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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...

Thursday, April 23, 2020

Beomaster 4400 Type 2419: Power on/off switch rebuild completed

I had some time tonight to finish preparing the rebuilt Beomaster 4400 power on/off switch for re-installation into the receiver.

My method of wiring the switch this time was to cut and fit the bus bars first. Then I attached the relative wire pieces to the bus bars before attaching everything to the switch contacts.

When I did attach the mini-assemblies to the switch contacts I used some solder shield clamps to prevent any heat from reaching the plastic switch housing.

Here is the power on/off switch fully wired back up and ready for re-installation.

I was very pleased with the wire connection results.  Now to check the switch operation again.

Very nice. I exercised the switch actuator a bunch of times and never had a case of a contact failure.
The contacts in fact remained nice and solid. No movement in them whatsoever.

This switch is ready to be re-installed.

Wednesday, April 22, 2020

Beomaster 4400 Type 2419: Rebuild 2 of the power on/off switch

Using the various Beomaster 4400 power on/off switch piece parts I selected the best switch components to rebuild a good switch for this project.

I secured the new switch contacts in the top housing using some instant epoxy. It is pin point so I could just place a drop around each contact coming through the housing. That secured the contacts and allowed me to test fit the two switch housing halves to make sure the contacts go into their respective slots.

Here is a picture of the contacts and actuator in the top housing half ready for mating with the lower housing.  I have the contacts that open and close turned around so that I am using the unused sides of the contacts. These refurbished contacts look way better than what switch contacts looked like previously.

So far, so good.

I installed the actuator lever and the lower housing, then checked the switch operation with an ohmmeter multiple times.  The switch operated perfectly each time.

Satisfied with the rebuilt switch I sealed the two housings with a bead of black hot glue.  This type of glue does a great job of hold things together but can easily be peeled off it access to the switch contacts is ever needed again.

The next step will be to carefully connect the switch wiring (including the two wires to my arc suppression device) without overheating the plastic switch housing.

I am also designing how I will re-attach the switch to the Beomaster 4400 switching assembly. I will need to somehow strap it in place.

Tuesday, April 21, 2020

Beomaster 4400 Type 2419: Rebuilding another power on/off switch

I looked over the three broken Beomaster 4400 power on/off switch components. That included two sets of pretty badly charred contacts. When I first looked at them I figured I would just toss them away. Fortunately I waiting and thought about it more. I also did a little research and confirmed that I can't just go find and purchase replacement contacts. The best thing would to be to try and salvage what I have. Then I remembered one of the most important tools in the workshop...the Dremel.

I used the Dremel and an ultrasonic cleaner to refurbish the damaged switch contacts. The results came out pretty good I think. I finished up the cleanup with a Deoxit treatment on the contacts and here is what they look like now.

Here are the cleaned up switch housings and actuators.

I have a decent selection of parts now to come up with a working Beomaster 4400 power on/off switch.

This set of components looks like my best bet.

The large switch housing piece has the hole in it from a burned contact but the rest of it looks pretty decent. After I re-install the contacts I can fill that hole with some epoxy.

For mating the two switch housing halves I can use a bead of hot glue again but I am thinking about drilling and tapping three M2 screw holes where the wide part of the housings (where the old mating tabs are). If I go that route I will use nylon M2 screws to join the parts.

Once I have the stationary switch contacts pressed back into the smaller housing I will solder on some connection wires to use when I place the switch back into the Beomaster.  I will make sure I protect the plastic switch housing when doing that soldering this time around.

Monday, April 20, 2020

Beogram 4002 DC Motor Restoration: Oil Infusion of Bearings, Replacement of Spark Snubbers, and Repair of a Disconnected Pickup Coil

A Beogram 4002 DC Motor arrived from Michigan. This shows the motor as received:
A bench test quickly revealed that the rotor was mechanically impeded, i.e. the motor would not spin at all when connected to a bench supply.
I opened it up and found that someone already had given it a try:
The brushes were bent out of shape and the pickup coil pin broken out. I took everything apart to get to the bearings:
The bearings are the two small donuts on the black pad. When I pressed out the brush carrier, the coil next to the missing pin turned out to be loose and disconnected.
I immersed the bearings into motor oil and pulled a vacuum:
Immediately, vigorous bubbling started indicating that air was drawn from the porous Oilite material, making room for oil diffusion into the bearing.
After about 72 hours the bubbling stopped and I extracted the bearings from the oil:
Before reassembling the motor I cleaned everything in the ultrasonic bath to remove the oil from a previous lubrication attempt, and then I reinstalled the ripped out pickup coil. Since the very fine leads of the coil were ripped short, I needed to extend them with some thin wire to be able making contact with the contacts on the brush carrier:
I put the lower bearing in place and pressed the brush carrier back in. Then I installed the straightened brushes, put in the coil and soldered one of the leads to the contact on the carrier.
I pulled the other lead through the hole left behind by the broken out pin and then glued the lead into the hole with some superglue gel to fix it in place:
Then I tested the resistance across both pickup coils:
This measurement yielded 34 Ohm, which is a normal value (it typically ranges between 32 and 45 Ohm depending on the vintage of the motor). So far so good!
I put the motor back together and installed in one of my 4002s for a RPM stability test with the BeoloverRPM device:

After about 24 hrs I was able to plot the blue curve in the graph below. Not very Beolovely at all!
This measurement result suggested that one or more of the spark snubbers was shorting out occasionally with an increasing tendency. I took the motor apart again to replace the spark snubbers with modern transient voltage suppressor (TVS) devices. This shows the rotor with the original snubbers installed:
I removed the snubber ring. This shows it together with the new TVS devices prepared for soldering across the rotor windings:
I soldered the TVSs between the winding poles:
Now it was time to reassemble the motor and run another 24 hrs test. The red curve in the graph above shows the result of this measurement. This is as good as it gets with the 4002 DC motor. This motor is ready for duty again!

Beomaster 4400 Type 2419: Power On/Off Switch Woes

This Beomaster 4400 would be ready to resume testing again if only its power on/off switch would work properly.

If you remember the original power on/off switch caught fire and had badly burned contacts.

For the replacement power on/off switch I pulled a switch out of a spare parts, donor Beomaster 4400 unit. I had no idea of the condition of that unit and when I opened up the power switch it had some pitting but overall wasn't too bad. A little cleaning and it was ready to install and that should have been the end of it.  It wasn't of course :-).

While the replacement switch initially measure a nice 0.1 ohm to 0.2 ohm "On" resistance when it was installed and in use the switch became unreliable and needed some fiddling with the buttons to get the Beomaster to turn on. Something mechanical was not right.

My next plan was to grab a second replacement, donor power on/off switch from another parts unit. The switch didn't look too bad until I checked it out with an ohmmeter. Off measured fine but the "On" resistance jumped around in the 100 to 300 ohm range. Not a good reading.

So I opened up this third Beomaster 4400 power on/off switch and it was about as badly burned as the first one.

Here is the third switch (second replacement candidate).

Very ugly and very disappointing to say the least.

I don't even want to try to clean that up.

When I reopened my first replacement candidate switch its contacts still looked pretty good but the switch contacts had shifted position so good contact was not being made. That explained the mechanical inconsistency.

I had to stop and think about my options.  I could really go for a nice 3D printed replacement switch about now.  Unfortunately that doesn't exist (yet).

My best chance here is to select my best contacts and my best plastic housing components to put together a solid working power on/off switch.

I think my first replacement switch attempt failed because I soldered too many connections to the outer terminals.  They heated up and then shifted internally which caused the poor switching performance.

This time I will make sure to make the other connections away from the switch and just attach two wires to the switch contacts. In addition I will use some heat protection while the contacts are soldered.

Here are my collection of Beomaster 4400 power on/off switch contacts.

If I turn the best set of contacts around I will have fresh new surfaces to mate for the power on switching. I will clean up the switch housing on the lower right to use in the new switch assembly attempt as it is the most structurally sound.

Another problem involving the power on/off switch that I will have to solve is remounting the switch on the switching assembly.  There are damaged mounting tabs so I will have to construct something to secure the switch when I mount it.

Sunday, April 19, 2020

Beomaster 4400 Type 2419: Finding some power grounding problems

In the last post I ended with being successful in playing music through the Beomaster 4400 via an iPod Nano connected to Tape 1. The power on/off switch was not making good "on" contact and I had to help it connect by moving the "Off" switch very slightly.

I had intended on proceeding with some of the other audio source tests before revisiting the power switch but to my surprise the FM tuner was not functioning. Time to go over the Beomaster 4400 wiring again.

I soon discovered that I had a power grounding problem. The +15VDC regulator was no longer putting out +15VDC. It was at +22VDC and the regulator ground did not measure to the same power ground as the rest of the Beomaster 4400 power ground points. The Beomaster grounds should all be connected and also connected to the metal frame.  This Beomaster 4400 was not.

Carefully going through the boards again I discovered two broken traces on the PCB 5 circuit board. Both traces were for power ground and that explains the problem.

I'm not sure when exactly the traces failed but I believe it occurred when I was having the problem with the power on/off switch and when the fault relay was rapidly toggling. After that incident I did not notice the broken traces but I see them now.

These first two pictures are of a broken ground trace at the +15VDC regulator ground connection.

This second broken trace is at the ground connection between the FM3 PCB and the FM2 PCB.
The FM3 PCB gets its power ground from PCB5 via P9-2.  Power ground on the FM3 PCB routes to P5-5 back to PCB5 and over to the FM2 PCB connector P2-2.

The picture below shows the broken trace between those points.

That explains the problem with the FM source.  It doesn't expose the source of the problem though.
I repaired the broken traces but I will need to check out the FM1 and FM2 boards to see if they caused the problem or are the result of a problem somewhere else.

Too much current must have flowed through the broken traces. Perhaps they were already weak from an older problem. Interestingly during my testing of this Beomaster none of the fuses have blown during these power problems.

Here are photos of my repair of the broken traces.

The +15VDC regulator ground lead now measures as connected to the rest of the Beomaster 4400 power grounds again. I also measure continuity between FM2 PCB P2-2 and FM3 PCB P5-5.

As I mentioned earlier, I will have to wring out the FM1 and FM2 boards for any shorts to ground. I will check out FM3 as well just for good measure but it didn't have any signs of burned ground traces.

While I had the Beomaster 4400 front panel loose again I connected up my DMM to check the operation of the power on/off switch using the ohmmeter function. It confirmed what I had been observing when applying actual power on the Beomaster. The "Off" switch always disconnects the switch contacts but pressing a source switch (like Tape 1, Phono, Tape 2 or FM) does not. I can get the switch to make "On" contact by selecting Phono, then slightly press down on the Off button until I see the contacts engage on the ohmmeter. So there is definitely a mechanical issue there. That means removing the power on/off switch again and taking it apart.

Monday, April 13, 2020

Beomaster 4400 Type 2419 - Power on testing: Part 2

The Beomaster 4400 is finally reassembled for a second round of power on testing.  In the previous post I had to replace the power on/off switch because the original switch was badly burned.  The new switch is a rebuilt switch that I tested in the last post.

While planning the reassembly of this Beomaster I looked at various options for preventing deterioration of the power on/off switch contacts during switching. I know there is arcing going on when the mechanical switch makes the line connection to the Beomaster power transformer. The original switch was totally burned up and the replacement switch also showed signs of arcing on its contacts. I cleaned and smoothed the contacts the best I could and I don't want another one of these switches to burn up.

A number of audio manufacturers used RC snubber devices and small safety capacitors across switch contacts to reduce the arcing when the switch is operated. In my investigation of those devices I am not convinced they are as effective as I would like them to be.  I finally found a device specifically for arc suppression across contacts. It is called the NOsparc GGXAC1F480.  It is designed for use in protecting the contacts of relays on HVAC units so I can see where someone would think it is overkill for this power on/off switch case ;-).  Never the less I was impressed by the Arc Suppression Technologies video that showed how effective their arc suppression device is. I called the company up and spoke with one of their engineers to find out if their product would work in my Beomaster 4400 on/off switch application. He confirmed that it would work so that is the route I took.

The NOSparc device is pretty good sized as seen in the photos below. I found a good mounting spot on the bracket that holds the reservoir capacitors then tapped a couple of M3 holes in the bracket and mounted the NOSparc device right there.

Here is the NOSparc device connected to the Beomaster 4400 power switch. I attached small connection terminals to all of the wires that connect to the switch. I also used a larger gauge jumper wire between the switch contacts from what was there originally.

I reapplied line voltage to the Beomaster in steps like I did the first time...a variac to slowly increase line voltage while monitoring current and a dim bulb tester.

No issues applying the power that way so I removed the dim bulb tester from the circuit and just connect the Beomaster directly to a line outlet.

The Beomaster turns on and I was able to check voltages.
Here are the rail measurements again.

I also checked the 24V input to Beomaster 4400 +15V regulator.  The voltage is good and the measurement stays at 24V this time.

Confident in the results so far I adjusted the no-load current for the output amplifiers to 14mV across the emitter resistors (on both the left and right channel).

After that I connected an iPod Nano to the Beomaster 4400 Tape 1 source input and listed to it via headphones. Finally...good sound is emitting from this receiver again.

Now for a bit of bad news :-(.  While I was testing voltages on the Beomaster 4400 the power switch started to act up again and would not always switch on.  It has no problem switching off but the power on function is proving to be unreliable. I can tell this is a mechanical problem so I see myself replacing this Beomaster 4400 power switch at least one more time.

I can continue to get this receiver to come on so I will be able to continue testing the Beomaster 4400 performance. Now to start looking for another power switch.

Sunday, April 12, 2020

Beogram 4002 DC Motor Restoration: Oil Infusion of Bearings and Installation of New Spark Snubbers

A Beogram 4002 DC motor arrived from Washington state for a restoration. This shows the motor as received:
A bench test revealed the usual squeaking bearings, so I took the motor apart to extract the bearings for oil infusion under vacuum:
The two small donuts on the black pad up front are the bearings. I immersed them in motor oil, and pulled a vacuum:
Immediately, vigorous bubbling started, indicating escaping air from the pores of the Oilite bearing material. This escaping air makes room for oil diffusion into the bearing. After about three days the process stopped and I extracted the bearings:
I reassembled the motor and installed it in one of my Beogram 4002s for testing with my BeoloverRPM device. It allows logging the RPM over extended periods of time. The blue curve in the graph below is what I measured after about 24 hrs:
Not a very happy result. So I opened the motor up again for replacing its spark snubbers with modern transient voltage suppressors. This shows the rotor with the original suppressors mounted:
I removed them and prepared the new devices by bending out their solder tabs a bit:
The I soldered them across the rotor poles:
I put the motor back together for a new test. This yielded the red curve in the above graph. Much better! This motor is ready for duty again!