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Why I "dislike" electronics


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I have always found it frustrating to diagnose and repair, as one's attempts are too often unfruitful and and hindered by lack of costly and difficult to master equipment. I have had my highlights as in diagnosing hardware bugs from my software point of view, or saving good money by replacing a power supply capacitor, but will never get to love it.

Latest failure, tried to repair my old label printer, the LCD would go crazy flickering when displaying more than 5 letters out of the 10, but it was printing just fine. All I did was to remove for measuing and fit back the single non-SMD capacitor, which proved fine, and testing in circuit two or three of the SMD ones - which of course was inconclusive. I am absolutely sure to not have slipped probes or the like. Now the LCD lits all the segments as if the CPU doesn't start. There is a decent service manual available but is not like on can go crazy after something like that. Really I like better to work on an hairsping at least I can directly see my mistakes and progresses.

 

20200822_140451_copy_600x800.jpg

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It is an all to familiar story. I used to fix electronic equipment for a living (or at least part of my living was made by repairing electronic stuff). Sadly most "stuff" these days is not designed to be fixable. Typically there are no schematics, no spare parts, and proprietary vendor lock-in designed into the product to force you to bin it and buy another. 

Ink jet printers are perhaps the prime example of cynical engineering. A device which forces you to buy ink (basically carbon black, or cheap pigment in a suspension) at prices that make it more expensive per gram than exotic perfumes, or rare elements.

I'm a fan of open source software and hardware, and tend to use it where possible.

My guess with your device is poor solder some where. Second guess would be cracks in the PCB or bad connector contacs. Third would be a failed capacitor. The next suspect would be, that blue ceramic resonator in the top left. All guesses base on previous experiences. Sadly the cost of your time usually outweighs the cost of replacement for the majority of this stuff, so off to the landfill they go.

Edited by AndyHull
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Update, now it works as before, that is with the unstable LCD, all I did was taking a break to write the above. Capricious and vengeful stuff really, which is the entire point of my whining.

I wonder how the tiny difference in current absorbed or whatelse can make the LCD fail only when displaying more than 3 characters?

PCB appears whole and takes gentle flexing without a fuss. The blue component is the CPU oscillator measured as per spec. Thank you cheap DMM.

I will focus on calligraphy for my next labels.

 

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Right there with you. Electrickery! 

In the middle of a similar project. A cheap-o Chinese 6J1 powered phono preamplifier purchased on Ali-X. Showed up with broken tubes, so I got new ones (after a refund for the amplifier was received). Once I fired it up though, there's no gain at all. My guess is that there are some incorrect or misplaced resistors in the gain stage, but I can't for the life of me find a schematic of the little **BLEEP**! If I want to make it work, I'm going to have to take it apart, make a schematic from scratch as it sits, then math it all out to figure out what the values are SUPPOSED to be, THEN if I'm lucky and it's just a component transposition error, put them back where they should be. If I'm not, I'll have to get really lucky to find a proper resistor in my stash or wait until the next time I need enough components to warrant the shipping cost.

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1 hour ago, spectre6000 said:

A cheap-o Chinese 6J1 powered phono preamplifier purchased on Ali-X. Showed up with broken tubes, so I got new ones (after a refund for the amplifier was received). Once I fired it up though, there's no gain at all.

When I need an humbling moment I watch a random video from the guy below. If he can't get a schematic he draws it and then proceeds to not just explain what is wrong with the box at hand, then to improve the whole shebang. And  there is another tubes guy way more extreme. Oh well.

 https://www.youtube.com/c/MrCarlsonsLab

 

Edited by jdm
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On 8/22/2020 at 5:28 PM, spectre6000 said:

If I want to make it work, I'm going to have to take it apart, make a schematic from scratch as it sits, then math it all out to figure out what the values are SUPPOSED to be, THEN if I'm lucky and it's just a component transposition error, put them back where they should be

I might take a slightly different aproach, and simply search online for 6J1 amplifier schematic.

There are dozens of similar amplifiers, but they all tend to use the same basic schematics.

For example.

5cd3ff69-de62-44c6-82b1-a6394927255c.jpg

 

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  • 3 weeks later...
On 8/22/2020 at 1:25 PM, jdm said:

I have always found it frustrating to diagnose and repair, as one's attempts are too often unfruitful and and hindered by lack of costly and difficult to master equipment. I have had my highlights as in diagnosing hardware bugs from my software point of view, or saving good money by replacing a power supply capacitor, but will never get to love it.

Latest failure, tried to repair my old label printer, the LCD would go crazy flickering when displaying more than 5 letters out of the 10, but it was printing just fine. All I did was to remove for measuing and fit back the single non-SMD capacitor, which proved fine, and testing in circuit two or three of the SMD ones - which of course was inconclusive. I am absolutely sure to not have slipped probes or the like. Now the LCD lits all the segments as if the CPU doesn't start. There is a decent service manual available but is not like on can go crazy after something like that. Really I like better to work on an hairsping at least I can directly see my mistakes and progresses.

 

20200822_140451_copy_600x800.jpg

Have you tried to hit its side or top with your palm/fist?

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1 hour ago, luiazazrambo said:

Have you tried to hit its side or top with your palm/fist?

That helps when the issue is with the contact pads, as in some segments staying off always. Not the case here.
I have got a new Brother printer, cheap as chips and has with more functions. Still I was perfectly OK with the old one :(

Edited by jdm
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On 8/25/2020 at 3:33 AM, AndyHull said:

I might take a slightly different aproach, and simply search online for 6J1 amplifier schematic.

There are dozens of similar amplifiers, but they all tend to use the same basic schematics.

 

In this particular case, it looks like the component values are actually screen printed on the board under the components, it's just not readable with the components installed on top of the printed values. I'll probably desolder it some day and see if I can't find the errant resistor values, but at the moment it's cost me nothing but some time, and can sit in a cubby in my desk for a while until I get my electronics tools back out for some other thing down the road.

Meanwhile, I decided to take a different and more deliberate path to phono preamp fun. I found a proven schematic online utilizing better quality components, and just need to find time and hobby funds to make all the parts show up on my desk. It'll be much higher quality all around.

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You might also find this link useful.

https://www.circuitlab.com/editor/#?id=9vnehk

 

image.thumb.png.cfb76d6c2d56ad12c4c5e06c7ef0e010.png

BTW you do know that the circuit typically uses a 12V AC power supply, not DC, as it needs to use a doubler to make the +/- 28V supply rails. If you feed it DC, the tubes will light, but the thing wont do much else.

EDIT: Given the low power nature of those two dinky little tubes, I doubt if the thing will be capable of much output anyway. Fine as a headphone amp, but not much use for more than a few hundred milliwatts, maybe a watt max. The nearest equivalent non Chinese tube I could find was capable of a maximum dissipation of 1.7 Watts, so allowing for losses etc. you wont exactly be able to crank the thing up to 11 and annoy your neighbours. 

image.png.1a8903351e6b134e6ede2fd0dbea5474.png

 

https://www.radiomuseum.org/tubes/tube_6j1.html

 

Edited by AndyHull
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https://media3.giphy.com/media/3o72F8t9TDi2xVnxOE/giphy.gif

It does want a 12V[b]AC[/b] supply... I'm so used to DC supplies that it didn't register... I just assumed they were relying on a DC power supply for rectification to cut part count and costs, and the doubler never registered in my mind as needing AC... There was exactly a sum total of 0 documentation with the thing, and the ad copy was just bad chinglish. I tried to find a schematic for this particular amplifier, but never quite found one that matched what was in front of me. OK... So maybe the first step here is to find a suitable power supply... 

Edited by spectre6000
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On 9/15/2020 at 3:43 PM, spectre6000 said:

So maybe the first step here is to find a suitable power supply... 

You may already have something lying about that you could use. If you have an older style non switch mode 12V wall wart, you may be able to grab the AC voltage before it hits the bridge rectifier.
Failing that old computer modem power supplies were often AC, as were some older desk phones. I doubt if the voltage is critical, so 15V AC would probably work just as well.

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  • 2 weeks later...

Another less than brilliant step in the muddy waters of moving electrons. Got myself the below for €20 or so, but is not the best thing ever.

Pros: it does what I took it for, to show pulses in a quartz module circuit. Comes with needle probes, needed to poke in the small holes or pads. But surely I could have done the same with something lighter and simpler.

Cons: it's stupidly large. It needs two set of batteries to activate all functions. Mine at least has a large error, at least in DCV mode, a brand new alkaline battery reads 1.3V when it is almost 1.6V on the digital meter.

 

 

1528_proskit_mt2017.jpg

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It isn't easy to find a good analog moving coil meter any more. There are quite a few like the one you bought that are OK ish, but I suspect if you want a good analog meter you would need to ether spend a wad of cash, or go for an used Avo meter or something similar.

If you only want something just to "follow the beat' as it were, say for audio or watch coils, then these Chinese meters are OK, but if you want precision, accuracy or long term reliability, then proper "old school" is the way forward.

The same is true to some degree with oscilloscopes. Sometimes an old school CRT scope hits the spot. No strange digital aliasing artifacts to confuse you, no menu system to fight with, it just does what it was designed to do.

Of course for more than  MHz of bandwidth, you are back to parting with a shed load of cash.

Edited by AndyHull
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On 8/22/2020 at 12:28 PM, spectre6000 said:

Right there with you. Electrickery! 

In the middle of a similar project. A cheap-o Chinese 6J1 powered phono preamplifier purchased on Ali-X. Showed up with broken tubes, so I got new ones (after a refund for the amplifier was received). Once I fired it up though, there's no gain at all. My guess is that there are some incorrect or misplaced resistors in the gain stage, but I can't for the life of me find a schematic of the little **BLEEP**! If I want to make it work, I'm going to have to take it apart, make a schematic from scratch as it sits, then math it all out to figure out what the values are SUPPOSED to be, THEN if I'm lucky and it's just a component transposition error, put them back where they should be. If I'm not, I'll have to get really lucky to find a proper resistor in my stash or wait until the next time I need enough components to warrant the shipping cost.

You really  need to build  your own tube gear.  Or rebuild  it.

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On 9/20/2020 at 8:17 PM, AndyHull said:

You may already have something lying about that you could use. If you have an older style non switch mode 12V wall wart, you may be able to grab the AC voltage before it hits the bridge rectifier.
Failing that old computer modem power supplies were often AC, as were some older desk phones. I doubt if the voltage is critical, so 15V AC would probably work just as well.

Many consumer  electronics use  rectified 12vac. If you have an old boom box laying about  you might want to check for a transformer  there. Rule of thumb is that transformers of this type are good  for about 1 amp per pound

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On 10/1/2020 at 7:38 PM, yankeedog said:

You really  need to build  your own tube gear.  Or rebuild  it.

Yeah. That's really where I'm at. I bought the Chinese amplifier because I was buying something else from the same Ali-X seller, shipping would combine, and it was super cheap. I figured it was worth throwing a few dollars at for giggles. I also bought some USB adapters at the same time. 

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On 10/1/2020 at 9:17 PM, jdm said:

Mine at least has a large error, at least in DCV mode, a brand new alkaline battery reads 1.3V when it is almost 1.6V on the digital meter.

Sorted. It just needed few good pats on the back.

Still l want to get something smaller, I am considering this iconic one that is domestically made for many decades, now in the 7th revision. The manual includes circuit-level repair instructions.

 

0-334ab0ce-800-Tester-analogico-professionale-ICE-680R-VII-serie-originale.jpg

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There is an advantage In larger multi meters. They tend to stay where you put them,and their larger parts tend to break less.Once upon a time I used a Simpson 260. It was tough and accurate and did not move with every wiggle  of the leads.I was a young marine  at the time,and from experience  I can tell  you the Simpson  is as jarhead  proof  as it gets.

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