UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Radio (domestic)

Notices

Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only.

Reply
 
Thread Tools
Old 12th Jun 2021, 1:55 am   #1
iceman303
Diode
 
Join Date: Jun 2021
Location: Lisbon, Portugal.
Posts: 3
Default Troubleshooting Philips BX 526A.

hello friends. i am troubleshooting a bx526. when i got it, b4 got ( too ) hot, and there was low audio on the speaker and (some stations heard) some hum. i inspected the set and did some troubleshooting. v++ was connected to only one of the wires (of one of the windings ) of the transformer ( s23 ) also the cathode of b4. and that winding was broken. i took out the transformer and fixed that winding that was making no contact. i have continuity there now. so i connected v++ coming from the rectifier tube to one side of the transformer ( also goes to r1 i think ) and the cathode and c33 to the other wire. i have v+ disconnected. out of the rectifier tube, i am getting 285v dc ( with v+ disconnected, maybe it should not be), and not anything else connected ( v++ should be 270 it seems according to the schematic ). when i connect it on the transformer winding it kind of arcs, or pops, and i think the rectifier gets hot. i have also tried the set now, all connected to only one wire s23, and with v+, and c32 disconnected. b4 is not getting hot anymore. i think c1 and c2 are ok, i cannot test uf capacitors, but they are not shorted, and r1 tests ok. i tested all the other caps and resistors near b4, and they all seem ok. thanks in advance for reading.
any help is very appreciated
Attached Thumbnails
Click image for larger version

Name:	philips1.jpg
Views:	62
Size:	70.7 KB
ID:	235745  
Attached Files
File Type: pdf philips_bx526a_radio_1952_sm.pdf (946.4 KB, 41 views)
iceman303 is offline   Reply With Quote
Old 12th Jun 2021, 1:01 pm   #2
Robert Gribnau
Pentode
 
Join Date: May 2017
Location: The Hague, The Netherlands
Posts: 170
Default Re: Troubleshooting Philips BX 526A.

With V+ disconnected the screengrid volatge of B4 is 'zero'/floating. Under these circumstances B4 should hardly be passing anode current because in pentodes the anode current depends largely on the screen grid voltage (and control grid voltage) but hardly on the anode voltage.

What happens when you remove B4 with V++ still connected to S23 and V+ still disconnected? Does the rectifer than still struggle? How do you know it struggles? Rectifiers and power valves get hot even when working normaly. Can you measure the current between the rectifier and C1?

Addition: If there really was no connection between the anode of B4 and S23 than I do not see how you would be able to still hear some stations.
__________________
Robert

Last edited by Robert Gribnau; 12th Jun 2021 at 1:28 pm. Reason: Correction & addition
Robert Gribnau is offline   Reply With Quote
Old 12th Jun 2021, 2:33 pm   #3
crackle
Dekatron
 
crackle's Avatar
 
Join Date: Mar 2011
Location: Basildon, Essex, UK.
Posts: 4,050
Default Re: Troubleshooting Philips BX 526A.

Change C32 for a new capacitor (0.01uF 630v polyester).
Mike
__________________
BVWS Member, 2E1MJE
The KB Museum

My collection in the Radio Museum
crackle is offline   Reply With Quote
Old 19th Jun 2021, 8:17 pm   #4
iceman303
Diode
 
Join Date: Jun 2021
Location: Lisbon, Portugal.
Posts: 3
Default Re: Troubleshooting Philips BX 526A.

thanks for the help guys. it seems that b4 is not get overheatead anymore with both v+ and v++ connected. too bad i fixed the transformer, but ended shorting s23 again, and now i have to rewind it. i will let you guys know how it's going when i make more progress.
thanks.

joao g.
iceman303 is offline   Reply With Quote
Old 21st Jun 2021, 5:28 am   #5
Robert Gribnau
Pentode
 
Join Date: May 2017
Location: The Hague, The Netherlands
Posts: 170
Default Re: Troubleshooting Philips BX 526A.

Hello Joao,

I still do not understand how you could hear some stations while S23 was interrupted. If S23 was really interrupted, there is no way that signal could get at the loudspeaker.

If S23 shorted again (by which I assume you mean that S23 got interrupted again) than probably there is too much current running through S23. That could be caused by B4 passing too much current or something else.

Mike already advised you to change C32. If C32 would be leaky, than the control grid of B4 would go positive and B4 would start to pass more current than it normaly would.

If C33 would be leaky, the current through S23 would also be higher. You could also change that capacitor (that capacitor has to have a high voltage rating; something like 1500 V will do).

The wire which connects S23 to the anode of B4 is a screened one. The screening is connected to ground. You could check if there is a short between this screening and the wire itself.

A short between S23 and S24 is also a possibility.

It is not good for B4 to work with its anode at 0 V while its screen grid is connected to V+ because too much current would start to pass through the screen grid with the risk it will get damaged. A short in C33 or a short between the screening and the wire between S23 and B4 or a short betweeen S23 and S24 would also lead to the situation that the anode of B4 has no (or much lower) voltage. In these situations the screen grid of B4 would also pass more current than it normaly does.
__________________
Robert
Robert Gribnau is offline   Reply With Quote
Old 22nd Jun 2021, 4:15 pm   #6
iceman303
Diode
 
Join Date: Jun 2021
Location: Lisbon, Portugal.
Posts: 3
Default Re: Troubleshooting Philips BX 526A.

hello rob. thanks for the reply. when i got the radio both wires of s23 were shunted, and everything was connected to that spot. and it made sound like that. i am curious because on the schematic it seems that s23 is shunted also, which is a bit strange, its hard to see but it seems so, i even made a jpg of that area on the post. the way i burned s23 is what you described, i shorted the screened wire. i realized that ( a bit to late ). i am going to replace c32 as you advise. ( its not connected atm ). i replaced c33, seemed to be leaky. should i use another xformer or rewind s23, tedious but doable. if you have time, take a look at the schematic and see what you think about s23 being shunted.
many thanks, will keep you posted.
iceman303 is offline   Reply With Quote
Old 23rd Jun 2021, 5:13 am   #7
Robert Gribnau
Pentode
 
Join Date: May 2017
Location: The Hague, The Netherlands
Posts: 170
Default Re: Troubleshooting Philips BX 526A.

Hello Joao,

I do not see anything shunting (= bypassing = connected parallel to) S23 in the schematic.

I find it hard to understand your description of the problem. Since I already described most of the possible causes for S23 shorting, I do not think I can help you any further.

Good luck with the repairs.
__________________
Robert
Robert Gribnau is offline   Reply With Quote
Reply

Thread Tools



All times are GMT. The time now is 3:02 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2021, vBulletin Solutions, Inc.
Copyright ©2002 - 2021, Paul Stenning.