Leak Delta 30 Amplifier - One Channel Down - Page 3 - UK Vintage Radio Repair and Restoration Discussion Forum

Wage Slave · 3rd Oct 2010, 1:32 pm

Quote:

Originally Posted by Station X

What voltage do you have on the base and emitter?

Normal. Base 1.9V and emitter 1.6V.

Alistair D · 3rd Oct 2010, 1:32 pm

The link I have says E C B

http://www.datasheetcatalog.org/data...ild/BC184L.pdf

Station X · 3rd Oct 2010, 1:37 pm

Alistair.

There's no difference in what we say about leadouts. We're just looking at different orientations of the transistors. However you've posted a link with a nice picture which is better.

Wage Slave. Check that the transistors are fitted correctly.

Wage Slave · 3rd Oct 2010, 1:37 pm

Quote:

Originally Posted by Alistair D

The link I have says E C B

http://www.datasheetcatalog.org/data...ild/BC184L.pdf

And the board is wired according to this.

Alistair D · 3rd Oct 2010, 1:37 pm

Quote:

Originally Posted by Alistair D

The link I have says E C B

http://www.datasheetcatalog.org/data...ild/BC184L.pdf

Sorry Ignore that it was a seior moment

Wage Slave · 3rd Oct 2010, 1:42 pm

Quote:

Originally Posted by Station X

Alistair.

There's no difference in what we say about leadouts. We're just looking at different orientations of the transistors. However you've posted a link with a nice picture which is better.

Wage Slave. Check that the transistors are fitted correctly.

They are correct.

Alistair D · 3rd Oct 2010, 1:42 pm

Quote:

Originally Posted by Alistair D

Quote:

Originally Posted by Alistair D

The link I have says E C B

http://www.datasheetcatalog.org/data...ild/BC184L.pdf

Sorry Ignore that it was a senior moment

Time for a cup of beef tea and a nap in the bath chair.

Station X · 3rd Oct 2010, 2:01 pm

T4 is pulling current from somewhere. It's coming out of the collector and passing through R32 giving a volt drop of 1.6V across it indicating a current of 1mA. That current must be coming from somewhere. If it were entering the base it would have to pass through R29 giving a large volt drop across it. However the base voltage is normal. The current can't be coming through R31 as 1mA flowing through it would give a volt drop of about 15V. I conclude that the current is coming through T5. Remove T5 and see if that makes any difference to the readings on T4. While T5 is out test it.

Wage Slave · 3rd Oct 2010, 2:08 pm

So I redid all the transistor measurements. Almost identical:

T5
Collector 34.2V (spec=35V)
Base 30.7V (spec=14V)
emitter 30.2V (spec=13.5V)

T4
Collector 31.3V (spec=14V)
Base 1.9V (spec=2V)
emitter 1.6V (spec=1.5V)

T3
collector 32.9V (spec=31V)
Base 29.5V (spec=19.5V)
emitter 28.8V (spec=19V)

T2
collector 31.8V (spec=19.5V)
Base 0.6V (spec=4.0V)
emitter 0.1V (spec=3.5V)

T1
collector 0.2V (spec= 4V)
Base 0.1V (spec= ?)
emitter 0.0V (spec=?)

Wage Slave · 3rd Oct 2010, 2:09 pm

Quote:

Originally Posted by Station X

Remove T5 and see if that makes any difference to the readings on T4. While T5 is out test it.

I have had T5 out and tested it already. It seemed fine. I think I did did some other measurements too. Hang on.

Wage Slave · 3rd Oct 2010, 2:19 pm

No, I was wrong. I didn't do any measurements, just tested T5 with the diode testing range of the multimeter. It seemed fine. Do you want me to go ahead and pull it again to measure the effect on T4?

Station X · 3rd Oct 2010, 2:21 pm

Check the voltages across R34 and R35. With near 30V on the emitter of T5 they should both have about 15V across them.

Wage Slave · 3rd Oct 2010, 2:22 pm

Hang on. I'm taking it out.

Wage Slave · 3rd Oct 2010, 2:32 pm

OK T4 with T5 removed is:

Collector 41V
Base 2.3V
Emitter 2.0V

Testing it again.....

Wage Slave · 3rd Oct 2010, 2:39 pm

Quote:

Originally Posted by Station X

Check the voltages across R34 and R35. With near 30V on the emitter of T5 they should both have about 15V across them.

Drat. I didn't see this before pulling T5. I will have to come back to it.

Station X · 3rd Oct 2010, 2:44 pm

The emitter of T4 is reading 2V, so there's now 2mA flowing through it. This current can't be coming through R31 or there'd be a volt drop of about 30V across it, which there clearly isn't. The only other way into T4 is through the base and the current doesn't seem to be entering T4 there either. I need a long think about this. In the mean time it would be useful to measure the voltage across the resistors around T4/T5 with T5 out.

Alistair D · 3rd Oct 2010, 2:53 pm

Hi Guys Looking at all those measurements and the different transistors I am now wondering if the schematic is not the correct one for this board. I am also now wondering is the board has DC coupled stages. Originally it seemed that there were 2 faults (T1/2 & T4/5). It could be that there is only 1. I am suspicious of R15 (470K), T1 being a little leaky or T2 drawing too much base current.

Al

Wage Slave · 3rd Oct 2010, 2:56 pm

Quote:

Originally Posted by Station X

The emitter of T4 is reading 2V, so there's now 2mA flowing through it. This current can't be coming through R31 or there'd be a volt drop of about 30V across it, which there clearly isn't. The only other way into T4 is through the base and the current doesn't seem to be entering T4 there either. I need a long think about this. In the mean time it would be useful to measure the voltage across the resitors around T4/T5 with T5 out.

OK, well many many thanks for the help. It is getting on for 11 o'clock here and I have an early start so I will come back to it tomorrow.

Enjoy the rest of Sunday guys.

Edit: T5 seems to test OK.

Station X · 3rd Oct 2010, 3:04 pm

Quote:

Originally Posted by Alistair D

Hi Guys Looking at all those measurements and the different transistors I am now wondering if the schematic is not the correct one for this board. I am also now wondering is the board has DC coupled stages. Originally it seemed that there were 2 faults (T1/2 & T4/5). It could be that there is only 1. I am suspicious of R15 (470K), T1 being a little leaky or T2 drawing too much base current.

One way to determing that would be for Wage Slave to measure the transistor voltages on the other (working) board. If they're close to those on the diagram it's probably the correct one. If they're close to the readings on the faulty board we probably have the wrong diagram.

Alistair D · 3rd Oct 2010, 3:11 pm

Even comparative resistance measurements might help narrow down where the problem lies.
My earlier comment about T1 and R15 would only apply if that part of the board matched the cct.

Al

3rd Oct 2010, 1:32 pm	#42
Alistair D Nonode Join Date: Jan 2010 Location: Edinburgh, UK. Posts: 2,008	Re: Leak Delta 30 Amplifier - One Channel Down The link I have says E C B http://www.datasheetcatalog.org/data...ild/BC184L.pdf __________________ I won't tell you how I discovered that.

3rd Oct 2010, 1:37 pm	#43
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: Leak Delta 30 Amplifier - One Channel Down Alistair. There's no difference in what we say about leadouts. We're just looking at different orientations of the transistors. However you've posted a link with a nice picture which is better. Wage Slave. Check that the transistors are fitted correctly. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

3rd Oct 2010, 2:01 pm	#48
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: Leak Delta 30 Amplifier - One Channel Down T4 is pulling current from somewhere. It's coming out of the collector and passing through R32 giving a volt drop of 1.6V across it indicating a current of 1mA. That current must be coming from somewhere. If it were entering the base it would have to pass through R29 giving a large volt drop across it. However the base voltage is normal. The current can't be coming through R31 as 1mA flowing through it would give a volt drop of about 15V. I conclude that the current is coming through T5. Remove T5 and see if that makes any difference to the readings on T4. While T5 is out test it. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

3rd Oct 2010, 2:08 pm	#49
Wage Slave Hexode Join Date: Sep 2010 Location: Tsu, Japan. Posts: 452	Re: Leak Delta 30 Amplifier - One Channel Down So I redid all the transistor measurements. Almost identical: T5 Collector 34.2V (spec=35V) Base 30.7V (spec=14V) emitter 30.2V (spec=13.5V) T4 Collector 31.3V (spec=14V) Base 1.9V (spec=2V) emitter 1.6V (spec=1.5V) T3 collector 32.9V (spec=31V) Base 29.5V (spec=19.5V) emitter 28.8V (spec=19V) T2 collector 31.8V (spec=19.5V) Base 0.6V (spec=4.0V) emitter 0.1V (spec=3.5V) T1 collector 0.2V (spec= 4V) Base 0.1V (spec= ?) emitter 0.0V (spec=?)

3rd Oct 2010, 2:19 pm	#51
Wage Slave Hexode Join Date: Sep 2010 Location: Tsu, Japan. Posts: 452	Re: Leak Delta 30 Amplifier - One Channel Down No, I was wrong. I didn't do any measurements, just tested T5 with the diode testing range of the multimeter. It seemed fine. Do you want me to go ahead and pull it again to measure the effect on T4?

3rd Oct 2010, 2:21 pm	#52
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: Leak Delta 30 Amplifier - One Channel Down Check the voltages across R34 and R35. With near 30V on the emitter of T5 they should both have about 15V across them. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

3rd Oct 2010, 2:22 pm	#53
Wage Slave Hexode Join Date: Sep 2010 Location: Tsu, Japan. Posts: 452	Re: Leak Delta 30 Amplifier - One Channel Down Hang on. I'm taking it out.

3rd Oct 2010, 2:32 pm	#54
Wage Slave Hexode Join Date: Sep 2010 Location: Tsu, Japan. Posts: 452	Re: Leak Delta 30 Amplifier - One Channel Down OK T4 with T5 removed is: Collector 41V Base 2.3V Emitter 2.0V Testing it again.....

3rd Oct 2010, 2:44 pm	#56
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: Leak Delta 30 Amplifier - One Channel Down The emitter of T4 is reading 2V, so there's now 2mA flowing through it. This current can't be coming through R31 or there'd be a volt drop of about 30V across it, which there clearly isn't. The only other way into T4 is through the base and the current doesn't seem to be entering T4 there either. I need a long think about this. In the mean time it would be useful to measure the voltage across the resistors around T4/T5 with T5 out. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

3rd Oct 2010, 2:53 pm	#57
Alistair D Nonode Join Date: Jan 2010 Location: Edinburgh, UK. Posts: 2,008	Re: Leak Delta 30 Amplifier - One Channel Down Hi Guys Looking at all those measurements and the different transistors I am now wondering if the schematic is not the correct one for this board. I am also now wondering is the board has DC coupled stages. Originally it seemed that there were 2 faults (T1/2 & T4/5). It could be that there is only 1. I am suspicious of R15 (470K), T1 being a little leaky or T2 drawing too much base current. Al __________________ I won't tell you how I discovered that.

3rd Oct 2010, 3:11 pm	#60
Alistair D Nonode Join Date: Jan 2010 Location: Edinburgh, UK. Posts: 2,008	Re: Leak Delta 30 Amplifier - One Channel Down Even comparative resistance measurements might help narrow down where the problem lies. My earlier comment about T1 and R15 would only apply if that part of the board matched the cct. Al __________________ I won't tell you how I discovered that.