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Hantarex polo 25 no image

Printed From: ukVac.com
Category: Technical
Forum Name: Tech, Maintenance & Repairs
Forum Description: Need Help? Ask Here
URL: http://www.ukvac.com/forum/forum_posts.asp?TID=379579
Printed Date: 23 Sep 2020 at 10:30am


Topic: Hantarex polo 25 no image
Posted By: justez
Subject: Hantarex polo 25 no image
Date Posted: 11 Sep 2020 at 7:34am
Hello,

I am trying to fix a hantarex polo 25.
I have connected a 40w bulb to the collector of the bu508.
The light bulb lights correctly and I have the following values.

TP6  +140V
TP8   +27V
TP9  +15V

BU508 is ok and I hear Flyback works but i have no image.
Normally in tp6 I have 145v, I don't know if I have to increase the voltage of the PS, or there is another problem that I can check.




Replies:
Posted By: gunblade
Date Posted: 11 Sep 2020 at 8:23am
140v is a little low but nothing important

have turned up the screen volts on the flyback and still no raster?


Posted By: justez
Date Posted: 11 Sep 2020 at 8:46am
Originally posted by gunblade gunblade wrote:

140v is a little low but nothing important

have turned up the screen volts on the flyback and still no raster?


Yes, it was the first thing I did.
Is there any way to measure in the socket that the screen line is arriving correctly?


Posted By: gunblade
Date Posted: 11 Sep 2020 at 8:57am
you can read the g2 with a hv probe/meter
do you have tube heaters?


Posted By: justez
Date Posted: 11 Sep 2020 at 10:02am
Originally posted by gunblade gunblade wrote:

you can read the g2 with a hv probe/meter
do you have tube heaters?


I don't have a hv probe/meter.
I do not see light in the tube.
I tested r37 and c20 and seems ok.


Posted By: gunblade
Date Posted: 11 Sep 2020 at 10:06am
there could be a lot of things causing this, is the horizontal drive transformer reading 27 ohms one side and around 1 ohm the other?
is the 2.2k load resistor on the side of the chassis reading ok?


Posted By: justez
Date Posted: 11 Sep 2020 at 11:35am
Originally posted by gunblade gunblade wrote:

there could be a lot of things causing this, is the horizontal drive transformer reading 27 ohms one side and around 1 ohm the other?
is the 2.2k load resistor on the side of the chassis reading ok?


Yes, I checked, 2.2k resistor, is ok.

Drive transformer in another chassis that I fix its malfunction, it no longer allowed the PS to start and blocked the chassis in protection mode.
But I'm going to test it anyway.


Posted By: justez
Date Posted: 15 Sep 2020 at 4:55pm
Originally posted by gunblade gunblade wrote:

there could be a lot of things causing this, is the horizontal drive transformer reading 27 ohms one side and around 1 ohm the other?
is the 2.2k load resistor on the side of the chassis reading ok?


I finally found a burnt resistor here



But I still don't have an image.

Now, At pin 7 of the flyback there is voltage, about 127v

I checked the signal with oscilloscope in tp32 but I don't have a square signal


There has to be something else that messes up the signal, somewhere else where I could test?


Posted By: gunblade
Date Posted: 16 Sep 2020 at 7:27am
could be a bad flyback


Posted By: justez
Date Posted: 16 Sep 2020 at 8:54am
Tomorrow I get a new one from efiter diemen, I'll try it.


Posted By: gunblade
Date Posted: 16 Sep 2020 at 9:00am
how is r240 looking?


Posted By: justez
Date Posted: 16 Sep 2020 at 9:16am
Originally posted by gunblade gunblade wrote:

how is r240 looking?

r240 is ok.
In TP32 there is voltage one 27v but no square signal.


Posted By: M K L
Date Posted: 16 Sep 2020 at 11:44am
It's the horizontal drive that you should check. Without that a good flyback will never work.


Posted By: justez
Date Posted: 17 Sep 2020 at 7:08am
Originally posted by M K L M K L wrote:

It's the horizontal drive that you should check. Without that a good flyback will never work.


In the horizontal section, check with the bulb to the HOT collector that B + (138v) arrived correctly
The horizontal transistor and the transformer measured them and they are ok.


Posted By: M K L
Date Posted: 17 Sep 2020 at 8:19am
It's the pulse signal that goes from pin 3 of IC104 and through T113, TH102, T114 to pin 1 of the flyback. All the parts and B+ can be good but if no pulse comes from pin 3 the flyback will not work.


Posted By: justez
Date Posted: 17 Sep 2020 at 1:11pm
Originally posted by M K L M K L wrote:

It's the pulse signal that goes from pin 3 of IC104 and through T113, TH102, T114 to pin 1 of the flyback. All the parts and B+ can be good but if no pulse comes from pin 3 the flyback will not work.


Ok, I am going to check Tp23 and Tp27 with the oscilloscope and check the signal.
I have also purchased a high voltage test probe from Diemen.


Posted By: justez
Date Posted: 21 Sep 2020 at 2:06pm
Today I got the high voltage probe.




I have measured EHT and I get 24.6KV, matches the flyback scheme
I have also measured TP27 and I get a correct square signal at 50V / 20us as it appears in the schematic.
In TP32 I still don't have a correct signal
Cry.



Posted By: M K L
Date Posted: 21 Sep 2020 at 4:19pm
Heater voltage (about 6.0Vrms) at pin 9 of the CRT socket?


Posted By: justez
Date Posted: 21 Sep 2020 at 4:31pm
Originally posted by M K L M K L wrote:

Heater voltage (about 6.0Vrms) at pin 9 of the CRT socket?


on pin 9 of the socket I have between 4 and 5 mV


Posted By: M K L
Date Posted: 21 Sep 2020 at 5:05pm
Are you measuring on the pin coming from R35? Did you set the meter to AC? Is it a true RMS meter? Measure on both legs of R35 (one at a time, black lead on ground). If the correct voltage is only on one leg the resistor is open. If no voltage at all there must be something that pulls the voltag down. The flyback output that provides the heater voltage is also used for other things. We'll see later.


Posted By: justez
Date Posted: 21 Sep 2020 at 7:47pm
Originally posted by M K L M K L wrote:

Are you measuring on the pin coming from R35? Did you set the meter to AC? Is it a true RMS meter? Measure on both legs of R35 (one at a time, black lead on ground). If the correct voltage is only on one leg the resistor is open. If no voltage at all there must be something that pulls the voltag down. The flyback output that provides the heater voltage is also used for other things. We'll see later.


I had it in DC, I have put it in AC and I have the following measurements in r35 and it seems that it has tension in both legs but mV not V.
Does not go to 5-6 volts

On pin 9 the following voltage:



 R35 both legs.




Maybe something is wrong in this area



Posted By: M K L
Date Posted: 22 Sep 2020 at 7:56am
Desolder pin 6 of the flyback and see if it has the correct voltage. if it doesn't the winding in the flyback is likely to be bad. Do you have the other voltages, +200V, -190V? If you have the heater voltage on the pin, check the parts that are connected to it: T1, R10, D1 on the neckboard, the test pattern circuit (that is superfluous anyway) and also the things you circled.


Posted By: justez
Date Posted: 22 Sep 2020 at 10:02am
Originally posted by M K L M K L wrote:

Desolder pin 6 of the flyback and see if it has the correct voltage. if it doesn't the winding in the flyback is likely to be bad. Do you have the other voltages, +200V, -190V? If you have the heater voltage on the pin, check the parts that are connected to it: T1, R10, D1 on the neckboard, the test pattern circuit (that is superfluous anyway) and also the things you circled.


I have installed a new flyback that came from Diemen and the chassis still does not work.
T1, R10, D1 are ok
I desolder pin 6 and measured pin 9 in the socket and I still have no voltage.

+200V, -190V is present. (TP30 TP33)

What I have seen is that pin 9 of the socket has continuity with ground.
Perhaps there is the fault.

I checked and ok: R237 c176 r242 d138 r245 T115 t116 c165 r232 c176 d150 r236 r240 r239 c160 c165 d141 r246 d139


Posted By: M K L
Date Posted: 22 Sep 2020 at 11:09am
Originally posted by justez justez wrote:

I desolder pin 6 and measured pin 9 in the socket and I still have no voltage.

You need to measure at the flyback pin. Not easy, I know. Try attaching an alligator clip to the pin.

Originally posted by justez justez wrote:

What I have seen is that pin 9 of the socket has continuity with ground.
Perhaps there is the fault.

Pin 5 of the flyback is grounded and it's internally connected by windings to pins 6, 9, 10 (see the drawing in the schematics) so you're measuring the low resistance (like 1 ohm) of the winding in the flyback across pin 5 and 6. If you have other working chassis you'll see the same thing.


Posted By: justez
Date Posted: 22 Sep 2020 at 11:25am
Originally posted by M K L M K L wrote:


You need to measure at the flyback pin. Not easy, I know. Try attaching an alligator clip to the pin.

I unsolder pin 6 and in 9 I have 63V (AC)


Posted By: M K L
Date Posted: 22 Sep 2020 at 11:41am
On pin 9 of the socket? How can you have any voltage there if you desoldered pin 6?

And if you meant pin 9 of the flyback why did you do that? You have already proved that output is fine (200V).


Posted By: justez
Date Posted: 22 Sep 2020 at 11:56am
Originally posted by M K L M K L wrote:

On pin 9 of the socket? How can you have any voltage there if you desoldered pin 6?

And if you meant pin 9 of the flyback why did you do that? You have already proved that output is fine (200V).


I understood that you wanted me to measure on pin 9 flyback.

On pin 9 of the socket with pin 6 of the desoldered flyback I have no voltage.

Before I had already measured that it had the voltages
+ 200V, -190V is present. (TP30 TP33)


Posted By: M K L
Date Posted: 22 Sep 2020 at 12:14pm
Originally posted by justez justez wrote:

On pin 9 of the socket with pin 6 of the desoldered flyback I have no voltage.

Of course. Now you just need to measure AC voltage at pin 6 of the flyback (with solder sucked off the pin).


Posted By: justez
Date Posted: 22 Sep 2020 at 12:28pm
Originally posted by M K L M K L wrote:

Originally posted by justez justez wrote:

On pin 9 of the socket with pin 6 of the desoldered flyback I have no voltage.

Of course. Now you just need to measure AC voltage at pin 6 of the flyback (with solder sucked off the pin).


Solved!
Thank you very much for your help MKL !!

I have noticed that pin 6 has continuity with the components but the track of pin 6 does not, and has a micro break.



now the image comes out saturated with blue and the cut off of blue to the minimum does nothing, maybe it is a transistor or the integrated circuit LM1203?




Posted By: M K L
Date Posted: 22 Sep 2020 at 12:44pm
Possibly. You can rule out a heater-to-cathode short in the tube by sucking solder off pin 11 (blue cathode). If blue remains the short is in the tube, otherwise it's in the blue circuit.


Posted By: justez
Date Posted: 22 Sep 2020 at 3:38pm
Yes, it was the blue transistor, which is wrong.
Repair Solved!







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