Hacker Herald RP37A Speaker Thump on Power-up - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

mhennessy · 15th Dec 2016, 10:19 pm

Yes, I suggested that earlier. Even at minimum, the pot still lets through a little audio.

McMurdo · 15th Dec 2016, 10:31 pm

Here are some of mine being turned on for reference!

https://youtu.be/tH3R_QgCArY

mhennessy · 15th Dec 2016, 10:37 pm

Excellent

Note the RP35 Herald is silent the first time, but clicks on subsequent goes. If you leave it a bit longer before powering it back up, that click won't be there. About 5 seconds is enough.

Ti Pwun · 17th Dec 2016, 12:34 pm

Thanks for the input guys - really helpful.

Even though I couldn't find fault with the switch itself and I had smooth deflection on the AVO while testing the pot, I replaced the switch/pot anyway. There was a slight improvement.

I then remade the grounding connections to a new silver plated lug and fitted that in place of the original (tarnished) lug and there was further improvement.

The Mullard cap tested OK, if a little high, but I temporarily replaced it anyway and there was further improvement so I made the replacement permanent.

Very strange to me that changes I would usually consider to be unnecessary have made a marked difference to the thump but that's the case so I'm happier now with the way the radio powers up.

I was quite ill yesterday due to my diabetes but after resting I want to look into some of the other suggestions today to see if I can soften the thump further. I wouldn't say it is overly excessive now but I do feel that there is room for improvement.

I'll see what today brings.

Ti Pwun · 21st Dec 2016, 11:45 am

Just a quick update on this:

After remaking the remaining Gnd connections to the chassis the nasty thump has gone. It still clicks but no alarming thump so the radio is now on its way back to the owner.

Hard to name an actual cause - bit of everything, I think...

mhennessy · 21st Dec 2016, 1:35 pm

That's good news - thanks for the update

My money was on the grounding. As you say, it's hard to know for sure what exactly was going on, but overall, all the work you've done is good "preventive maintenance" - those are parts that might well have needed replacing at some point in the future...

Thinking again about the grounding of those tone controls has reminded me of another fault that I've seen on these: weak bass, with the bass control having no effect.

It turned out to be a short within the bass potentiometer. But it went away when I applied a DC current - just 10mA or so (bass turned to max, so no real current flowed via the wiper and the track). I'm guessing something like a tin whisker was inside the pot.

I've got another 2 or 3 VHF Heralds with exactly this symptom, and when I eventually get around to looking at them, I'll be a bit more careful to establish exactly what is happening. But here's the mystery: that amp and bass control is used in many other sets, yet I've only ever seen that fault with the VHF Herald. I can think of no logical reason for that!

Radiocruncher · 21st Dec 2016, 6:30 pm

Quote:

Originally Posted by Ti Pwun

After remaking the remaining Gnd connections to the chassis the nasty thump has gone. It still clicks but no alarming thump so the radio is now on its way back to the owner.

Hard to name an actual cause - bit of everything, I think...

Good job Jon. I knew you would get there in the end.

Graham

wireless_john · 21st Dec 2016, 7:31 pm

Sovereign 2 - no thump.
Herald RP35 - ever so slight on switch on - more of a thump on switch off.

Never noticed either till this discussion started!!

John

Ti Pwun · 31st Jan 2017, 3:46 pm

UPDATE:

I sent this radio back to the owner and he said it was working great. Not long after, though, he only got a hiss from the speaker. I asked that he send it back to me.

When it arrived, after switching on I used a plastic tool to tap the boards and I got the radio hissing noise when I got to the T309 board (as opposed to just an amp hiss). I tugged gently on the wires and sure enough, there was some movement. Only slight, but I could easily make the hissing come and go.

That board had to be removed to repair it (there is a plate attached to the underside) and I got to see where the actual problem was. There were dry joints everywhere. None of that showed up when I last worked on it and other than the thump, there wasn't anything I was concerned about. The soldering seemed fine after a visible inspection but it was only a matter of time.

So, if you have any thumping issues, take the time to remove that board and go over the soldering. There were areas beneath the plate that needed attention and they couldn't be seen without getting the board out, so do inspect closely. Don't do what I did and assume that because a lot of other people are experiencing this same problem, it is in any way normal or acceptable. I knew it wasn't but it worked and I convinced myself that it's OK. I had managed to calm it down but I should have gone with my gut and took the board out, as involved as that is.

Needless to say, after resoldering everything, there is nothing more than the normal mechanical click on power up. There are other issues I need to attend to because I think some other component(s) failed and I only get the hiss (no actual stations), but the problem I originally had is now completely gone.

If you just have the thump and the radio is with you and you can work on it later if need be, you can access the edge connections (wire posts) so even though they might look fine, resolder them anyway. Remove the old stuff first if you have a desoldering pump/gun.

Hope that helps someone.

Radiocruncher · 1st Feb 2017, 1:45 pm

Hi Jon. That's useful info. Usually these Hacker boards are very well put together. I suppose after time and possibly a humid atmosphere, corrosion can set in. Well done on finding it though, that was a bit of a marathon.

Graham

Ti Pwun · 1st Feb 2017, 2:27 pm

Oh, it's not over yet, Graham - ha!

I've had to remove the board again to investigate further - no actual radio stations at all at the moment. I double-checked everything but can't see a fault yet. Maybe the power-up surge because of those solder connections took out a transistor or something. We'll see.

Not often, but sometimes it seems that the more you repair, the more it creates or shows up another weak area. This thing will be practically new when I'm done but at least it should be rock solid. All good fun and I should have tested the soldering on that board regardless so no charge to the owner (two way postage paid by me for the return)...

Radiocruncher · 1st Feb 2017, 8:21 pm

I should think that it's near perfect by now. Strange that it won't pick anything up. I'm sure you will get there. Let me know if you need any bits.

Graham

crackle · 1st Feb 2017, 9:32 pm

Even Hacker had some problems with soldering, here are some dry joints I found on a Hacker RP72.
The first one was only touching intermittently against the side of the hole, the second photo was a stress crack in the solder.

Mike

Ti Pwun · 2nd Feb 2017, 1:35 pm

Indeed - mine looked fine, if a little dull, but after waggling the wires to really see what was going on, it was obvious.

Perhaps resoldering the wires on the top end of the posts broke whatever solder bond that was there and left it working but ready to fail.

Two transistors and a diode were taken out because of it but given the initial thump, I'm surprised it didn't happen sooner.

All working now, though - just need to put it all back together.

As a final act of defiance, I now have the dial string to sort out. I had taped the dial pulley to the chassis to keep the string in place when I removed the T309 board and tuner but just as I had the thing working again, I turned the chassis upside down to check something and the tape came loose. The pulley fell to the floor, followed a few seconds later by the string and pointer.

That's just great!

15th Dec 2016, 10:19 pm	#21
mhennessy Dekatron Join Date: Jul 2007 Location: Evesham, Worcestershire, UK. Posts: 4,244	Re: Hacker Herald RP37A Speaker Thump on Power-up Yes, I suggested that earlier. Even at minimum, the pot still lets through a little audio.

15th Dec 2016, 10:31 pm	#22
McMurdo Dekatron Join Date: Jun 2009 Location: Staffordshire Moorlands, UK. Posts: 5,271	Re: Hacker Herald RP37A Speaker Thump on Power-up Here are some of mine being turned on for reference! https://youtu.be/tH3R_QgCArY __________________ Kevin

15th Dec 2016, 10:37 pm	#23
mhennessy Dekatron Join Date: Jul 2007 Location: Evesham, Worcestershire, UK. Posts: 4,244	Re: Hacker Herald RP37A Speaker Thump on Power-up Excellent Note the RP35 Herald is silent the first time, but clicks on subsequent goes. If you leave it a bit longer before powering it back up, that click won't be there. About 5 seconds is enough.

17th Dec 2016, 12:34 pm	#24
Ti Pwun Heptode Join Date: Aug 2013 Location: Bradford, West Yorkshire, UK. Posts: 888	Re: Hacker Herald RP37A Speaker Thump on Power-up Thanks for the input guys - really helpful. Even though I couldn't find fault with the switch itself and I had smooth deflection on the AVO while testing the pot, I replaced the switch/pot anyway. There was a slight improvement. I then remade the grounding connections to a new silver plated lug and fitted that in place of the original (tarnished) lug and there was further improvement. The Mullard cap tested OK, if a little high, but I temporarily replaced it anyway and there was further improvement so I made the replacement permanent. Very strange to me that changes I would usually consider to be unnecessary have made a marked difference to the thump but that's the case so I'm happier now with the way the radio powers up. I was quite ill yesterday due to my diabetes but after resting I want to look into some of the other suggestions today to see if I can soften the thump further. I wouldn't say it is overly excessive now but I do feel that there is room for improvement. I'll see what today brings.

21st Dec 2016, 11:45 am	#25
Ti Pwun Heptode Join Date: Aug 2013 Location: Bradford, West Yorkshire, UK. Posts: 888	Re: Hacker Herald RP37A Speaker Thump on Power-up Just a quick update on this: After remaking the remaining Gnd connections to the chassis the nasty thump has gone. It still clicks but no alarming thump so the radio is now on its way back to the owner. Hard to name an actual cause - bit of everything, I think...

21st Dec 2016, 1:35 pm	#26
mhennessy Dekatron Join Date: Jul 2007 Location: Evesham, Worcestershire, UK. Posts: 4,244	Re: Hacker Herald RP37A Speaker Thump on Power-up That's good news - thanks for the update My money was on the grounding. As you say, it's hard to know for sure what exactly was going on, but overall, all the work you've done is good "preventive maintenance" - those are parts that might well have needed replacing at some point in the future... Thinking again about the grounding of those tone controls has reminded me of another fault that I've seen on these: weak bass, with the bass control having no effect. It turned out to be a short within the bass potentiometer. But it went away when I applied a DC current - just 10mA or so (bass turned to max, so no real current flowed via the wiper and the track). I'm guessing something like a tin whisker was inside the pot. I've got another 2 or 3 VHF Heralds with exactly this symptom, and when I eventually get around to looking at them, I'll be a bit more careful to establish exactly what is happening. But here's the mystery: that amp and bass control is used in many other sets, yet I've only ever seen that fault with the VHF Herald. I can think of no logical reason for that!

21st Dec 2016, 7:31 pm	#28
wireless_john Heptode Join Date: Apr 2011 Location: Gosport, Hampshire, UK. Posts: 606	Re: Hacker Herald RP37A Speaker Thump on Power-up Sovereign 2 - no thump. Herald RP35 - ever so slight on switch on - more of a thump on switch off. Never noticed either till this discussion started!! John __________________ GQRP Club 4704 - BVWS Member

31st Jan 2017, 3:46 pm	#29
Ti Pwun Heptode Join Date: Aug 2013 Location: Bradford, West Yorkshire, UK. Posts: 888	Re: Hacker Herald RP37A Speaker Thump on Power-up UPDATE: I sent this radio back to the owner and he said it was working great. Not long after, though, he only got a hiss from the speaker. I asked that he send it back to me. When it arrived, after switching on I used a plastic tool to tap the boards and I got the radio hissing noise when I got to the T309 board (as opposed to just an amp hiss). I tugged gently on the wires and sure enough, there was some movement. Only slight, but I could easily make the hissing come and go. That board had to be removed to repair it (there is a plate attached to the underside) and I got to see where the actual problem was. There were dry joints everywhere. None of that showed up when I last worked on it and other than the thump, there wasn't anything I was concerned about. The soldering seemed fine after a visible inspection but it was only a matter of time. So, if you have any thumping issues, take the time to remove that board and go over the soldering. There were areas beneath the plate that needed attention and they couldn't be seen without getting the board out, so do inspect closely. Don't do what I did and assume that because a lot of other people are experiencing this same problem, it is in any way normal or acceptable. I knew it wasn't but it worked and I convinced myself that it's OK. I had managed to calm it down but I should have gone with my gut and took the board out, as involved as that is. Needless to say, after resoldering everything, there is nothing more than the normal mechanical click on power up. There are other issues I need to attend to because I think some other component(s) failed and I only get the hiss (no actual stations), but the problem I originally had is now completely gone. If you just have the thump and the radio is with you and you can work on it later if need be, you can access the edge connections (wire posts) so even though they might look fine, resolder them anyway. Remove the old stuff first if you have a desoldering pump/gun. Hope that helps someone. __________________ Jon. Last edited by Ti Pwun; 31st Jan 2017 at 3:54 pm. Reason: Clarification

1st Feb 2017, 1:45 pm	#30
Radiocruncher Hexode Join Date: Dec 2013 Location: Torrington, Devon UK. Posts: 446	Re: Hacker Herald RP37A Speaker Thump on Power-up Hi Jon. That's useful info. Usually these Hacker boards are very well put together. I suppose after time and possibly a humid atmosphere, corrosion can set in. Well done on finding it though, that was a bit of a marathon. Graham

1st Feb 2017, 2:27 pm	#31
Ti Pwun Heptode Join Date: Aug 2013 Location: Bradford, West Yorkshire, UK. Posts: 888	Re: Hacker Herald RP37A Speaker Thump on Power-up Oh, it's not over yet, Graham - ha! I've had to remove the board again to investigate further - no actual radio stations at all at the moment. I double-checked everything but can't see a fault yet. Maybe the power-up surge because of those solder connections took out a transistor or something. We'll see. Not often, but sometimes it seems that the more you repair, the more it creates or shows up another weak area. This thing will be practically new when I'm done but at least it should be rock solid. All good fun and I should have tested the soldering on that board regardless so no charge to the owner (two way postage paid by me for the return)... __________________ Jon.

1st Feb 2017, 8:21 pm	#32
Radiocruncher Hexode Join Date: Dec 2013 Location: Torrington, Devon UK. Posts: 446	Re: Hacker Herald RP37A Speaker Thump on Power-up I should think that it's near perfect by now. Strange that it won't pick anything up. I'm sure you will get there. Let me know if you need any bits. Graham

1st Feb 2017, 9:32 pm	#33
crackle Rest in Peace Join Date: Mar 2011 Location: Basildon, Essex, UK. Posts: 4,100	Re: Hacker Herald RP37A Speaker Thump on Power-up Even Hacker had some problems with soldering, here are some dry joints I found on a Hacker RP72. The first one was only touching intermittently against the side of the hole, the second photo was a stress crack in the solder. Mike Attached Thumbnails

2nd Feb 2017, 1:35 pm	#34
Ti Pwun Heptode Join Date: Aug 2013 Location: Bradford, West Yorkshire, UK. Posts: 888	Re: Hacker Herald RP37A Speaker Thump on Power-up Indeed - mine looked fine, if a little dull, but after waggling the wires to really see what was going on, it was obvious. Perhaps resoldering the wires on the top end of the posts broke whatever solder bond that was there and left it working but ready to fail. Two transistors and a diode were taken out because of it but given the initial thump, I'm surprised it didn't happen sooner. All working now, though - just need to put it all back together. As a final act of defiance, I now have the dial string to sort out. I had taped the dial pulley to the chassis to keep the string in place when I removed the T309 board and tuner but just as I had the thing working again, I turned the chassis upside down to check something and the tape came loose. The pulley fell to the floor, followed a few seconds later by the string and pointer. That's just great! __________________ Jon.