00 -0600, David DiGiacomo
<daviddigiacomo@gmail.com> wrote: The 7A13 "pull for x10 Vc" function would require another x10 switchedWas it the pushbutton switches which they kept in later plug-ins orI'm not sure what you are saying, but the white relays were used in input attenuator to implement without relays. I am just suggesting that Tektronix made more effort to stop using the relays than to stop using the pushbuttons. I remember seeing a price list somewhere showing that Tektronix was OEMing the relays for a price in the $50 range until alternative products became available. After a certain time, it seems like the 7A13 was the only product using them. Also, there are lots of other plugins (and mainframes) where changingI think the only problem is easy access which as has been pointed out, is a major problem in many cases. My 7A12 needs new bulbs installed. The on flakey pushbutton switch that I need to repair is on my 7T11A.
|
|
|
|
Don Black <donald_black@...>
I wonder if reducing the lamp voltage slightly to increase their
life would be worthwhile? Perhaps a silicon diode in series with
their supply would give about 0.7 volts drop and improve life (a
diode would give a constant drop however many lamps were lit where a
resistor would depend on load).
toggle quoted messageShow quoted text
Don Black.
On 17-Jul-13 3:38 PM, David wrote:
|
|
|
|
Reducing the incandescent lamp voltage has a huge effect on life which
is inversely proportional to the 16th power of the voltage. Most (all?) of the 7000 mainframes have adjustable lamp voltage and I just leave it set to minimum. On Wed, 17 Jul 2013 15:48:13 +1000, Don Black <donald_black@bigpond.com> wrote: I wonder if reducing the lamp voltage slightly to increase their life
|
|
|
|
Hi guys,
toggle quoted messageShow quoted text
may I ask why you don't replace those with LEDs? Thanks, D.
On Wed, Jul 17, 2013 at 8:10 AM, David <davidwhess@gmail.com> wrote:
Reducing the incandescent lamp voltage has a huge effect on life which
|
|
|
|
Hi,
toggle quoted messageShow quoted text
I keep forgetting about the lamp switch on the back of the power supply. Otherwise the rheostat on the front only controls the graticule lamps on my 7704A. The biggest problem on jobs like the 7A12 is the nut that retains the input connectors. On this one ch2 had a 12 sided nut that required using a chisel to back it off. Ch1 had a slotted ring that that was much easier to remove. Only one lamp on my 7A12 was working and it was scorched almost completely black. Adding a diode or resistor would require a lot off etch cuts and using a diode would require getting the polarity right. I modified one plugin to use leds and found that you must be careful to get an led with wide angle radiation. Some leds do not shine well to the side. Consult the data sheets. You also want to use the clear lens versions. Be careful to test the lamps BEFORE you reassemble. Jerry Massengale
-----Original Message----- From: David To: TekScopes Sent: Wed, Jul 17, 2013 1:11 am Subject: Re: [TekScopes] Re: jobs from hell Reducing the incandescent lamp voltage has a huge effect on life which
is inversely proportional to the 16th power of the voltage. Most (all?) of the 7000 mainframes have adjustable lamp voltage and I just leave it set to minimum. On Wed, 17 Jul 2013 15:48:13 +1000, Don Black <donald_black@...> wrote: >I wonder if reducing the lamp voltage slightly to increase their life >would be worthwhile? Perhaps a silicon diode in series with their supply >would give about 0.7 volts drop and improve life (a diode would give a >constant drop however many lamps were lit where a resistor would depend >on load). > >Don Black. > >On 17-Jul-13 3:38 PM, David wrote: >> >> On Tue, 16 Jul 2013 17:50:00 -0600, David DiGiacomo >> <daviddigiacomo@... <mailto:daviddigiacomo%40gmail.com>>; wrote: >> >> >> Was it the pushbutton switches which they kept in later plug-ins or >> >> the relays? I imagine those relays were expensive which would be >> >> another reason to get rid of them. >> > >> >I'm not sure what you are saying, but the white relays were used in >> >the 7A13 for a long time after the 7A12 was gone. >> >> The 7A13 "pull for x10 Vc" function would require another x10 switched >> input attenuator to implement without relays. >> >> I am just suggesting that Tektronix made more effort to stop using the >> relays than to stop using the pushbuttons. I remember seeing a price >> list somewhere showing that Tektronix was OEMing the relays for a >> price in the $50 range until alternative products became available. >> After a certain time, it seems like the 7A13 was the only product >> using them. >> >> >Also, there are lots of other plugins (and mainframes) where changing >> >the lamps is no fun at all. Soldering incandescent lamps just seems >> >like a bad idea. >> >> I think the only problem is easy access which as has been pointed out, >> is a major problem in many cases. My 7A12 needs new bulbs installed. >> >> The on flakey pushbutton switch that I need to repair is on my 7T11A. >> >>
|
|
|
|
I have not found any white T-3/4 sized LEDs which have the proper
viewing angle to work with the light pipes. There is also not really enough room to add series resistors. The grain of wheat bulbs just work. On Wed, 17 Jul 2013 12:07:08 +0200, "cheater00 ." <cheater00@gmail.com> wrote: Hi guys,
|
|
|
|
For a bunch of talented handymen/engineers who are not afraid to get their fingers dirty, I see a lot of excuses on this topic.
Take a cheap standard 3mm or 5mm LED with between 15,000 to 50,000mcd, sand it opaque with a simple piece of sandpaper, calculate the value for the dropping resistor, and you've got a perfect substitute for those incandescent lamps. The LED's light illuminates in all directions, and you don't have to waste time searching datasheets, because the perfect LED just doesn't exist. Your talents make it SO! Menahem Yachad http://www.condoraudio.com
|
|
|
|
David DiGiacomo
On Wed, Jul 17, 2013 at 9:13 AM, dehav7 <yachadm@gmail.com> wrote:
For a bunch of talented handymen/engineers who are not afraid to get their fingers dirty, I see a lot of excuses on this topic.Sigh, have you ever changed the lamps in a 7A12? I'd really like to see you stuff a 5mm LED in there.
|
|
|
|
David,
his idea might not be the greatest, but maybe there's some truth to it. A SMT resistor and diode could work well together stacked. The LED could be made opaque by dropping it in something that'll attack the plastic, such as watered-down thinner. Cheers, D. On Wed, Jul 17, 2013 at 5:15 PM, David DiGiacomo <daviddigiacomo@gmail.com> wrote: On Wed, Jul 17, 2013 at 9:13 AM, dehav7 <yachadm@gmail.com> wrote:For a bunch of talented handymen/engineers who are not afraid to get their fingers dirty, I see a lot of excuses on this topic.Sigh, have you ever changed the lamps in a 7A12? I'd really like to
|
|
|
|
Craig Sawyers <c.sawyers@...>
Well, I've just measured some spare Tek lamps, and they are 3mm diameter and
toggle quoted messageShow quoted text
7mm from the top of the dome to the wire lead outs. So a standard 3mm white LED should fit nicely. Need to figure out a way of getting from whatever the supply voltage is in the plugin or mainframe down to about ~3.5V (the drop for a white LED). But since coloured LED's in the same physical size are available to run directly from 5V or 12V, I'll bet there is a white LED with this feature that should be a direct drop in. Caig
-----Original Message-----SMT resistor and diode could work well together stacked. The LED could be madewatered- down thinner.those incandescent lamps.waste time searching datasheets, because the perfect LED just doesn't exist.
|
|
|
|
Craig - too expensive a solution.
toggle quoted messageShow quoted text
Tell me the supply voltage, and how many white LED's you want to run on the same lighting circuit (paralleled), and I'll tell you what resistor you need. Also, if it's AC current, it's desirable to insert a 1N4004 in the supply circuit to rectify the current, EVEN THOUGH the LED's can rectify the current. A more "reliable" voltage-drop for white LED's is 3.1V, not 3.5V. The LED runs cooler, and lasts longer, with no appreciable drop in brightness in this application. You can even get creative and add in a 100uF 10V bypass capacitor, to steady any fluctuations and give a nice shutdown effect. I have converted hundreds of machines from incandescent to LED's, and it's a simple and doable job! Menahem
But since coloured LED's in the same physical size are available to run
|
|
|
|
cheater00 . wrote:
There are tiny SMD LEDs I recently bought a reel of 1500 TLMY3101-GSO8 LEDs on Ebay for a project for $11. SMD resistors come in sizes down to 0102. :)
|
|
|
|
I have not seen white LEDs with built in drivers yet. I think the
problem there is that they are intended to be run at such high currents compared to indicator LEDs that the additional power dissappation from an integrated driver would be a problem. The SiC or GaN processes they use may not support that level of integration anyway. The T-3/4 and matybe T-1 LEDs definately fit but the problem is that they direct most of their light forward missing the surrounding light pipe. They do make wide angle units but not in the T-3/4 format that I have seen yet. A countersink could be used to cut a 45 degree conic section into the front of the LED body and then silver paint or metalization could be added to reflect the light evenly 90 degrees but that is more trouble than just buying the T-3/4 5 volt grain of wheat bulb. There is not enough room to add an external reflector. I tried. On Wed, 17 Jul 2013 17:32:30 +0100, "Craig Sawyers" <c.sawyers@tech-enterprise.com> wrote: Well, I've just measured some spare Tek lamps, and they are 3mm diameter and
|
|
|
|
On Wed, 17 Jul 2013 13:32:37 -0400, "Michael A. Terrell"
<mike.terrell@earthlink.net> wrote: cheater00 . wrote:Mounting the SMD LED would be a problem and if it uses the originalThere are tiny SMD LEDs I recently bought a reel of 1500 circuit pads, it will be directing most of its light perpendicular and past the light pipe. Duplicating the power the original 5 volt bulb used for maximum LED brightness would exceed the power rating of a tiny SMD resistor. With derating, I would not want to go below 1/4 watt.
|
|
|
|
David DiGiacomo
On Wed, Jul 17, 2013 at 10:32 AM, Craig Sawyers
<c.sawyers@tech-enterprise.com> wrote: But since coloured LED's in the same physical size are available to runWhite 5V resistor LEDs are not a standard part. There isn't enough voltage headroom between the supply and the LED forward voltage, so it's difficult to get acceptable matching. Anyway, we are talking about 7000 plugins, where you have the problem of the low setting on the lights voltage. I don't think it's well defined, so it may not even turn on white LEDs. So then you have to put it on high, and if you haven't converted all the lights to LEDs, it will burn out the remaining bulbs faster. Or you could hack up your LED-converted plugins to run the lights from a different supply instead of lights power, or you could modify the mainframe so you could set the lights power to exactly the right value, but bleh. Why didn't Tek just use socketed bulbs?
|
|
|
|
David DiGiacomo
On Wed, Jul 17, 2013 at 10:56 AM, dehav7 <yachadm@gmail.com> wrote:
Craig - too expensive a solution.The supply voltage is 3.5VDC or 5VDC. 1 LED per circuit. There's no room for a resistor. Now what?
|
|
|