Venerable AIM TTI PL303QMD-P needs help - [was Output] Overvoltage trip error

[Zucca]

Basically the master right part shows the Output trip error and become irresponsive to any button press.
It is a for parts ebay purchase, the price was low and I could not resist.

Still have to try to connect by ETH and see what it is going on by reading the error codes.

Meanwhile I am doing my homework, if somebody knows something about this problem... I would appreciate any help.

Teardown and more analysis will be here soon, stay tuned!

Thanks!

[m k]

Maybe you can gain something by swapping feedbacks.

[ace_ventura]

I have the PLH version and this error means overheating. I had the same error with faulty connection to TIP31A transistor for temperature measurement located on the common heat sink.

[Zucca]

Thanks ace_ventura... unfortunately I have to fix my truck first then I will have time to attack the PL303QMD.
Looks promising... can't wait to open it up and see.

here the datasheet
https://www.st.com/resource/en/datasheet/tip31a.pdf

oh I did not know that:
https://www.ti.com/lit/pdf/sboa433

so they are using a BJT as a temp sensor?

[ace_ventura]

Yes, that's right. The fan is controlled by PWM according to the temperature sensing by BJT.

You can check inside compartment of PL601 in the thread by Baliszoft https://www.eevblog.com/forum/reviews/thurlby-thandar-not-a-happy-bunny/msg146518/#msg146518

I cannot find schematic or SM for this type of power supply but I took inspiration from the TTi QL series. On KO4BB website: http://w.ko4bb.com/getsimple/index.php?id=download&file=06_Misc_Test_Equipment/Thurlby_TTi/TTi_QL_Series_Bench_Power_Supply_Service_Manual.pdf on page 44 (fan control). Output section with MOSFET is also very similar.

[m k]

Seems to be a PL-P model.
New PL & PL-P Series Instruction Manual page 4 has that there's more for PL-P models.

Maybe it's in analog remote mode.

Manual page 17 has Over-temperature Protection.
There the message is OtP triP.

[Zucca]

Baby steps... I was able via Auto-IP to get this:


I was hoping for something different... but I am happy the LAN seems to work!

Next step finally open the puppy up...

EDIT: I couldn't resit, I opened it up.

Nothing obvious! There was a little of solder residual here and there....

Good news the Master and Slave boards are 1:1 the same, so I have one board working and the chance to repair the other one are very high!

What to do next? Swap boards and see if the errors follow the board or dig in into the schematics and make the circle smaller in the bad one?

Promising!

[Zucca]

00:40 in the night here... I was about to stand up from my bench when...
on the master (faulty) board, WTF...

[m k]

Do some front panel button eyeballing.

Can you say that faulty side is ever used?

[Gertjan]

Hi Zucca,

I have got a TTi PL303QMD power supply too. It is my favourite Power supply. Very stable, very clean and easy to operate. Only thing I am regretting now is that I did not buy the programmable version....
So your PL303QMD-P is certainly worth the effort to repair it!

Shoot TTi support an e-mail. I found them friendly and helpful.
In a PM I will send you the schematics I got from them.

good luck & regards, Gertjan.

[Zucca]

Shoot TTi support an e-mail. I found them friendly and helpful.
In a PM I will send you the schematics I got from them.

Gertjan, your post made me jump for joy on my bench, in my planet:

Code: [Select]

IF schematics THEN device_value = device_value ^ 3
So the legend is real! I was aware about the very nice and friendly TTi support, who are willing to release schematics, but never needed to (well it would have been my next step...)... this is also why I pulled the trigger on that sick puppy in ebay...
What a beautiful company! I will send them a message thanking them...
Finally someone who understand that releasing the schematics is a good thing to do!
One more reason to be proud to have ONLY AIM TTI Power Supply and DC load on my bench...

Back to my problem... not sure if you spotted it from my previous post...

this can't be right... wondering if this is the tragicomic culprit.

PS: For everybody who helped here, if you ever come in USA, SC... free beer on me day and night!

[Zucca]

Yesterday night report:

1) schematics are like water in the desert!
2) the misaligned molex connector above I think it is on purpose... in the aligned position there is just more filtering for VC signal.
3) Both TIP31A base(=collector) in master/slave board are sitting at 0.58V
4) Both master/slave fans are spinning at the same speed, did not measured it. I assume if the PIC was in thermal protection mode the fan would blow with 100% PWM. It is not the case.

Tonight I will swap the power boards position and see where the error goes..
I bet the problem it is not in the power board.

[Zucca]

Swapped power boards. Master stays in output trip.
Measured FAN voltage at master power board = 5.9V, which is about 50% PWM.

The power boards are fine as expected.

Next step swap the control PIC boards... stay tuned the circle is getting smaller.

[Gertjan]

Hi Zucca,

Measured FAN voltage at master power board = 5.9V, which is about 50% PWM

Normally, both fans are always rotating, but at very low speed (inaudible)
Only when the supply is dissipating a lot of power, the fans will spin up.

regards, Gertjan.

[Zucca]

Normally, both fans are always rotating, but at very low speed (inaudible)
Only when the supply is dissipating a lot of power, the fans will spin up.

Seems to be the case also in mine, even with output trip at the master.
Both fans are spinning low, looks equal and very quietly. I measure yesterday the one at the master and it was  50%PWM... which is about reasonable as lowest point.

[Zucca]

Okay, the problem is in one the digital PIC board (originally master).
Swapped the two and the error follows the PIC board, the other side was fixed.

Two corrections from before:
1) the misaligned molex (on the master power board) does not play a role... it is correct in both position misaligned or not..
2) the two power boards are identical but there is a hard jumper in the master (LK1)... so for basic tests you can swap them temporarily but them put them back in place.

getting closer!

[Zucca]

Sorry for the delay, I am selling some stuff (go to the buy/sell section to check it out) and my 2015 Ford F150 needed some immediate attention.

Will resume this adventure soon, I am confident I will fix it.

[Zucca]

uP board has some digital and analog stuff.

As a quick check the analog parts looks good.
Next I will check the DAC and ADC with a scope.

Can't be the uP because the display "Output trip" is sent by the uP iself.

[Gertjan]

Hi Zucca, good to hear that you are still at it! 
This very nice power supply needs to be in use on your bench, instead of sitting in your repair que 

[m k]

On the bench already.

MCU can have separated on/off info pins for both channels.

[Zucca]

All measurement in VDC



Please confirm me something is wrong here.

[m k]

It is in balance if 2.5V has its own source.

[Zucca]

sorry my bad, everything is fine there

[Zucca]

According to my investigation "Output trip error" meas the output is disabled because an error is detected.
One error could be the over temperature, but it is unclear what are all the possible errors leading to an output trip condition.
Unfortunately there are no details about these in the manual.

@TTI Tech: It would be nice to have a little more info here...

Example, if I use my other PL303 as DC load (with a small current just for testing purposes), I can reproduce the output trip error condition that can be cleared once I disconnect the inputs and press the output button.

That said back to my unit.....somewhere in this control board there is a problem.



Some tips for future repairs:
1) The left leg (see blue circle) of the big "Mexico" R79 is GND
2) There are many SMD fuses (very robust design) to check "FBxx" (see yellow circle as example)

To the best of my knowledge all the analog input and output sections are working properly.
Since the uP goes in output trip error immediately after power up, it is detecting something is off and the output are turned off.

By pressing the output button there are no changes in the output analog sections, which tells me the problem is not a consequence of a bad output state but something is the inputs independently from the output state.

Some of those inputs are processed directly by the ADCs in the uP PIC (like the over temperature analog signal) and some go through the IC7 ADS1241 ADC.
The display shows OPT Trip so I tend to assume the uP PIC is good. So if I have to bet, the IC7 ADS1241 is the bad guy.
I could just take and install the known good IC7 ADS1241 front the other control board, but first I want to be more sure about my theory.
The next days I will try to dig into the digital signals I2C, clocks and so on....

I will now also contact the awesome TTI support and see what they say.

PS: There are also the programming pins for the uP available (PJ6), does it make sense to connect a PICKIT to diagnose the problem? Sorry for the idiot question I have not played with PIC uP too much.....

[Zucca]

Aim TTI support already responded, these guys are awesome!

Plot twist: the display OUP tRiP means OVP Trip, overvoltage protection!

I am embarassed now, I did not noticed that OtP tRiP (mentioned in the manual) != OUP tRiP

more to come...