G07 recap shorting

drowtales

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Chassis was working , albeit coated in an inch of magnetized dirt. I washed it, changed the cap(Ian kellog's kit) and changed the hot.
But this was my first GO7 and i made a bad mistake when changing the hot : I did not put the rubber isolation padding. End result, no image on display, f901 blows, Hot seem shorted.
Alright, install a fuse holder, new 1.25a fuse, check resistors, check big grey cap, put the old hot back in with the rubber padding this time, which tested fine, then back in the roadblaster it goes--
Nothing.
14-16 volts only on the R1 if i recall correctly. No glow. Fuses are fine.
bring it back out, check the hot, it test shorted.
disconnect the hot, test it, it's not shorted. Both HOT gets a 50 on multimeter. But as soon as the yellow wire touch the lower leg of the hot, it goes down to 0.

It seem like i'm missing the obvious. Could anyone with more experience point me the right direction?
 

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The first thing is:
A g07 must get a new flyback when you recap it.

Nobody (myself included) would waste their time troubleshooting a g07 that has
new caps and an original flyback.
 
I don't always replace the flybacks in G07 and my returned failure rate is still very similar for new flybacks.


To answer your issue drow, you probably blew the fusible resistor in the b+ circuit.
its a 220 ohm 1/2w fusible flame proof resistor.

https://iankellogg.com/parts-by-monitor/electrohome/electrohome-g07/220-ohm-0-5w-5-mf-fusible.html


Also you can't test a HOT in circuit, there is a transformer on the base to emitter which has a low resistance which will show up as a short.
 
Thank you Ian for both pointers.
The FR901 reads 221. Thanks to your link i can confirm the resistor is working. And thanks to you i can now stop fussing over the wiring of the hot. There must be another cause somewhere else that prevent the current from flowing in the aftermath of the f901 fuse blow.
 
You mentioned in the original post that you recapped it and changed the hot? Why did you change the hot? Was the old one bad? Edit: you said the monitor was working , right?


Now your b+ voltage is only 14-16 volts DC?
 
Thank you Ian for both pointers.
The FR901 reads 221. Thanks to your link i can confirm the resistor is working. And thanks to you i can now stop fussing over the wiring of the hot. There must be another cause somewhere else that prevent the current from flowing in the aftermath of the f901 fuse blow.

when your blowing F901 the most common causes are a shorted HOT and a bad flyback. when you only replace cap on the go-7 i have personally seen too many times something else goes as soon as you power up. i personally won't rebuild a go-7 without replacing caps, flyback, usually width coil, HOT, and VR and add in fuse holder clips, and complete reflow. i wouldn't recommend all that with most other monitors but go-7 that is my opinion and what i do with mine because my time is valuable too so the cost of parts is cheap. if you need flybacks they are back in stock on my site.
 
i really don't understand the mentality of replacing the HOT let alone the width coil. the ONLY time the width coil even matters is when you need to change the width. It isn't going to magically go bad. the life span on the insulation should be hundreds of years.
 
Tronguy : I did a newbie mistake on the multimeter. Tenfold that reading. It's too high instead of too low. I've removed x701 by following the flowchart. Screen still did not turn on. But getting 0 on x01(which i assume is the black metal chassis). Checked voltage on the neck's cap, also getting voltage that's too high. If the flowchart is to be trusted, somewhere there's a bad soldering or as you said, it's the flyback that just gave up.
As to why changing the hot, yourself and Security above are good exemple : Change everything if you have the parts. I did have a spare hot, while the flyback was not in stock. I've now ordered a set from a different place but it'll take two weeks to arrive.
changing the hot might not have been a good idea in hindsight. Should've started easy...

Also tried reversing c303 as Ian's backsheet schematic pointed the positive to a different direction than some people previously advised on klov. That didn't change anything. Cap still tested fine either way.
 
Last edited:
i really don't understand the mentality of replacing the HOT let alone the width coil. the ONLY time the width coil even matters is when you need to change the width. It isn't going to magically go bad. the life span on the insulation should be hundreds of years.

it's cause they normally break. not the coil itself, but the plastic housing for it.

can you hot glue something like that back together?
 
i've since fixed the error in instructions on Rev05. but it wouldn't really have affected anything anyways for what purpose the cap had in circuit.


as with any monitor repair, first step is making sure b+ is working correctly. I didn't see that mentioned anywhere that you tested it before.
 
i really don't understand the mentality of replacing the HOT let alone the width coil. the ONLY time the width coil even matters is when you need to change the width. It isn't going to magically go bad. the life span on the insulation should be hundreds of years.

Tronguy : I did a newbie mistake on the multimeter. Tenfold that reading. It's too high instead of too low. I've removed x701 by following the flowchart. Screen still did not turn on. But getting 0 on x01(which i assume is the black metal chassis). Checked voltage on the neck's cap, also getting voltage that's too high. If the flowchart is to be trusted, somewhere there's a bad soldering or as you said, it's the flyback that just gave up.
As to why changing the hot, yourself and Security above are good exemple : Change everything if you have the parts. I did have a spare hot, while the flyback was not in stock. I've now ordered a set from a different place but it'll take two weeks to arrive.
changing the hot might not have been a good idea in hindsight. Should've started easy...

Also tried reversing c303 as Ian's backsheet schematic pointed the positive to a different direction than some people previously advised on klov. That didn't change anything. Cap still tested fine either way.

I don't change the HOT unless it is bad. Flyback , yes. Especially if it is for somebody other than myself. Width coil onky if it is broken, brittle , or the top is busted off.
 
i really don't understand the mentality of replacing the HOT let alone the width coil. the ONLY time the width coil even matters is when you need to change the width. It isn't going to magically go bad. the life span on the insulation should be hundreds of years.

width coils are usually brown crumbling or top broke off (and yes they still may work) but i replace because i want my stuff in great shape and don't want to constantly be working on it. if something is suspect its gone because one time i have to pull a monitor for something costs me way too much in labor. if you don't and you would rather replace things one at a time as they go bad then that's your choice and this is only what i do.
 
i've since fixed the error in instructions on Rev05. but it wouldn't really have affected anything anyways for what purpose the cap had in circuit.


as with any monitor repair, first step is making sure b+ is working correctly. I didn't see that mentioned anywhere that you tested it before.

I'm assuming the big white resistor R1, connector nearest to the tube is the B+ checkpoint. Reads 151.8v I've moved around the B+ wheel, it reads the same regardless which direction i'm moving it. For fun i've measured the voltage on f901 and getting nothing. Considering there was something on the first try post-cap, which blew f901 , that should be a hint. But beside just my soldering being bad, i'm not sure what the hint could lead to. I've tested continuity everwhere i thought that my soldering could be in doubt. There's no hairline cracks anywhere.
 
it's cause they normally break. not the coil itself, but the plastic housing for it.

can you hot glue something like that back together?

of course you can, as long as the ferrite slug is in place and the coils are still wound it will work just fine.


you can measure b+ on R01 but only on the one leg, the other leg is the raw DC voltage.
 
Obviously your B+ is too high, but try turning the screen adjustment to see if you actually do have a picture. Are you sure you have your HOT installed the right way? The legs need to be centered. Make sure there's no shorts.
 
Ian: 151 on one b+ leg, 157 on the raw leg at the last check. Thanks now i know what the other leg is for.

Joec2003: Dead screen, no glow on the tube. Still, since this chassis used to take a full minute to warm up i've left it on for a while and played with brightness. nothing.
I've resoldered the hot on and off, exchanged it with the other several times. It always test shorted once soldered to the yellow line , but as Ian pointed out earlier in the thread, that appears to be a normal thing. Feel free to look at the photo and point out if you see something wrong.
 
It is probably in the best interest to replace your flyback at this point. with you installing the HOT without an insulator you could have severely damaged the flyback. If the flyback is broken it won't be able to pull enough load onto the b+ to allow regulation.
 
Changed the flyback. And shorten the replacement resistors legs. Tested continuity on the flyback pads to ensure no lifted traces.
Same result, except the voltage on R1(b+ side) now reads 147 volts. Slightly lower than before. Still no voltage going through either of the fuses.
If you could answers these two questions to help with the troubleshooting
-Is the HOT supposed to read around 50 when outside the circuit? Perhaps both my g07 HOTs are blown and i can't tell as they both read the same
-Should there be voltage going through the fuses after the initial boot?
 
Changed the flyback. And shorten the replacement resistors legs. Tested continuity on the flyback pads to ensure no lifted traces.
Same result, except the voltage on R1(b+ side) now reads 147 volts. Slightly lower than before. Still no voltage going through either of the fuses.
If you could answers these two questions to help with the troubleshooting
-Is the HOT supposed to read around 50 when outside the circuit? Perhaps both my g07 HOTs are blown and i can't tell as they both read the same
-Should there be voltage going through the fuses after the initial boot?

i suspect your testing something wrong with your meter or its settings. the monitor voltages are tested in AC volts and DC volts depending on what your testing on the chassis. for instance the fuses are AC volts and the B+ is DC volts. you can't have 147vdc without your fuses having power but they are AC volts and can only have one lead on either end and the other lead to neutral/gnd on the AC side not DC side.

fuses will always have voltage on them after the "initial boot" if your monitor otherwise your monitor won't work.

are you testing the HOTs with a diode test on your DDM?
 
Changed the flyback. And shorten the replacement resistors legs. Tested continuity on the flyback pads to ensure no lifted traces.
Same result, except the voltage on R1(b+ side) now reads 147 volts. Slightly lower than before. Still no voltage going through either of the fuses.
If you could answers these two questions to help with the troubleshooting
-Is the HOT supposed to read around 50 when outside the circuit? Perhaps both my g07 HOTs are blown and i can't tell as they both read the same
-Should there be voltage going through the fuses after the initial boot?

you're still in HV shutdown.

check for cracked traces/pads around the flyback.

check R908 and 912.

-Is the HOT supposed to read around 50 when outside the circuit? Perhaps both my g07 HOTs are blown and i can't tell as they both read the same
-Should there be voltage going through the fuses after the initial boot?

50 what?
vdc, ohms ???

use my video to help you.


if your still stuck and hit a brick wall, your welcome to send it in.

Peace
Buffett
 
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