Hameg HM8143 broken, need a little help.

[shempe]

Hello,

I bought a "working" Power Supply a few weeks ago. It was not....ok.
I agreed with the seller on some return money because I think it is a good Power supply and worth a repair.
So after I bought it, my money box is mostly empty in the moment, and R&S ask for a hand and a limb in repair.
I decided I will try to repair it and if I can't fix -> R&S must do it.

First all looks ok and working, it start´s without an Error, I can set the Parameters local and remote.
But, when I enable the Output, Cannel 1 and 3 there is no regulation, Volts goes to some other Values and Amps are not there.
So it looks something is broken.
Because im lacking a Service Manual I can only guessing what is broken.

So I Inspected the Circuit and found something suspicious, one chip looks like it was loosing his smoke.

Can someone Identify this ic ?

Here the Smoky one



Here the other one from Channel 1.




A few pics from the Board´s because I know, someone like to see the whole thing.







Thanks a lot for your time and help.
Stefan

[bktemp]

Looks like a TL431 shunt regulator.

[mij59]

The TL431 is a good candidate, but its not the only problem, maybe the transistors close to the TL431.
Seems to me you got two identical boards, assuming that one is working you can compare it with the faulty one. 

[shempe]

TL431B could be possible.

Yes there are 2 identical Boards but the regulation on the output is on both not working,
maybe because one channel is broken it affected also the other channel.

I will compare the components with the "working ?" channel.

Maybe it will give me a clue, what also wrong.

[mij59]

Yes there are 2 identical Boards but the regulation on the output is on both not working,
maybe because one channel is broken it affected also the other channel.

Both channels should be galvanic isolated, the only thing they have in common is the controller board for setting the voltage and current, maybe there is a problem with data transfer, e.g. by I2C or SPI.

[shempe]

Both channels should be galvanic isolated,
the only thing they have in common is the controller board for setting the voltage and current,
maybe there is a problem with data transfer, e.g. by I2C or SPI.

Thank you for your suggestions.

Yes, there are isolated, and normally I would expect, that one channel is running, it is not so, both behave the same.

I must admit I2C and SPI is out of my skill set to debug.
Without a Service manual I think it looks more and more for a case to fill my Piggybank.

[Fraser]

Hameg will often provide the schematic for their equipment by return email. Have you asked Hameg customer services yet ? Service manuals are harder to obtain.

Fraser

[shempe]

Hameg will often provide the schematic for their equipment by return email. Have you asked Hameg customer services yet ? Service manuals are harder to obtain

No I don't, I was thinking, that they don't provide Service Manuals for products that they are actual selling, only for older products.

But I will give it a try maybe they provide the schematics.

Thank you Fraser.

[Fraser]

They used to provide the schematic at the rear of their manuals but stopped for reasons unknown. I have never had a problem obtaining the schematics, even for current equipment. Policies do change though and R&S may have different views on support for current models. I have obtained the schematics for their current frequency counter, signal generator and function generators though.

Always ensure that in any communications relating to repair, that the OEM knows that you are a technical person with the competence and skills to safely open the case. OEM's can get nervous about liability etc.

Good luck.

Fraser

[shempe]

I have obtained the schematics for their current frequency counter, signal generator and function generators though.
.

Sounds promising.

I saw in an Interview with an R&S CEO, they support repair and they don't like to see that someone throw´s away there stuff.
But, it was not so clear if repair means by there facilities or repair by the owner of the equipment.

Btw. good point about competence I will have it in my mind.

Thanks Fraser.

[anotherlin]

I can confirm that Hameg will send you for sure the pdf for all their discontinued products.
As for current product, I've never tried.

If it can help, I have the pdf of the service manual for the HM8142. This is the previous revision of this PSU.
It should be very similar, specs are almost same, except that the 2 outputs are up to 2A instead of 1A.

[tec5c]

If you have a DMM then do a diode test across pins 1 and 7, if shorted then the IC is most likely at fault... out of circuit test to confirm if it reads short in circuit.

[shempe]

I wrote at the Hameg support yesterday, let´s see what will happen.

If it can help, I have the pdf of the service manual for the HM8142. This is the previous revision of this PSU.
It should be very similar, specs are almost same, except that the 2 outputs are up to 2A instead of 1A.

Yes sure I like to see it.  Thank you.
It looks like the HM8142 has a total different Layout but I think it is worth a look.

If you have a DMM then do a diode test across pins 1 and 7, if shorted then the IC is most likely at fault.

Will try it after Work.
Im sure this chip is blown, question is, what else is blown in the path and which parts are in the path.

[anotherlin]

https://drive.google.com/file/d/1-Is0VRF70_UMd_U3M2oTfy1NEZetlJU_/view?usp=sharing
(updated google drive link to manual)


At the end of the user manual is the full schematic along with a short one page very high level description of the operating principle.
Text is in french, it basically states that this is a "classic" two-quadrant (can act as load) linear power supply, digitally controlled. But not that much.
Use google translate, or I can help if you need it on specific point.

[shempe]

Im looking at the components now on one channel of the board to make me a picture what parts we have.

I managed so far:

Part 1
1 Atmega64 with ISP
1 CY62256N    256-Kbit ( 32 K × 8 ) Static RAM
2 LTC1666      12-Bit 50Mps Dac´s
1 LTC1298IS8 12 Bit A/D

Part 2
1 ez745 ( 431i ) ???
1 ez610 ????
3 LTC2051HVIS8  Dual Opamps with Zero Drift
1 LT1236CIS8-5   5V Precision Reference

Part3
1 LT1037IS8  Low Noise, High Speed Precision Operational Amplifiers
3 OP275G     Dual Bipolar/JFET, Audio Operational Amp


Someone recognize the Logo on this Chip or can identify it.

At the end of the user manual is the full schematic along with a short one page very high level description of the operating principle.
Text is in french, it basically states that this is a "classic" two-quadrant (can act as load) linear power supply, digitally controlled. But not that much.
Use google translate, or I can help if you need it on specific point.

Thank you for the schematic anotherlin

[Rick60]

That's almost certainly an  LM258DT from st.com the ez610 must be a batch code
http://www.st.com/web/en/resource/technical/document/datasheet/CD00000464.pdf

[mij59]

On page M13 of the HM8142 manual is a block diagram of the power supply, there is only one set of opto-couplers for the second channel.
The power supply for the micro is directly connected to the first channel.
If the HM8143 is also configured this way, a fault in one of the power rails of the micro could result in data lost for both channels.

[shempe]

That's almost certainly an  LM258DT from st.com the ez610 must be a batch code

You made my Day. Thank you.
ST it is...


Right Part of the Board

1 Atmega64    with ISP
1 CY62256N    256-Kbit ( 32 K × 8 ) Static RAM
2 LTC1666      12-Bit 50Mps Dac´s
1 LTC1298IS8 12 Bit A/D
2 SFH6186      Optocoupler


Central Part of the Board

1 TL431I              Programmable voltage reference
1 LT1236CIS8-5   5V Precision Reference
1 LM 258             Low-power dual operational amplifiers
3 LTC2051HVIS8  Dual Opamps with Zero Drift


Left Part of the Board

1 LT1037IS8  Low Noise, High Speed Precision Operational Amplifiers
3 OP275G      Dual Bipolar/JFET, Audio Operational Amp

[shempe]

On page M13 of the HM8142 manual is a block diagram of the power supply, there is only one set of opto-couplers for the second channel.
The power supply for the micro is directly connected to the first channel.
If the HM8143 is also configured this way, a fault in one of the power rails of the micro could result in data lost for both channels.

Yes I saw it.
 
It is possible. But when you look at the Picture 3 from Page 1 you see from every Channel a Cable going to the Display board.
And near every Cable are the Optocoupler for the communication to the Display board.
The Layout for the HM8143 is different to the HM8142

These are 2  SFH6186 Optocoupler

Channel 1


5V Channel 2

[shempe]

Day 3, still no answer from the Hameg Service.

Not so Promising 

[mij59]

The opto-couplers could be used for a low speed I2C or UART.
Please post a photo of the display board.
Got an Oscilloscope ?

[anotherlin]

Day 3, still no answer from the Hameg Service.
Not so Promising 

It's current production model whereas 8142 is beginning of 90s (20 years) model.
It is understandable they don't want to provide schematic.

[shempe]

The opto-couplers could be used for a low speed I2C or UART.
Please post a photo of the display board.
Got an Oscilloscope ?

For a Photo from the Display Board, I need to disassemble the Front Plate need´s to be done.
Yes I have a Oszzi.

It's current production model whereas 8142 is beginning of 90s (20 years) model.
It is understandable they don't want to provide schematic.

Yes, I agree and I have no Problem to understand and accept that fact.

I find it only a little rude, after writing such a nice Email, not to get an answer at all.
Imho not a good business behavior.

[shempe]

Day 4 no response from Hameg. 

I had a little time yesterday evening, to look in the Communication from Channel 1 Board to the Front Panel.

This is Channel 1 , Channel 3 looks the same.


First Block is the Voltage Setting, second is the Ampere Setting and Signal for Output enable.
You can change it with the Encoder on the Frontpanel and the Buttons for Volt and Amp for Channel 1 and 3
If Output is enabled the measurements are send to the Front Panel and displayed.

And I found a little more ... 

It is a more than the 431I broken on Chanel 3.



Here more Pics for the interested one´s.

0.22 Ohm 1% PBH-R220 Shunt Isabellenhütte Big Black one in the middle


BD139 and Tip147 Identified..


The 5 Volt Channel



Backside Channel 1



Backside Channel 3

[mij59]

And I found a little more ... 

And more to come, check the power transistors on the heatsink and pcb of both channels.
Both channels have failed in a similar way, maybe by connecting the  outputs antiparallel.