Author Topic: Is this feasible ? And I apologize for the vagueness. (Read 10882 times)

Hextejas · « **Reply #50 on:** August 09, 2018, 11:24:17 pm »

Re the 32v into the main circuit .
Do designers typically only design one entry point ? I am going to go hunting for another but it would be nice to know that typically there will only be one.
As to what I will do in order to debug this beast, I will try to find the 1/2 way point in the circuit and pull out a component so I can take some measurements.
If you have a better idea, and I am sure that you do, I would love to gear it.

Thanks

james_s · « **Reply #51 on:** August 09, 2018, 11:30:21 pm »

I'm not entirely sure what you mean, but if I understand right, yes, designers typically only provide one path for a given signal. Sometimes this path will snake all over in order to get to the destination, sometimes it will switch multiple times from top to bottom on a double sided board, or pass through jumper wires to cross over other traces but generally there is only one. Having multiple paths for the same signal creates a loop and in some cases that can have undesirable effects, plus there is no real advantage.

Removing a component that is in line somewhere is a perfectly valid troubleshooting technique. When possible I usually desolder just one end and bend it up so the part doesn't run off or get mixed up with others.

Hextejas · « **Reply #52 on:** August 10, 2018, 03:06:33 am »

Quote from: james_s on August 09, 2018, 11:30:21 pm

I'm not entirely sure what you mean, but if I understand right, yes, designers typically only provide one path for a given signal. Sometimes this path will snake all over in order to get to the destination, sometimes it will switch multiple times from top to bottom on a double sided board, or pass through jumper wires to cross over other traces but generally there is only one. Having multiple paths for the same signal creates a loop and in some cases that can have undesirable effects, plus there is no real advantage.

Removing a component that is in line somewhere is a perfectly valid troubleshooting technique. When possible I usually desolder just one end and bend it up so the part doesn't run off or get mixed up with others.

Yes James, you deciphered my meaning exactly and I hadn't thought about leaving one end still connected. I will get back at it tomorrow.

Hextejas · « **Reply #53 on:** August 10, 2018, 09:32:42 pm »

I dont know of this is right or not but the voltages coming out of the xformer are 12v AC and 20v AC. As soon as I plug in the 3 pin cable coming from T-1, to the PCB and turn the power on, one of the fuses starts to get really really bright. I turn it right off since I am running out of fuses. The xformer is an EL-48.

I dont know what to do now. I wanted to put power to it so I could start reading voltages but when I do that, I blow fuses.

Maybe I should give it up.

Gyro · « **Reply #54 on:** August 10, 2018, 09:37:16 pm »

Search for 'Dim bulb tester'.

Basically if you wire a mains lamp in series with the mains supply, it should limit the current enough for you to debug without blowing fuses. Start with a low wattage bulb.

Hextejas · « **Reply #55 on:** August 10, 2018, 09:59:01 pm »

Quote from: Gyro on August 10, 2018, 09:37:16 pm

Search for 'Dim bulb tester'.

Basically if you wire a mains lamp in series with the mains supply, it should limit the current enough for you to debug without blowing fuses. Start with a low wattage bulb.

Thank you Gyro.
When the fuse lights up like that, is it an indication that something is drawing a lot of current ?
Would you or anyone else like to predict which component it is ?

james_s · « **Reply #56 on:** August 10, 2018, 10:20:43 pm »

Yes, it most certainly means something is drawing a lot of current. When did this new symptom start? Are you sure the insulating hardware for the regulator has not been damaged or displaced?

Hextejas · « **Reply #57 on:** August 10, 2018, 11:59:48 pm »

Quote from: james_s on August 10, 2018, 10:20:43 pm

Yes, it most certainly means something is drawing a lot of current. When did this new symptom start? Are you sure the insulating hardware for the regulator has not been damaged or displaced?

I can't quite pinpoint the time it started. I don't remember doing anything different. I think that tomorrow I will turn it on and see if it blows.
The regulator is isolated and not touching the metal plate like before. I can't answer what is different.
What I did do was to push some components apart so as to be able to see their numbers.
It's a puzzle.

james_s · « **Reply #58 on:** August 11, 2018, 12:03:17 am »

Well, something has shorted out somewhere. I would check continuity between that regulator tab and the heatsink, then look around for a solder bridge between two pads.

Hextejas · « **Reply #59 on:** August 11, 2018, 03:53:59 pm »

I found 3 wires from a component that had not been cut off and might have been touching the chassis so I snipped them.
Turned it on and still got the hot fuse but it did not blow.Are fuses supposed to look like this ?

What do you think now ? Is it still drawing too much current ?

james_s · « **Reply #60 on:** August 11, 2018, 05:12:03 pm »

Are you sure that's a fuse and not a light bulb? There are some bulbs with the same form factor as fuses. A fuse most certainly should not be glowing.

Hextejas · « **Reply #61 on:** August 11, 2018, 08:25:01 pm »

Quote from: james_s on August 11, 2018, 05:12:03 pm

Are you sure that's a fuse and not a light bulb? There are some bulbs with the same form factor as fuses. A fuse most certainly should not be glowing.

Nah, it's a fuse so that means that I have to look harder. Grrrrrrr.

Zucca · « **Reply #62 on:** August 12, 2018, 08:52:18 pm »

the more you work the more you can learn and be quicker in the next reapair. It's not time wasted at all.

Hextejas · « **Reply #63 on:** August 13, 2018, 01:37:10 am »

I built a dim bulb tester and I am not so sure what to expect when I use it.
I think that it will still let 120V to the NAD but limit the current ?
Will it affect the DC voltage readings at various places on the board ?
I have never used one before so I didnt know what to expect. The 1st time I tried it, with a 100W bulb and the NAD light up. I pulled 1 side of the glowing fuse out and put my ammeter in series and it was reading 3.5 A !! WOW. I dont know how I could have gotten such a high reading with a fuse rated at 315MA.
Next was a 60W clear, but the fuse still glowed but not so brightly. Curious that when I started to turn the NAD around so I could look at the front, it blew one of the fuses, the glowing one.
Oh well.
So, I took out the 60W clear light and replaced it with a 60W yellow and the fuse did not start to glow. I again pulled 1 side of the fuse so as to read the current and it read 41ma. I think. Then I left it alone and started taking readings.
After about 30 minutes of taking readings, I think that I might have shorted a transistor.
Very frustrating.
More on Tuesday when more fuses get here.
And I need to start taking better notes. As I read what I just wrote, some things seem impossible.

Peace and ciao.
George KG5TKY

james_s · « **Reply #64 on:** August 13, 2018, 04:07:13 am »

There is no real need for the dimbulb tester here, you already know something is pulling WAY too much current. If you do use the bulb, 100W is too large, 60W is probably still larger than you need, but it doesn't really matter. Again you already know something is pulling way too much current so you need to figure out where the short is. This wasn't happening before, you created a short somewhere.

Hextejas · « **Reply #65 on:** August 13, 2018, 10:39:43 am »

Quote from: james_s on August 13, 2018, 04:07:13 am

Again you already know something is pulling way too much current so you need to figure out where the short is. This wasn't happening before, you created a short somewhere.

Is there a better way to do this or do I just eyeball it ?

Thanks

james_s · « **Reply #66 on:** August 13, 2018, 03:20:54 pm »

Well, use some deductive reasoning. Look at which fuse is getting hot, look at the schematic and find paths between that fuse and ground. Look at parts of the board that you have disturbed, the fault is almost always in an area you have messed with. It was working before, now it isn't, you changed something somewhere that caused the fault condition.

Hextejas · « **Reply #67 on:** August 13, 2018, 06:31:52 pm »

Quote from: james_s on August 13, 2018, 03:20:54 pm

Well, use some deductive reasoning. Look at which fuse is getting hot, look at the schematic and find paths between that fuse and ground. Look at parts of the board that you have disturbed, the fault is almost always in an area you have messed with. It was working before, now it isn't, you changed something somewhere that caused the fault condition.

James, this thing never did work. At one point it became able to power on, and I started checking things, but it never worked.
When the next load of fuses get here I am going to take another look at the 5V rail.

Thanks again

james_s · « **Reply #68 on:** August 13, 2018, 07:07:00 pm »

It didn't work, but it wasn't making the fuse glow was it? I don't see how the voltage rails could be anywhere near correct with something drawing that much current.

Hextejas · « **Reply #69 on:** August 14, 2018, 02:50:41 am »

Quote from: james_s on August 13, 2018, 07:07:00 pm

It didn't work, but it wasn't making the fuse glow was it? I don't see how the voltage rails could be anywhere near correct with something drawing that much current.

The fuse glow came later in the game. In the beginning it would blow fuses as soon as I plugged it in. When i 1st got it out of the closet it had 2 blown fuses.

james_s · « **Reply #70 on:** August 14, 2018, 03:51:01 am »

Well the fact that the 32V output from the power supply is effectively zero and the fuse is glowing certainly suggests a shorted component related to that.

Hextejas · « **Reply #71 on:** August 19, 2018, 07:28:46 pm »

Progress I think.
I think that it is not blowing fuses now, at least it hasn't for the last hour. Truthfully, I am not sure what I did to fix it. I noticed some electrolytic capacitors that looked a bit swollen so I replaced them along with a few more capacitors and 2 diodes. Anyway it stays on and is drawing only about 10ma across the fuses.
Which prompts a question.

When I am reading voltages do I read it in ref to ground or is it across the component in question, or maybe both ?

So now, the front panel stays lit and shows nothing. I took a few more voltage readings but I dont know where to look next.

There is an off page connector that shows 5V+ but I dont know if it is an input or output 5V. In any respect it is 000.

2 photos attached showing the 5V in question along with the LM7000. It seems like there should be more activity there, but I have no clue. I would probably replace the LM7000 and pray.

thanks

james_s · « **Reply #72 on:** August 19, 2018, 08:00:24 pm »

Swollen capacitors is a pretty good indication that they are bad, the top of an electrolytic cap should never appear bulged at all, if it does then it is bad.

Voltage measurements are normally to ground, if the schematic lists a voltage at a particular node then that is always referenced to ground. Sometimes there is reason to measure the voltage across a component but in that case it will be specified, if not mentioned then assume it is a measurement to ground.

If you are missing a voltage somewhere, figure out where you do have 5V if anywhere, start at the regulator, if 5V is present on the output then follow the circuit, checking for 5V at other nodes that should be connected and find out where it is missing.

Hextejas · « **Reply #73 on:** August 19, 2018, 10:46:02 pm »

Quote from: james_s on August 19, 2018, 08:00:24 pm

If you are missing a voltage somewhere, figure out where you do have 5V if anywhere, start at the regulator, if 5V is present on the output then follow the circuit, checking for 5V at other nodes that should be connected and find out where it is missing.

Thank you James and following the schematic is where I am having a problem. From the voltage regulator, +5, +12, and -12, all go to one thick line, which goes to the upper level schematic. The +32v just goes to an arrowhead. Do the engineers really mean to have those 3 voltages on one wire ?
You can guess that I am new at this ?
Do schematics typically read left to right ?

james_s · « **Reply #74 on:** August 20, 2018, 12:42:55 am »

The thick line on a schematic is called a bus, it can be thought of as a bundle of separate wires that have similar function or go from one general area of a schematic to another. It is done purely for visual clarity, which may not seem intuitive if you don't know what it means but consider this. Say you have a 32 bit address bus on a microprocessor which connects to 10 other ICs. Imagine what it would look like if you tried to draw 32 separate wires in parallel, each connecting to all those ICs, you would have an absolute rat's nest that would be hard to follow. Instead you draw a thick line or in some cases a wide stripe and have the individual signals go in and out of that stripe, labeled where they enter and exit, the result is much more clear.

That's what's going on with the voltages, all of the power supply voltages here are drawn as a bus, with each wire identified by its label.

Schematics are not read in any particular direction, they are normally organized by functional blocks, often with little or no relation to the physical layout of the circuit. The schematic is there to describe the way the circuit works and group together components that are part of a certain function, like the power supply, the front panel buttons, the RF front end, and so on. Sometimes the parts of a subsection are physically clustered together but they could be spread all over the board if there were reasons for it to be done that way.


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Author Topic: Is this feasible ? And I apologize for the vagueness. (Read 10882 times)

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