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Philips 30PW8420/37 Unknown / Bad CRT?    
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Jrat



Joined: 21 Jun 2009
Posts: 9
Location: Brighton, MI

PostPosted: Fri Jan 22, 2010 7:25 pm    Post subject: Philips 30PW8420/37 Unknown / Bad CRT? Reply with quote

Chassis L05U AA - I have the service manual if it would help someone help me, or you just need it.

This set recently died and wouldn't power on - flashing error code 3. (High beam (BCI) protection)

I ended up replacing the vertical IC (TDA8177F), which allowed the set to power on fully, but with no horizontal defl (one thin vertical line).

While testing voltages with CRT connected, some strange noises would come from the general area of the defl yoke/CRT/CRT board. Sounded like a short/arc almost. Stupid me I'm guessing, as was doing all of this while the CRT was running and probably frying phosphors at the very least, given I wouldn't let it run for more than 30 seconds at a time. The image (thin line) was visibly grainy and jittery, and would cut out here and there.

On to now, I've just replaced the line transistor (BU2527DX) as a result of my voltage checking findings. The set now tries to start - The flyback screams/chirps, and the set powers down displaying errors 3 and 11 (Black current loop instability protection).

If I disconnect the filament/heater line from the CRT socket, the noise from the flyback stops, and I can hear the HV come up before shutting down with the same errors.

Can someone point me in the right direction and (hopefully) tell me that the CRT isn't gone? Razz
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Jesse Mack



Joined: 22 May 2008
Posts: 600
Location: The Last Frontier

PostPosted: Sat Jan 23, 2010 3:51 pm    Post subject: Reply with quote

This set has separate plugs for vertical and horizontal deflection. Maybe you did not get the horizontal deflection plug inserted correctly or maybe not at all??

Jesse


Quote:
but with no horizontal defl (one thin vertical line).
Jrat



Joined: 21 Jun 2009
Posts: 9
Location: Brighton, MI

PostPosted: Sat Jan 23, 2010 4:45 pm    Post subject: Reply with quote

Thank you for the response.

I had considered this and made sure everything was connected. I also checked all related solder joints, and nearby components for shorts or open circuit.

Aside, I probably should have been clearer:

The current status of the set after replacing the line transistor is protection shutdown (no raster/vertical line) with error codes 3 and 11. The FBT screams except with heater/filament supply disconnected. Although it (FBT) acted up once with heater disconnected - but in general it stops the continuous chirp and I can hear HV come up.

My reason for replacing the line transistor in the first place was by following the flowchart in the service manual. The specified voltages were way out of spec.

"Is VBE between
200mV to 30mV & VCB
approximately 500mV"
Jesse Mack



Joined: 22 May 2008
Posts: 600
Location: The Last Frontier

PostPosted: Sat Jan 23, 2010 4:49 pm    Post subject: Reply with quote

Please define vertical line. Is it top to bottom or from left to right?

Jesse
Jrat



Joined: 21 Jun 2009
Posts: 9
Location: Brighton, MI

PostPosted: Sat Jan 23, 2010 5:00 pm    Post subject: Reply with quote

Top to bottom. No horizontal deflection.
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Jrat



Joined: 21 Jun 2009
Posts: 9
Location: Brighton, MI

PostPosted: Sat Jan 23, 2010 6:13 pm    Post subject: Reply with quote

Alright, upon further experimenting:

I pulled the new BU2527DX transistor and reinserted the old. These new FETs do look questionable - like typical cheap chinese boots (do I smell a refund?). All of the sudden, I am back to having a raster with vertical line.

Someone pointed out to me that this should mean I *do* have horizontal output, but no scan. I've already at the very least touched up any solder joints that look even remotely questionable.
Jrat



Joined: 21 Jun 2009
Posts: 9
Location: Brighton, MI

PostPosted: Sat Jan 23, 2010 6:57 pm    Post subject: Reply with quote

If I do unplug the horizontal coil, the symptoms (vertical line) remain the same. Possibly indicating an open circuit?
JTS1957



Joined: 21 Jan 2009
Posts: 2395
Location: Far, Far Away

PostPosted: Sat Jan 23, 2010 11:54 pm    Post subject: Reply with quote

Do you have B-Plus on the collector pin of line output?
Jrat



Joined: 21 Jun 2009
Posts: 9
Location: Brighton, MI

PostPosted: Sun Jan 24, 2010 12:52 am    Post subject: Reply with quote

Yes. 144v - service manual has vague mention of correct B+ being 126v, but I'm unclear whether this is the case. voltage at pin 1 (B+) of flyback and on horizontal coil is the same as well.

I don't have a scope to check the waveform unfortunately, but a frequency checker says (and dead stable, no fluctuation) 16.87kHz at the horizontal coil. What's missing? Sufficient current to produce the required field?
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