Bush srp41 humming! - Page 3 - UK Vintage Radio Repair and Restoration Discussion Forum

geofy · 1st Apr 2009, 9:37 am

The picture this time, the two AD's can just about be seen on the panel.

thegreat26 · 1st Apr 2009, 9:53 am

as for the disassebly i did it . it is quite the same like the srp51. if you take the metalic panel it easy to access the transistors . my only worry is that i am a complete amateur in doing this. I want to learn but i do not know if its sth i can handle it. if you think i can do it by myself i will give it a try.But i like this player and i want to use it.

geofy · 1st Apr 2009, 12:56 pm

You seem to be doing all right so far. Provided you can solder and have a suitable soldering iron then you should be able to change the transistors, preferably if you have some experience of doing this type of work.

They have to be accessed from other side of the panel and the AD161 has insulating mica washer and plastic bushes on the fixing screws, held on by 6 BA nuts I believe. These must be refitted to the new transistor. The wires can be unsoldered from the transistor and should still go straight onto the new transistor, making note of which pin they came from. The white heatsink grease should still be good for the new transistors, it should be retained as much as possible.

The colours are;

Blue; Collector going to the tag

Green; Base

Yellow; Emitter.

The transistors ideally should be checked to see which one of the junctions has gone faulty by using a multi-meter on the diode range across the base collector emitter forward and reverse. I am making the assumption you are familiar with this. The driver transistor should be checked though this being silicon has more than likely survived. If it has failed it may have damaged the base bias adjustable pot VR5 50 Ohm which otherwise would not need touching until the new transistors are in place and the overall current measured in the pink lead.

This is not the easiest of repairs and if you are not familiar with electronics it would be better to find a repairer to carry out the work.

Geof

thegreat26 · 1st Apr 2009, 2:59 pm

i suppose the only think left is to find them somewhere and buy them.

Steve_P · 1st Apr 2009, 8:57 pm

Did you disconnect the Mains Transformer?

Cheers,

Steve P.

geofy · 1st Apr 2009, 9:24 pm

Quote:

Originally Posted by Steve_P

Did you disconnect the Mains Transformer?

Cheers,

Steve P.

Seems the control panel where the output transistors are just below is getting very hot. This could have had a knock on effect of damaging the transformer and rectifiers if they where run overloaded for too long. A substitute load connected to the power supply would show if it is still working without getting hot. A leakage tester would show up a faulty transformer but that is not likely to be available.

Geof

thegreat26 · 2nd Apr 2009, 1:00 pm

Quote:

Originally Posted by Steve_P

Did you disconnect the Mains Transformer?

Cheers,

Steve P.

no when should i disconnected it. or just to check if its the transformers fault.

geofy · 2nd Apr 2009, 2:58 pm

If the panel is getting very hot then this would be the main problem, if the wires to the output transistors can be located on the inside of the panel then a meter on the diode check range can check the combination of emitter collector base to see if a junction is faulty. The rectifiers can be checked in the same way. If the transformer stays cool when disconnected then this should be ok, the pilot light should also light normally unless the transformer has a shorted turn which is probably unlikely, the transformer would buzz louder than normal if it was being loaded due to a short.

thegreat26 · 2nd Apr 2009, 9:20 pm

ok i ve disconnected the pink and black cable and after 20 minutes of operation there was no sign of heat.

thegreat26 · 3rd Apr 2009, 2:01 pm

He he strange but i found ad 161/2 in cyprus i ll have them tomorrow!

thegreat26 · 4th Apr 2009, 11:22 am

i ve manage to replace the ad 161/2 and there is no more humming. There is slightly humming but at normal levels. After one side of playing a record the mains is just warm . so i supposed i fixed it. Thank you all for your support.

geofy · 4th Apr 2009, 12:16 pm

Seems that you have fixed it, the bias level should be the same and will not need readjusting, though it might have been an idea to see what the overall current being drawn is to make sure you are not overdriving the base current of the replacements. The driver has survived if the unit is working. And it would have been interesting to know which of the transistors had failed by measuring the forward and reverse junctions.

thegreat26 · 4th Apr 2009, 6:20 pm

ok i ve still have it open. If its not difficult for you inform me what to do step by step and what should i check to prevent future failures

geofy · 5th Apr 2009, 10:27 am

You simply measure the quiescent current with a mA meter connected in series with the pink wire. It should read about 10mA with the volume turned down.

And for the transistors you removed the diode range could be used to see if one of the junctions was leaky, though if they where both still working as such this would be more difficult to determine. It is my guess one transistor had gone short collector emitter.

But as you have essentially finished the repair the thread is getting off topic so any more on this will have to be a new one.

Geof

thegreat26 · 5th Apr 2009, 11:00 am

ok thanx again. And please you can close the thread problem solved.

1st Apr 2009, 9:37 am	#41
geofy Retired Dormant Member Join Date: Jun 2006 Posts: 1,798	Re: Bush srp41 humming! The picture this time, the two AD's can just about be seen on the panel. Attached Thumbnails

1st Apr 2009, 9:53 am	#42
thegreat26 Tetrode Join Date: Aug 2008 Location: Larnaca, Cyprus. Posts: 59	Re: Bush srp41 humming! as for the disassebly i did it . it is quite the same like the srp51. if you take the metalic panel it easy to access the transistors . my only worry is that i am a complete amateur in doing this. I want to learn but i do not know if its sth i can handle it. if you think i can do it by myself i will give it a try.But i like this player and i want to use it.

1st Apr 2009, 12:56 pm	#43
geofy Retired Dormant Member Join Date: Jun 2006 Posts: 1,798	Re: Bush srp41 humming! You seem to be doing all right so far. Provided you can solder and have a suitable soldering iron then you should be able to change the transistors, preferably if you have some experience of doing this type of work. They have to be accessed from other side of the panel and the AD161 has insulating mica washer and plastic bushes on the fixing screws, held on by 6 BA nuts I believe. These must be refitted to the new transistor. The wires can be unsoldered from the transistor and should still go straight onto the new transistor, making note of which pin they came from. The white heatsink grease should still be good for the new transistors, it should be retained as much as possible. The colours are; Blue; Collector going to the tag Green; Base Yellow; Emitter. The transistors ideally should be checked to see which one of the junctions has gone faulty by using a multi-meter on the diode range across the base collector emitter forward and reverse. I am making the assumption you are familiar with this. The driver transistor should be checked though this being silicon has more than likely survived. If it has failed it may have damaged the base bias adjustable pot VR5 50 Ohm which otherwise would not need touching until the new transistors are in place and the overall current measured in the pink lead. This is not the easiest of repairs and if you are not familiar with electronics it would be better to find a repairer to carry out the work. Geof

1st Apr 2009, 2:59 pm	#44
thegreat26 Tetrode Join Date: Aug 2008 Location: Larnaca, Cyprus. Posts: 59	Re: Bush srp41 humming! i suppose the only think left is to find them somewhere and buy them.

1st Apr 2009, 8:57 pm	#45
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: Bush srp41 humming! Did you disconnect the Mains Transformer? 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...?

2nd Apr 2009, 2:58 pm	#48
geofy Retired Dormant Member Join Date: Jun 2006 Posts: 1,798	Re: Bush srp41 humming! If the panel is getting very hot then this would be the main problem, if the wires to the output transistors can be located on the inside of the panel then a meter on the diode check range can check the combination of emitter collector base to see if a junction is faulty. The rectifiers can be checked in the same way. If the transformer stays cool when disconnected then this should be ok, the pilot light should also light normally unless the transformer has a shorted turn which is probably unlikely, the transformer would buzz louder than normal if it was being loaded due to a short.

2nd Apr 2009, 9:20 pm	#49
thegreat26 Tetrode Join Date: Aug 2008 Location: Larnaca, Cyprus. Posts: 59	Re: Bush srp41 humming! ok i ve disconnected the pink and black cable and after 20 minutes of operation there was no sign of heat. Last edited by thegreat26; 2nd Apr 2009 at 9:43 pm.

3rd Apr 2009, 2:01 pm	#50
thegreat26 Tetrode Join Date: Aug 2008 Location: Larnaca, Cyprus. Posts: 59	Re: Bush srp41 humming! He he strange but i found ad 161/2 in cyprus i ll have them tomorrow!

4th Apr 2009, 11:22 am	#51
thegreat26 Tetrode Join Date: Aug 2008 Location: Larnaca, Cyprus. Posts: 59	Re: Bush srp41 humming! i ve manage to replace the ad 161/2 and there is no more humming. There is slightly humming but at normal levels. After one side of playing a record the mains is just warm . so i supposed i fixed it. Thank you all for your support.

4th Apr 2009, 12:16 pm	#52
geofy Retired Dormant Member Join Date: Jun 2006 Posts: 1,798	Re: Bush srp41 humming! Seems that you have fixed it, the bias level should be the same and will not need readjusting, though it might have been an idea to see what the overall current being drawn is to make sure you are not overdriving the base current of the replacements. The driver has survived if the unit is working. And it would have been interesting to know which of the transistors had failed by measuring the forward and reverse junctions.

4th Apr 2009, 6:20 pm	#53
thegreat26 Tetrode Join Date: Aug 2008 Location: Larnaca, Cyprus. Posts: 59	Re: Bush srp41 humming! ok i ve still have it open. If its not difficult for you inform me what to do step by step and what should i check to prevent future failures

5th Apr 2009, 10:27 am	#54
geofy Retired Dormant Member Join Date: Jun 2006 Posts: 1,798	Re: Bush srp41 humming! You simply measure the quiescent current with a mA meter connected in series with the pink wire. It should read about 10mA with the volume turned down. And for the transistors you removed the diode range could be used to see if one of the junctions was leaky, though if they where both still working as such this would be more difficult to determine. It is my guess one transistor had gone short collector emitter. But as you have essentially finished the repair the thread is getting off topic so any more on this will have to be a new one. Geof

5th Apr 2009, 11:00 am	#55
thegreat26 Tetrode Join Date: Aug 2008 Location: Larnaca, Cyprus. Posts: 59	Re: Bush srp41 humming! ok thanx again. And please you can close the thread problem solved. Last edited by thegreat26; 5th Apr 2009 at 11:12 am.