- Tek 7141 graticule backlight - no voltage on connector - 4 Updates
- Your Toughest Job - 3 Updates
- black microwave with diode not the problem - 2 Updates
| Nife Sima <gorplop@sdf.org>: Feb 20 03:25PM +0100 I've picked up a Tek 7141 PAL vectorscope not a long time ago and fixed various odds and ends in it. However I'm having trouble finding out the cause of the broken backlight circuit. The SCALE knob on the front doesn't do anything. I've opened it up and the backlight is handled by 2 groups of 3 lightbulbs arranged in a way they light up the proper graticule depending on the mode selected (waveform mon./vectorscope). There are 4 wires going to the backplane via a pin header. There's no voltage on any of the 4 pins of the backplane (even with the light board unplugged). Two of the lightbulbs are open, so that's one fault. However, what else should I check that may be causing no voltage at all on the header? Cheers Nife |
| "pfjw@aol.com" <peterwieck33@gmail.com>: Feb 20 06:51AM -0800 First, the obvious, stupid stuff... (been there, done that): a) Are there any internal fuses? Often, there will be board-mounted fuses and/or fusible links to protect sub-assemblies not immediately visible. If you have a schematic (you DO have a schematic??), look for one of these symbos: https://qph.fs.quoracdn.net/main-qimg-4b55be07eaaa83bc46a640b083cc4e4f-c b) Corroded and/or broken trace in the voltage path. Follow the voltage for the lamps back to the source and look for anything that could cause a discontinuity. c) Are you sure you are using/measuring to the correct 'ground' for those lamps? In some few cases, the lamps are part of the active circuit, such that voltage must be measured across the correct points, not to the common ground. Again, I have no schematic, I am just enumerating the stupid-before-doing-surgery-diagnostics-as-general-practice. Please let us know. Peter Wieck Melrose Park, PA |
| Michael Terrell <terrell.michael.a@gmail.com>: Feb 20 08:05AM -0800 On Thursday, February 20, 2020 at 9:25:30 AM UTC-5, Nife Sima wrote: > should I check that may be causing no voltage at all on the header? > Cheers > Nife Are you sure of the model number? Even Tektronix has no information on it. Ther are several 174x series TV scopes including a 1741A. These are not simple lights with a Rheostat like older products, it uses an IC to drive them. From the 1740A/1741A manual: Graticule Lights U1D is an oscillator with a 600 ms period. Its output drives U1A directly and U1B through a comparator (U1C). The output of U1A and U1B is a 50% duty cycle, with each amplifier driving two of the four graticule light bulbs. Only two of the bulbs are lit at one time. The schematic is on page 299 of the Tektronix 070-8469-03 manual: http://w140.com/tekwiki/images/d/d2/070-8469-03.pdf |
| Nife Sima <gorplop@sdf.org>: Feb 20 05:21PM +0100 On 20.02.2020 17:05, Michael Terrell wrote: > U1B through a comparator (U1C). The output of U1A and U1B is a 50% duty cycle, with each amplifier driving two of the four graticule light bulbs. Only two of the bulbs are lit at one time. > The schematic is on page 299 of the Tektronix 070-8469-03 manual: > http://w140.com/tekwiki/images/d/d2/070-8469-03.pdf Yes, you are right.. It's 1741 my bad. Not 1741A as that one is substantially different. The 1741 is mostly analog, no readouts on the CRT like in the later Tek devices. Sadly I can't find a schematic or even a manual for the early model. |
| Jon Elson <elson@pico-systems.com>: Feb 19 02:15PM -0600 On Wed, 12 Feb 2020 16:27:01 -0800, Jeff Urban wrote: > The ones that separate the Men from the boys. OK, one crazy one was a Datum mag tape controller on a PDP-11 computer. These had one big standard board and a smaller plug-in board to customize it to the specific computer. The logic was just a whole bunch of TTL random logic, no microcode. It was totally dead, all registers read back as zero when you wrote to them. So, I started looking at the global reset. It was not being reset by the CPU, but the buffered side on the board was held in reset (low). I changed a few chips, and that didn't fix it. So, I then measured resistance to ground with power off, and it was REALLY low, like 2 Ohms. I started cutting traces, and finally got down to a 2" stretch of PCB trace that was shorted to ground. There was NO grounded trace within 1/4" of that trace that was at ground. I peeled the trace off the board, there was no speck of copper visible anywhere. I finally put a piece of wire wrap wire across where I'd peeled off the trace, being sure the insulation was intact. The unit worked fine until the end of its life. That was one of the stranger ones. Jon |
| John Robertson <spam@flippers.com>: Feb 19 12:45PM -0800 On 2020/02/19 12:15 p.m., Jon Elson wrote: > the end of its life. > That was one of the stranger ones. > Jon The ShortSqueek by Global Specialties is handy for finding shorts on circuit boards... https://flippers.com/pdfs/GlobalSpecialities_ShortSqueek_Model_SQ-1.pdf It gets a bit of a workout here in my shop every now and then when we have a shorted trace. John ;-#)# |
| Chuck <chuck23@deja.net>: Feb 20 09:54AM -0600 On Wed, 12 Feb 2020 16:27:01 -0800 (PST), Jeff Urban >So, anyone have anything like that " I got others, I bet Allison also does, maybe a few others. I would like to hear about them. you are being a desk potato (or in Quaylese potatoe) on the internet, what else you gonna do ? >I am not a democrat or a liberal but Dan Quayle was not an exemplary...whatever. Anything really. Should not even be trusted to teach grade school spelling and VP of the country. Man Bush 2 was really fucking stupid, couldn't find oil in Texas. Are you kidding me ? >Anyway, back to the topic. Your hardest job, brainwise. In the early 80s,our shop had an19" Hitachi tv that had a ghosting problem. I spent hours in the video circuit but found no defective components. I finally hooked the chassis to a crt on another Hitachi tv and the ghosting was gone. Replacing the crt repaired the set. At the time we were the largest Hitachi dealer in the U.S. but only saw the problem two other times. All were 19" Hitachis. |
| delvon daily <delvondaily@example.com>: Feb 19 07:32PM -0600 Can you help me choose a microwave to fit the hole I already have? Especially how to get the exact size I need? And how important is "inverter technology? I need to replace a dead built-in black microwave without spending $800 to replace it with the original Jenn-Air M170B countertop 1200W 1.6cf unit. The existing fabricated black aluminum faceplate apparatus is pre-set to: Length = 22-1/8" Height = 13-3/8" Depth = 12-5/8" (but it can be deeper) Watts = 1200W Volume = 1.6cf Costco has a #1325470 Panasonic NN-SC668S for $119.99 Length = 20-7/16" Height = 12-3/8" Depth = 16" Watts = 1200W Volume = 1.3cf with something called "Inverter Technology". https://www.costco.com/panasonic-1.3cuft-stainless-steel-countertop-microwave-oven-nn-sc668s.product.100500583.html Home Depot has a #1003366983 Magic Chef for $109.00 Length = 20-3/4" Height = 12" Depth = 15-1/2" Watts = 1100W Volume = 1.6cf https://www.homedepot.com/p/Magic-Chef-1-6-cu-ft-Countertop-Microwave-in-Stainless-steel-with-Gray-Cavity-HMM1611ST2/305708071 Target has a #NN-SN67HS Panasonic for $119.99, which is Length = 20-11/16" Height = 12-1/4" Depth = 15-13/16" Watts = 1200W Volume = 1.2cf https://www.target.com/p/panasonic-1-2-inverter-microwave-stainless-steel-nn-sn67hs/-/A-52689506 Target also has a #072-1-282 Oster for $64.99 Length = 23.9" Height = 14.4" Depth = 18.4" Watts = 1000W Volume = 1.1cf https://www.target.com/p/oster-1-1-cu-ft-1000w-microwave-stainless-steel-ogcmdm11s2-10/-/A-53383982 |
| "pfjw@aol.com" <peterwieck33@gmail.com>: Feb 20 05:01AM -0800 The Troll is back. Please do not feed the troll! |
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