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I’m restoring another 5005, and I elected to try another technique for retrofitting a TR11 BC547 transistor into the datalink path of PCB1.
I started with a new BC547 transistor I bought from Mouser. When looking at the flat face, the pins from left to right arre (C) Collector (B) Base and (E) Emitter.
I unsoldered R42 on the side nearest the I/O cable, and drilled a small hole 2-3cm from it, taking care not to pierce any existing traces, or the adjacent R45 resistor.
Next, I took the BC547 and placed the (C) pin through the vacant R42 hole, and the (B) pin through the newly drilled hole. I bent the (E) pin towards the R42 resistor.
Turning the board over, I unsoldered the jumper adjacent to R30, and squeezed a 10K resistor through the hole. Theere was just enough room to have both the resistor and jumper in the same hole, which I resoldered in order to make a permanent connection.
I covered the resistor lead with heat shrink, and soldered the end to the (E) pin of TR11. This heat shrink is just a security blanket to prevent future shorts on the board.
I finished with attaching the TR11 (E) pin to the R42 resistor, and covered the end with a piece of heat shrink. IMHO, this looks much nicer than the other solution.More “remote” work – today it’s a Master Control Panel 7700, which may have been living in a moldy attic for a few decades. Seems to mostly function, with a few non-working buttons. I thought I’d try my hand at ribbon replacement, given the crusty and brittle original ribbon cables. I did the easy one first, just to see how it would go.
On to the more complex cable controlling the LCDs … big mistake. One dead LCD later, I concluded that there’s no obvious way that I can see to replace the connection to the LCD screens except to splice into the existing ribbon cable. The LCDs seem to be connected to the ribbon cable using some sort of random membrane that I cant make sense of. Oh well – thankfully this was just a poor-condition unit I acquired to verify the MCL output, which still works.
A Beolab Terminal that I bought for $50 had lost a battle with a glass of some sort of sticky cocktail. Half the buttons were non-responsive, so I took it apart and bathed the components in Iso. Luckily all the traces were undamaged and tested fine.
Everything looked and worked great after re-assembly.
I still need to re-tape the button pad. The original is very much a one-time-use material. Does anyone have a “favorite tape-medium” they use for this purpose? I was just thinking clear or perhaps thin black packing tape would work fine, and provide a bit of protection.Received a complimentary Form1 with another purchase, it the usual condition – without foam. After reading the archives on the issues everyone was having with the original foam, I bought a cheap set of Logitech 150 foam replacements for $10-for-2-sets, and affixed them with trim adhesive. Not ideal nor exact replacements, but serviceable given the time and effort I was willing to put into it. If someone ever has a better solution, I can always shave them off. Unit seems to work fine without the upper cushions, but then, I’m not overly concerned with comfort, fit and finish of this particular headset. Hopefully someone else can find this information useful to repair their sets without foam.
Just to document the needed changes to add discreet “Play/Off” function to an early Beogram, these are the steps.
The “Play” button is fixed in place with a black bracket, which holds the button in the appropriate place on the front panel.
It’s wired directly to the “Play” button on the top surface, so it only can perform the same function as the “Play” button under the cover. The large PCB3 is removed by carefully moving the 4 black tabs that hold it firmly in place, and wiggling the PCB up and back out of its mount.
I was surprised to see that these buttons were exposed – typically, they are covered with black tape to help hold them in place (and probably also to keep moisture and debris out from them – they are a slightly cheap design, and can easily be made inoperable with a bit of contaminant). I fixed the vulnerability by adding a bit of electricians tape myself. Next, I severed the connections of the small PCB, and added two additional wires to it, per the new design specification.
Last, I ran these new wires back through the cover, using the same clamps used for the existing wires. A bit of trimming later, and everything was hooked up per the late-model specifications. A fairly straightforward modification.
I’ve elected to not add an RIAA to this unit, as I need something I can use to test with earlier variants of Beomasters with built-in RIAA. So this unit is upgraded as much as it can be, and ready for work.On to the final steps – finish routing the wiring, and connecting the RIAA. The original wires ended up being just a bit short to wire around the underside of the board as I would have liked, but at this point I didn’t care – I wanted to see if my upgrade had worked!
With the wiring complete, I re-calibrated the board based on the service manual (recall, I had swapped out the original 5500 board with a later board that had a discrete “Play/Off” feature, like the Beogram 7000).Moment of truth! Triple check to make sure everything was as-planned, and hook it up to my Beomaster 7000. Everything worked as expected – Lovely! Special thanks to @adyan for making a few RIAA boards for this project. I have no doubt the TX-2 will work as well, but I’ll go through the steps to document the process.
On reading, re-reading, and re-re-reading the latest version of the service manual RIAA schematic, I came to the conclusion that the “Old Version” PCB 11 would need a modification in order to electrically emulate the “New Version” mute circuit. The original PCB11 is wired such that LG and RG from the stylus are not connected to chassis ground or shield ground until the wiring reaches the Beomaster. Further, the mute circuit is implemented by grounding the L and R to LG.
New boards designed for dual use as RIAA or non-RIAA implement a sightly different protocol, which necessitates the cutting of a wire bridge between some of the solder pads to achieve the desired circuit. Also, the LM and RM wires work a bit in “reverse”, where the mute circuit acts to ground the amplified signal on mute activation, before it reaches the output cable. The only way I could see to mimic this implementation was to grind a cut on the PCB itself, isolating L and R from the original mute circuit. [EDIT – I’ve made a small change to the schematic, and included both versions for comparison]
Original Version combines L+ R during ‘unmute’ – potentially undesirable:
Final Version – isolates L&R outputs during ‘unmute’:
With that mental hurdle cleared, all that remained was to wire PCB11 with a jumper between LG, RG, and chassis ground, which meant that the mute circuit was now also connected to chassis ground. I considered that LM and RM are really the same signal and could actually just be activated together using a single wire [EDIT – I’m not actually sure this is 100% true in all scenarios, although it did appear to function correctly], but I went ahead and wired a separate LM and RM to the mute switch, per the schematic. [EDIT – even though the Original Version worked as wired, I realized later that I’d connected L+R in a way that might lead to some odd behavior when unmuted, so I moved one of the channels to a new position, where they would be isolated during ‘unmute’. The original wiring solution didn’t seen to affect the performance of the circuit, but the final version is representative of the original schematic] With L & R inputs reattached in their original spot, I was set to finish wiring up the RIAA.Original Version:
Final version:
Admittedly sloppy, but it all toned out properly, so I left it as-is, and re-installed PCB11.I decided I’d upgrade the 5500 first, on the thought that the wiring would be a bit easier. This proved to not be the case – B&O supplied the original output cable with an extra unattached blue wire, which was not connected to pin 7. I made the decision to disassemble the Din connector to attach it. This is strictly not necessary for my planned use, but I wanted to observe the convention that “Beograms with RIAA run Datalink on Pin 7”.
Upon disassembly, I found that not only was the blue wire not attached, it was truncated to the point where I’d have to un-solder all the pins and re-cut them to the new length. This is fiddly work which I’m personally not terribly fond of. I just happen to appreciate the coolness of a removable pin 6 and 7, and want to preserve that feature. I wired up both pin 6 and 7 with the blue and yellow wire. Without thinking about it first, I moved the yellow wire to pin 7, and soldered the blue wire to pin 6. Inside the turntable I’ll have the blue wire available on pin 6 for a future new project I’m dreaming about.
After a bit of squinting, cursing, and double checking my work for shorts, I was ready to reassemble the connector. Then came the “one-way” step of snipping the cable at a point I thought would provide enough wire on either side of the RIAA card to connect everything together using the original wires.
Next step is adding a power plug for the RIAA amps I purchased from adyan. His design mimics the original RIAA boards used in the 6500-7000 models, and therefore also needs a 22V and 12V supply, which it gets from the transformer on a plug from PCB2. None of my US-Spec TX2 transformers – early or late models – have this 2-pin plug, so I had to tap into the PCB at the correct spots. Here again I contemplated drilling PCB2 to add a surface-mount plug. And once again, for simplicity I opted to add a pre-wired 2-pin connector instead. I attached the red wire lead to the existing 12V wire hookup (post IC), and the black wire lead to the 25V output from the rectifier. This way, Red would consistently be the 12V supply. The plugs are male/female, so there’s no way anyone could accidentally feed a 25V input to PCB1 ground by mistakingly hooking up the incorrect plug.
With these straightforward updates completed, I’m ready to tackle installing the RIAA board. I’ve opted to upgrade my 5500 and TX-2 simultaneously, in order to teach myself a bit about both upgrade paths.Here’s a “Old vs. New” 59XX schematic connecting the CPU to the Datalink bus. The new schematic includes a 547 transistor and 10K resistor hardwired to 5V, so it will be active as soon as the Beogram is plugged into power.
OLD SCHEMATIC
NEW SCHEMATIC
It turned out to be a fairly straightforward process adding a transistor to PCB1. I took a 547 equivalent transistor, and soldered a 10K resistor to the B pin, and added a bit of heat shrink to prevent a short. Next, I repositioned R42 by removing the Datalink bus leg from the board, and soldering it to the C pin of TR11. Last, I placed the TR11 E pin into the now-empty hole which previously connected R42 to the Datalink bus, completing the circuit. I contemplated drilling holes in the board and routing the wire underneath the board, but in the end my eventual solution was much simpler to execute, and I think it turned out looking OK – the parts are basically in the same spot they would appear in a later board, so it will be simple enough to understand what the retrofit’s purpose is. This is a picture from a 5005 board I had retrofitted earlier:
With the Beogram power supply, the story is much the same as the main PCB – the supplies all have the same basic capability across models, but depending on the model and region, the way they were wired varies slightly. With the deployment of an On-board RIAA of the 6500, it became necessary to power the IRAA via two power feeds from the PS. This necessitated the inclusion of a small 2-wire pin to the PCB, from where the RIAA could be powered
Of the US-based TX-2 that I’ve seen, it appears that both early and late examples utilized the power supply setup as seen below, irrespective of which generation main PCB was installed. This supply was wired for 120V, with a large fuse taking up much of the PCB #2 real estate, and no support for an RIAA hookup:
Later Euro TX-2 examples appear to have the 2-pin RIAA hookup, as shown here (photo 1 supplied by adyan, who has extensive knowledge on RIAA for these systems, and has supplied me with a pair of boards for this upgrade)
Here is a picture of a BG 6500 PS, which resembles the example that adyan has in his late TX-2, and also has the 2-pin power hookup.:
These 2-pin RIAA hookups draw from power points which are readily accessible from any of the TX-2/5500 ps, but it does require a bit of retrofit work to tap into them. My plan is to solder a plug onto the board that will allow access to the same power that the boards with built-in RIAA hookups have. On the board below, soldering a hookup to the bus leading to pins labelled 1 and 3 (center of board) of the IC I/O will give the needed result of having a 22V and 12V supply, respectively.
