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Pet Peeve - bad/incorrect/no documentation
Pet Peeve - bad/incorrect/no documentation
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Old 11th August 2018, 11:31 AM   #1
campsquire is offline campsquire  United States
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Default Pet Peeve - bad/incorrect/no documentation

I've been reviving a Teac A4010-S reel to reel lately and have had difficulty finding a correct schematic for it. In Teac's defense, they sold a quarter million of these (with good reason) and the design evolved. I believe there are no less than five variants that occurred between the mid 60s and early 70's that are quite different. I have found three schematic variants so far but I can't find mine. Really hats off to a company that will evolve a product even though it's selling well......but......
Can you keep the documents pertinent and dated with reference to production dates?
Geesh......I have spent hours chasing down a problem only to conclude my schematic is not representative.
I have concluded that the guy who drew it apparently only had a symbol for a PNP transistor and not one for an NPN, and furthermore, this did not stop him from incorrectly showing PNP everywhere!
This got me to thinking. This seems to be a repetitive theme for me when fixing audio, current pieces or vintage.
If I have a correct schematic/bom/layout, I can fix anything within a half hour and will have identified the exact component(s) that are bad. Unfortunately, multiply that time exponentially if I'm missing any of the three, especially a correct schematic!
I find the biggest challenge when troubleshooting to be identifying signal flow. Typically there many features in an integrated audio piece of gear and this results in confusing signal routes. For example, many units from the seventies (the apogee of audio quality IMO) will panel mount controls and wire down to the board rather than PCB mount the controls which I applaud for reliability reasons. However, this allows the designer to put them anywhere on a panel with no deference to the signal flow. You must agree when troubleshooting one must identify a point where the signal is good then the point where it goes bad. This can be challenging with a feature laden piece of gear. This is where, yet another document, a block diagram comes into play. My Marantz 2245 docs include this and it has been immensely beneficial to reducing fix it time.
So...my point?
Any of you DIY folks, do yourself and the community a favor and create good documents. Someone may have to service your gear some day in the future when you are lying horizontal terra ferma.
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Old 11th August 2018, 12:36 PM   #2
mt490 is offline mt490
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Maybe they don't want you to really know how their equipment works, just where the parts are?
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Old 11th August 2018, 12:41 PM   #3
scott wurcer is offline scott wurcer  United States
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Years ago I always immediately ordered a full tech service manual for any piece of gear I bought. SONY's especially were very good.
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Old 11th August 2018, 12:52 PM   #4
wintermute is offline wintermute  Australia
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Pet Peeve - bad/incorrect/no documentation
I'm sure I've read that it is common practice to put errors into schematics deliberately to throw off would be cloners.

Whether there is any truth to that or not I'm not sure.

Tony.
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Old 11th August 2018, 12:59 PM   #5
scott wurcer is offline scott wurcer  United States
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Originally Posted by wintermute View Post
Whether there is any truth to that or not I'm not sure.

Tony.
Never saw that with a major. What I have seen are potted internal modules that had to be ordered as complete units from the manufacturer as well as custom markings on ordinary parts.
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Old 11th August 2018, 02:16 PM   #6
Ken Newton is offline Ken Newton  United States
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Quote:
Originally Posted by mt490 View Post
Maybe they don't want you to really know how their equipment works, just where the parts are?
An parts placement guide is of little use without an schematic, as far as troubleshooting is concenred.

Last edited by Ken Newton; 11th August 2018 at 02:19 PM.
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Old 11th August 2018, 07:02 PM   #7
nigelwright7557 is offline nigelwright7557  United Kingdom
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Sometimes mistakes are deliberate and other times by accident.

I bought a Maplin 225WRMS amp kit.
The parts list was wrong in a couple of places.
For a beginner it could have been a disaster if it was powered up with components wrong.
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Old 13th August 2018, 12:45 AM   #8
campsquire is offline campsquire  United States
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Update - I finally located the correct service manual. Turns out I have the Teac S-1040SL model which came out toward the end of the model life. It has tape bias type switches so one can play the newer 1/4" tape that had come out in the early 70s. I'd say the schematic in the manual is 99% correct which was very helpful. It's amazing how much the electronics changed design, even topology, over it's product life. I had a distorted right channel which turned out to be an NPN transistor pair that some how exhibited an out of spec gain. Really odd - I've never seen that before. Usually if you can measure a a transistor's base/collector and base/emitter forward drop using the diode scale on a volt meter then it's ok. Not this time! The bias point had drifted to the point the lower half of the waveform was severely compressed. I found a substitute transistor type in my mediocre collection, replaced them, and now the deck sounds great. Nonetheless, somebody shoot me if I ever design a single sided PCB with no reference designators! That was a b!@#$ to trouble shoot and repair. I lifted a couple pads by mistake in fact.
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Old 13th August 2018, 10:04 PM   #9
wintermute is offline wintermute  Australia
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Pet Peeve - bad/incorrect/no documentation
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Old 13th August 2018, 10:39 PM   #10
Bare is offline Bare  Canada
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Originally Posted by scott wurcer View Post
Never saw that with a major. What I have seen are potted internal modules that had to be ordered as complete units from the manufacturer as well as custom markings on ordinary parts.
In 80's YAMAHA used to pot their Motorcycle Ignition and control electronics with an epoxy slurry FULL of broken Glass shards.. (Can't begin to make this level of Stupidity up)
All that to protect their market leading (in their wee minds) 8 bit technology
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