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 Post subject: Transformer failing?
PostPosted: Feb Thu 14, 2019 9:30 pm 
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Feeding my addiction, picked up a cheap HP 3314A. Dead as a doornail, no power, transformer puts out nadda. Took it out and it indeed has open windings. I know HP stuff is built well and wanted to know, what likely caused this to go bad? No evidence of burns or anything melted. My guess would be plugged into 220V without switching line voltage?

Second question, when something happens like this, does stuff down the line from the transformer likely get cooked? Got another transformer on the way but just wondering if this could make a door stop out of this project?


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 Post subject: Re: Transformer failing?
PostPosted: Feb Thu 14, 2019 9:39 pm 
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My guess would be that there was some type of excessive load on a secondary and someone installed an incorrect fuse on the primary.


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 Post subject: Re: Transformer failing?
PostPosted: Feb Thu 14, 2019 10:16 pm 
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It will show open if you are checking between different windings. Did you go by the schematic and check each winding. It is very unusual for this transformer to go bad.

Dave


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 Post subject: Re: Transformer failing?
PostPosted: Feb Thu 14, 2019 11:19 pm 
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What winding is open? The primary has 2 windings, one for 120v and another for 240v. The secondary only has one winding.


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 Post subject: Re: Transformer failing?
PostPosted: Feb Fri 15, 2019 1:37 am 
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I must have goofed somewhere in my testing. Nothing is open, must have measured the wrong terminals or bad connection. Retested the power switch, tests good. There was 60V input with respect to ground on all the leads going in to the transformer (connected to variac). Nothing coming out of it. Below is the resistance readings:

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 Post subject: Re: Transformer failing?
PostPosted: Feb Fri 15, 2019 2:00 am 
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Resistance on the secondary?


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 Post subject: Re: Transformer failing?
PostPosted: Feb Fri 15, 2019 2:17 am 
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Scott wrote:
Resistance on the secondary?


Whoops, sorry, didn't upload fully edited file. :oops:

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T M.png
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 Post subject: Re: Transformer failing?
PostPosted: Feb Fri 15, 2019 3:35 am 
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Well, don't I feel like a dope. I bench tested the transformer with 110v and it's works perfectly. I don't get what the deal is??? Gotta be either that switch or maybe more likely that EMI filter? My HP scope had a buggered EMI filter that wouldn't let it power up. There was voltage coming out of the EFI and voltage going to the transformer is what I don't get. No resistance with the switch connections :?: :oops:


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 Post subject: Re: Transformer failing?
PostPosted: Feb Fri 15, 2019 4:09 am 
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Quote:
There was 60V input with respect to ground on all the leads going in to the transformer (connected to variac). Nothing coming out of it.

If you have the same voltage on all the primary leads there shouldn't be anything coming out. There has to be a voltage difference ACROSS the winding to generate an output. If both ends are at the same voltage the transformer has nothing to work with.

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 Post subject: Re: Transformer failing?
PostPosted: Feb Fri 15, 2019 5:22 am 
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There is nothing to check with respect to ground.
I assume the fan is not running because you said it is completely dead.
That leaves the switch, the fuse or the input filter.
Check the voltage across the line working back from the 120/240v switch and see what you have.
This should be a quick easy fix.

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 Post subject: Re: Transformer failing?
PostPosted: Feb Fri 15, 2019 6:14 am 
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Well, it's that EFI filter. I bypassed the filter and it works fine. What are the odds I could get two pieces of equipment in the past few months and both have those go bad? It's an 3EF1 that isn't made anymore. Digikey says a 3EF1F is a direct replacement. Is the same except for a 1.5Mohm resistor in parallel. Should be ok?

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3EF1F.jpg [ 78.7 KiB | Viewed 376 times ]


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 Post subject: Re: Transformer failing?
PostPosted: Feb Fri 15, 2019 6:45 am 
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Location: Mpls, Minnesota
You can get one of those from an old computer power supply.

Dave


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 Post subject: Re: Transformer failing?
PostPosted: Feb Fri 15, 2019 10:21 am 
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Could be that solder connection at the terminal. It's out of focus but it looks a bit odd.


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 Post subject: Re: Transformer failing?
PostPosted: Feb Fri 15, 2019 1:22 pm 
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Yes, that new one should work fine. It will also work fine without any input EMI filter but will probably be putting hash onto your power lines. Or visa versa.

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 Post subject: Re: Transformer failing?
PostPosted: Feb Sat 16, 2019 7:49 am 
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The added resistor in the new filter is a safety measure. It discharges the capacitors (at least the line to neutral one) when the unit is unplugged.

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 Post subject: Re: Transformer failing?
PostPosted: Feb Sat 16, 2019 8:59 pm 
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Ya, dummy of the week nominee here. :oops: So, when I checked the fuse, it visually looked good. Was gonna test it with meter and phone rang or something and didn't do it. Since I was getting voltages going into the transformer, I assumed the fuse was good. Dummy me failed to remember that Variac supplies voltage on hot and neutral. Good news is, put a fuse in and it fired up, sort of. Cooling fan comes on, an LED on he PCB board lights but no lights on the front panel. The three power supply voltages check perfect, +15, -15 and +5.1. The fuse was supposed to be a 1V fast and there was a 1V slow blow in it. Maybe cuz something was acting up causing it to blow, I dunno.

If you connect the ground and +5v supply from the ribbon connector to the front board, all LED's light up. This probably ain't good. The controller board feeding the front display board must have an issue. Looks like it may end up a paper weight after all... :(


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 Post subject: Re: Transformer failing?
PostPosted: Feb Sat 16, 2019 10:11 pm 
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tbone8 wrote:
Ya, dummy of the week nominee here. :oops: So, when I checked the fuse, it visually looked good. Was gonna test it with meter and phone rang or something and didn't do it. Since I was getting voltages going into the transformer, I assumed the fuse was good. Dummy me failed to remember that Variac supplies voltage on hot and neutral. Good news is, put a fuse in and it fired up, sort of. Cooling fan comes on, an LED on he PCB board lights but no lights on the front panel. The three power supply voltages check perfect, +15, -15 and +5.1. The fuse was supposed to be a 1V fast and there was a 1V slow blow in it. Maybe cuz something was acting up causing it to blow, I dunno.

If you connect the ground and +5v supply from the ribbon connector to the front board, all LED's light up. This probably ain't good. The controller board feeding the front display board must have an issue. Looks like it may end up a paper weight after all... :(

The Schematic (see above) shows a 1A slo-blo. As for the rest of what you said, I can only scratch my head and tell you to send it to me. It sounds like a fun repair.


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 Post subject: Re: Transformer failing?
PostPosted: Feb Sat 16, 2019 10:36 pm 
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Scott wrote:
tbone8 wrote:
Ya, dummy of the week nominee here. :oops: So, when I checked the fuse, it visually looked good. Was gonna test it with meter and phone rang or something and didn't do it. Since I was getting voltages going into the transformer, I assumed the fuse was good. Dummy me failed to remember that Variac supplies voltage on hot and neutral. Good news is, put a fuse in and it fired up, sort of. Cooling fan comes on, an LED on he PCB board lights but no lights on the front panel. The three power supply voltages check perfect, +15, -15 and +5.1. The fuse was supposed to be a 1V fast and there was a 1V slow blow in it. Maybe cuz something was acting up causing it to blow, I dunno.

If you connect the ground and +5v supply from the ribbon connector to the front board, all LED's light up. This probably ain't good. The controller board feeding the front display board must have an issue. Looks like it may end up a paper weight after all... :(

The Schematic (see above) shows a 1A slo-blo. As for the rest of what you said, I can only scratch my head and tell you to send it to me. It sounds like a fun repair.


Ok, my bad. I went off the part number in the manual of 2110-0312 what I assumed was a 312 fast acting fuse. I got it for a "fun" repair but might be outside my repair pay grade. We shall see.


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 Post subject: Re: Transformer failing?
PostPosted: Feb Sun 17, 2019 8:56 pm 
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Maybe narrowed down the issue. There is a 16pin ribbon connector going from the controller board to the front panel. Every connection except pin 13, when jumpered, will let the front panel briefly light up when powering up. If pin 13 is connected, front remains un-lit. That pin measures .09V while all the other range from 4-5V. Pin 13 connects eventually to pin 40 on the CPU. Found in the manual voltage specs for some pins on the CPU:

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U206.PNG
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Some measurements are off from specs. I don't know if bad RAM/ROM can cause the CPU to be off like this? Below is a link to the CPU controller circuit.

https://www.docdroid.net/mAivaQJ/cpu.pdf

I don't know how common it is for a CPU chip to go bad. According to the manual, the RAM/ROM does need periodic replacing. From what I found, the RAM/ROM is not available, CPU's can be found. Don't even know if I am on the right track or not. As mentioned before, front panel LED's all light up with just +5v supply and ground attached. The fact the line fuse blew maybe means the CPU fried and drew a current surge?


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 Post subject: Re: Transformer failing?
PostPosted: Feb Sun 17, 2019 9:13 pm 
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Back in the day CPU failures were rare unless someone had “ tried to fix it”.....usually due to something getting shorted out or sparked by a slipped probe or something. Don’t ask how I know this

If chips are in sockets try reseating them. Pin 40 looks like a reset line, although that is usually abbreviated as RST. You can perhaps isolate it by making up a test ribbon cable with that line open.....see what happens

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Last edited by Barry H Bennett on Feb Sun 17, 2019 10:01 pm, edited 1 time in total.

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