Neotek Elite PS-3 Repair Help

[Tyler Crawford]

Hi everyone,

My first post on here.

I'm working on repairing a Neotek Elite power supply, the PS-3.

The client had the power supply go out on them during a session, heavily distorted audio. They have a spare supply and the console is currently running well with that one.

As for the defective supply, the +18V DC was giving 25V DC at it's output. The rest of the voltages test correctly.

I initially replaced the TIP36 transistor and the 5534 @ U1 and the supply was back to giving the +18V DC at the output.

When the unit was hooked back up to the console, it worked for about 3 minutes and the it popped again.

I'm going to have a second look at it this week and was planning to try replacing the TIP31 as well.

I had been working off a blurry copy of the schematic, but thanks to the group I found a much clearer version with voltage probe notes...should be a huge help.

Does anyone have experience with this exact issue? Is it possible there is something I'm not thinking of that could be causing this issue? Something in the current or voltage limiting circuits shared between the two channels?

I'm wondering if it might be a good idea to fully rebuild the +/-18V DC supply, rectifier, caps and all the transistors / opamps...I've seen some others mention doing a full rebuild. Would it be necessary to replace all the diodes as well?

Thanks!

Tyler Crawford

[Ike Zimbel]

Tyler,

    I had a PS-3 one time that worked properly and put out the correct
voltages, but would blow the TIP-36 if you looked at it sideways. This
turned out to be one of the high wattage resistors in the circuit, but I
can't recall if it was the 0.1R 5w (R124) or one of the 10r 2 watt ones,
R-131, R-132.

iz

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[Jim]

Greetings,

Hi Tyler, go thru and clean up every solder joint and remove all the
old flux between traces; particularly the off board pass transistors.
Look carefully for wire whiskers, bent component leads that may be
touching, etc.. he IC sockets weren't the best quality and may be a bit
loose so they could be worth replacing. I've seen all of the above cause
issues. Check the cable where it enters the supply for possible damage
and the connector/pins on the console end. ALL ElCaps should be
replaced, don't even bother to measure them. Lastly, take a good look
around for signs of any previous work; may not be up to par.

Good luck!

Regards, Jim

[Tyler Crawford]

Ike and Jim, thank you very much for the input and information.

I'm going to do another round of parts replacement with this info in mind.

One other thing I wanted to ask...I'm trying to find a solution for a dummy load to test the PSU under load on the bench before it hooks up to the console. Do you know approximately how much current is being drawn from the +/-18V rails on an Elite that's listed as 68 mono inputs and 4 stereo?

[Jim]

Greetings,

 I go by the fuse rating on the +/-18V rails.

The last supply I worked on had 7A fuses, so that would be 126W, which is one way to look at it.

 The other way to look at it is what load R you have available. I haven't found it necessarily to go to absolute full load for testing as most problems come up at far lower levels (anything over 50% seems to work out).  Anyway, for the supply above it would be about a 3R/150+W load resistor and it would get VERY hot!  A pair of 4R/200W power resistors is what I used to get close. I have a selection of large W resistors that I can put together in S/P for various tests. I believe the more important part to watch out for is to test the +/- rails at the same time into the same load R.

Sorry but no info on the Elite channel draw. Use the fuse rating method and work your R value out from that.

OH, watch out for those aluminum "fin" resistors. They are way over rated IMO and need a huge heat sink to get close to the rated power.

Good luck!

Regards, Jim

On 12/3/2020 12:05 PM, Tyler Crawford wrote:

Ike and Jim, thank you very much for the input and information.

I'm going to do another round of parts replacement with this info in mind.

One other thing I wanted to ask..I'm trying to find a solution for a dummy load to test the PSU under load on the bench before it hooks up to the console. Do you know approximately how much current is being drawn from the +/-18V rails on an Elite that's listed as 68 mono inputs and 4 stereo?

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[Matt Syson]

Hi
You can get some idea of the current draw with a bit of effort and a
calculator. Each SECTION of a TL0?? device nominally takes about 3
milliamps (according to the data sheets). So a 071 would be 3 mA, 072
about 6 mA and an 074 about 12mA. Multiply out by the number of chips
per channel and number of channels and you are getting pretty close.
There are some NE553? chips in some places I believe and they pull twice
as much as a TLO device.
As Jim says, those 'aluminium block' resistors are named with a power
rating on the assumption that it is properly fixed to an 'infinite'
heatsink. Again, the de-rating curves are available on the internet if
you look them up.
As Jim says, they don't usually need loading up to 'maximum' if you are
just proving they work as a unit with a fault is likely to pack up with
about half loading.
Happy fixing.
Matt S

[theis mikkelsen]

I have an elite/ps3.

On the 18V it draws approx 4.6A on both + and -

The Logic draws approx 0.8A

Meter approx 2.8A

The issue im having, is that it either works, and works for hours until its switched off. OR the current limits lights up and the 18+ switches off, when switching on the PSU connected to the desk.

Been monitoring the voltage levels with an oscilloscope, they are solid.

both tip transistors on the 18+ have been replaced, and all large capasitors are new. 6.2 zeners have been replaced (they were black) 

I have power-resistors connected to outputs on the psu for testing, and its the same behavior as with the desk connected. when only having resistors on the +18, it is current limiting everytime it gets switched on. Any ideas?

[Ike Zimbel]

Have you measured the actual voltages? You don’t mention them in your post.  If I’m reading this correctly, you’re saying the supply will run indefinitely with no load, but with a load, either the desk or your load resistors, it goes into current limit immediately? If by “running” you mean that the +/-18v leds light up, that isn’t telling you much. Do the fuses ever blow?

Ike Zimbel,

Zimbel Audio Productions

416-720-0887

www.zimbelaudio.com

Sent from my vintage iPhone

On May 14, 2022, at 5:54 PM, theis mikkelsen <theismik...@gmail.com> wrote:



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[theis mikkelsen]

Thank you for your reply!

No blown fuses.

With PSU connected to the desk, there are 2 scenarios when PSU switches on, either:

1 everything is working fine. all voltage stable, both +&- 18 is +&-18, logic 25 and so on. Runs for hours.

2 current limit immediately, 18+ is zero. 

With PSU to resistorload, the scenarios are either:

1 same as above

2 same as above

3 With load only on the 18+, current limit immediately everytime.

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[Jeff Brown]

Here is a question for Matt or Ike... are the regulators in this supply protected from shut down due to one voltage coming up slightly before the other?  I'm not looking at the schematics.

I have had to modify a couple of console supplies where it was a game of chance whether both rails would come on at power up.  Usually only one rail worked and the other remained off.  Repeatedly turning off and then turning back on would eventually get both rails up, but it was stressful on both the console and the owner.  Adding a couple of diodes solved the issue.

Jeff

At 04:12 AM 5/16/2022, you wrote:

Thank you for your reply!
No blown fuses.

With PSU connected to the desk, there are 2 scenarios when PSU switches on, either:

1 everything is working fine. all voltage stable, both +&- 18 is +&-18, logic 25 and so on. Runs for hours.
2 current limit immediately, 18+ is zero.Â

With PSU to resistorload, the scenarios are either:
1 same as above
2 same as above
3 With load only on the 18+, current limit immediately everytime.

Den søn. 15. maj 2022 kl. 02.29 skrev Ike Zimbel <ik...@zimbelaudio.com >:

Have you measured the actual voltages? You don’t mention them in your post.  If I’m reading this correctly, you’re saying the supply will run indefinitely with no load, but with a load, either the desk or your load resistors, it goes into current limit immediately? If by “running†you mean that the +/-18v leds light up, that isn’t telling you much. Do the fuses ever blow?

Ike Zimbel,

Zimbel Audio Productions

416-720-0887

www.zimbelaudio.com

Sent from my vintage iPhone

On May 14, 2022, at 5:54 PM, theis mikkelsen < theismik...@gmail.com> wrote:



I have an elite/ps3.

On the 18V it draws approx 4.6A on both + and -

The Logic draws approx 0.8A

Meter approx 2.8A

The issue im having, is that it either works, and works for hours until its switched off. OR the current limits lights up and the 18+ switches off, when switching on the PSU connected to the desk.

Been monitoring the voltage levels with an oscilloscope, they are solid.

both tip transistors on the 18+ have been replaced, and all large capasitors are new. 6.2 zeners have been replaced (they were black) 

I have power-resistors connected to outputs on the psu for testing, and its the same behavior as with the desk connected. when only having resistors on the +18, it is current limiting everytime it gets switched on. Any ideas?

fredag den 4. december 2020 kl. 21.04.48 UTC+1 skrev matt.syson:

Hi

You can get some idea of the current draw with a bit of effort and a

calculator. Each SECTION of a TL0?? device nominally takes about 3

milliamps (according to the data sheets). So a 071 would be 3 mA, 072

about 6 mA and an 074 about 12mA. Multiply out by the number of chips

per channel and number of channels and you are getting pretty close.

There are some NE553? chips in some places I believe and they pull twice

as much as a TLO device.

As Jim says, those 'aluminium block' resistors are named with a power

rating on the assumption that it is properly fixed to an 'infinite'

heatsink. Again, the de-rating curves are available on the internet if

you look them up.

As Jim says, they don't usually need loading up to 'maximum' if you are

just proving they work as a unit with a fault is likely to pack up with

about half loading.

Happy fixing.

Matt S

On 04/12/2020 20:23, 'Jim' via Neotek wrote:

>

> Greetings,

>

> Â I go by the fuse rating on the +/-18V rails.

>

> The last supply I worked on had 7A fuses, so that would be 126W, which

> is one way to look at it.

>

> Â The other way to look at it is what load R you have available. I

> haven't found it necessarily to go to absolute full load for testing

> as most problems come up at far lower levels (anything over 50% seems

> to work out).  Anyway, for the supply above it would be about a

> 3R/150+W load resistor and it would get VERY hot!  A pair of 4R/200W

> power resistors is what I used to get close. I have a selection of

> large W resistors that I can put together in S/P for various tests. I

> believe the more important part to watch out for is to test the +/-

> rails at the same time into the same load R.

>

> Sorry but no info on the Elite channel draw. Use the fuse rating

> method and work your R value out from that.

>

> OH, watch out for those aluminum "fin" resistors. They are way over

> rated IMO and need a huge heat sink to get close to the rated power.

>

> Good luck!

>

> Regards, Jim

>

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[Matt Syson]

Hi Jeff
I have not looked at the schematic, it is buried on my hard drive somewhere but I am fairly sure the negative #half' has the reference diode LM???? which establishes the minus 18 Volts and the positive rail is n 'inverting amplifier that basically copies the negative rail. So they should both come up together really unless one or other rail has some issue with current limiting. Reverse connected diodes certainly won't harm anything. Ike may be around with his advantage of having played with lots of these units, or I might get back onto it later.
Best
Matt

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[ik...@zimbelaudio.com]

Matt’s description is correct, so no, the supply rails can’t come up at different times. The voltage reference is an LM399. I too have had power supplies for other consoles with that issue and it’s typically a result of cobbling a supply together from off-the-shelf modules without making any attempt to get those individual supplies to work together with proper delayed turn on, over-voltage protection / mutual shut down etc. Not a fan of that approach.

To the OP: I once had a PS-3 that “worked”, put out all the correct voltages etc. but would short the TIP-36B on the +18v output with the slightest mishap…like momentarily shorting the rail when a test lead slipped. That turned out to be, IIRC, R-124, 0r1/5 watt having failed. So I would look at that resistor and the two 10r/2W (R-131,132).

               That said, the intermittent nature of the fault also means it’s a good idea to have a very thorough look for bad solder joints, especially where the TIP-36 solders to the board. This has always been a weak point in the design. My approach to this has always been to completely remove all solder (and the transistor while you’re doing that) so you have flat, clean pads on the board. Then, bend the transistor leads so they sit flat against the pads (I also bend a slight, half-loop, or kink, in the leads, between the edge of the board and the body of the transistor, so they have some “give” for thermal expansion/contraction). Fasten the transistor to the heat sink (using an appropriate heat transfer/insulating pad and bushing…I use Sil-Pads. Note that the metal tab on the transistor should NOT be electrically connected to the heat sink. I have seen people miss this detail…). Then, when the transistor is mounted properly, solder the leads to the pads, making sure that they are covered by the solder with a good fillet along the edges.

               I have had PS-3’s that I have refurbished run for over 20 years with zero failures, just FYI.

Best,

 

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   ~Ike Zimbel~

   Wireless frequency coordination specialist.

   Manufacturer's Representative

   Radio Active Designs (Canada)

       ~416-720-0887~

FCC:WRBX645

   http://www.zimbelaudio.com/wireless-frequency-coordination/

 

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