Phonola TV2424 problems - UK Vintage Radio Repair and Restoration Discussion Forum

Jimmyhaflinger · 6th May 2010, 8:33 am

I'm restoring an Italian Phonola TV2424 set, a 4-valve mono hybrid from 1972

I replaced the EHT winding on the LOPTx and resoldered many dry joints, then fired up the set and it worked fine for several hours.

Then... SNAP!! it started arcing occasionally between the PY88's top cap and the nearby metal cage.
I tried to insulate the PY88's top cap better, then it started arcing to ground from the PCB trace where the lead from the PY88's top cap goes.
The set still works fine despite the arcing.

I tried to replace the 220pf 4kv cap but this made no difference, the set still sparks every few seconds, especially during dark scenes,

Maybe the replacement EHT winding is to blame for this? the ground lead from the EHT winding goes on the same PCB trace where the PY88's top cap is connected, or maybe the PY88 itself is to blame?

Heatercathodeshort · 6th May 2010, 8:47 am

Hello Jimmy,
Just a thought. It is the PY88 boost diode that is arcing and not the EHT rectifier possibly a DY802 type unless it uses a stick rectifier?
You have only replaced the EHT overwind so this cannot increase boost voltage. Most odd. The fault may simply be poor insulation or a breakdown in the insulating properties of the LOPT case. Not sure of your term 'PCB trace'. These high pulse top cap lead connections often break down where they pass close to chassis metalwork or pass through holes drilled in it. If it is working OK I feel it is just an insulation problem.
Regards, John.

Jimmyhaflinger · 6th May 2010, 9:19 am

This set uses a TV18 EHT rectifier stick mounted in a plastic holder on top of the LOPTx, so that's unlikely to be involved.

even when there's no arcing, the whole PCB (Printed Circuit Board) chassis area under the line output stage is sizzling loudly, so i think the boost voltage is way too high.

the paxolin of the PCB is still in good conditions with no signs of heat damage/blackening or carbon tracks.

Tazman1966 · 6th May 2010, 9:43 am

I see you have a trusty assistant to help!

Have you got a figure for the boost voltage? Is the width correct?

Jimmyhaflinger · 6th May 2010, 11:00 am

I don't have a schematic for this set so i don't know the correct figure for the boost voltage.

The picture width is correct.

I connected the new EHT overwind exactly like the old one, on the same LOPTx pin that goes to the top cap of the PY88, however the line output stage was bodged in the past so i'm not sure if this is the correct configuration.

The "assistant" was actually checking the set for edible parts like paper stickers

ENGLISH VICTOR · 6th May 2010, 11:58 am

Whilst I have no knowledge of your particular set I suggest you ensure that the new overwind cold end wire should in fact go to the PY88 rather than the anode of the line output valve. if you get it wrong it could upset the 3rd harmonic tuning of the transformer and result in higher voltages appearing on the primary winding, a part of which will be fed from the PY88 cathode (top cap) if the stage has previously been bodged I would also check the connections of the 220pf 4KV tuning cap. A circuit diagram will solve the mystery I expect.
Victor.

Steve_P · 6th May 2010, 12:00 pm

Clean all connections, make sure all the soldering is good and also clean the printed circuit board.

This sounds to me like a lead in the wrong place or something like that. Try re-routing leads away from areas where they would 'arc' to and possibly change the PY88.

Has the new EHT winding generating too much EHT? Try lowering the voltage to the LOPT stage slightly??

Cheers,

Steve P.

Welsh Anorak · 6th May 2010, 12:50 pm

Hi
I would disconnect the new overwind and see if it still makes the noise, then turn the lights off - it might be a capacitor breaking down which you might see. If the width's OK I would think the boost voltage is fine.
It's always hard to locate this sort of 'splashing' by ear.
Glyn

Jimmyhaflinger · 8th May 2010, 12:07 am

Well, a new PY88 made no difference, i'll put this set on hold until i find a schematic.

Jimmyhaflinger · 25th May 2010, 11:03 am

I have finally found a schematic,
I rewired the EHT overwind following the schematic but it's still arcing, the only difference is that it's now arcing in another place (from a PCB track connected to the PL504's plate to ground)

Is it a good idea to try to remove the EHT overwind's bottom end from the PL504 plate and route it straight to chassis ground? any other way to lower the EHT?

I have attached the schematics of the power supply and the line output/EHT section.
The red arrow points to a VDR on the vertical height pot which is neatly broken in half, i can't find a replacement for this VDR here, is this a critical part? the vertical height seems to be more or less unaffected by the broken VDR

Steve_P · 25th May 2010, 12:10 pm

As I said earlier, check soldering and cleanliness first. Is the HT high?

Also, try reducing the line drive, as the EHT is dependant on this. And you could try moving the coil as you describe. Might help.

Try spraying the board with EHT sealant?

Cheers,

Steve P.

Welsh Anorak · 25th May 2010, 12:38 pm

Hi
Not quite sure what you mean by 'plate' - is that the top cap of the PL504?
I think you need to determine whether the EHT is correct. If it were wrong, I'd expect the arcing to come from the EHT side of the rectifier, not the feed. Does the width control have any effect? This should vary the EHT. I notice several high-value resistors here. If the width's OK and can be varied, then I'd go with Steve and suspect something breaking down that shouldn't be. If however the EHT's excessive, then I'd play with some high voltage capacitors from the top cap to earth to see what that does.
Let's get this done then worry about the height VDR - I doubt it'll make much difference.

Glyn

Sideband · 25th May 2010, 7:50 pm

Quote:

Originally Posted by Welsh Anorak

Hi
Not quite sure what you mean by 'plate' - is that the top cap of the PL504?

Yes. Plate = Anode.

Is this a Philips set in disguise?

SB

Jimmyhaflinger · 26th May 2010, 11:01 am

FIMI Phonola had been bought by Philips in about 1969 but this one is still a "real" Italian FIMI Phonola set, probably one of the very last ones, the only Philips parts used in this set are the preset drawer, the tube, the valves and a few electrolytic capacitors, the rest of the set is 100% Italian.

In about 1974 Philips converted the FIMI factory to make industrial and medical monitors, and began to use the Phonola name to rebadge some of their cheaper sets (like they did with Pye in the UK)

Anyway, i'll try to put a capacitor between the PL504 top cap and chassis ground to see if it stops arcing, is a 220pf 4kv disc capacitor suitable?

6th May 2010, 8:33 am	#1
Jimmyhaflinger Heptode Join Date: Feb 2007 Location: La Spezia, Italy Posts: 834	Phonola TV2424 problems I'm restoring an Italian Phonola TV2424 set, a 4-valve mono hybrid from 1972 I replaced the EHT winding on the LOPTx and resoldered many dry joints, then fired up the set and it worked fine for several hours. Then... SNAP!! it started arcing occasionally between the PY88's top cap and the nearby metal cage. I tried to insulate the PY88's top cap better, then it started arcing to ground from the PCB trace where the lead from the PY88's top cap goes. The set still works fine despite the arcing. I tried to replace the 220pf 4kv cap but this made no difference, the set still sparks every few seconds, especially during dark scenes, Maybe the replacement EHT winding is to blame for this? the ground lead from the EHT winding goes on the same PCB trace where the PY88's top cap is connected, or maybe the PY88 itself is to blame? Last edited by Jimmyhaflinger; 6th May 2010 at 8:39 am.

6th May 2010, 8:47 am	#2
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: Phonola TV2424 problems Hello Jimmy, Just a thought. It is the PY88 boost diode that is arcing and not the EHT rectifier possibly a DY802 type unless it uses a stick rectifier? You have only replaced the EHT overwind so this cannot increase boost voltage. Most odd. The fault may simply be poor insulation or a breakdown in the insulating properties of the LOPT case. Not sure of your term 'PCB trace'. These high pulse top cap lead connections often break down where they pass close to chassis metalwork or pass through holes drilled in it. If it is working OK I feel it is just an insulation problem. Regards, John.

6th May 2010, 9:19 am	#3
Jimmyhaflinger Heptode Join Date: Feb 2007 Location: La Spezia, Italy Posts: 834	Re: Phonola TV2424 problems This set uses a TV18 EHT rectifier stick mounted in a plastic holder on top of the LOPTx, so that's unlikely to be involved. even when there's no arcing, the whole PCB (Printed Circuit Board) chassis area under the line output stage is sizzling loudly, so i think the boost voltage is way too high. the paxolin of the PCB is still in good conditions with no signs of heat damage/blackening or carbon tracks. Attached Thumbnails Last edited by Jimmyhaflinger; 6th May 2010 at 9:28 am. Reason: added picture

6th May 2010, 9:43 am	#4
Tazman1966 Nonode Join Date: May 2006 Location: St Albans, Herts, UK. Posts: 2,193	Re: Phonola TV2424 problems I see you have a trusty assistant to help! Have you got a figure for the boost voltage? Is the width correct? __________________ All the very best, Tas

6th May 2010, 11:00 am	#5
Jimmyhaflinger Heptode Join Date: Feb 2007 Location: La Spezia, Italy Posts: 834	Re: Phonola TV2424 problems I don't have a schematic for this set so i don't know the correct figure for the boost voltage. The picture width is correct. I connected the new EHT overwind exactly like the old one, on the same LOPTx pin that goes to the top cap of the PY88, however the line output stage was bodged in the past so i'm not sure if this is the correct configuration. The "assistant" was actually checking the set for edible parts like paper stickers Last edited by Jimmyhaflinger; 6th May 2010 at 11:06 am.

6th May 2010, 11:58 am	#6
ENGLISH VICTOR Hexode Join Date: Feb 2008 Location: Sydney, Australia Posts: 356	Re: Phonola TV2424 problems Whilst I have no knowledge of your particular set I suggest you ensure that the new overwind cold end wire should in fact go to the PY88 rather than the anode of the line output valve. if you get it wrong it could upset the 3rd harmonic tuning of the transformer and result in higher voltages appearing on the primary winding, a part of which will be fed from the PY88 cathode (top cap) if the stage has previously been bodged I would also check the connections of the 220pf 4KV tuning cap. A circuit diagram will solve the mystery I expect. Victor.

6th May 2010, 12:00 pm	#7
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: Phonola TV2424 problems Clean all connections, make sure all the soldering is good and also clean the printed circuit board. This sounds to me like a lead in the wrong place or something like that. Try re-routing leads away from areas where they would 'arc' to and possibly change the PY88. Has the new EHT winding generating too much EHT? Try lowering the voltage to the LOPT stage slightly?? Cheers, Steve P. __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

6th May 2010, 12:50 pm	#8
Welsh Anorak Dekatron Join Date: Apr 2005 Location: North Wales, UK. Posts: 6,927	Re: Phonola TV2424 problems Hi I would disconnect the new overwind and see if it still makes the noise, then turn the lights off - it might be a capacitor breaking down which you might see. If the width's OK I would think the boost voltage is fine. It's always hard to locate this sort of 'splashing' by ear. Glyn

8th May 2010, 12:07 am	#9
Jimmyhaflinger Heptode Join Date: Feb 2007 Location: La Spezia, Italy Posts: 834	Re: Phonola TV2424 problems Well, a new PY88 made no difference, i'll put this set on hold until i find a schematic.

25th May 2010, 11:03 am	#10
Jimmyhaflinger Heptode Join Date: Feb 2007 Location: La Spezia, Italy Posts: 834	Re: Phonola TV2424 problems I have finally found a schematic, I rewired the EHT overwind following the schematic but it's still arcing, the only difference is that it's now arcing in another place (from a PCB track connected to the PL504's plate to ground) Is it a good idea to try to remove the EHT overwind's bottom end from the PL504 plate and route it straight to chassis ground? any other way to lower the EHT? I have attached the schematics of the power supply and the line output/EHT section. The red arrow points to a VDR on the vertical height pot which is neatly broken in half, i can't find a replacement for this VDR here, is this a critical part? the vertical height seems to be more or less unaffected by the broken VDR Attached Thumbnails Last edited by Jimmyhaflinger; 25th May 2010 at 11:10 am.

25th May 2010, 12:10 pm	#11
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: Phonola TV2424 problems As I said earlier, check soldering and cleanliness first. Is the HT high? Also, try reducing the line drive, as the EHT is dependant on this. And you could try moving the coil as you describe. Might help. Try spraying the board with EHT sealant? Cheers, Steve P. __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

25th May 2010, 12:38 pm	#12
Welsh Anorak Dekatron Join Date: Apr 2005 Location: North Wales, UK. Posts: 6,927	Re: Phonola TV2424 problems Hi Not quite sure what you mean by 'plate' - is that the top cap of the PL504? I think you need to determine whether the EHT is correct. If it were wrong, I'd expect the arcing to come from the EHT side of the rectifier, not the feed. Does the width control have any effect? This should vary the EHT. I notice several high-value resistors here. If the width's OK and can be varied, then I'd go with Steve and suspect something breaking down that shouldn't be. If however the EHT's excessive, then I'd play with some high voltage capacitors from the top cap to earth to see what that does. Let's get this done then worry about the height VDR - I doubt it'll make much difference. Glyn

26th May 2010, 11:01 am	#14
Jimmyhaflinger Heptode Join Date: Feb 2007 Location: La Spezia, Italy Posts: 834	Re: Phonola TV2424 problems FIMI Phonola had been bought by Philips in about 1969 but this one is still a "real" Italian FIMI Phonola set, probably one of the very last ones, the only Philips parts used in this set are the preset drawer, the tube, the valves and a few electrolytic capacitors, the rest of the set is 100% Italian. In about 1974 Philips converted the FIMI factory to make industrial and medical monitors, and began to use the Phonola name to rebadge some of their cheaper sets (like they did with Pye in the UK) Anyway, i'll try to put a capacitor between the PL504 top cap and chassis ground to see if it stops arcing, is a 220pf 4kv disc capacitor suitable?