Beomaster 8000 Microcomputer PCB Damage

Back to the Beomaster 8000. Today I looked at the missing display segments. First, I thought it is the usual dead LEDs on the boards. The display looked like this:

So I removed the three main displays. Luckily, I decided to plug them into the display 'harness' I made with a breadboard for the last display repairs. Powering them up yielded this:

This is the first Beomaster 8000 display I see that fully works. This told me the problem is elsewhere. I soldered the displays back in and looked at the circuit diagram. The particular LED segments that were out suggested a problem in the drain path to the SN74247 7-segment driver responsible for these segments (IC 2). I checked the signals on plug P-75 and indeed the pins responsible for the c and d segments were at 5V and did not show any strobe signal. This suggested a contact problem. I removed the display board and cleaned the plugs and resoldered the p-75 plug and socket. To no avail. The segments remained dead.

I followed the current path towards the SN74247 and found that the plug pins did not connect to the respective current limiting resistors R21 and R22. This meant that the PCB traces between P-75 and these resistors were broken somewhere. 

A closer look revealed that there had been the same problem at some point in the past with pin 3 as indicated by the white jumper soldered between capacitor and resistor:

I did the same for pins 7 and 8:

This brought the segments back:

The question now is whether to refurbish the displays anyway or leave them as they are.

2004 Crown Victoria Blower Control Module Repair

Today I had to take a break from restoring B&Os...the blower motor in my 2004 Crown Vic started behaving erratically, and poor A/C in summer in Florida is not an option. So I had to take a look. The car has an "EATC" unit (maybe "Electronic Automatic Temperature Control" -  not sure) which means one can set the desired temperature, and it will then adjust air temperature and blower speed automatically. At some point it started huffing and puffing, i.e. the blower motor would change its speed erratically. I found an interesting post at crownvic.net (http://www.crownvic.net/ubbthreads/ubbthreads.php?ubb=showflat&Number=1811924) where this topic is discussed with the usual mix of comments from pros and inexperienced hobbyists. But there is enough  information to learn that the most likely culprit is a weak solder joint in the blower control module, which is mounted in the air intake of the A/C system near the firewall. The above post has some confusion about how to take this module out, which is the reason I am posting this today.

It turned out that it is not very difficult despite the comments on vic.net. Anyway, here are my pictures of the process:

The module is below this hose spaghetti, i.e. they need to be removed

Luckily the hoses to the heater core are at the top of the cooling system, i.e. one does not have to drain the system. Only a little fluid comes out when the hoses are removed when the engine is cold (it is absolutely a good idea to do this in the morning before driving the car - otherwise there is a real danger to hurt yourself with hot water squirting out of the system when removing the hoses). I put a plastic tub underneath the car below the work area to catch the fluid.

After removing: The blower control module is the black unit with the orange tag in the center of the photo. Two screws hold it to the A/C box.

A 5/16 nut does the job:

Module after removal. The two screws that hold it to the plastic enclosure need to be removed to get the board out:

Board w/o plastic enclosure:

What needs to be resoldered are the five pins of the connector assembly. As prediced in the vic.net posts the contact to the left large connector pin was intermittent. I was able to see this on the multimeter when wiggling the contact. The other 4 were o.k. I resoldered all 5 of them for good measure. Here is a pic of the contacts. 

It was difficult to do this since the board seems to be coated with some kind of protective film, which messed the solder flow up. But I think it did the job. After reinstallation everything seemed to work fine.

Beomaster 8000 Power Supply Board Rebuild

Today some routine work on my 3rd Beomaster 8000: Recapping of board 6 (power supply). These capacitors get warm, i.e. they should definitely be replaced when refurbishing a BM 8000. This board was different from my previous two Beomasters in that the large reservoir caps were not glued to the board with silicone, but rather with a strip of double sided tape, similar to that type used in the Beogram 8000 models to attach the brushed aluminum panels. Of course this tape was degraded, and the capacitors came off easily. Therefore, no heating required. Here are some pictures:

The original board:

After removing the reservoir capacitors (this 'foam' is the degraded tape, which I removed through scraping and ethanol):

With new capacitors:

What is left to do are the left output, the display, the main reservoir caps and the speaker switches, which failed on both my other beomasters and seem to be a weak spot of this design.

Beomaster Volume Encoder Repair

I finally got around to looking into the not-working volume wheel (encoder). I put a strong LED flashlight on it, and it worked. This told me that the IR emitter in the encoder pickup must have died. A voltage measurement across the diode confirmed this suspicion. The entire 5V showed on the meter, indicating that no current flows through the limiter resistor.
I replaced the emitter with a "OPTEK TECHNOLOGY - OP240A - IR EMITTER 890NM 0.76MM SIDE LOOKING" from Newark (08F2957). The device has exactly the same package as the original defective unit and pops right in. It has a wavelength of 890 nm and a 1.8V voltage drop. The encoder works now like new.

Beomaster 8000 Rebuilding the Power Amps

Today I rebuilt the right output stage. I put in new electrolytic capacitors and replaced the no-signal current trimmer. It was a good idea since a look at the old one revealed that it was intermittent when turning it. Adjusting the voltage between TP200/201 to 18 mV according to spec yielded a nice cool heat sink, even after a 1hr run. Here are before and after pics:

after:

At the end I adjusted the offset of the differential amplifier input with R200 to 0mV at the speaker jack. On to the left channel!

Third Beomaster 8000 - First Life Signs

This is turning into a fully blown addiction. I bought a third Beomaster 8000!!! Of course broken...gotta have some fun! Today, I finally opened it up with the plan to bring it on line slowly. I disconnected the 45V power supply from the output stages (pulled red and black cables on L and R output boards). The purpose was to avoid a potential burnout of the output transistors in case the trimmers have contact problems. After disconnecting, I checked the main capacitors on board 6 (power supply) to see if they still work. They showed reasonable values. Then I connected the Beomaster to the mains. Without pressing a button, it immediately showed some random segments on the displays:

No response to any buttons. This made me think and pull out the circuit schematics. After some study I came to the conclusion that it is time to check the voltages relevant for the microcontroller and the displays. I measured on P48 on board 6 that the pins that should carry 5V only measured 2V. This means that the microcontroller is starved below its minimum voltage of about 2.7V. The circuit diagram shows that these pins are directly connected to the output of the 5V voltage regulator. That left practically only one possibility (aside from an (unlikely) short somewhere on the microcontroller board): C35 must be bad. Indeed a measurement with my capacitance meter indicated a capacitance of 2.3 nF instead of 10 uF. I immediately replaced the capacitor with a new one. Plugged the Beomaster back in and it started up normally. After pressing a button I got this:

As usual, several segments are dead and these displays need to be refurbished. A worrisome phenomenon: No response to turning the volume encoder...well, it would be boring if they always had the same problems. More about this in the near future.

Mr. Clean Cleans Old Vinyls Very Well

Recently I bought some used vinyls on ebay to relive some youth memories. Also I like to use my lovely Beogram 4002 once in a while. Spotify is cool, but just does not have that vinyl feel...;-). Unfortunately, once the vinyls arrived I had to acknowledge that they were in bad shape...one of my less exciting ebay experiences. They played pretty rough, lots of dirt in the grooves. Not many scratches, though. Anyway, emboldened by a recent experience with Mr. Clean "Magic Eraser" pads, which allowed me to restore the brushed aluminum panels of my various Beomasters to practically new condition, I put one of the pads to one of the dirty ebay records. A previously unthinkable way to treat a cherished record, but here I did not have any choice! To my amazement, the record now sounds much better. The distortion in the voice parts and trebles is much reduced, also crackle is much less.
Here is what I did:
I wet the pad, then put it with relatively firm pressure on the record, which was situated on a towel on the floor. I moved the pad in concentric motions around the tracks covering the entire disc. I took care to not touch the label in the middle to not damage it. A little bit of foam developed from the detergent of the pad. One can feel how the micro foam grips into the grooves-the pad 'wants' to move in a concentric orbit around the record because of this. After a few rounds, I rinsed the record thoroughly with tap water and then with some filtered water from the fridge to remove minerals from the tap. The label got a bit wet/drenched by this treatment, but it dried after without visible traces.
Then I put the record back on the towel and dried it in concentric motions with an old t-shirt.
Done.
After this I also cleaned the stylus of the 4002 with the pad. Under the microscope I observed how the crud came off...the needle looks now like new again. Quite impressive!
Mr. Clean Rocks!!...;-). Enjoy!