LED VU meter problem

I have a commercial mid 1980s solid state stereo preamp/mixer, which has
a dual LED Bar Meter. (about 6 green on the bottom, two yellow above
that, and a red on the top).

The preamp/mixer works well, but the LED meter is flakey. I have never
worked with one of these, so before I tear into it, I want to know if
these are all complete units, and are they fed off the actual preamp, or
do they have a separate amp of their own?

What it's doing:
One channel lights up every so often, and moves like it should. Then it
goes off for awhile. The other channel does not light at all.

However, both channels do momentarily light up the red LED for a split
second when I turn on the power to this preamp. So, that tells me that
there is obviously power going to this LED meter, and that the meter
LEDs do work.

I'll begin by looking for any loose connections, but what is the way to
troubleshoot these if all connections are tight?

If I measure voltages with my VOM, what sort of voltage would be normal?

(I have not been able to find a schematic for this device, so I'm on my
own).

 

[Phil Allison]

The olds moron wrote...

I have a commercial mid 1980s solid state stereo preamp/mixer,

** So the make / model is a HUGE secret is it ??

Wot a PITA moron.

What it's doing:
One channel lights up every so often, and moves like it should. Then it
goes off for awhile. The other channel does not light at all.

** Check the leds first, cracked solder on the legs is very common and so are dead leds.



..... Phil

 

[Dave Platt]

In article <vndkgcdp111c70tgb174dv29l8era9itj7@4ax.com>,
<oldschool@tubes.com> wrote:

However, both channels do momentarily light up the red LED for a split
second when I turn on the power to this preamp. So, that tells me that
there is obviously power going to this LED meter, and that the meter
LEDs do work.

I'll begin by looking for any loose connections, but what is the way to
troubleshoot these if all connections are tight?

If I measure voltages with my VOM, what sort of voltage would be normal?

(I have not been able to find a schematic for this device, so I'm on my
own).

A lot of these meters use an LM3914 (linear) or LM3915 (logarithmic)
dot/bar display driver IC, or an equivalent. They take in a signal
voltage, accept a "reference" voltage to set the full-scale reading,
and drive LEDs or other display elements.

If one of these is what your device uses, it probably wouldn't need a
separate preamp circuit - it ought to be able to sample the audio
voltage on the main bus (or output) directly. Their might be a half-
or full-wave peak detector circuit between the input and the
display-driver IC.

The data sheets for these ICs are instructive.

 

[Trevor Wilson]

On 4/05/2017 6:14 AM, oldschool@tubes.com wrote:

I have a commercial mid 1980s solid state stereo preamp/mixer, which has
a dual LED Bar Meter. (about 6 green on the bottom, two yellow above
that, and a red on the top).

The preamp/mixer works well, but the LED meter is flakey. I have never
worked with one of these, so before I tear into it, I want to know if
these are all complete units, and are they fed off the actual preamp, or
do they have a separate amp of their own?

What it's doing:
One channel lights up every so often, and moves like it should. Then it
goes off for awhile. The other channel does not light at all.

However, both channels do momentarily light up the red LED for a split
second when I turn on the power to this preamp. So, that tells me that
there is obviously power going to this LED meter, and that the meter
LEDs do work.

I'll begin by looking for any loose connections, but what is the way to
troubleshoot these if all connections are tight?

If I measure voltages with my VOM, what sort of voltage would be normal?

(I have not been able to find a schematic for this device, so I'm on my
own).

**Since you have elected not to tell us what the brand on model of the
device is, any assistance can only be of a generic nature. LED failures
are common, but it could be a connector. Who knows? Without more
information, it is impossible to say.

--
Trevor Wilson
www.rageaudio.com.au

 

[Phil Allison]

Trevor Wilson wrote:

**Since you have elected not to tell us what the brand on model of the
device is, any assistance can only be of a generic nature. LED failures
are common, but it could be a connector. Who knows? Without more
information, it is impossible to say.

** I know I have seen LED ramps where OC failure of one LED disables all the ones beneath it. Maybe in some Soundcrafts ?

Not ones that use the LM3914/5.


..... Phil

 

[Trevor Wilson]

On 4/05/2017 10:44 AM, Phil Allison wrote:

Trevor Wilson wrote:


**Since you have elected not to tell us what the brand on model of
the device is, any assistance can only be of a generic nature. LED
failures are common, but it could be a connector. Who knows?
Without more information, it is impossible to say.



** I know I have seen LED ramps where OC failure of one LED disables
all the ones beneath it. Maybe in some Soundcrafts ?

Not ones that use the LM3914/5.

**I used to see it in early cassette decks that used LEDs. As you said,
the failure of one LED usually condemned all below.


--
Trevor Wilson
www.rageaudio.com.au

 

000000On Thu, 4 May 2017 10:32:45 +1000, Trevor Wilson
<trevor@SPAMBLOCKrageaudio.com.au> wrote:

On 4/05/2017 6:14 AM, oldschool@tubes.com wrote:
I have a commercial mid 1980s solid state stereo preamp/mixer, which has
a dual LED Bar Meter. (about 6 green on the bottom, two yellow above
that, and a red on the top).

The preamp/mixer works well, but the LED meter is flakey. I have never
worked with one of these, so before I tear into it, I want to know if
these are all complete units, and are they fed off the actual preamp, or
do they have a separate amp of their own?

What it's doing:
One channel lights up every so often, and moves like it should. Then it
goes off for awhile. The other channel does not light at all.

However, both channels do momentarily light up the red LED for a split
second when I turn on the power to this preamp. So, that tells me that
there is obviously power going to this LED meter, and that the meter
LEDs do work.

I'll begin by looking for any loose connections, but what is the way to
troubleshoot these if all connections are tight?

If I measure voltages with my VOM, what sort of voltage would be normal?

(I have not been able to find a schematic for this device, so I'm on my
own).


**Since you have elected not to tell us what the brand on model of the
device is, any assistance can only be of a generic nature. LED failures
are common, but it could be a connector. Who knows? Without more
information, it is impossible to say.

It's an Altec Lansing 1692A preamp mixer.

I was able to locate a poor schematic for it. Poor in the sense that the
manual is a zip file containging about 12 JPG files that are all
positioned sideways (I had to use a graphic editor to fix that), and
it's very difficult to fit the pieces together. Plus there are sections
missing.

After getting these schematics semi useful, I tore into the device. I
playing music thru it while measuring voltages from the power board,
which is putting out +15 and -15 volts (as it should).

The LEDs were working on one channel but not the other. Then all of a
sudden one channel became disrtorted, then quit playing music. I removed
the main board (which meant tearing apart the whole thing.

Using my old Paco audio tracer, I was able to determine that the audio
signal works up to the 5532A op amp chip. (U9) It gets thru the first #1
section of that chip, and vanishes when it enters the second #2 section.
That #2 section is also the driver for the LED display.

(However, with the board pulled, the LED display is not plugged in,
because the readout LEDs are atached to the front panel, which cant be
attached while signal tracing.

I decided to get the audio working on that channel first, before going
back to the LED problem. That's when I touched that (U9) 5532A chip, and
nearly burned my hand.

(The identical chip and circuitry on the working channel is barely
warm).

So, I am pretty sure at this point that this 5532A chip is bad.

I will perform a check with my VOM to make sure there are no shorts, but
aside from a few caps for the tone control section, there is not much to
short out. (I looked for any bad solder joints and/or darkened
resistors, everything looks fine).

I have a feeling that once I get the audio working properly, the LED
meter may work. If not, there must be a bad LED strip.
Which reminds me, can these strips be purchased?

These LED strips have 5 holes where pins plug into the,
THey are labelled as:

1. -15V
2. +15V
3. Unregulated Power supply (+20V)
4. Connects directly to the preamp output
5. Common

I guess before I can do much more, I have to find a place to order a
5532A chip (or several of them so I have spares).

[I should note that I dont normally work on anything with IC chips. I
repair tube equipment and sometimes some real early transistor stuff.
But this is my own preamp, and if I dont fix it, no one will. Plus, this
is a fairly simple circuit..... if only I had a better schematic].

I have to mention that my over 50 year old tube type Paco audio tracer
has been the most valuable means to test this unit, but with one
problem. The probe tip is too thick to get it on those tiny IC pins
without shorting across two pins. And with my poor eyesite and shaky
hands, it was near impossible. I finally used an alligator clip lead,
with a piece of a paperclip for a probe tip, wrapped that paperclip wire
in electrical tape, and clipped the other end to my probe.

WHAT THE HECK DO YOU GUYS USE FOR PROBES ON THOSE TINY PINS? DO THEY
SELL SPECIAL PROBES OR PROBE TIPS FOR THIS PURPOSE?

The good thing is that all the ICs in this device are plug in socket
types. Thank God for that!!!

 

On Thursday, 4 May 2017 11:02:18 UTC+1, olds...@tubes.com wrote:

000000On Thu, 4 May 2017 10:32:45 +1000, Trevor Wilson
trevor@SPAMBLOCKrageaudio.com.au> wrote:
On 4/05/2017 6:14 AM, oldschool@tubes.com wrote:

I have a commercial mid 1980s solid state stereo preamp/mixer, which has
a dual LED Bar Meter. (about 6 green on the bottom, two yellow above
that, and a red on the top).

The preamp/mixer works well, but the LED meter is flakey. I have never
worked with one of these, so before I tear into it, I want to know if
these are all complete units, and are they fed off the actual preamp, or
do they have a separate amp of their own?

What it's doing:
One channel lights up every so often, and moves like it should. Then it
goes off for awhile. The other channel does not light at all.

However, both channels do momentarily light up the red LED for a split
second when I turn on the power to this preamp. So, that tells me that
there is obviously power going to this LED meter, and that the meter
LEDs do work.

I'll begin by looking for any loose connections, but what is the way to
troubleshoot these if all connections are tight?

If I measure voltages with my VOM, what sort of voltage would be normal?

(I have not been able to find a schematic for this device, so I'm on my
own).

It's an Altec Lansing 1692A preamp mixer.

I was able to locate a poor schematic for it. Poor in the sense that the
manual is a zip file containging about 12 JPG files that are all
positioned sideways (I had to use a graphic editor to fix that), and
it's very difficult to fit the pieces together. Plus there are sections
missing.

After getting these schematics semi useful, I tore into the device. I
playing music thru it while measuring voltages from the power board,
which is putting out +15 and -15 volts (as it should).

The LEDs were working on one channel but not the other. Then all of a
sudden one channel became disrtorted, then quit playing music. I removed
the main board (which meant tearing apart the whole thing.

Using my old Paco audio tracer, I was able to determine that the audio
signal works up to the 5532A op amp chip. (U9) It gets thru the first #1
section of that chip, and vanishes when it enters the second #2 section.
That #2 section is also the driver for the LED display.

(However, with the board pulled, the LED display is not plugged in,
because the readout LEDs are atached to the front panel, which cant be
attached while signal tracing.

I decided to get the audio working on that channel first, before going
back to the LED problem. That's when I touched that (U9) 5532A chip, and
nearly burned my hand.

(The identical chip and circuitry on the working channel is barely
warm).

So, I am pretty sure at this point that this 5532A chip is bad.

I will perform a check with my VOM to make sure there are no shorts, but
aside from a few caps for the tone control section, there is not much to
short out. (I looked for any bad solder joints and/or darkened
resistors, everything looks fine).

I have a feeling that once I get the audio working properly, the LED
meter may work. If not, there must be a bad LED strip.
Which reminds me, can these strips be purchased?

These LED strips have 5 holes where pins plug into the,
THey are labelled as:

1. -15V
2. +15V
3. Unregulated Power supply (+20V)
4. Connects directly to the preamp output
5. Common

I guess before I can do much more, I have to find a place to order a
5532A chip (or several of them so I have spares).

[I should note that I dont normally work on anything with IC chips. I
repair tube equipment and sometimes some real early transistor stuff.
But this is my own preamp, and if I dont fix it, no one will. Plus, this
is a fairly simple circuit..... if only I had a better schematic].

I have to mention that my over 50 year old tube type Paco audio tracer
has been the most valuable means to test this unit, but with one
problem. The probe tip is too thick to get it on those tiny IC pins
without shorting across two pins. And with my poor eyesite and shaky
hands, it was near impossible. I finally used an alligator clip lead,
with a piece of a paperclip for a probe tip, wrapped that paperclip wire
in electrical tape, and clipped the other end to my probe.

WHAT THE HECK DO YOU GUYS USE FOR PROBES ON THOSE TINY PINS? DO THEY
SELL SPECIAL PROBES OR PROBE TIPS FOR THIS PURPOSE?

a pin sticks to the metal better. You could coat most of it if sight & steadiness are a problem.

The good thing is that all the ICs in this device are plug in socket
types. Thank God for that!!!

I've had a lot of DIL socket failures.


NT

 

[Trevor Wilson]

On 4/05/2017 7:01 PM, oldschool@tubes.com wrote:

000000On Thu, 4 May 2017 10:32:45 +1000, Trevor Wilson
trevor@SPAMBLOCKrageaudio.com.au> wrote:

On 4/05/2017 6:14 AM, oldschool@tubes.com wrote:
I have a commercial mid 1980s solid state stereo preamp/mixer, which has
a dual LED Bar Meter. (about 6 green on the bottom, two yellow above
that, and a red on the top).

The preamp/mixer works well, but the LED meter is flakey. I have never
worked with one of these, so before I tear into it, I want to know if
these are all complete units, and are they fed off the actual preamp, or
do they have a separate amp of their own?

What it's doing:
One channel lights up every so often, and moves like it should. Then it
goes off for awhile. The other channel does not light at all.

However, both channels do momentarily light up the red LED for a split
second when I turn on the power to this preamp. So, that tells me that
there is obviously power going to this LED meter, and that the meter
LEDs do work.

I'll begin by looking for any loose connections, but what is the way to
troubleshoot these if all connections are tight?

If I measure voltages with my VOM, what sort of voltage would be normal?

(I have not been able to find a schematic for this device, so I'm on my
own).


**Since you have elected not to tell us what the brand on model of the
device is, any assistance can only be of a generic nature. LED failures
are common, but it could be a connector. Who knows? Without more
information, it is impossible to say.

It's an Altec Lansing 1692A preamp mixer.

I was able to locate a poor schematic for it. Poor in the sense that the
manual is a zip file containging about 12 JPG files that are all
positioned sideways (I had to use a graphic editor to fix that), and
it's very difficult to fit the pieces together. Plus there are sections
missing.

**There you go. You're on your way.

After getting these schematics semi useful, I tore into the device. I
playing music thru it while measuring voltages from the power board,
which is putting out +15 and -15 volts (as it should).

The LEDs were working on one channel but not the other. Then all of a
sudden one channel became disrtorted, then quit playing music. I removed
the main board (which meant tearing apart the whole thing.

Using my old Paco audio tracer, I was able to determine that the audio
signal works up to the 5532A op amp chip. (U9) It gets thru the first #1
section of that chip, and vanishes when it enters the second #2 section.
That #2 section is also the driver for the LED display.

(However, with the board pulled, the LED display is not plugged in,
because the readout LEDs are atached to the front panel, which cant be
attached while signal tracing.

I decided to get the audio working on that channel first, before going
back to the LED problem. That's when I touched that (U9) 5532A chip, and
nearly burned my hand.

(The identical chip and circuitry on the working channel is barely
warm).

So, I am pretty sure at this point that this 5532A chip is bad.

**Oh yeah. The 5532 was, in it's day, a very high performance audio OP
amp. Nowadays, they're a dime a dozen. Still a decent OP a though. Well,
dual OP amp. For test purposes, you could try almost anything. Such as:
TL072, LF353, LM1458, LM833 (the closest equivalent to the 5532). Best
to stick to the 5532 though, as it can source more current than most OP
amps. One point: When you whack a new one in, check for DC offset and
oscillation. A remote possibility, but a real one.

I will perform a check with my VOM to make sure there are no shorts, but
aside from a few caps for the tone control section, there is not much to
short out. (I looked for any bad solder joints and/or darkened
resistors, everything looks fine).

I have a feeling that once I get the audio working properly, the LED
meter may work. If not, there must be a bad LED strip.
Which reminds me, can these strips be purchased?

These LED strips have 5 holes where pins plug into the,
THey are labelled as:

1. -15V
2. +15V
3. Unregulated Power supply (+20V)
4. Connects directly to the preamp output
5. Common

I guess before I can do much more, I have to find a place to order a
5532A chip (or several of them so I have spares).

**They should be very easy to locate. I keep a dozen or so in stock.

[I should note that I dont normally work on anything with IC chips. I
repair tube equipment and sometimes some real early transistor stuff.
But this is my own preamp, and if I dont fix it, no one will. Plus, this
is a fairly simple circuit..... if only I had a better schematic].

I have to mention that my over 50 year old tube type Paco audio tracer
has been the most valuable means to test this unit, but with one
problem. The probe tip is too thick to get it on those tiny IC pins
without shorting across two pins. And with my poor eyesite and shaky
hands, it was near impossible. I finally used an alligator clip lead,
with a piece of a paperclip for a probe tip, wrapped that paperclip wire
in electrical tape, and clipped the other end to my probe.

WHAT THE HECK DO YOU GUYS USE FOR PROBES ON THOSE TINY PINS? DO THEY
SELL SPECIAL PROBES OR PROBE TIPS FOR THIS PURPOSE?

**Yep. They sure do.

The good thing is that all the ICs in this device are plug in socket
types. Thank God for that!!!

**Your job is then dead easy.


--
Trevor Wilson
www.rageaudio.com.au

 

On Fri, 5 May 2017 17:06:22 +1000, Trevor Wilson
<trevor@SPAMBLOCKrageaudio.com.au> wrote:

(The identical chip and circuitry on the working channel is barely
warm).

So, I am pretty sure at this point that this 5532A chip is bad.

**Oh yeah. The 5532 was, in it's day, a very high performance audio OP
amp. Nowadays, they're a dime a dozen. Still a decent OP a though. Well,
dual OP amp. For test purposes, you could try almost anything. Such as:
TL072, LF353, LM1458, LM833 (the closest equivalent to the 5532). Best
to stick to the 5532 though, as it can source more current than most OP
amps. One point: When you whack a new one in, check for DC offset and
oscillation. A remote possibility, but a real one.

I am sticking with the 5532, but it will be a 5532P not 5532A. I cant
locate the 5532A anywhere.

Can you please explain what you mean and what I am supposed to do to
perform this test for DC offset and oscillation......

I guess before I can do much more, I have to find a place to order a
5532A chip (or several of them so I have spares).

**They should be very easy to locate. I keep a dozen or so in stock.

I have found many of the 5532P, but the 5532A is not showing up. I
though the "P" was an upgrade, but from what I read, the TI (Texas
Instruments) ones have the "P" suffix. I hope the "P" versions work as
replacements. I ordered 20 of them from ebay for about $4.50. Thats
surely cheap enough. They are TI brand.

[I should note that I dont normally work on anything with IC chips. I
repair tube equipment and sometimes some real early transistor stuff.
But this is my own preamp, and if I dont fix it, no one will. Plus, this
is a fairly simple circuit..... if only I had a better schematic].

I have to mention that my over 50 year old tube type Paco audio tracer
has been the most valuable means to test this unit, but with one
problem. The probe tip is too thick to get it on those tiny IC pins
without shorting across two pins. And with my poor eyesite and shaky
hands, it was near impossible. I finally used an alligator clip lead,
with a piece of a paperclip for a probe tip, wrapped that paperclip wire
in electrical tape, and clipped the other end to my probe.

WHAT THE HECK DO YOU GUYS USE FOR PROBES ON THOSE TINY PINS? DO THEY
SELL SPECIAL PROBES OR PROBE TIPS FOR THIS PURPOSE?

**Yep. They sure do.

Could you provide a URL link so I know what to look for.
I did do a search on ebay, Parts Express and Digikey. There are a
million probes and tips. Some look more usable on chips, simply because
they have thin pointy tips. One even had a coating on the whole tip
except the very tip, but without having them in hand, I am not sure what
will work best. So, a URL would help so I know what you and others use.

There are lots of those ones that have a hook on the end, which you push
the top and it opens. I have some of those, and they are handy to clip
on the leads of a part, but are not real useful for chips.

The good thing is that all the ICs in this device are plug in socket
types. Thank God for that!!!

**Your job is then dead easy.

As soon as I get my chips, I'll change that one that appears to be bad.
The fact that it's running very hot pretty much tells me it's bad. I an
not seeing any other bad parts around it, by doing a simple test with
the device OFF and using the ohm scale on my VOM.
I dont have anything to test chips, and I dont even know if they make
such a thing, because every chip has a different pinout.

Like I said before, I dont normally even tackle devices with IC Chips.
But this circuit is simple enough I am, and confident I can fix it.
What's nice about a preamp (or amp) is that I can just use my Paco and
listen for sound. I started at the beginning and moved ahead till there
was no sound (by this chip). I also worked backward from the output and
determined that there was no sound anywhere after this chip. I only
found that this chip was hot, when I was trying to move a cap so I could
read the part number on the board, and when I touched that chip, I
nearly burned my finger.

Incidentally, this is the same chip that powers the LED VU meter. So it
all ties together.

I think what happened was this chip was failing. I had audio on both
channels, but one was quieter than the other. (I am not sure which one
it was though). I compensated by adjusting the volume accordingly. Then
I lost the audio on that channel entirely. I assume that chip completely
failed at that point (after I had it powered up for a few hours). That
chip probably overheated and self destructed.

Thanks for your help!

 

[Dave M]

oldschool@tubes.com wrote:

On Fri, 5 May 2017 17:06:22 +1000, Trevor Wilson
trevor@SPAMBLOCKrageaudio.com.au> wrote:


(The identical chip and circuitry on the working channel is barely
warm).

So, I am pretty sure at this point that this 5532A chip is bad.

**Oh yeah. The 5532 was, in it's day, a very high performance audio
OP amp. Nowadays, they're a dime a dozen. Still a decent OP a
though. Well, dual OP amp. For test purposes, you could try almost
anything. Such as: TL072, LF353, LM1458, LM833 (the closest
equivalent to the 5532). Best to stick to the 5532 though, as it can
source more current than most OP amps. One point: When you whack a
new one in, check for DC offset and oscillation. A remote
possibility, but a real one.


I am sticking with the 5532, but it will be a 5532P not 5532A. I cant
locate the 5532A anywhere.

Can you please explain what you mean and what I am supposed to do to
perform this test for DC offset and oscillation......

I guess before I can do much more, I have to find a place to order a
5532A chip (or several of them so I have spares).

**They should be very easy to locate. I keep a dozen or so in stock.


I have found many of the 5532P, but the 5532A is not showing up. I
though the "P" was an upgrade, but from what I read, the TI (Texas
Instruments) ones have the "P" suffix. I hope the "P" versions work as
replacements. I ordered 20 of them from ebay for about $4.50. Thats
surely cheap enough. They are TI brand.

You're probably correct in your diagmosis that the 5532A is bad. It
shouldn't be running hot at all - slightly warm, maybe, but not hot.
I looked at datasheets from several manufacturers, and the only difference
that I saw was that the "A" model has a gurarnteed input noise voltage
specification, whereas the non-"A" model is not guraanteed, So, you'll be
OK with your chips from Ebay.

Cheers,
Dave M

 

[Phil Allison]

Trevor Wilson wrote:

**Oh yeah. The 5532 was, in it's day, a very high performance audio OP
amp. Nowadays, they're a dime a dozen. Still a decent OP a though. Well,
dual OP amp. For test purposes, you could try almost anything. Such as:
TL072, LF353, LM1458, LM833 (the closest equivalent to the 5532).

** Beware of the LM833, its is highly prone to oscillating at several MHz.

More often than not, if used to replace the others mentioned above, the damn thing will have a steady oscillation at its output and much higher than normal THD in the audio range.



...... Phil

 

[Trevor Wilson]

On 6/05/2017 4:19 AM, oldschool@tubes.com wrote:

On Fri, 5 May 2017 17:06:22 +1000, Trevor Wilson
trevor@SPAMBLOCKrageaudio.com.au> wrote:


(The identical chip and circuitry on the working channel is barely
warm).

So, I am pretty sure at this point that this 5532A chip is bad.

**Oh yeah. The 5532 was, in it's day, a very high performance audio OP
amp. Nowadays, they're a dime a dozen. Still a decent OP a though. Well,
dual OP amp. For test purposes, you could try almost anything. Such as:
TL072, LF353, LM1458, LM833 (the closest equivalent to the 5532). Best
to stick to the 5532 though, as it can source more current than most OP
amps. One point: When you whack a new one in, check for DC offset and
oscillation. A remote possibility, but a real one.


I am sticking with the 5532, but it will be a 5532P not 5532A. I cant
locate the 5532A anywhere.

Can you please explain what you mean and what I am supposed to do to
perform this test for DC offset and oscillation......

**Hang your multimeter and CRO off the audio output pins (1 & 7) and
check for excessive DC or HF oscillation.

I guess before I can do much more, I have to find a place to order a
5532A chip (or several of them so I have spares).

**They should be very easy to locate. I keep a dozen or so in stock.


I have found many of the 5532P, but the 5532A is not showing up. I
though the "P" was an upgrade, but from what I read, the TI (Texas
Instruments) ones have the "P" suffix. I hope the "P" versions work as
replacements. I ordered 20 of them from ebay for about $4.50. Thats
surely cheap enough. They are TI brand.

**Should be fine.

[I should note that I dont normally work on anything with IC chips. I
repair tube equipment and sometimes some real early transistor stuff.
But this is my own preamp, and if I dont fix it, no one will. Plus, this
is a fairly simple circuit..... if only I had a better schematic].

I have to mention that my over 50 year old tube type Paco audio tracer
has been the most valuable means to test this unit, but with one
problem. The probe tip is too thick to get it on those tiny IC pins
without shorting across two pins. And with my poor eyesite and shaky
hands, it was near impossible. I finally used an alligator clip lead,
with a piece of a paperclip for a probe tip, wrapped that paperclip wire
in electrical tape, and clipped the other end to my probe.

WHAT THE HECK DO YOU GUYS USE FOR PROBES ON THOSE TINY PINS? DO THEY
SELL SPECIAL PROBES OR PROBE TIPS FOR THIS PURPOSE?

**Yep. They sure do.

Could you provide a URL link so I know what to look for.
I did do a search on ebay, Parts Express and Digikey. There are a
million probes and tips. Some look more usable on chips, simply because
they have thin pointy tips. One even had a coating on the whole tip
except the very tip, but without having them in hand, I am not sure what
will work best. So, a URL would help so I know what you and others use.

There are lots of those ones that have a hook on the end, which you push
the top and it opens. I have some of those, and they are handy to clip
on the leads of a part, but are not real useful for chips.



The good thing is that all the ICs in this device are plug in socket
types. Thank God for that!!!

**Your job is then dead easy.


As soon as I get my chips, I'll change that one that appears to be bad.
The fact that it's running very hot pretty much tells me it's bad. I an
not seeing any other bad parts around it, by doing a simple test with
the device OFF and using the ohm scale on my VOM.
I dont have anything to test chips, and I dont even know if they make
such a thing, because every chip has a different pinout.

**I built a small test board just for OP amps. A +/- 15 Volt supply, two
sockets and some RCA input and output sockets. A couple of resistors to
set the gain at 2 and it's all good to go. One socket is for single OP
amps (5534, LF351, TL071 etc) and one socket is for dual OP amps (5532,
LF353, TL072 etc). That covers 99% of OP amps. Then there are single
in-line ones, but they're pretty rare nowadays. So, no, they don't have
different pinouts. They mostly have standard pinouts.

Like I said before, I dont normally even tackle devices with IC Chips.
But this circuit is simple enough I am, and confident I can fix it.
What's nice about a preamp (or amp) is that I can just use my Paco and
listen for sound. I started at the beginning and moved ahead till there
was no sound (by this chip). I also worked backward from the output and
determined that there was no sound anywhere after this chip. I only
found that this chip was hot, when I was trying to move a cap so I could
read the part number on the board, and when I touched that chip, I
nearly burned my finger.

Incidentally, this is the same chip that powers the LED VU meter. So it
all ties together.

I think what happened was this chip was failing. I had audio on both
channels, but one was quieter than the other. (I am not sure which one
it was though). I compensated by adjusting the volume accordingly. Then
I lost the audio on that channel entirely. I assume that chip completely
failed at that point (after I had it powered up for a few hours). That
chip probably overheated and self destructed.

Thanks for your help!

--
Trevor Wilson
www.rageaudio.com.au

 

On Tue, 9 May 2017 07:39:22 +1000, Trevor Wilson
<trevor@SPAMBLOCKrageaudio.com.au> wrote:

**I built a small test board just for OP amps. A +/- 15 Volt supply, two
sockets and some RCA input and output sockets. A couple of resistors to
set the gain at 2 and it's all good to go. One socket is for single OP
amps (5534, LF351, TL071 etc) and one socket is for dual OP amps (5532,
LF353, TL072 etc). That covers 99% of OP amps. Then there are single
in-line ones, but they're pretty rare nowadays. So, no, they don't have
different pinouts. They mostly have standard pinouts.

I'd be interested in seeing a schematic and maybe building one of these
testers. Is there a schematic for it online?