7500 can't adjust horiz size

coinopjunkie

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Okay so I blew up my 7500 (another thread) so after finding a donor tube (used 7500 yoke) replaced the backward caps, got the whole screen working I can't adjust the horizontal size with the remote board it use to prior to me installing two reversed caps. According to the w/g repair guide the suggest checking Q703, Q709, Q710, R745, R750, C734 I pulled R745 and R750 and the test fine I replaced C734 that only leaves the Q's which here in lies the question of the day for Q710 W/G calls for a BDX53A installed was a BDX53B and I can find a BDX53C anyone know if these are interchangeable? Anyone know how to test a BDX53B? Also any other ideas on what to check?
 
you should have a transistor that is mounted to a small L shaped piece of metal that is mounted off the main chassis....this is a common issue with horizontal size failure. If this transistor fails or the connector is attached in reverse, you can't adjust the size. You can reverse the plug to the transistor without damage to it to see if this is your issue. If this doesn't allow you to adjust your size, you should test it to see if it is bad or swap another one in if you have a spare. There are other components that can cause this issue, but this is the most common problem and where I would start checking for problems.
 
still stuck

According to the w/g repair guide the suggest checking Q703, Q709, Q710, R745, R750,C734 so I replaced everything but the two resistors as they measured correctly when pulled. Any other Ideas? Could it be the yoke even though the picture looks pretty good just way to wide?
 
the resistor that burned feeds power to the verticle section, and is known to go bad from time to time. As far as your issue with the width....check the 10ufd NON polarized cap @50vdc. I've only seen one of two go bad....but it is in the horizontal section and sits by the control transistor.
 
So I found a shorted diode d708 replaced it and r402 caught on fire? This thing keeps getting worst instead of better anyone?

D708 damper diode
will cause image to be to wide
anytime the width is to wide
it has something to do with
the horiz-output circuit.
the HV caps change their value over time
and when to far out it will short the damper diode
because its in series with another diode it doesn't cause
damage to the B+ or HOT.
When the HV caps open it would cause the image
to be narrow and still have HV.as well as the drive circuits.
So you should replace c724 the HV S-cap
As you know the r402 feeds the vertical ic.
and can damage d302 and r303 in some case's.
when the ic kills the 27v supply voltage.
you can still have HV and no vertical deflection
so if you desolder the ic and replace the resistor
you will know what is causing the resistor to open.
Even if you had vertical deflection the ic draws
alot of current and should be replace at least once in its
chassis life,its on the second largest heatsink in any chassis.
Also check for any solder bridges in case you made some
in and around the path to the vertical which could kill any voltages
to the ic.
The bdx trans is for pincushion circuit see picture
it shapes the edges and corners but when the image is to wide
it has nothing to do with that part,the image could be like picture
or narrow image. if the bdx is out of circuit or not working.
C729 is for the pincushion circuit after you fix the width
remove it or the bdx and see how the picture looks
it won't be to wide.sorry im not to good at one liners
and if i explained it good enough.
Let us know how it works out for you
 

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clean picture

Anyone have a picture of a clean 7500 so I can check for solder bridges, My board is kinda hacked up and I'm not sure what should touch and what shouldn't. I'd love to see a picture of the solder side of a clean 7500.
 
Anyone have a picture of a clean 7500 so I can check for solder bridges, My board is kinda hacked up and I'm not sure what should touch and what shouldn't. I'd love to see a picture of the solder side of a clean 7500.

Heres a picture
are you reading a short off that resistor.
Maybe best to download to your computer
to get better tools to see board.
Or see picture from here.
 

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I'm not sure

To test for a short I used a dmm touched the pads of the resistor to ground and did not get the beep is there a better way? the picture below shows the area of most concern this area was in bad shape and the trace the line is pointing to lifted completely off the board but from what I could make out they were just connected so that is what I did. I also touched up a bunch of solder connections as well as changed a few caps prior to the resistor catching on fire, so I'm not sure where the problem is. I had to order the resistors and I now have them but I'm scared of doing more damage by putting it in and turning it on I obviously did something wrong somewhere.
Heres a picture
are you reading a short off that resistor.
Maybe best to download to your computer
to get better tools to see board.
Or see picture from here.
 

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I'm keeping an eye on this because I am having the exact same problem. I can't adjust the horizontal on my K7502. I can't find any shorted parts or broken traces. If I find anything, I will post it here in hopes that it will help you.

The way I have been testing for a short is to de-solder one leg of the diode and testing it that way.
 
To test for a short I used a dmm touched the pads of the resistor to ground and did not get the beep is there a better way? the picture below shows the area of most concern this area was in bad shape and the trace the line is pointing to lifted completely off the board but from what I could make out they were just connected so that is what I did. I also touched up a bunch of solder connections as well as changed a few caps prior to the resistor catching on fire, so I'm not sure where the problem is. I had to order the resistors and I now have them but I'm scared of doing more damage by putting it in and turning it on I obviously did something wrong somewhere.

You didn't say you desolder the vert-ic or removed it,we or i can't see
what your doing you have to say it...Odds are when you replaced the diode
you got your width back but either part can be shorted and still have HV
and the HV cap will effect the damper diode,very seldom does this diode go bad
its usally because of something else in the circuit.

The idea of using a ohm meter is to findout where the short is
all short are not zero ohm it could be 100 ohms or less..
you need to know how many ohms it is to ground!!
matching solder connections may be very hard to decide where
it is or not.
all circuits have a circuit resistance which may look like a discharge on your meter
under say 2k ohm scale.. because of caps on that line

If the one side shows some ohms tell us what it is..
as you remove suspects you would see the ohms go higher or stay
the same..
May need to send it out for repair if it becomes to much for you..
Or it will just make you a better tech when you fix it..

For the symptom you should'nt need voltage untill you have very high ohms on both
sides of r402..then you can plug it in, otherwise you will burnup each new resistor.
Let us know after you have tested the circuit good,using the schematic
it can guide you to the suspects that use this voltage.
See wellsgardner website for manual.
Removing the caps you put in, may help if you just shorted
one of those sence you last power up if in backwards!!
 
tda1771

Okay I soldered the resistor back in and it is shorted zero ohms took out the vertical ic tda1771 as I believe that is what you wanted me to do no change. Of course I didn't power on because of the obvious.
You didn't say you desolder the vert-ic or removed it,we or i can't see
what your doing you have to say it...Odds are when you replaced the diode
you got your width back but either part can be shorted and still have HV
and the HV cap will effect the damper diode,very seldom does this diode go bad
its usally because of something else in the circuit.

The idea of using a ohm meter is to findout where the short is
all short are not zero ohm it could be 100 ohms or less..
you need to know how many ohms it is to ground!!
matching solder connections may be very hard to decide where
it is or not.
all circuits have a circuit resistance which may look like a discharge on your meter
under say 2k ohm scale.. because of caps on that line

If the one side shows some ohms tell us what it is..
as you remove suspects you would see the ohms go higher or stay
the same..
May need to send it out for repair if it becomes to much for you..
Or it will just make you a better tech when you fix it..

For the symptom you should'nt need voltage untill you have very high ohms on both
sides of r402..then you can plug it in, otherwise you will burnup each new resistor.
Let us know after you have tested the circuit good,using the schematic
it can guide you to the suspects that use this voltage.
See wellsgardner website for manual.
Removing the caps you put in, may help if you just shorted
one of those sence you last power up if in backwards!!
 
?

You eliminated the vertical ic by removing it.
as a suspect for now.
Ok what is the ohms to ground at the resistor
both sides without the resistor in place?


The spot your talking about may be ok..
you can compare the ohms at that spot
to the ohms you get from the test point at the resistor readings..
my guess at r402 one side is very high ohms and the other is O ohms.
The short will lead you to a solder splash or shorted part.
I see a jumper w111 open one side then measure the ohms at the tp of resistor again..
both sides??
if high on both side now at resistor then you need to go to the other side of
jumper and check for the o ohms again,your looking for what is shorted on that
pcb trace..
 
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