2014. október 25., szombat

Display "harvesting" 1. - Power Up

As I have nothing more to do with the logic analyzer now (there is national holiday here in Hungary and I'll have other things to do on the next week, I've no chance to get a new quieter fan and work with it till 2nd November), I picked something waiting to me from the drawer.

I've around fifty of this. I've no PBX for this anymore, so it is useless except for some parts "harvesting".
First of all I disassembled one, and realized, that the only part can be useful is the display unit. I need to reverse engineer a little bit to find out, how can I drive it.
I was looking around but nothing found on the internet. No information, no service manual, no schematic design. In addition the display driver chip is the regular silicon mounted on the board type:

(how I hate these)
So, the first thing, to power it up somehow, because without the PBX, I not even know what kind of power source is needed. It was obvious for the first look that the main board contains a switching regulator:

I looked to the regulator IC, it wasn't familiar to me:

But I assumed that -5 mark means 5V. If I connect a little bit more than 5V to the +- pins of the rectifier bridge:

It will bring the unit alive. And around 8V:

The unit started.
To be continued...

2014. október 22., szerda

Logic analyzer project 2. - first "repair"

After thinking a lot (2 sec) and reading thoroughly the service manual (5 min) with a long hard work (30 sec) I repaired the bigger fault of the Logic Analyzer. The soft key button error:

And the high tech advanced tool used for the repair:

You see correctly it is a cosmetic cotton pad (a dirty one).
The unit has touch screen. This called "soft keys". Because of the age of the unit it is not a capacitive or resistive touch screen but an optical grid created with infrared LEDs and phototransistors.

  1. When I first seen the error I think that one of the LEDs may failed (2 sec)
  2. Then I read the manual what the error code is about (5 min)
  3. When it proved that my theory is close to the possible cause, first cleared the frame of the display (30 sec)

Logic Analyzer project

I was crawling on eBay, and found an old Tektronix 1240 logic analyzer for a few bucks. The seller stated, it is defective because the picture intensity is weak on the screen (and it has defective soft buttons as it can be seen on the pictures).

I was thinking a little bit. This logic analyzer may not the best for today's digital electronics projects, but a good looking something what may deserve a restoration.
What if I replace the monitor with a same size LCD panel. So I took a bid on and bought it. Afterwards I found the service manual online. At a quick look in it found out that it produces an NTSC like TTL level signal for the display. I'm quite sure it is convertible to the current LCD screens.
After the bidding I was looking around the 7" LCD displays. Now I think it will be not so easy to do the conversion. Today's plan is the following:
Pick a low end FPGA (or a CPLD) attach some RAM to it. Read the signal into the RAM from the logic analyzer, and drive the LCD with the FPGA using the RAM as a frame buffer. (I can't do this in an MCU because the LCD panel needs 40MHz signaling)
To be honest, I've not even touched FPGA before ever, but this project could be a good one for learning. :-)
So I ordered an LCD and the necessary connectors and evaluating FPGA development boards.
After this introduction the Logic Analyzer arrived today.
I switched it on. And my colleague immediately found the contrast knob at the back side of the unit. So you can see here how week the display in reality:

As we see the todo changed:
- Repair the soft button problem
- Change the extremely noisy fan
I don't want to cancel my display change idea. I found that this series of logic analyzers has one bigger model: 1241. It has color display. What if I can "upgrade" mine to color one. If it is possible based on the Service Manual, I'll try. :-)

2014. október 18., szombat

Multimeterless 4. - Uni-T, Philips

I've some more information about my Multimeter business. The problems with the Uni-T shipment finally got a resolution. I was waiting endlessly to the seller to resend them. A day before the resolution deadline from ebay, I sent one last message without answer, so I escalated the case to the ebay. The money arrived back, but no multimeters.
Because finally I've plenty of them on hand, I highly thinking about this Uni-T ones. I'm not sure if I still need them. The only problem that not all of them was ordered to me, so I should discuss with my friend what to do.
After a long journey my Philips PM2525 also arrived. It was a some mistake by the shipping company. It went to the Czech Republic instead of Hungary, and afterwords back to Germany. The seller seen some strange information in the online tracking, so asked me if it arrived. I told him, that I haven't received it. He called up the shipping company and after some rerouting the multimeter arrived.
As it here, As usual, I made some measurements with it:
DC Voltage:

It looks on spot
When I first tried it was a mess. I finally find out that the test lead I'm using is a crap. And the result:

It looks like it is on spot. Great meter.
Finally I tried to look inside. It is a definite failure:

I just have a bit type Torx screwdriver what doesn't fit into the hole deep in the stands of the meter and I don't want to destroy the screwheads - go shopping! :-)

2014. október 14., kedd

POM #1 - Voltage inverter for breadboards 3.

The PCBs are arrived. I got 11 boards altogether what makes me possible to produce 44 inverters. The board quality is not worst than the ones created by seeedstudio's fusion service, and I got some nice stickers with the boards.

Thanks Ian!
I think this is not the last time I ordered from DirtyPCBs.

2014. október 9., csütörtök

Engineer joke - Continuance

Wednesday - Last week:
Today I dived deeper into the oscilloscope and it's service manual.
Now I know what the messages are mean:

CAN'T COMMUNICATE WITH UFO - I can't communicate with the front panel (handles)
WRONG AI HARDWARE VERSION - That AI is not AI but A1. I can't communicate with the analog board
NO ACKNOWLEDGE ON IIC - This evidently comes from the first two.

The construction of the unit is something like this:
There is a main board what is a passive backplane. The power supply and the processor board is plugged into this. A cable from the processor board goes to the analog unit and from the main board one to the front panel and one to the display electronics. From this the communication between the display and processor board is working.
The processor is not able to communicate with anything else. This points me to some I2C bus error. I  tried out what happens if I disconnect the two cable of the error designated units one-by-one. This action doesn't eliminated the other board's error in any case. I presume based on this that I've a general problem with the I2C bus. Maybe the pullup is missing (the I2C is some kind of Open Collector bus, so not works without pullup resistors) or the clock generation has problems.
I think, I'll not solve this. So goes to a repair guy or back to the seller.
I visited Mr. Urban (he is a famous shop owner/designer/repair guy here in Budapest). After looking to the unit, he said, he not take it, because it is a newer construction that he have knowledge on.Monday:
I still wanted a working unit. Asked the seller if I can send it back for repair and I pay both of the shipping charges.
He said that his technician is only able to use it but not able to repair it. So I've two options. I send it back and I get back my money(without the shipping costs), or I keep the unit and he sends back the half of the money. I chosen the later option.
Now I've two original probes (I had before only two Chinese crap and a half broken, repaired Philips), and a bad scope.
I take a deep breath and try to repair it. Most probably this effort will fail, but I'll learn a lot from it.Yesterday:
I've a little more chance. I found a processor board on the ebay, what together with the shipping charges cost less than the amount will be refunded from the scope. Now I just need to proof if this card is bad.
to be continued ... (when I start to repair it)

2014. október 3., péntek

Multimeterles 3. - Engineering Masterpiece

A multimeter arrived today. Now I've four of them, what is close to I'm expected on the beginning.
I wasn't aware of what is this thing when I was bidding on it on the ebay. But after it arrived I'm absolutely sure it worth every dime I payed for it. If I where in the place of Dave Jones, I would create a long YouTube teardown video with many "awesome" and "beauty" in it. But I'm not, so photos and some text coming.
After a such long introduction let see, what we talking about.
A Fluke 8500A 6.5 digit bench multimeter.

As you see this is not a unit manufactured today. To be honest, I don't know the exact manufacturing date, but the manual I found on the internet was created in 1977. This give us the hint that the unit is roughly 35 years old. 1977 you know, the year of Star Wars. :-)
It is coming from the ages when the products of the US companies was manufactured in the U.S.A.

The unit is heavy. It is around 10Kg. And in addition it was packed and sealed in the way in the box like it would survive even an atomic war.
When I switched on, it started immediately. I made some measurements against my references, together with my HP multimeter.

It is slightly off, so it will need some calibration if I'll use as a reference as I planed.

It looks on spot. By the way it would be nice to use the 4-wire resistance measurement, but I should buy some proper test leads (Kelvin clips) for it.

After the testing I opened the box (This was the second time. The first time was in the office with my colleague).

 I was shocked. Never ever seen such order in any equipment (specially in something what is old like this). This looks like an engineering masterpiece.
Every single board is enclosed in a separate plastic cover. Every single board's plastic cover has a foldable door on the top of it, allowing access to calibration handles:

And finally a card with cover opened:

I'm really happy, that I'm the owner of this equipment now on.

2014. október 1., szerda

Multimeterles 2. - Story of my stupidity

For today the power sourcing of my HP benchtop multimeter has been finished. Here is the finished 110V transformer:

Connected the multimeter to it. Switched on everything. Nothing.
I looked under the hood. There is a TO-3 cased 5V regulator in it.
On the output I measured a little more than 4.4V:

Because the Fluke just arrived and it is used I checked it with the Agilent also:

This is  ~12% minus. Doesn't look good.
On the regulkator's input:

Less than 6V.
The regulator itself is an:

HP 1826-0536. There is a National Semiconductor logo on it. On the internet I found a cross reference what states that is a LM340AK-5.
This is a normal regulator and not an LDO. And the dropout is:

2V. Based on this the regulator's input should be at least 7V.
What is on some miracle this is not a 120V unit.
I found a service manual on the internet. My gratitude to HP/Agilent/Keysight. On the actual website you can find correctly scanned the service manual of such an old unit.
In the service manual I found this:

And after some searching in the board also:

And what was the original setting? Of course 240V.
110V transformer removed, unit switched on, works.
If we are here, lets check some accuracy. My 5V-os reference:

Some reference resistance:

What is this reference resistor?

So I've a working bench multimeter and an unnecessary 110V transformer. It will be good when I got a real 110V something.