My SA - 7100 Drops in and out of Protection

[patfont]

ok center trimmers should be the 4.7K and are the mid-point potential adjustment using pins 2 and 17. I never use multiturns.


outside trimmers are idle current, (100) and are adjusted at points 1 and 3 on one side and 16 and 18 on the other.

If you are trying to rotate a trimmer in circuit you very well may not be able to get a measurement. If you go across both outer legs it will tell you if it is the 100 or 4.7K. (In circuit) You would have to pull if you wanted to rotate and set at a cetain setting like the old trimmers. I think Mark wants to make sure you have the 4.7K trimmers on the inside and the 100 on the outside.

 

[markthefixer]

correct, to be sure that the 4.7k trimmers and the 100 ohm trimmers are installed at the correct locations.

The 100 ohm pot in the 4.7k position would be harmless, but the 4.7k ohm pot where the 100 ohm pots should be would result in probable damage upon power up. While the DBT would protect the outputs it is very likely to smoke the drivers and their associated components. At the impedances involved in that circuit, it would act like a broken thermal bias diode wire

- I was very reticent to jump in because you have been doing quite nicely and have a lot of effort invested.:yes::thmbsp:

I was concerned for both the smoking ruin that could result,, as well as the overall loss of confidence in the forum if we start smoking units.

all from one small misunderstanding.

 

[patfont]

Thanks for standing guard Mark. I only input transistor, cap, diode comments if I have actually done it myself, and has worked well. I have corrected my notes on my trimmer adjustment index card, as I noted ass backwards.

 

[Awesomeaudio]

Thanks for clearing up the misunderstanding guys.

Pat no hard feelings here mate, I appreciate your continued help.

Mark, thanks for having our backs on this.

OK. I did the check this morning and can verify that I have the correct trimmers in the correct locations.
As previously mentioned, I did go off the parts list and schematics prior to installation.

Here are my readings (resistance) in circuit from the 2 outer pins:

Two inners: VR 1: 3.90 K ohms. VR 2: 3.89 K ohms.

Two outers: VR 3: 49.6 Ohms. VR 4: 50.5 Ohms.

Here's a question.

Are these figures acceptable enough for me to power on with or do I need to pull them to bring them closer to where they should be ?

 

[patfont]

1st question, do you still have the old trimmers?

So what we have gathered: the center 2 trimmers VR1 and VR2 should be set to midpoint for turn on. Since these are multiturn and to be safe pull from the board and with one lead on the center wiper and one lead on an outer leg get as close to center as possible 4.7K, so I think you ordered 5K trimmers set at 2.5K.

For the outer VR3 and VR4: There are 2 different set ups I have seen.

In the Advent 300 receivers I work on each trimmer is set up via looking at the scat as the same:*******So when properly set they both read the same which is somewhere like 1 o' clock. When both are fully counter clockwise they are each the same. (min res.)

On a marantz 2215B I just did: If you look at the scat the trimmers are "mirror imaged" so when set properly one is at 10 o'clock and one is at 2 o, clock and the settings are correct.

The Pioneer SA-7100 looks to be set up like the Marantz so these trimmers for example the left trimmer may be min. at full counter clock wise, while the other side may be min at fully clock wise. This is why I always measure my trimmers when I pull them and set the new ones as close as possible. I am comfortable telling you to set the VR1 and VR2 at the center 2.5K for start up, I will wait on VR3 and VR4 hoping you have the old.

 

[markthefixer]

every time work is done, the idle current should start out at minimum, which is zero ohms in this circuit. The adjustment is touchy and this does not risk the idle current being too high.

If it's good enough for me....

After which, power it up on the dbt.

You do know about my idle current test procedure? Trial set idle current while on the dbt to try to hit specified idle current (to tease out any faults while on dbt) then turn back to zero (that test setting of idle current would be too high when dbt removed and unit is directly powered up) and repeat for the other channel.

 

[Awesomeaudio]

Trimmer adjustment

1st question, do you still have the old trimmers?

So what we have gathered: the center 2 trimmers VR1 and VR2 should be set to midpoint for turn on. Since these are multiturn and to be safe pull from the board and with one lead on the center wiper and one lead on an outer leg get as close to center as possible 4.7K, so I think you ordered 5K trimmers set at 2.5K.

For the outer VR3 and VR4: There are 2 different set ups I have seen.

In the Advent 300 receivers I work on each trimmer is set up via looking at the scat as the same:*******So when properly set they both read the same which is somewhere like 1 o' clock. When both are fully counter clockwise they are each the same. (min res.)

On a marantz 2215B I just did: If you look at the scat the trimmers are "mirror imaged" so when set properly one is at 10 o'clock and one is at 2 o, clock and the settings are correct.

The Pioneer SA-7100 looks to be set up like the Marantz so these trimmers for example the left trimmer may be min. at full counter clock wise, while the other side may be min at fully clock wise. This is why I always measure my trimmers when I pull them and set the new ones as close as possible. I am comfortable telling you to set the VR1 and VR2 at the center 2.5K for start up, I will wait on VR3 and VR4 hoping you have the old.

Yes I still have the old trimmers. Although, I suspect the values may have changed on these upon removal as the adjusters on these are very touchy.

Here's a rough idea what I measured from these this morning.
(THESE ARE THE OLD TRIMMERS )
Both 4.7K trimmers: 3.60 K ohms and 3.75K ohms
Both 100 ohm trimmers measure around 60 ohms each.
I measured from the centre pin to the left top pin.

I will be pulling the NEWLY INSTALLED 4.7K trimmers (Specs say 5K Ohm, but measure closer to 4.7K mark), from the board now to measure and set as specified and report back shortly. So if I set these to 2.5K that would be safe to power up on the DBT, and, after idle current (100ohm) trimmers set ? (MTF recommends these be set to zero for starters.)

What values would you typically find on the old VR3 and 4 ?

 

[Awesomeaudio]

VR 1, VR 2 results

I've pulled these from the board and adjusted resistance as specified.

See attachment for full results.

With regards to VR 3 and 4.. I am able to get close to zero ohms on both by rotating dial to full Clockwise position. These being in circuit.

Is this right ? or do I also need to pull these to set up to zero ?

In my mind it seems ok but need confirmation please.

 

[Awesomeaudio]

every time work is done, the idle current should start out at minimum, which is zero ohms in this circuit. The adjustment is touchy and this does not risk the idle current being too high.

If it's good enough for me....

After which, power it up on the dbt.

You do know about my idle current test procedure? Trial set idle current while on the dbt to try to hit specified idle current (to tease out any faults while on dbt) then turn back to zero (that test setting of idle current would be too high when dbt removed and unit is directly powered up) and repeat for the other channel.

Mark, I'll have to come back to you on this once I get past the VR 1 and 2 set up. Thanks again. :thmbsp:

 

[patfont]

For the outside trimmers (VR3 and VR4)

*******I am only going by my memory on this and as before I had it backwards and I do not want you smoking your unit on my account*******

I am saying left and right and measuring from top side of boards.

If you put your probes on the outside terminals of VR3 and VR4 in circuit and turn all the way clockwise it should read 0. If you now put one probe on the center "wiper" and one on the left leg it should also be 0. I think if you put on center wiper and right leg it will read 0 at all times. So on the SA-7100 turning all the way clock wise you should be at zero, and if I remember correctly this usually coresponds to the side of the trimmer where the wiper and one leg share the same trace.

!!!!!!!Again please wait for the ok from Mark or another more knowledgable then me AKer before you proceed. And as Mark mentions please use the dim bulb tester.

I've pulled these from the board and adjusted resistance as specified.

See attachment for full results.

With regards to VR 3 and 4.. I am able to get close to zero ohms on both by rotating dial to full Clockwise position. These being in circuit.

Is this right ? or do I also need to pull these to set up to zero ?

In my mind it seems ok but need confirmation please.

 

[Awesomeaudio]

Thanks again Pat, I promise there will be no smoke. I will not even contemplate DBT until
it's good in my mind along with the nod.
I am taking it as carefully as required.
I've come too far, mentally, physically, and financially to let it go to ruin..

 

[markthefixer]

The 4.7k offset pots are harmless if misadjusted, the worst consequence is the offset is high enough to keep the protect relay from pulling in, and is easily corrected by adjustment. You need a more involved procedure to set a potentiometer tap (like used by the offset circuit) to exactly what the old one was at when removed - and are just (needlessly) increasing your risk of physical damage when needlessly removing the pot to measure it out of circuit.
I won't catalog the reasons or procedure to do that because I don't want to confuse you. Let it just be said that the normal tolerance variations of the circuit and the presence of the new pot, make trying to hit that exact point before power up difficult.
AND
THAT EXACT POINT WILL NOT BE THE CORRECT SETTING because it's a whole new deck of cards when you replaced the troublesome a725 and c1451 transistors.
THAT'S why I say - set it in the middle and adjust.

the function of the variable resistance used in the 100 ohm pots, where one end of the pot and the wiper are connected together can be replicated exactly, BUT ANY changes in the power supply or amplifier circuits (new transistors, caps etc in your case it's a whole new deck of cards by replacing the troublesome a725 and c1451 transistors) will have an effect upon the setting, possibly a large effect.

"The more they over think the plumbing, the easier it is to stop up the works" -
you are getting to the overthinking point and pushing precision settings the circuit will not return to -
thus the need for the trimpots...

 

[patfont]

Mark I am in 100% agreement with your statements.

-The setting of the new trimmers to the measurements of the old trimmers is not meant to be a end all solution. It is a starting point so you can be maybe be close "at turn on" and then adjust from there.

-The removal of the Bournes multiturns was because with a multiturn you really can not tell exactly where you are. I "never" use multi turns. Some people say they use multiturns because the settings with single turns are not as rock solid as they would like. I love the 3329 Bournes and although they are more expensive they are smooth and not jittery. If the OP had single turns in the 2 center positions on his 7100 I would easily say just center them.

The outside trimmers can be:

both ccw=0
both cw=0
or mirrored=adjusted to the outside of board=0
or mirrored=adjusted to the inside of the board=0

*******Just wanted to add-so for the OP's 7100 this would be both cw=0

So for those that are not highly technical or so it is here so it may help others I will offer this up:

Center trimmers (midpoint adj.) Start at "center position"
Outside Trimmers (idle adj.) Turn trimmer all the way in the direction to the side where the center "wiper" pin and one of the legs share a trace.

Mark again please tell me if you agree with the above settings in non-technical terms as it may help others.

And to AwesomeAudio please wait for Marks ok.

 

[Awesomeaudio]

Roger that. Thanks

 

[Awesomeaudio]

Bump

 

[Awesomeaudio]

Ok.

So I have both outside trimmers turned fully Clockwise for an almost close to 0 ohms reading. These are soldered in.
The two centre trimmers I have removed as requested to set "in the Middle" to approximately 2.5Kohms. This is now done.
I haven't soldered these back in yet and just awaiting confirmation and next step prior to powering on DBT and setting up to correct specs.
Thanks

 

[patfont]

I believe your answer is in Marks post #135, read it carefully.

 

[markthefixer]

Tower: MTF to Flight Awesomeaudio:

Permission to proceed, use solder in trimpots taxiway routing to dim bulb tester runup box for engine testing.

Please remember to return each tested engine to minumum thrust before testing next engine.

Upon successful completion of engine tests, depart dim bulb runup box, proceeding to the threshold of the active runway.

Upon arrival at the threshold of the active runway, you are clear to advance engine throttles to specified settings, and when necessary trim each engine balance to 0.000v to engage protection relay.

Upon reaching these conditions, you are clear for takeoff, have a good flight.

Please advise when reaching flight level, have a good flight.

tower over but not out.

 

[Awesomeaudio]

Hi gents. Sorry for my absence.

I had a day off work today and decided to delve back into this amp.

I disconnected wires 1,2,3 plus 16,17,18 on AWH 021 as per the SM idle current procedure. Wires insulated.

Placed amp onto DBT, nervous deep breath.. switched on. (I'm using a 60 watt globe as this is the highest I have. Is this ok or do i need to go higher?).

Anyway, The bulb dimmed slightly and slowly brightened to full illumination. (Have a video record).

No magic smoke ! and a huge sense of relief.. So far so good.

Sorry for these dumb questions, but..

Qu 1. Are we measuring in DC voltage ? No where can I see otherwise( I measured in DC assuming this to be right)
I have +probe on terminal 1 and - probe on terminal 3. Under dim bulb I have 0.465v DC in the full clockwise position. I have a similar reading on the other side.

Qu 2. I'm a little confused. Why am I reading 0.465 when I have the pot set to almost zero resistance ??
I tried turning it counter clockwise and it goes up. So I put it back.

Qu 3. Did I do something wrong here.
I removed the DBT and powered up in order to read the voltages and make the necessary adjustments. Unit powered on ok, hear the click, protection light goes out, then nothing. Power light goes out. No sign of life. Faaark !! :headscrat:cry:

Where to now ? Have I just thrown all my work down the tube ?

 

[patfont]

ooops, you should have waited, when powering up on the DBT at first the bulb is bright and then should dim down to almost nothing. You had the opposite, it got bright-problem!

Hi gents. Sorry for my absence.

I had a day off work today and decided to delve back into this amp.

I disconnected wires 1,2,3 plus 16,17,18 on AWH 021 as per the SM idle current procedure. Wires insulated.

Placed amp onto DBT, nervous deep breath.. switched on. (I'm using a 60 watt globe as this is the highest I have. Is this ok or do i need to go higher?).

Anyway, The bulb dimmed slightly and slowly brightened to full illumination. (Have a video record).

No magic smoke ! and a huge sense of relief.. So far so good.

Sorry for these dumb questions, but..

Qu 1. Are we measuring in DC voltage ? No where can I see otherwise( I measured in DC assuming this to be right)
I have +probe on terminal 1 and - probe on terminal 3. Under dim bulb I have 0.465v DC in the full clockwise position. I have a similar reading on the other side.

Qu 2. I'm a little confused. Why am I reading 0.465 when I have the pot set to almost zero resistance ??
I tried turning it counter clockwise and it goes up. So I put it back.

Qu 3. Did I do something wrong here.
I removed the DBT and powered up in order to read the voltages and make the necessary adjustments. Unit powered on ok, hear the click, protection light goes out, then nothing. Power light goes out. No sign of life. Faaark !! :headscrat:cry:

Where to now ? Have I just thrown all my work down the tube ?