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Cydrome Leader <presence@MUNGEpanix.com>: Dec 03 05:24PM > past.   > Re-live some past glories?   > The first time you traced down a bad reset line for a microprocessor?   My first computer was a Franklin Ace 1000 that was give to me broken. It had complete schematics so I was able to trace out what was in fact a bad reset signal going to the CPU. Pretty sure it was a 74S161 (something that ran hot and wasn't LS series) that had to be swapped out and it was fine again. Donor chip came from an arcade machine board. Looking that part up I see it's a 4 bit counter- if that's correct it may have someting to do with the video timing signals which were a weird hack in the Apple ][ which this machine was an improved clone of.

Trevor Wilson <trevor@SPAMBLOCKrageaudio.com.au>: Dec 04 06:49AM +1100 On 3/12/2015 11:34 PM, Mark Zacharias wrote:   > Any more recent successs stories to brag about?   > C'mon, don't we all enjoy patting ourselves on the back, really?   > Mark Z.   **I recall the first time (1980-ish) I discovered those fusible resistors that go high after a few years. With no obvious signs of distress. Now I just head straight for the buggers.   Then there's those low value (</=47 Ohms), 1/4W cracked carbon resistors that go O/C when subjected to ca. 60+ Volts with no signs of burning (Marantz 1200b, 240, 250M, 500 models). Over the years, I learned to suspect any resistor over the value of 100k, if the circuit is displaying some kind of mysterious fault that cannot be explained by a semiconductor failure or cap leakage.   -- Trevor Wilson www.rageaudio.com.au   --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus

etpm@whidbey.com: Dec 03 03:53PM -0800 On Fri, 4 Dec 2015 06:49:10 +1100, Trevor Wilson >suspect any resistor over the value of 100k, if the circuit is >displaying some kind of mysterious fault that cannot be explained by a >semiconductor failure or cap leakage. That resistor story is interesting. About two years ago I had a linear power supply fail in one of my CNC machines. I did the troubleshooting bit and discovered a bad -15 volt regulator. So I replaced it and then a few weeks later something else went bad and I couldn't find it. I took it to a friend who is an electronics engineer and he discovered an open resistor. I asked why he checked it because there was no visual reason for it to be bad. It wasn't cracked or discolored. He said that's what he usually did first, check for open resistors. He said it was a common fault. Since then the power supply has been operating fine. Eric

"Mark Zacharias" <mark_zacharias@sbcglobal.net>: Dec 03 07:30PM -0600 <etpm@whidbey.com> wrote in message news:e5l16bt7rbnma2osrvomlur6aqscnjtf9o@4ax.com... > said it was a common fault. Since then the power supply has been > operating fine. > Eric   Yeah - when "the usual suspects" don't pan out, I start looking for bad high value resistors.   Had a bad 150K 1/8 watt carbon on a late model Pioneer surround receiver the other day.     Mark Z.

amdx <nojunk@knology.net>: Dec 03 07:34PM -0600 On 12/3/2015 6:34 AM, Mark Zacharias wrote:     > C'mon, don't we all enjoy patting ourselves on the back, really?   > Mark Z.   I posted this an hour ago, but it hasn't shown up, so I'll do it again.   Back 30 years ago I stopped at a consumer electronics/TV repair shop and presented my resume. I had been to many manufacturer service training seminars and had a hand full of certificates of completion. The owner looked it over and said, "I just hired a guy, I wish you came in earlier." So I went home and about 45 minutes later he called and said, "I see you have a lot of Sony training, I have this projection TV in here that nobody can fix, I'd be happy to pay you for looking at it." So I drove down and got the manual, noted the problem was, no output from the 3 tubes. I started poking around in the HV section, and within minutes the owner said, hey you got it working! I didn't know it was working ;-} I put my head out front and it had an output. Hmm, I unhooked my scope probe and the picture went with it. From there, we, more he, figured out one of the other techs replaced a cap with 1/10 the proper value, the scope probe hanging on the test point had enough capacitance to make the set work. He hired me that day, it was good, within two blocks of my house. So, I got a job by accident. Mikek

makolber@yahoo.com: Dec 04 07:13AM -0800 One of my favorite stories is from electronics lab in college.   We had to build a small two stage transistor audio amp in the lab with parts from the stock room, onto a protoboard like breadboard.   My lab partners and I were experienced hams and got ours working in no time , no problems.   The PHD proffesor called me over to help him troubleshoot another groups that they could not get to work.   The design had a 10uf cap between the two stages.   I looked at the other groups breadboard and immediatly saw a tiny ceramic cap with a 10 printed on it between the two stages.   I pointed to the cap and said, that doesn't look right.   Got an A in that lab.   =========================   Oh another one.   I worked for a company that made CATV settop boxes. I wandered into the lab where a group of young engineers were stuck troubleshooting a new box design. The picture was black and white and they could not figure out why there was no color. Looking into the box I saw a crystal marked 3.579545.   On a total whim, I put my fingers on the crystal.   The picture immediatly snapped into color!!!!   I was amazed myself but didn't let it show....I just cooly said, there is your problem and walked away. :-)       And lastly, in the same vein you will all enjoy this story   http://www.rfcafe.com/references/popular-electronics/me-technician-you-engineer-february-1963-popular-electronics.htm   Have fun   Mark             Mark... ====================

sound.service@btconnect.com: Dec 04 08:26AM -0800 On Thursday, December 3, 2015 at 12:34:56 PM UTC, Mark Zacharias wrote:   > C'mon, don't we all enjoy patting ourselves on the back, really?   > Mark Z.       My favourite - I was working for a Pro PA hire compoany in London. They had supplied a monitor system for a BBC recording of Public Image Ltd at Maida Vale Studios, London. The system was buzzing like crazy and none of the Sound Company or BBC engineers could work out why. They were about to pull the whole gig. They sent me down as a last faint hope.   It was obviously some kind of mains problem, but everything seemed to check out fine on multimeters. Earths, Neutrals were all at 0v. Eventually I decided to plug in my scope, to discover that instead of a nice straight line accross the display, it was massively modulated. Clearly the scope's Earth wasn't a proper Earth but had some mains on it. I then was able to track down the fault - one multi-way extension cable attatched to the many, many pieces of equipment had Earth and Neutral reversed, thus connecting all Earths and Neutrals in the middle of the studio as well as back at the mains Intake.   Ripped the offending extension out, the buzzing ceased immediately, and the BBC and Public Image Limited got their recording and the Sound Company didn't lose the gig or it's reputation.       Gareth.

sound.service@btconnect.com: Dec 04 05:45AM -0800 Hi,   what's the best type of battery for a busking amp?   I have a couple of Electro Harmonix Freedom amps here. Apparently this is the original they were supplied with.   http://www.ecomelectronics.com/prodinfo.phtml?id=3323523&gclid=CPyCsMqxn74CFcgRMwodl0cA5Q       Cheers,     Gareth.

N_Cook <diverse@tcp.co.uk>: Dec 04 02:46PM > Cheers,   > Gareth.   Local buskers to me , tend to get 12V, 10Ah ones , second hand, from a local motorcycle insurance write-off scrapper/parts seller. Busker use is much lighter use than starter motors, and his basic check over before sale , is adequate.

"Gareth Magennis" <sound.service@btconnect.com>: Dec 03 07:41PM "N_Cook" wrote in message news:n3pcr2$lef$1@dont-email.me...   The owner cannot detect a difference. Other than different gain settings are obvious, how to set up and test? . I've not put a scope on there yet, but what set of parameters to confirm there is a difference, compressor or no compressor, max or min of contour settings, what sort of level and frequency of presumably over-driven input? Test not requiring guitar input and ear-drums, as then it becomes subjective/musical ears required. The valve actively tests fine.   Incidently seriously crap "engineering" on the speaker outlet board, especially as it is PbF. 2 legged 1/4 inch socket, no extra dummy legs for mechanical strength, so 2 simple active PbF joints supposed to hold the pcb and 2 thick unconstrained supply wires , laughable.           There is a lot of audible difference between the valve stage and the transistor stage in the HA3500, it's deliberately designed in. If the owner can't hear this there is no point in him owning such an amp.     As for "testing" this stage, I would have to ask why do you need to test this stage? What do you hope to achieve by doing so? How are your results actually going to make any sense?       Sometimes there is just no substitute for a pair of ears and a brain.         Gareth.

N_Cook <diverse@tcp.co.uk>: Dec 03 08:01PM On 03/12/2015 19:41, Gareth Magennis wrote:   > Gareth.   So how does he or I determine whether things are as they should be or that there is some failure with one or both of those channels? I'll put a scope on there and suck it and see with different sine f and levels of input and different other control settings.

N_Cook <diverse@tcp.co.uk>: Dec 03 08:57PM This is an ebay purchase. Forgot to say I pulled the valve and that fully killed throughput of the tube channel. Reasonable looking DC on the valve base. No provision in the schematic for adjusting bias , other than component change in the self-biasing chain. Another engineering problem with this amp. Steel cab bolts into tapped alumimium and seized threads (whetever that steel/Al semi-welding process is, not corrossion, melding?) . Previous person had ended up sheering one of the bolts and stripping the heads of the remaining ones. Matter of removing the corner protectors off the cab , then remove the other bolts to the angle plates, then mole-grips on the sheered bolt stem. Vaseline on all such threads before returning, including the replacement 4 x 6mm replacement front retaining bolts.

N_Cook <diverse@tcp.co.uk>: Dec 04 12:51PM Monitoring send out. All controls mid, except graphic out, solid tate 0, tube mid and compressor off. Minimum sine input to show soft clipping is at about 400Hz, requiring 1.05V rms in. Then hard clipping coming in about 1.5V rms. I'll take that as normal "tube" function

sound.service@btconnect.com: Dec 04 05:59AM -0800 On Friday, December 4, 2015 at 12:51:11 PM UTC, N_Cook wrote: > Minimum sine input to show soft clipping is at about 400Hz, requiring > 1.05V rms in. Then hard clipping coming in about 1.5V rms. > I'll take that as normal "tube" function       Few bass players will drive this amp into clipping the tube. The tube circuit has a very different EQ to the transistor circuit, which I would guess is pretty much flat.     Cheers,     Gareth.

Cydrome Leader <presence@MUNGEpanix.com>: Dec 03 10:41PM >> neons for a digital display.   > See https://picasaweb.google.com/111741851908838288378/CEDRICProject? > authuser=0&feat=directlink   Nice case. How old is that thing? What's inside?

Cydrome Leader <presence@MUNGEpanix.com>: Dec 03 10:36PM > Living in the south I doubt much if any of that 'odd ball' power was used. > About the only "odd" voltage I see is some 208 volts phase to phase with 120 > to the neutral instead of the 240 p to p.   208 phase to phase means you're looking at two legs of three phase power, and not split phase 120-120 like in a typical home.

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