Leak Delta 30 Amplifier - One Channel Down - UK Vintage Radio Repair and Restoration Discussion Forum

Wage Slave · 28th Sep 2010, 2:23 pm

New to the forum and I don't know a lot at all about these things so please bear with me

I bought a Leak Delta 30 and speakers just before I moved to Japan 4 years ago. I have used it a fair bit for listening to internet radio and for listening practice while teaching English. I like the sound a lot.

It always had problems. The only input that has ever worked for me is the tape monitor playback. All the others are completely dead. Both channels worked for a while but recently one only gives a muffled distorted sound. I now have both speakers wired in parallel to the remaining channel. Not great but it's doing the job.

Could I ask for some advice on where to start poking around? I seem to have found a circuit diagram here and I can read the basics (just! (sort of)). I can solder/desolder and have a multimeter.

amp_mangler · 28th Sep 2010, 9:14 pm

hmm I dont want to dampen your enthusiasm BUT "poking around" may not be the way to go. Anyway FWIW all the voltages are marked on the circuit diagram, you will need to identify each component and then measure it according to the circuit diagram. You may be lucky and have the components printed on an overlay on the PCB, if not you will have to "nut it out". You have one advantage, ALL the components are readily available, and in good condition this amp will sound delightful

Regards

Joe

Wage Slave · 28th Sep 2010, 11:55 pm

Thanks Joe. Your point is well taken. It still sounds pretty good even in its current state so I would like to try and repair it. Finding someone around here to do it will likely be impossible or if not, cost an astronomical sum.

I hadn't noticed the voltages were marked so thanks for that. I could probably manage to find most of the components but it will be very slow. Here's hoping they are marked on the board.

Regarding the inputs, it seemed to me that there is probably something wrong with the switch unless I can find a connection that has come off and I haven't so far.

Is their any benefit in spraying the switch with WD40? If not is there any other spray recommended? How about cleaning PCB connectors, sockets etc - What do people use.

'LIVEWIRE?' · 29th Sep 2010, 9:37 am

Servisol Super 10 is, IMHO, a better choice for cleaning switch contacts, volume control tracks, and the like. I's available from all the usual suppliers, such as RS, Farnell, etc., and may be available locally in Japan

Wage Slave · 29th Sep 2010, 10:40 am

So, some progress. Just the fact you guys are all see the sense in doing this has inspired me to crack on.

Somewhat mysteriously both channels of the power amp work fine now. So I can play things though the tape replay bypass in stereo. It could be a matter of cleaning and tightening the input and speaker sockets which are covered in oxidisation. Knowing my luck there is an intermittent fault though. I suppose I will just have to wait until it recurs before I can do much more.

Plugging a source into the tuner inputs produced great sound in one channel and a very faint reproduction in the other with a slight hum. Swapping the preamp boards around caused the problem to swap channels. So, at least I know where my problem is. Also, I could easily wrap the board up in cotton wool or something and post it to someone in Australia or the UK to have it fixed.

I was wondering though. Given all I hear about the caps being likely suspects , the fact they are cheap and easy to change out makes me wonder if it is worth me just changing all the ones on my faulty pre-amp board for new ones and seeing what that does. Does that make sense?

On that subject. I have read the electrolytic caps are the components most likely to have degraded. How much value is there in going through and changing all the electrolytics? Would you change the very big ones as a minimum?

@livewire I will have a search for Servisol Super 10 - You never know. If I can't get it, do I take it that some form of contact cleaner is better than WD40 type stuff?

jjl · 29th Sep 2010, 11:10 am

These amps have separate plug-in boards for the preamp and power amp driver circuitry for each channel, 4 boards in all. The edge connector fingers on the boards and the connectors themselves often cause problems. The fingers can be cleaned with a fibreglass brush and the connector contacts tightened, but exercise care if you try this as it is easy to make things worse.

The cause of your intermittent failure of one channel is almost certainly due to the edge connectors on the offending driver board.

If only the tape monitor input has ever worked this indicates a problem associated with the preamps as, in the tape monitor position, the preamps are bypassed. As both channels were affected something common to both e.g. their power supply or possibly input switching are likely causes. Voltage checks will help to indicate the cause.

The Delta 30 is a good amplifier and it's well worth getting yours working properly.

John

Wage Slave · 29th Sep 2010, 11:45 am

@ John. Yep many thanks for that. It's been a long time since I actually tested the inputs. It seems one channel is actually working fine and the other is almost dead. I have narrowed the problem down to the board and am pondering what to do next.

Thanks for the thoughts on my intermittent power amp problem. I will indeed clean the fingers. The boards feel pretty tight. I'm curious though. How do you tighten the edge connector contacts? Are there an adjustment screws at either end? I will give them a clean anyway as soon as I can locate a suitable product here in Japan. So far I have found CRC 2-26 and Shell Advance Contact Cleaner .

Guys, thank you all for your attention and advice. It is really appreciated.

jjl · 29th Sep 2010, 1:00 pm

The edge connector contacts can be tightened by gently bending them inwards i.e. towards where the board sits using a small tool but I would avoid doing this unless absolutely necessary as it is very easy to bend them too far and / or break them.

You can safely swap the preamp boards with each other to aid in diagnosing faults but this is not such a good idea with the driver boards as the output stage bias adjustment preset will be set to suit its respective channel's output transistors.

John

Wage Slave · 29th Sep 2010, 1:33 pm

Quote:

Originally Posted by jjl

... but this is not such a good idea with the driver boards as the output stage bias adjustment preset will be set to suit its respective channel's output transistors.

Noted. Ta, very much. I might well have tried that.

I will take your advice about cleaning and if the problem comes back then look to sending the board to someone who knows what they are doing assuming I can find someone who can work on that basis.

I'm still wondering about the electro caps. That is something I certainly could do and it shouldn't be too hard to get the parts. It might well be just as easy to get them from the UK and have them posted.

SteveCG · 30th Sep 2010, 6:01 pm

Wage slave,

I have a Leak Delta 30 - and it has had the collection of problems that you describe. I found that cleaning the edge contacts on the plug-in cards using cotton buds dampened with Iso-Propyl Alcohol (IPA) soved one intermittent. I've also found that the input selector switch sometimes needs a gentle wiggling to make contact - yes, I've already tried contact cleaners on it.

Other than that I'm pleased with it - in my opinion it is far better than the Leak Stereo 30 which I also had for a while.

I have not changed any components in it, but if I remember correctly when I got it a few years ago I did check the output stage bias settings. I also found the same basic circuit and cards in a Goodmans branded amplifier.

Wage Slave · 1st Oct 2010, 5:43 am

Steve,

Glad your ears agree with mine! A lot of people around here think I am nuts but there again I see a lot of people using Apple headphones so that just shows how much notice they take of how good things sound.

I am now wondering if my best move might be to just buy a unit with cosmetic damage on ebay and cannibalise it for a preamp board in the short term and for other bits in the longer term. I should be able to pick one up for £30 or so I think.

I just happen to have plenty of IPA available as I use it to clean my whiteboard - Will give all the boards a good clean with some cottonbuds.

I have ordered a set of caps. They are so cheap and easy to swop out I may as well do so. Keeps me away from booze, fast cars and loose women for a while.

dave cox · 1st Oct 2010, 10:25 am

Start with the supply voltages on the faulty preamp board. Checking the voltage accross C2 and C3 would be a good place to start.

If thats OK start on T5 emitter, which should be +19.5 above gnd with +35 on the collector (equal to voltage accross C3).

BTW, if you don't already have any minature probe clips get some or you will end up shorting something out (and attach them before turning the power on)

dave

SteveCG · 1st Oct 2010, 2:56 pm

Wage Slave,

Quote: "I have ordered a set of caps. They are so cheap and easy to swop out I may as well do so".

True, but be careful that you do not lift the copper tracks on the cards when removing the older capacitors. As I said I have not changed them in mine - not because I cannot do it, rather because I believe in only changing something when it isn't working, so minimising any collateral damage!

qualityten · 1st Oct 2010, 10:44 pm

As a newcomer to working on transistor amps from this era, I have made both the errors warned about by dave cox and SteveCG! So, I'd endorse their comments. There are helpful people on this site who will guide you with this repair, but it is harder to 'roll back' multiple errors or inadvertent damage.

If you do want to replace the caps, I suggest taking hi-res pics, checking operation after each change, and making notes of your observations.

Wage Slave · 2nd Oct 2010, 2:46 am

Great advice there guys. Special thanks to Dave. I will get some miniature probe clips today and take those measurements.

Wage Slave · 2nd Oct 2010, 4:58 am

Quote:

Originally Posted by dave cox

Start with the supply voltages on the faulty preamp board. Checking the voltage accross C2 and C3 would be a good place to start.

If thats OK start on T5 emitter, which should be +19.5 above gnd with +35 on the collector (equal to voltage accross C3).

BTW, if you don't already have any minature probe clips get some or you will end up shorting something out (and attach them before turning the power on)

dave

Thanks again for this Dave

. So here's what I found:

Across C2 34.8V (spec=31V)
Across C3 37.4V (spec=35V)

I am running the unit on 100VAC with it set to 110V. There isn't a setting for 100V and that's just what the mains is here.

T5 on the faulty board
Collector 33.7V (spec=35V)
Emitter 29.7V (spec=19.5V)
Base 30.3V (spec=14V)

So how to interpret those results? Does it mean the transistor is broken?

Out of interest I also measured T5 on the working board.

Collector 37V (spec=35V)
Emitter 14.8V (spec=19.5V)
Base 15.4V (spec=14V)

Does the low emitter reading indicate that this transistor is partly failed?

The circuit diagram is not in fact for a Delta 30 but a Stereo 30 Plus which is apparently electrically very similar. However, I have just noticed that T5 in the diagram is a BC105 or BC107. T5 on my board is a BC142.

Wage Slave · 2nd Oct 2010, 12:10 pm

Quote:

Originally Posted by dave cox

Start with the supply voltages on the faulty preamp board. Checking the voltage accross C2 and C3 would be a good place to start.

If thats OK start on T5 emitter, which should be +19.5 above gnd with +35 on the collector (equal to voltage accross C3).

BTW, if you don't already have any minature probe clips get some or you will end up shorting something out (and attach them before turning the power on)

dave

Dave

Looking at the circuit with a magnifying glass I think the emitter voltage should actually be 13.5V not 19.5V. In that case the readings for my "good" board are about right.

Alistair D · 2nd Oct 2010, 2:52 pm

Hi Wage Slave.
I am pretty sure that you will find that the voltages on T4 are wrong as well since the voltage for T5 base comes directly from T4 collector.
Can you measure T4 in the same way as T5.
Please also carry out a close inspection of R30 and R32 as these are the most likely reason for the voltages being high. Pay particular attention broken tracks on the PCB and the soldering quality.

Al

SteveCG · 2nd Oct 2010, 2:54 pm

Quote:

The circuit diagram is not in fact for a Delta 30 but a Stereo 30 Plus which is apparently electrically very similar.

I am 99.9% certain that they are one and the same. However the Stereo 30 is a very different beast from a Stereo 30 Plus.

Wage Slave · 2nd Oct 2010, 4:23 pm

Quote:

Originally Posted by Alistair D

Hi Wage Slave.
I am pretty sure that you will find that the voltages on T4 are wrong as well since the voltage for T5 base comes directly from T4 collector.
Can you measure T4 in the same way as T5.
Please also carry out a close inspection of R30 and R32 as these are the most likely reason for the voltages being high. Pay particular attention broken tracks on the PCB and the soldering quality.

Al

Thank you for the help Al.

T4
Collector 30.6V (spec=14V)
Base 31.8V (spec=2V)
emitter 1.6V (spec=1.5V)

T3
collector 32.0V (spec=31V)
Base 31.8V (spec=19.5V)
emitter 31.1V (spec=19V)

T2
collector 31.8V (spec=19.5V)
Base 0.1V (spec=4.0V)
emitter 0.1V (spec=3.5V)

T1
collector 32.0V (spec= 4V)
Base 0.0V (spec= ?)
emitter 0.0V (spec=?)

R30 and R32 both look fine as does the soldering and the tracks. C36 has been shoehorned into the PCB between R33 and R32. C36 doesn't have a space on the overlay so the hole at one end of R33 and one of R32 have two pigtail leads to accommodate it. It wasn't very well done and the pigtails on C36 were bent sharply. That has caused some physical damage where the pigtail enters the cap. I can even see a bit of metal plate under the magnifying glass. Could that be the cause? It has been like that since it left the factory though.

28th Sep 2010, 2:23 pm	#1
Wage Slave Hexode Join Date: Sep 2010 Location: Tsu, Japan. Posts: 452	Leak Delta 30 Amplifier - One Channel Down New to the forum and I don't know a lot at all about these things so please bear with me I bought a Leak Delta 30 and speakers just before I moved to Japan 4 years ago. I have used it a fair bit for listening to internet radio and for listening practice while teaching English. I like the sound a lot. It always had problems. The only input that has ever worked for me is the tape monitor playback. All the others are completely dead. Both channels worked for a while but recently one only gives a muffled distorted sound. I now have both speakers wired in parallel to the remaining channel. Not great but it's doing the job. Could I ask for some advice on where to start poking around? I seem to have found a circuit diagram here and I can read the basics (just! (sort of)). I can solder/desolder and have a multimeter.

28th Sep 2010, 9:14 pm	#2
amp_mangler Retired Dormant Member Join Date: Aug 2010 Location: Mareeba, Queensland, Australia. Posts: 140	Re: Leak Delta 30 Amplifier - One Channel Down hmm I dont want to dampen your enthusiasm BUT "poking around" may not be the way to go. Anyway FWIW all the voltages are marked on the circuit diagram, you will need to identify each component and then measure it according to the circuit diagram. You may be lucky and have the components printed on an overlay on the PCB, if not you will have to "nut it out". You have one advantage, ALL the components are readily available, and in good condition this amp will sound delightful Regards Joe

28th Sep 2010, 11:55 pm	#3
Wage Slave Hexode Join Date: Sep 2010 Location: Tsu, Japan. Posts: 452	Re: Leak Delta 30 Amplifier - One Channel Down Thanks Joe. Your point is well taken. It still sounds pretty good even in its current state so I would like to try and repair it. Finding someone around here to do it will likely be impossible or if not, cost an astronomical sum. I hadn't noticed the voltages were marked so thanks for that. I could probably manage to find most of the components but it will be very slow. Here's hoping they are marked on the board. Regarding the inputs, it seemed to me that there is probably something wrong with the switch unless I can find a connection that has come off and I haven't so far. Is their any benefit in spraying the switch with WD40? If not is there any other spray recommended? How about cleaning PCB connectors, sockets etc - What do people use.

29th Sep 2010, 9:37 am	#4
'LIVEWIRE?' Rest in Peace Join Date: Mar 2006 Location: N.W. Oxfordshire(Chipping Norton) Posts: 7,306	Re: Leak Delta 30 Amplifier - One Channel Down Servisol Super 10 is, IMHO, a better choice for cleaning switch contacts, volume control tracks, and the like. I's available from all the usual suppliers, such as RS, Farnell, etc., and may be available locally in Japan

29th Sep 2010, 10:40 am	#5
Wage Slave Hexode Join Date: Sep 2010 Location: Tsu, Japan. Posts: 452	Re: Leak Delta 30 Amplifier - One Channel Down So, some progress. Just the fact you guys are all see the sense in doing this has inspired me to crack on. Somewhat mysteriously both channels of the power amp work fine now. So I can play things though the tape replay bypass in stereo. It could be a matter of cleaning and tightening the input and speaker sockets which are covered in oxidisation. Knowing my luck there is an intermittent fault though. I suppose I will just have to wait until it recurs before I can do much more. Plugging a source into the tuner inputs produced great sound in one channel and a very faint reproduction in the other with a slight hum. Swapping the preamp boards around caused the problem to swap channels. So, at least I know where my problem is. Also, I could easily wrap the board up in cotton wool or something and post it to someone in Australia or the UK to have it fixed. I was wondering though. Given all I hear about the caps being likely suspects , the fact they are cheap and easy to change out makes me wonder if it is worth me just changing all the ones on my faulty pre-amp board for new ones and seeing what that does. Does that make sense? On that subject. I have read the electrolytic caps are the components most likely to have degraded. How much value is there in going through and changing all the electrolytics? Would you change the very big ones as a minimum? @livewire I will have a search for Servisol Super 10 - You never know. If I can't get it, do I take it that some form of contact cleaner is better than WD40 type stuff?

29th Sep 2010, 11:10 am	#6
jjl Octode Join Date: Jan 2003 Location: Ware, Herts. UK. Posts: 1,082	Re: Leak Delta 30 Amplifier - One Channel Down These amps have separate plug-in boards for the preamp and power amp driver circuitry for each channel, 4 boards in all. The edge connector fingers on the boards and the connectors themselves often cause problems. The fingers can be cleaned with a fibreglass brush and the connector contacts tightened, but exercise care if you try this as it is easy to make things worse. The cause of your intermittent failure of one channel is almost certainly due to the edge connectors on the offending driver board. If only the tape monitor input has ever worked this indicates a problem associated with the preamps as, in the tape monitor position, the preamps are bypassed. As both channels were affected something common to both e.g. their power supply or possibly input switching are likely causes. Voltage checks will help to indicate the cause. The Delta 30 is a good amplifier and it's well worth getting yours working properly. John

29th Sep 2010, 11:45 am	#7
Wage Slave Hexode Join Date: Sep 2010 Location: Tsu, Japan. Posts: 452	Re: Leak Delta 30 Amplifier - One Channel Down @ John. Yep many thanks for that. It's been a long time since I actually tested the inputs. It seems one channel is actually working fine and the other is almost dead. I have narrowed the problem down to the board and am pondering what to do next. Thanks for the thoughts on my intermittent power amp problem. I will indeed clean the fingers. The boards feel pretty tight. I'm curious though. How do you tighten the edge connector contacts? Are there an adjustment screws at either end? I will give them a clean anyway as soon as I can locate a suitable product here in Japan. So far I have found CRC 2-26 and Shell Advance Contact Cleaner . Guys, thank you all for your attention and advice. It is really appreciated.

29th Sep 2010, 1:00 pm	#8
jjl Octode Join Date: Jan 2003 Location: Ware, Herts. UK. Posts: 1,082	Re: Leak Delta 30 Amplifier - One Channel Down The edge connector contacts can be tightened by gently bending them inwards i.e. towards where the board sits using a small tool but I would avoid doing this unless absolutely necessary as it is very easy to bend them too far and / or break them. You can safely swap the preamp boards with each other to aid in diagnosing faults but this is not such a good idea with the driver boards as the output stage bias adjustment preset will be set to suit its respective channel's output transistors. John

30th Sep 2010, 6:01 pm	#10
SteveCG Nonode Join Date: Jun 2009 Location: Herefordshire, UK. Posts: 2,495	Re: Leak Delta 30 Amplifier - One Channel Down Wage slave, I have a Leak Delta 30 - and it has had the collection of problems that you describe. I found that cleaning the edge contacts on the plug-in cards using cotton buds dampened with Iso-Propyl Alcohol (IPA) soved one intermittent. I've also found that the input selector switch sometimes needs a gentle wiggling to make contact - yes, I've already tried contact cleaners on it. Other than that I'm pleased with it - in my opinion it is far better than the Leak Stereo 30 which I also had for a while. I have not changed any components in it, but if I remember correctly when I got it a few years ago I did check the output stage bias settings. I also found the same basic circuit and cards in a Goodmans branded amplifier.

1st Oct 2010, 5:43 am	#11
Wage Slave Hexode Join Date: Sep 2010 Location: Tsu, Japan. Posts: 452	Re: Leak Delta 30 Amplifier - One Channel Down Steve, Glad your ears agree with mine! A lot of people around here think I am nuts but there again I see a lot of people using Apple headphones so that just shows how much notice they take of how good things sound. I am now wondering if my best move might be to just buy a unit with cosmetic damage on ebay and cannibalise it for a preamp board in the short term and for other bits in the longer term. I should be able to pick one up for £30 or so I think. I just happen to have plenty of IPA available as I use it to clean my whiteboard - Will give all the boards a good clean with some cottonbuds. I have ordered a set of caps. They are so cheap and easy to swop out I may as well do so. Keeps me away from booze, fast cars and loose women for a while.

1st Oct 2010, 10:25 am	#12
dave cox Nonode Join Date: Jan 2009 Location: Bristol, UK. Posts: 2,062	Re: Leak Delta 30 Amplifier - One Channel Down Start with the supply voltages on the faulty preamp board. Checking the voltage accross C2 and C3 would be a good place to start. If thats OK start on T5 emitter, which should be +19.5 above gnd with +35 on the collector (equal to voltage accross C3). BTW, if you don't already have any minature probe clips get some or you will end up shorting something out (and attach them before turning the power on) dave

1st Oct 2010, 2:56 pm	#13
SteveCG Nonode Join Date: Jun 2009 Location: Herefordshire, UK. Posts: 2,495	Re: Leak Delta 30 Amplifier - One Channel Down Wage Slave, Quote: "I have ordered a set of caps. They are so cheap and easy to swop out I may as well do so". True, but be careful that you do not lift the copper tracks on the cards when removing the older capacitors. As I said I have not changed them in mine - not because I cannot do it, rather because I believe in only changing something when it isn't working, so minimising any collateral damage!

1st Oct 2010, 10:44 pm	#14
qualityten Octode Join Date: Feb 2009 Location: Wallasey, UK. Posts: 1,314	Re: Leak Delta 30 Amplifier - One Channel Down As a newcomer to working on transistor amps from this era, I have made both the errors warned about by dave cox and SteveCG! So, I'd endorse their comments. There are helpful people on this site who will guide you with this repair, but it is harder to 'roll back' multiple errors or inadvertent damage. If you do want to replace the caps, I suggest taking hi-res pics, checking operation after each change, and making notes of your observations.

2nd Oct 2010, 2:46 am	#15
Wage Slave Hexode Join Date: Sep 2010 Location: Tsu, Japan. Posts: 452	Re: Leak Delta 30 Amplifier - One Channel Down Great advice there guys. Special thanks to Dave. I will get some miniature probe clips today and take those measurements.

2nd Oct 2010, 2:52 pm	#18
Alistair D Nonode Join Date: Jan 2010 Location: Edinburgh, UK. Posts: 2,008	Re: Leak Delta 30 Amplifier - One Channel Down Hi Wage Slave. I am pretty sure that you will find that the voltages on T4 are wrong as well since the voltage for T5 base comes directly from T4 collector. Can you measure T4 in the same way as T5. Please also carry out a close inspection of R30 and R32 as these are the most likely reason for the voltages being high. Pay particular attention broken tracks on the PCB and the soldering quality. Al __________________ I won't tell you how I discovered that.