New Wei-Ya 826HR chassis died while testing. Any ideas where to start poking?

[Pac-Fan]

Picked up a WeiYa 826 from Alva, tested about 9 donor TV tubes, from 23" to 27" with it all without incident. Total usage on time = less than 1 hour.

Picked up a couple 25" WG monitors with untested or missing chassis. Tested one of those tubes, no real problems exept horizontal and vertical was a bit jumpy and would go out of sync occassionally during game scene changes (to black screen and back). Thought sticky controls and not adjusted quite right yet.


What happened:
Removed the first tube, then connected the next 25" WG tube, powered up and had high voltage and seem to recall a faint image appearing (though it takes 10+ seconds to get bright enough from a cold tube anyway).  Then horizontal sounded like it was going out of sync, so grabbed the remote board to center it. As I was centering I could smell more 'warmth' than normal from the chassis.  Reached for the power strip switch and flipped off. Seem to recall hearing loss of HV while I was reaching for the switch, but can't be sure.

Did digging: The 5W5ohm ceramic square resistor R407 very hot. Q401 (c5296) transistor I think was warm. Q801 (D.402) transistor was hot, heatsink surrounding flyback that both were attached to was warmer than normal.   Neither the 2A or 6A fuse blew.

Rechecked connections, all correct, left off for 5 minutes, repowered up.. dead, nothing--no HV crackle, no 15.75KHz horizontal sound (that I can normally hear), though R407 and Q801 instantly got hot, but Q401 was cold after 3 seconds.


Yes, I triple checked the anode and ground wire and neckboard connection, both before connecting and when disconnecting. There was some HV left when discharging to remove the anode cap. Yes, I triple checked the yoke connection-- 1.5 ohm horizontal and 8.5 ohm vertical, and connected to the right posts. Measured after the failure and was the same (yoke didn't fry)

No burn marks or melted solder on the chassis, though some brown flux pooled around the BCE pins of the 5296 and nothing else on the board.


So, where to start? Anyone routinely work on these chassis?  The Q401 (2sc5296) reads a dead short between all 3 of BCE no matter the direction, but some surfing suggested that might be caused by flyback coil or internal devices in the transistor, but don't know for sure.

Biggest possibilities: 2sc5296 is dead and therefore no horizontal and therefore no HV, or the flyback shorted and then also took out the 5296.  Is that a good starting point assumption?  How best to test the flyback in circuit with a DMM?

Thanks for any assistance.  Anyone have a 5296 to try out if it was just that which died?

[Ken Layton]

The Wei-ya 826 chassis is designed for 26 and 27" tubes not 25. For 25" tubes you need the 825 chassis.

I have a feeling that the untested Wells monitor with missing chassis may have had a yoke with an internal arcing condition. The other Wells may have had a picture tube with an internal short (common in the crappy Zenith 25" tubes Wells used).

Can you get the 826 to work on the non-Wells tubes still?

Nobody has been able to get schematics to many of the Wei-ya chassis, but if you contact tech support at Wei-ya (www.weiya.com.tw/) in Taiwan they may be able to help. Be sure to write in as simple English as possible so they can translate as best as possible into their language. If I remember correctly, there was something about misadjusting the horizontal hold that would cause the monitor to into shutdown mode. I think they had written a procedure to readjust it to get the monitor back up again.

[Pac-Fan]

Thanks Ken. Responses below:

The Wei-ya 826 chassis is designed for 26 and 27" tubes not 25. For 25" tubes you need the 825 chassis.

Alva sold me the 826 as the 25" chassis when I ordered. Short response when ordering was basically 'works for all in that range' when I requested one that would work with 23 to 27 size tubes.

I didn't have problems at all with any tube size 23 to 27, the main difference was the amount of overscan at the Wide/Narrow jumper settings. All were bright and did not exhibit any visual or sounds of straining up until this point, until I started connecting the tubes from the WG monitors.

The other Wells may have had a picture tube with an internal short (common in the crappy Zenith 25" tubes Wells used).

Indeed, IIRC, the tube I was testing was a Zenith tube, where the first tube was one with both German and English warnings on the main sticker (can't remember the MFG right now).   Where was the short? Which pins should I use a DMM to test against on the tube to verify there was a short?

I assume that there should be 0 resistance between ALL pins except across the heaters, correct? Though I know some designs have a shared pin when looking in to see where the bands go inside.   If say the screen or focus grids were shorted, would that fry the flyback or simply take out the HOT?

I have a feeling that the untested Wells monitor with missing chassis may have had a yoke with an internal arcing condition.

I did not notice any shorts using a simple DMM against the yoke, left it set for about 15 seconds on each winding with no drop in resistance readings, however that doesn't account for the higher voltage running through the yoke when on.

Can you get the 826 to work on the non-Wells tubes still?

I have not retried it with a tube from a TV instead of the WG monitor.  Tonight, now that it's cooled down for more than 5 minutes, I will reconnect to a known good Philips tube from a Magnavox TV that worked well, recenter the horizontal hold to where it was working well and try again.

However, I have a feeling the HOT is probably fried. Hopefully just that and not the flyback. No signs or smells of burnt anything anywhere on it. Looks brand new in all of that area.

Thanks. Guess I should just instantly chuck any Zentith tubes or yokes with suggestions it came from a WG? Or at least test them first on a 25" TV chassis so I can fry it instead and toss it?

[castlesteve]

Best I can do is a composite scan.  Should be readable.

-Steve

[Pac-Fan]

Thank you very much Steve! Very helpful for me and also for others.

Update: I found that the same HOT is used in the 19" WeiYa, as well as the 19" Jen-Shin chassis, and amazingly the same flyback transformer as well in all 3. (Only the 25" Jen-Shin uses slightly different/significantly more components than the other 3)

I did some retesting using a Emerson TV chassis connected to the 25" tubes/yokes.   I determined out of 5 yokes, only 2 were good. The other three caused the Emerson TV chassis to sputter/click loudly and kill the anode power (but never killing its chassis). One even caused a spark between the yoke and the tube.  The one that blew the WeiYa chassis was one of the bad ones.  And sure enough, every one of the bad yokes were attached to Zenith tubes, the good ones were non-zenith tubes.

Therefore it appears that yoke the shorted the WeiYa.  Can I assume it is something pretty close to the horizontal yoke connector back to the HOT itself that blew? 

Are there any approved subs for this particular HOT (2sC5296) ? I have found numerous ones with very close, but not exact specs, from trolling through old TV chassis but nothing exact in part number.

[Ken Layton]

The 2SC5296 crosses to an NTE 2353 transistor.

If the yoke was arcing from itself to the tube then the yoke is shot. Probably all it took out was the horizontal output transistor or the vertical output transistor/IC. Possibly the damper diode might have shorted. It should be physically near the flyback or horizontal output transistor and you might have to unsolder one end of it to test it.

[Pac-Fan]

I see in Steve's schematic, they show Q401 as a 2sD1402 instead of a 5296.   

I found a few 14xx in various TV sets, don't recall if any were D1402's.  I see the schematic is dated 1986, while the build dates on my chassis were around 2005/2006 so I suspect they subbed in a newer transistor options along the way?

[grantspain]

if you download the datasheet for the original and then cross reference the ratings with your other transistors you may find a match.looks like a pretty standard crt deflection transistor without a damper diode

[aussietech]

Hi Guys here is an Weiya 825 h  schematic

[Ken Layton]

Thank you for posting the 825 schematic. I've been looking for that for quite a while.