Aeroflex COM-120B - ca it be brought back to life ?

[M0HZH]

Hi all,

I recently came in the possesion of an Aeroflex (IFR/Marconi) COM-120B; it would be an important addition to my small lab / ham shack and I want to try and restore it. It arrived with an Aeroflex label "beyond economical repair" and was told it needs a new Planar display control unit (datasheet: https://www.eldisplays.com/content/EL560.400-LP.pdf)



Turning it on, this happens:
- one beep, antenna LEDs come on/off one after the other
- 10 seconds later, a sequence of beeps seems to indicate some error code (..._.)
- display never comes on, nothing else happens
- PSU voltages seem to be fine at test points (+12V, +5V, +/-10V all within 5%)
- can't be turned off from the front panel button.

The display control unit looked like someone poked around and tried to redo the soldering (or unsolder to measure and then solder back ?) on one row of the SMPS transformer. One connection was interrupted (wire to pin) so I had to go around and fix all of them; I also checked all transistors/diodes and replaced the SMPS controller IC. Didn't help.



In fact, it looks like the display control unit is not getting the Enable signal from the display unit so probably that's why the 250V voltage is not coming on. The EL560.400 display unit is supposed to turn on when it detects video signal, however on the 4 video signal pins only clock is present (wave form below) but no Hsync / Vsync / Vdata. Looking at the Digital Tray, the TMS34010 graphics processor doesn't output any video signals and all the HD0-HD15 I/O bus pins are stuck on HIGH.



This points to the Controller Tray not providing the video data, but I have no idea where to start. Visually it looks good (no leaked caps etc) and the Lihium battery measures 3.695V.



Questions I'm trying to find an answer to:
- what does the audible error code (short-short-short-long-short beeps) mean ?
- is the Planar EL560.400 display unit supposed to start when it sees the video clock signal, or it waits for the other signals ?
- any other suggestions on how to approach this ?

Any help is very appreciated.

Thank you,
Razvan.

[George Edmonds]

Hi Razvan

There is a dedicated Marconi/IFR support group at

https://groups.io/g/Marconi-Test-Instruments

you may find more help there

73 George G6HIG

[M0HZH]

Thanks George, I'll try that.

In the mean time, I checked a few capacitors on the Controller Tray and Digital Tray, they all seem to be in spec.

Razvan.

[VE2JFQ]

it is possible that the ds1286 on your controller tray itself is not good, and the test set will start but you will never see your image on your el panel! I had the same problem ! the internal battery of the ds1286 becomes dead and it is the beginning of the mess! Me what I did, I took off the ds1286 (be careful, and especially very patient, because the board is very sensitive!) anti static bracelet and a good desoldering station. I solder an ic socket, and I installed an assembly that I did, it takes a ds1284 a 32.768 khz crystal solder on pin 2-3 on the ds1284 and a 3 volt lithium battery + batt to pin 25, -batt to pin 21). with that you should find your screen! but still the chip must be programmed and it is not obvious (I am still on this project! good luck Jacques

[M0HZH]

Hello Jacques,

Thank you for the reply. In the meantime I managed to find the issue and have it fixed.

I connected to it via the serial terminal and realised that the boot sequence was failing; looks like some of the firmware (there are 5 different parts stored on separate chips) was either corrupted or purposedly erased. I've seen this before on test equipment, if they think it can't be repaired they make sure the unit is properly decomissioned / unusable, either cut some wires, drill a hole somewhere, install a chip the wrong way in the socket etc. Barbaric.

I tried to rewrite the firmware with some files I found on the internet but it was incomplete (only 3 files out of the 5 needed) so in the end I got some help from a small company in the US that still repairs these (Cin-Com Service in Cincinnati, OH - can't praise John enough). I had to send the Controller Tray in and they fully restored it, all the 5 firmware files and a new DS1286 chip, plus some extra software options that weren't there originally. The calibration data is also backed up in the front panel unit so that recovered at the first boot (but it came back with a warning that it's old and should be recalibrated). After that, I also found a failed transistor in the Generator Tray that I've replaced.

I still have a small issue with it, that as it warms up some functions temporarily fail. At startup it's fine, after a few minutes all 5 meters fail (Aud Freq. Meter, RF Error Meter, Deviation Meter, Distortion Meter, Rcv. Level Meter, sometimes the Generator synthetiser unlocks too for a few minutes), after 20 minutes it works fine again and keeps going until the next cold start. Everything is in spec (voltages, frequency reference etc) as far as I can tell, I've replaced tantalum and some electrolytics on a few boards, used external power supply / clock source, still no go. Oh well, it might just need a complete recalibration.

Razvan.

[VE2JFQ]

Razvan

 I am very happy to hear that you have solved your problem! I have three com-120b so the ds1286 is dead! I found other ds1286 that I added a surplus external battery. not too much room, but with a bit of double side tape, they stay in place. at the moment, the self test is ok, my scope and my spectrum too. but not my options which are gone! apart from the if filter and the second gen which works well! I would like to have a copy of the firmware that you found on the internet, because I have not solved my problem with my options. I communicated with cin-comm and he replied that he was not interested in programming my controller tray? it's better like that! and you are talking about a serial port release with your com-120b. does it take an old computer to do this? Thank you and good day
Jacques

[M0HZH]

Hi Jacques,

You can use the serial port on the back to connect the COM-120B to the PC via terminal. A RS-232 port or RS-232 to USB adaptor would do (so can be done with any modern computer), I used Tera Term software as a terminal emulator but there are other options. You might have to guess the baud rate.

As soon as I get some time, I might try to do a dump of all my files and share with you; I should have them for backup anyway.

Most resources about these can be found on the Batlabs forums and on the Marconi Test Instruments discussion group.

Razvan

[George Edmonds]

Hi

There is a dedicated group for these monitors, it is

https://groups.io/g/IFR-Monitors/topics

George G6HIG

[VE2JFQ]

Razvan

I am not able to communicate with my com-120b !? i have a module which converts a usb-rs232 output with a db9 wire to my com-120b. I have tried several software. the only one that succeeds is the advanced serial port terminal software, but I can't see anything? I need help ! thank you

Jacques