Beomaster 4400 (2419): Tuner Repaired

The Beomaster 4400 that I am rebuilding right now seems to be running on all cylinders again. But a little more work was needed: 

After restoring the 15V rail the tuner came alive, but with a very weak output, while a standard 1Vpp signal piped into the tape input yielded a normal output response. So the problem was definitely not in the amp section. So I poked around on the IF board (#2). First I suspected a broken filter crystal, but the three turned out to be o.k. But while I was messing around out of a sudden the tuner started blasting full volume, indicating another broken trace/bad contact issue. I cleaned the contacts of the two board-to-board connectors and plugged it back in...no change. So I re-soldered all the contacts of the plugs and I also replaced the two electrolytic capacitor on this board with quality Japanese 105C types while I had it out. I also put in new headers and jacks for the signal meter connectors. They looked strangely corroded with some white coating. Here is a picture of the rebuilt board:

After I plugged everything back together the tuner came to life at full volume, but only on the presets. The main FM dial still did not work. This indicated some more contact issues, since the FM dial is nothing but another tuning voltage delivering trimmer in the context of the circuit diagram. Just looks more important...;-). I finally figured out that the culprit was a crack in the switches PCB (#6):

This was a pretty big one. It separated the 4.7V end of the main dial 100k pot from the voltage source, and so the pot was not able to change the tuning voltage from the 26V on the other end, i.e. the tuner was permanently set to 108 MHz independently of the pot setting.

I installed a jumper (grey) to bridge the crack (the grey/white wire goes to the pot):

This brought the FM dial back to life. Then I epoxied the PCB back together using a couple PCB snippets that I had laying around from designing Beogram 4000 scale illumination LED boards:

Here is a nice shot of the tuning indicators after the repair. Both tuning lights work again, and the stereo indicator is on. Beautiful! Beolove!

One the two capacitors that I replaced on the IF board was completely dead. It showed the characteristic cracks in the can, and measured 25nF instead of 4.7uF. This makes this Beomaster 4400 a definite candidate for a recap:

Beomaster 4400 (2419): 15V Rail Restored

I made some progress with trouble shooting the Beomaster 4400 (2419) that I am currently restoring. When turned on, the ON light did not come on, and also no sound from the tuner, but the Tape input worked...Both phenomena suggested that there is a problem with the 15V rail, since the ON bulb is powered via the 15V supply, while the tuner is the main part of the Beomaster that uses 15V. So I started following the 15V traces and wires. They are red throughout, that makes it a bit easier. I started out at C3 and the 15V were present. This meant the voltage regulator was working. I measured the resistance of the ON bulb (6 Ohm), which indicated the bulb is o.k. I finally found the spot where the 15V went lost: A crack in the main PCB (#5) under the Decoder board (#3) at one of the plastic clamps that hold it in place:

Since it is difficult to get directly to the trace at this location, I bridged directly from the power supply at R8. The red wire goes directly to the location after the crack:

This is where it comes out on the other side. I soldered it directly to the red jumper that goes from the main PCB to the PCB that connects the switches (#6):

This improved things:

Now the ON lamp is on and also one of the tuning light came on. However, there are more issues: The tuner only works with the presets and not with the main dial, and the volume is very low. This indicates that there is some issue on one of the tuner boards. Tomorrow is another day...;-)

Beomaster 8000: Shipping Damage Repair II

Today, had a look into the soft FM 'store' button. I took out the control panel and removed the PCB. This is what I found:

Some of the tabs that hold the PCB for the buttons were broken off. The previous owner had removed this PCB at some point and did not understand that it can be slid to the left after lifting the end of the PCB above the blocking plastic protrusion. So he broke the tabs off and re-attached them with the solder iron that he used as a welding tool when he put the board back in...very crafty! Unfortunately, this method does not yield very good bonds, which resulted in structural failure during the shipping accident. The tab that stabilized the PCB beneath the FM store button was missing, resulting in sagging of the PCB when the button is pressed. That resulted in a soft feel when the button was used.

I fixed the issue with a few dabs of heat gun glue essentially replacing the reattached tabs for a more lasting bond. The great thing about this type of glue is that it can be removed with a bit of mechanical force. That way one can get in there again if needed. Here is a picture:

Time to put the Beomaster back together for some testing.

Beomaster 8000: Shipping Damage Repair

A sad moment in Beolover's life! A Beomaster 8000 that I recently restored was damaged during return shipping to its owner. FedEx must have dropped the box off the truck. This Beomaster was even shipped in its original box, but this was apparently not good enough. Double boxing is really worth the effort! So far, I only had shipping issues with single boxed units.

Anyway, upon opening it up and plugging it in, the display looked like this:

The Beomaster also occasionally turned off by itself, when touching the processor PCB...all this suggested some broken tracks on this PCB. And indeed, a close inspection of the board revealed several broken traces around one of the slots for the shield in the PCB...I bridged the affected traces:

And everything started working again:

It is interesting to understand the phenomenon cause by the broken traces. All strobed display digits had a very low intensity. At first I was a bit confused how all of them could be affected at the same time, while the non-strobed segments ran at full intensity. But all cleared up once I realized that the ground connection of both 74247 7-segment decoders had a high resistance. This floated them, and hence they were not able to sink current anymore, and with that the LEDs were all dim.

So far so good. Unfortunately, there is some more trouble: The buttons of the control panel feel unusually tight. They still work, but there is definitely something wrong...