Beogram 4002 (5523): Repair of an Intermittent Sensor Arm Light Source

Recently a Beogram 4002 (5523) returned to my bench, about 14 months after I restored it in May 2022. The reason was a 'not working sensor arm LED'. This made me concerned since this deck was the first to receive my redesigned sensor arm LED assembly.

Luckily, when I set the deck up on my bench and plugged it in the LED was working normally! This indicated some kind of intermittent issue that somehow 'fixed itself' during shipping. 

I wiggled the plugs and cables a bit but to no effect. The LED stayed on! Only when I started to flex the main PCB a bit around P4 where the components of the sensor arm light power supply are grouped nearby, I was able to get the LED to turn off sporadically. 

A closer inspection of the solder points relevant to the sensor arm circuitry revealed a bad solder point on the collector of the transistor that powers the light, TR5:

The collector of TR5 is connected to the 24V power rail via 1R36, which powers the LED.

I re-soldered the point, and that solved the problem. 

This Beogram restoration was done before I realized that the H-bridge power transistors of the carriage drive also need to be replaced preventatively. They seem to frequently go bad after using the decks again for a while, so I decided to add their replacement to the Beolover '400x restoration canon'. Therefore, I used this occasion to update the main PCB in this respect. This shows the original BC144/143 cans in place:

I replaced them with more modern 2N3019 and 2N4033 components. They have the same package, i.e. drop right in:

I will play this deck a bit before it goes back to my customer in Colorado to make sure that there are no other issues.

Beogram 8000: Strange Behavior Caused by an Intermittent 5V Supply

**********************This post is a sequel to this restoration.***************************

I declared 'mission accomplished' after restoring a Beogram 8000 recently, and I sent it back. After about 2 weeks I received an email describing some strange behavior, where it would shut down during play, but sometimes only very briefly and then start up again etc...

The Beogram was sent back to me and I had a look. First I was not able to reproduce the issue, and after playing more than 20 albums, desperation set in. So I gave it a bit of impatient rapid play and stop and other buttons, hoping to provoke a reaction. And after a while, indeed, it gave me a signal. The display showed this after it returned home after pressing STOP:

The dot on the right should not be on! This encouraged me to continue pressing buttons and I got this:

and this:

After each of these display readings I was only able to go back to normal after pulling the power plug and reconnecting. I continued working it for a while, and finally I got it to loose power briefly, and then it came back on. So I started thinking there must be a problem with the 5V supply. The 800x often has power issues, but mostly due to bad capacitors or bad solder joints on the headers that connect to the transformer block. Of course I already had re-soldered these headers and installed new capacitors, i.e. these standard root causes could be ruled out.

Since the issue seemed to be based on very brief outages or brown-outs that confused the processor, I needed to find a way to monitor circuit nodes for brief voltage dips while playing with the buttons. I decided to use the external interrupt pins (2 and 3) of an Arduino nano board, which I outfitted with a npn transistor and a 20k resistor on one pin to be able to sense higher than 5V signals, so I could also go between the transformer and the 5V regulator. After the 5V regulator the voltage is stabilized, i.e. Arduino pins can directly be connected. LEDs were used to signal power drops on each pins. This shows the board:

First, I connected the two pins to the green marked nodes in the circuit diagram to test if the 5V chain was interrupted between regulator and the plug that connects to the micro controller can:

After I was able to produce another failure the Arduino told me that on both green points the voltage briefly dropped to zero. This verified my power outage hypothesis, but did not show me where it occurred. Suspecting a bad regulator, I connected the transistor-buffered lead to the red marked spot right at the transformer-facing side of the fuse holder.

I played the buttons again, and again, and after a long time, I was still not able to reproduce the problem anymore, while before it took me always less than 5 min! This indicated to me that I might have had accidentally fixed the issue when soldering the test lead to the solder spot on the board:

It turned out that this solder spot serves to connect a black jumper wire between the fuse holder and the 5V rectifier:

So I suspected that the wire had a bad connection, and re-soldering the solder point while tacking on the measurement jumper accidentally fixed the problem. I replaced the back jumper with a new one, and had a closer look at the connector:

Indeed, the wire had pulled out a bit from the solder terminal, but was now soldered to the terminal. I suspect that some of the solder I put on the point during attaching my Arduino jumper managed to go inside the terminal, which fixed the intermittent contact.

Therefore, in conclusion, I think that the wire was loose, but still stuck inside the solder terminal, and the intermittence of the 5V supply was caused by vibrations when I pressed the buttons in quick succession etc...I will play it for some longer, but I am pretty confident that this problem may have been fixed with the new wire.

Beomaster 8000: More Output Trouble - Broken TR207 Collector Trace

After I fixed the broken PTC thermistor lead in the left output of the Beomaster 8000 that I am restoring right now, I thought I was finally done with the outputs, but no: When I tested it for a while it ran happily, and then out of a sudden the fault switch triggered again a shutdown of the output supply. This one was difficult to find since it turned out to be intermittent. After a while I finally figured out that the trace that connects the collector of TR207 (voltage gain stage) to the positive 55V rail was cracked. After removing the delaminated trace, I fixed it with magnet wire:

I like to use magnet wire for fixing traces, since the polyurethane insulation of the wire can conveniently be burned off with the soldering iron, resulting in short circuit proof connections that are insulated right up to the solder point.

Unfortunately, this did not fully fix the output issue. While the 8000 came on again reliably, I realized that my repair efforts must have caused some other problems. More trouble shooting finally yielded another broken off lead to the heat sink. It must have broken off while I lifted the board up to do fix the trace. The many alterations on this board and also the left channel suggest that the previous owner had a hard time to pinpoint the issue with the intermittent trace and the fault switch issue, and therefore the board was lifted a few times too many for replacing components finally compromising the integrity of the leads that go to the heatsink. This time the (green) lead to the base of IC205 broke at the solder terminal on the PCB. This caused this Darlington to be turned off. It was remarkable that the output still amplified under this condition. I only noticed the issue since after repairing the trace I ran the output with external power supplies while measuring the voltage drop across the R236/7 emitter resistors, which could not be raised anymore above 3 mV. This indicated that there was something wrong. After I reconnected the base of IC205 everything was finally good again. Live and learn. No Beolove without some degree of pain, I guess...;-)

Beomaster 8000 Keyboard Restoration/Not Working Buttons

The final step to restore my Beomaster 8000 to its original glory was to fix a keyboard issue. I noticed earlier that the TP2 button only worked intermittently. I thought that this was a problem originating from corroded keyboard contacts since wiggling the button seemed to do the trick once in a while.... Hence, I took the keyboard apart to clean the contacts. While this was an interesting exercise, it turned out that this did not fix the problem. But more about that below. First a few pictures of the keyboard innards:

Removing the retaining washers turned out to be a pain. Since B&O used one-time use washers that need to be destroyed for removal I had to cut them off with a wire cutter:

This photo shows the buttons from below after removing the PCB and a plastic foil:

Here a shot of the PCB before cleaning:

For cleaning the contact pads have to be removed:

These contacts were quite oxidized (or probably rather sulfidized, assuming that the pads are silver coated)

Using a small head Eurotool fiber brush (I am grateful to Gunther at Beoworld.org for this excellent tip!!) I cleaned the contacts:

The above picture shows the PCB after reassembly.

I reinstalled the board using 3 mm external retaining rings from Grainger (113828) and #4 nylon washers. This is shown here:

So far so good. Plugging the keyboard back into the Beomaster and turning it on immediately revealed that this procedure did not fix the problem.

After playing a bit around I realized that the P4 button also not worked whenever TP2 was out. A look at the circuit diagram for the processor board immediately revealed that TP2 and P4 use the same input on the slave processor (it distinguishes between the two buttons via the strobe mechanism that also drives the LEDs of the display in three "phases"). The oscilloscope showed that after pressing the TP2 or P4 buttons the voltage at P81-7 (7th pin on plug 81 that goes to the microcontroller) was higher than on other pins connected to working buttons. This led to the conclusion that the connection between switch and microcontroller must be interrupted whenever the buttons ceased operation.

Hooking up an Ohmmeter between pin 7 and R103 indeed revealed a broken PCB trace, with an intermittent contact depending on the flex of the PCB in the vicinity of P81. I installed a bypass (pink wire in picture):

This seems to have done the trick. TP2 and P4 seem now stable.

After this I finally put the Beomaster back together. Tomorrow, I will swap it with the one I currently use in the living room and the next months will show if this rebuild is stable. At this point all features seem to work correctly. On to the next B&O!

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.