So I got this bag of fuses (1A 250V) and they looked good but I thought hey why not check one of these things 

So I came up with a plan....put the fuse in circuit with a 10 ohm fuse and run it up to 10v
while keeping an eye on it.

Well I started at 7.9v and the smoke show started quickly
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So I did some calculations wow I was going for one amp I never dreamed I would be cranking out some watts
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That resistor is like a quarter or half watt.
 

Btw the fuse survived 

But as I type this now it makes sense why I see these big ceramic wire wound ? resistors and they are low resistance

 
 

Ok this is what I did

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So I hooked everything up

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Then did some requested calculations

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Seems like a lot of trouble for nothing but I did get the "right answer" the book said for the 741c Op-Amp the typical value for the input offset voltage is 2 mv. 

I'm not yet running through the streets shouting eureka but hopefully later the significance of this will become apparent.

 

Before I buttoned it up I poked around a few capacitaters looking for direct shorts 🩳 to no avail.

I'm back to "dude...it's the relay"

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I was gonna try to 🦘 jump it but figured I would quit while I was ahead....or in the same place 

Meanwhile WOW what a transformer 
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Oh well nm 

Looks like I got some component removal and replacement practice
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I replaced the 1815 and it didn't fix the problem and all of the in circuit readings are identical

But ..at least it still "works" 

Ok guys did a little snooping around after work...compiled a list of transistors from the board.
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I checked all of them in diode/continuity mode and the testing was uneventful then crazy the last one I checked  I am focusing on.
Because the outer legs had a low (0.09v) voltage readings.
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I thought I was losing my mind until I remember they are like diodes and POS and neg leads matter...doh

But I compiled a summary of my examination of this particular device aka Q26
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So it's not much but it's something   

But now I'm thinking it must be a result of the circuit that it is in.

 

Time to look at the schematic 

This will be good.  I hope I dont report back with tales of falsely accused to-220 voltage regulators 

Lord I was born a rambling man (below):

I tried to find a source for the relay(s) even contacting one established high volume vendor and they didn't have an exact match.

Also some of the Internet lore indicates this PS works on a "break before make" (or vice versa) and is somewhat complicated. 

I had seen an advantage to having "the same" boards on each side" (remember working on drum brakes  ) but the two sides may not be identical)

Also the schematic (for the digital meter version) I don't see any test voltages anywhere  but maybe I missed them idk.

Anyhow I want to try and keep it simple and do some fundamental inspections without opening a can of worms. 

I have a topward dual power supply the left side doesn't get up to full voltage.
If you look in the swap meet section there is some discussion pictures and schematics.

I had an idea that maybe since there aren't that many parts just order some stuff and shotgun it.

However after reading about these units I saw a few instances where some transistor replacements fixed the problem(s).

So for the sake of clarity the focus of this discussion is to simply focus on transistors for the preliminary investigation.

Reading some old threads I saw where I can probe the collector and emitter of said devices in circuit and check for shorts. 
-if there is no short then move along
-if there is a short it may be good because of the circuit but remove and test

If I have interpreted this correctly I like this plan  because for starters the power is OFF. 

Also it will give me some experience discerning a voltage regulator from a transistor 

So if you like that then that is my plan nothing more or less.  Just check every transistor in circuit for C-E short and report back.

A major technological advance has been made.    Negative voltage has been achieved 
Thanks to G1 and Mick 

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So per instructions the (+) is connected to to ground on different power supply.

Pretty cool I confess I was fearful of some 🎆🎇 fireworks

I guess the important part is the negative of the power supply must not be grounded.  Then it would be the fourth of July 

So that's cool I have my chips and stuff on the way and it seems to be a common theme with these guys to connect V+ and V-

But then other ones had stuff like Vc and Vd but I'll worry about that when I get to it.

That's really cool looks like it would fit in the palm of your hand 

Thanks guys 

I have to go through my stuff and see which of these resistors and capacitaters  I have and don't have
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Shouldn't take more than a couple of weeks 

Hello sir welcome to the forum 

Being totally unfamiliar with either I watched a few videos they seem to both be nice amps but I would pick the Laney and also pick the lower wattage amp as well.  100w seems like a lot to me but I don't play out.

These days they have one and two watt amps that sound killer.

But whatever you do just enjoy the search lots of great stuff used out there as well.

I have a few items in cart at digikey I'm gonna finish my list tonight and get this stuff on the way.

This is some good stuff because I already have a problem 

So I'm looking at this diagram and getting stoked about doing it  but then I'm like oh no...
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How do I get a minus fifteen volts on the device   

So I had what I thought was a major epiphany and said ah ok just hook the neg of the power supply but make sure the neg is ungrounded
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Being proud of myself 💪 I said yeah I can test this and made the following circuit on breadboard.  And it didnt work (fortunately)

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Since it didnt work I figured ok maybe my negative is connected to ground so I checked for continuity and resistance and they are not connected.

To add to the confusion  as I type this I anticipate that perhaps the Op-Amp will show -15v because for lack of better words (maybe ?) it's not resistive.  Sorry for opening a can of worms.

But at least I'm getting out of the "dude...neg is ground" mindset.  Because sometimes it is.

I'm kinda glad I get to order a green 💚 jumper cord. 

Are they supposed to be insulated like with mica 

Quote from: g1 on November 26, 2024, 06:53:23 PMPlay it.

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