Need help with a WG K7191 , shorted caps, Making Progress

[NightWolfx03]

I have a K7191 chassis that I am working on and so far it's kicking my butt. I originally found that c36 had basically blown apart, I replaced C36 and the D1398 transistor that it was hooked to. I fired the board back up, it sounded like I had high voltage for about a second and then the slow blow fuse started glowing orange and blew. Going back to check again I found c37 and c38 shorted as well. This board has be changed in the past to use 2 double leg capacitors for c36 instead of the 4 legged one. Now I can replace c37 and c38, but I am wondering why they shorted. I took them off the board and tested them, got 0 ohms, applied a small voltage across them and they got hot, so I know they are dead.

Any suggestions would help!

[Ken Layton]

Those capacitors need to be "metalized polypropylene" types.

[qrz]

these caps are used for resonance tuning of the flyback.
if C36 is too far out of spec , the duty cycle( signal pulsewidth) of the output xistor changes.
generally, on times in excess of 15 microseconds (@15.75khz) is detrimental to the existor i.e. it shorts.
less than 8 microseconds usually allows the HV to exceed the XRP toggle point and shuts down the unit.
 C37 is part of pin cushion . D15 may well be questionable if C37 shorts
C38 is H yoke return - failure of these caps will affect horizontal sweep

[NightWolfx03]

Yeah I am looking at getting replacements, I will get them in and see if it will fire up, I'll check the diode there too. I just find it odd to find them all shorted like that, the picture was fine on the monitor up until the date it blew out.

Is there anything else I should check further back in before powering it up after I replace the caps ?


Also I am guessing it's not wise to power it up on the bench without being hooked to the CRT right ?

[MonMotha]

Also I am guessing it's not wise to power it up on the bench without being hooked to the CRT right ?

In general, this causes poppen corken mit spitzen sparken.  So yeah, it's not wise

You need something to terminate the HV lead, and the board usually needs at least the horizontal yoke hooked up to operate properly.  Running without these can be done in situations where it's absolutely required for some strange reason, but...well, this is almost never the case, and the things you have to do are more complicated than just hooking everything up to the tube/yoke.

[qrz]

 poppen corken mit spitzen sparken.  

     may i file this for future use ?    danke  


FYI, running the hv "open" was a diagnostic test i'd do ,when needed, to determine fault on the PTV169 projo chassis.
actually, the Flyback lead was connected to a WELL grounded HV probe dressed as far from the chassis as lead would allow .
the reason for this test was two seperate faults could cause the same shutdown condition .
IF the set would fire up in this test configuration , the HV distribution block was bad.
if it still shut down, the flyback was at fault .

was a "dirty" , yet accurate test for that chassis . and not RCA santioned 

[MonMotha]

 poppen corken mit spitzen sparken.  

     may i file this for future use ?    danke  

Sure, but only if you help me get my two broken monitors working, again

[Kevin Mullins]

when needed, to determine fault on the PTV169 projo chassis.

Oooh, I have one of those I inadvertently created a poppen corken mit spitzen sparken to and now it does less than before.
 

[NightWolfx03]

Lol, waiting to get the other 2 caps to replace and I might replace the one diode as well to see if it will fire up.

[boardjunkie]

[NightWolfx03]

Lol...

Anyways, replaced caps C36, C37, and C38. All 3 of these caps were shorted originally, c36 having literally exploded.

Now that I have replaced the caps, I powered the monitor up with a 2A Fast-Acting fuse, it doesn't blow, and I get high-voltage for about half a second and not enough time for the neck to start glowing, any idea's where I should check next ?

[boardjunkie]

Check the b+ voltage. See if it agrees with the voltage specified in the manual. If B+ goes too high, the chassis goes into protect/shutdown mode. X-ray protection....

[NightWolfx03]

I got back to looking at it, I think my voltage regulator is shorted.

it uses an STR 30130

I only have one other to compare it to, but legs 3 and 4 seem to be shorted. I get a reading of 1.5 ohms between them in either direction, the one off a smashed scrap board gives me 250 ohms in one direction, so either my scrap one is broke, or the true it my voltage regulator shorted.

Ideas ?

 I have a new STR 30130 on order for $3