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Beolover SyncDrive: DC Platter Motor Replacement for Beogram 4002 and 4004 (Type 551x and 552x)

Late Beogram 4002 and the 4004 (Types 551x and 552x), which have DC platter motors instead of the earlier synchronous AC motors usually suff...

Friday, July 31, 2020

Beogram 4002 Type 5513: Return to the workbench for a new phono cartridge mount - Conclusion

The new Beolover replacement phono cartridge mount is installed now in this Beogram 4002 Type 5513 turntable.

This type of restoration is always fun. My very first collaboration with Beolover was on one of my Beogram 4000 turntables where we decided there needed to be a replacement phono connector so the repair didn't have to use a donor Beogram. Since Beolover created this phono connector part it has saved many a Beogram turntable I am sure.

Certainly this Beogram 4002 Type 5513.

Here are the components again -

I like to replace the phono wires on this type of repair. I use color coded 36 awg wires.

Preparation for the repair means tinning the leads of the new wires and the connector assembly contacts.

I start with the two inside wires and finish with the outside wires.

Note that the bottom part of the Beogram phono connector assembly reuses the original connector part.

Before I join the two halves of the phono connector I use a some Aleene's Tacky glue to hold the wires in place and act as kind of a strain relief while I work on the repair.

This is why you keep old MMC phono cartridges...even if the the cantilever and stylus are gone.
They are perfect for this repair in making sure the phono cartridge assembly is put together correctly and inserted just right into the tone arm. Aleene's Tacky glue is used again on the joining of the two phono connector halves.

I also use a little more of the Aleene's Tacky glue inside the tonearm when I reinsert the phono connector assembly.  That insures the phono connector is secure but it could still be taken out again in the future. You don't want to use something permanent like epoxy here.

Now I just had to connect the phono wires to the signal transfer board and this repair will be done.

That concludes the Beogram 4002 Type 5513 phono cartridge connector repair.

Because this repair required so much handling of the tonearm I will have to go through all of the service manual tonearm adjustments again to make sure this Beogram is ready for use again.

Hopefully most of the components will still be adjusted correctly but they still have to be checked.

Monday, July 27, 2020

Beogram 4000: A Fun Time with a Suddenly Activating Solenoid, an Anemic Carriage Motor, and an AC Motor Driver with a Weak Driver Amplitude

I am making good progress with the Beogram 4000 that I recently started to restore. More about the standard restoration tasks in a following post. This post focuses on two non-standard issues with this Beogram that I encountered after rebuilding its boards and motors.

I started realizing there was something wrong when I adjusted the platter height relative to the arms. During this process I needed to drive the carriage, so I plugged the Beogram in and I realized that the carriage movement was a bit slow compared to other 4000s I had worked on previously. I measured the 24V rail, and it only showed 21V. A bit odd. Usually this is 25-26V due to a warm Schottky diode, or 23.8V in my case since I now always replace the original 1.3W diodes with a cool running modern 5W type, which brings the voltage down to 23.8V at the capacitor terminal. But in any way the presented voltage was way too low.
Then I accidentally touched the carriage in a way that it was lifted up in the back a bit. This briefly activated the arm lowering solenoid. Very strange!!
I was able to reproduce this and it dawned on me that there must be a major issue, somehow putting a significant voltage onto the carriage when it touches the floating chassis (the carriage is normally insulated due to the plastic components that hold it on the guiding rods. The solenoid issue even 'worked' with the Beogram turned off (but plugged in).

I put the multimeter to it, and after poking around for a while, I realized that the enclosure of the Beogram was at ~30V relative to the system ground. Not a good sign, I counted myself lucky that there had not already been some 'magic smoke' emitted from an unlucky component. I also realized at this point that the transformer got unnaturally warm. 
30V 'smelled' like the unwanted voltage originated from the 24V system, which is fed by about that voltage before the Schottky diode (OD2)/transistor (TR1) regulator stabilizes it to ~24V. 
I determined that there was a ~9 Ohm short between the positive end of the 24V 3000uF reservoir cap (0C4) and ground:
More precisely, the short was between the red lead connected to the cap and the chassis. I followed the red lead, which goes to the collector of 0TR1. So first I suspected 0TR1 might have an issue, but it turned out to be o.k..
But at the collector of the chassis-mounted 0TR1, the red wire from the cap meets a thin blue wire, which goes straight to the carriage circuit board, and from there to the right contact of the solenoid, supplying it with un-stabilized 30V for maximum action! The plot thickened. I successively unsoldered/measured/re-soldered all the connections as I 'moved away' from the collector of 0TR1 keeping an eye on the resistance to the chassis. I made it to the left solenoid contact, and then to the terminal where the solenoid connects to the collector of its driver, 0TR4. All the while the short remained, i.e. all that separated me from the chassis was now 0TR4. A closer look at 0TR4 revealed that previous 'creative human interaction' had caused the bolt insulator to go AWOL:
The way this transistor is bolted down, a direct short is made between its heat sink (=collector) and the chassis via the bolt. What was missing is a part like this, which I fortunately had in my stash:
I installed it
and this cured the spontaneous solenoid activation issue. Details, details!!...;-)

I measured the 24V rail again, but the voltage was still only at ~21V and the carriage still moved too slow. So there had to be a secondary issue draining power from the system. Also the transformer still ran pretty hot. The other 'power electronics' system of the Beogram 4000 is the AC platter motor. So I measured the AC platter motor signal just to make sure this was working properly. What I saw was a much too low signal, however:
The RMS voltage was only 2.5V with the motor pot adjusted to the maximum smooth waveform. It should be about 5.5-7V when everything is up to specs. This suggested the secondary issue was in the motor driver. I moved the main PCB out of the way and had a look at the push-pull output stage of the motor oscillator beneath it:
The left transistor is 0TR2 (NPN, push) and the right is 0TR3 (PNP, pull). Since the motor wave was about 50% of normal, I immediately suspected one of them being in trouble, causing the motor to run only on one 'cylinder' instead of two. I touched the transistors and I found the PNP to be pretty hot. I extracted it and measured it with my transistor tester, and it appeared to be in perfect working order. So it had to be the other one! I extracted it, too, and indeed, it had turned into a small resistor:
This basically caused the NPN transistor to carry a big DC component along with the AC fed to the motor, explaining the high heat load.
I replaced 0TR2 with a BD437G power transistor (45V, 4A - a bit stronger than the 3A original TIP32),
(this modern package does not need a bolt insulator since the heat sink is encased by plastic on all its bolt facing surfaces)
and that cooled down things while yielding a normal strong motor signal for 33 RPM
and 45 RPM:
After this the 24V rail also was fully restored to 23.8V, and the carriage now moved much more quickly. 
On to do the final adjustments and giving this baby its first restored spin!


My customer suggested: "You write that 0TR3 (PNP, pull) was hot but working.  Running transistors hot obviously shortens their lives and I’m just wondering, now that you know this circuit had a problem, would it be worthwhile to just replace 0TR3 pro-actively to make sure that there isn’t a latent issue that could lead to another failure downstream?"

I thought that made a lot of sense!...;-), and so I put in the complementary PNP (BD437) in, too:
If you do this at home, note that the BD437/438 SOT-32 packages have base and emitter reversed compared to the original TIP31/32 TO-220 types, i.e. the brown and blue/orange wires need to be reversed.

Beomaster 4400 Type 2419: Personal Project: Reassembled and Ready for Listening Tests

I decided I would reassemble this Beomaster 4400 and start performing some listening tests with it before I do any performance testing and before I complete the cosmetic restorations.

The reason for that is I want to get my second Beomaster 4400 started and completed as soon as possible...while the soldering iron is hot :-).  That way I can test and compare both units together.

The second Beomaster will also require a little bit of cosmetic repairs.

First though I must fix the power on lamp on this Beomaster unit.
Here is the power on lamp assembly housing. I is a black plastic lamp housing that fits onto a metal bayonet that is part of the lamp lens inside the front of the cabinet. It just pulls off the bayonet for access to change the lamp.

The lamps fit really tight inside the housing to it takes some careful pulling to remove one.

Once the lamp was replaced the power on lamp worked again as well as the radicator lamp.
That makes sense as the power for the radicator lamp comes through the power on lamp.

Moving forward with the reassembly I installed new cabinet feet on the Beomaster cabinet bottom cover.  These Beomaster 4400 cabinet feet are usually rusty and flat.

On this Beomaster the feet are a little smashed down and one foot is missing. No rust though. That is a welcome site.

The replacement feet are much better and have a metal tube for the screw so the rubber doesn't get flattened out if somebody over torques the mounting screw.

I reattached the front slider control bar then the bottom plate and the top cover. This Beomaster is ready for some listening tests.

After I recap and change trimmers in the second Beomaster 4400 I will return and do some cosmetic touch ups on this one. The rosewood cabinet looks nice in the photos but the finish is a little dull. Plus there is the small chip on the left side. I also need to order a cover plate for the FM preset tuning dials. I can get that from Martin Olsen's Beoparts store.

Sunday, July 26, 2020

Beomaster 4400 Type 2419: Personal Project: Initial Power Checks

I couldn't end the day with just having the board restoration work complete.

I am always curious whether the audio components will actually work now.

First step was to reinstall the preamplifier and FM boards.

The Beomaster is ready to power on. Like I always do with this type of amplifier I connect the power cord to my variac, ammeter, voltmeter and dim bulb test device.  That device will protect against any hidden short to grounds on the power signals and it will tell me if something is drawing too much current.

In this case...I got nothing. No lights, no voltage on the power supplies.

After a bit of investigation I discovered that one of the AC cable wires was not connected internally in the Beomaster.  That explains that.

I checked the other wires around it and checked for any shorts. Other than the disconnected AC wire everything else looked fine.

Here is my repair of the broken wire.

That looks much better.

On the second round of the power checks I still don't get any lights illuminating on the Beomaster 4400 but I do have power on the supplies.

Here are the +15 VDC and +35 VDC supply checks

and here are the ±35 VDC rail voltage checks

It looks like the Beomaster 4400 is ready for a quick listening check.

I did a quick, initial setting of the idle current for the output amplifiers by adjusting the left and right channel trimmers to get 10mVDC across the respective channel emitter resistors.

Once those were adjusted I connected an iPod Nano to the Tape 2 source input and used a pair of headphones to check if I had sound.


I connected up an FM antenna to the Beomaster 4400 antenna input and tried tuning a station.
Another success.  The FM tuner section is working great. The tuning indicator and stereo lamps do come on as well.

So for certain the Beomaster 4400 power on lamp is not working and the lamp that illuminates the radicator (the FM signal strength meter) is also not working.

I am not sure about the overload lamp but I can test that when I replace the power on lamp.

Saturday, July 25, 2020

Beomaster 4400 Type 2419: Personal Project: Preamplifier board and FM boards

The remaining boards requiring some recapping restoration are the preamplifier board and the FM boards of the Beomaster 4400.

Again, the previous post here, show the before state of the boards.

On the preamplifier board I also replaced the six, single-turn trimmers for the Phono, Tape 1 and Tape 2 source inputs.

Here is the preamplifier board after the restoration work -

Here are the three FM boards (FM1: Tuner, FM2: IF Section , FM3: Stereo Decoder and Indicator).
There is one 10uF, 10V tantalum capacitor in the FM1: Tuner board. I measured it and it is right on 10uF so I left that capacitor alone for now.

...actually that photo is a little premature.  The board still needs a 1uF and 0.47uF capacitors as shown added in this next photo.

Now for the big step of reinstalling the boards and setting up the first power on test of this Beomaster.