[marcham]

Hey Martin, I really appreciate the response.

Let me know if I’m misunderstanding your suggestion, but the 15V rail seems to work perfectly; it’s only the -15V that is MIA.

Here is a copy of the circuit readings I previously provided. 0TR1 seems to be working fine.

As for a break, do you see anything odd within the circuit readings?

Hoping between these and the section included above, they hold a clue.

Thanks again!

• This reply was modified 2 days, 15 hours ago by marcham.

[marcham]

I’m adding more information in the hope that someone can help me with the missing -15V rail. Three lines leading away from the power section, near TR21, are 00, DD, and II.

Tracing down II leads to the CPU outputting either 0V or 2.5V via the On/Off pin.

DD connects to the +5V supply and leads to an upper section that I have included below with readings. 00 also leads to this upper section, and I have included the readings as well.

From 00 is PP, which leads to the braking circuit. It feels like I’m getting close, as another problem right now is a constantly spinning platter.

From DD is NN, but that appears to lead to ground.

As always, any help is appreciated, thanks!

[marcham]

Just popping in with an update.

Still at the same point but been poking around the board and reading voltages.

I noticed that the main chip’s voltage on pin #38 (on/off) swaps between 0V and 2.5V. However, the chip seems to be getting its primary 5V at pin #30 without issue, so could the chip be the issue in any way? I tried reseating it, but it did not change.

Poking around TR19 and TR21 trying to figure out why there is still no -15V signal. I feel that’s the heart of the issue.

Thanks, all.

[marcham]

Hey Glitch, Thanks for the explanation; that makes sense.

Looking into TR21, the signal sits at .71V in standby and drops to .08V when switched on with the tonearm in motion. All readings in the diagram were taken in standby mode.

To help visually, I recorded a short two-minute video.

[marcham]

Afternoon, all. Hope everyone is having a good holiday.

I had the time to dive in and take more voltage readings.

As someone who doesn’t know exactly how a circuit flips a voltage from 15V to -15V, I would say that something looks a bit off around TR18, even though that transistor tested well. But, again, what do I know? 🙂

Any insight appreciated. Thanks, all!

[marcham]

Thanks for the info, Glitch. Checking at TR21, there is no voltage when the Beogram is on or off. If I check pin 38 of the CPU, the voltage is 2.5V when off and 0V when switched on. I can confirm that 5V is making it to the CPU at pin 30. As for C29, the voltage stays stable at all times around 24V. I’m not sure if this helps illuminate a picture.

I’ll try to test some other areas within the circuit, but hopefully, the above is a clue. Seeing it connected in the block diagram, I also tested transistors TR6, TR22, and TR23 — all look good.

I’m trying to find a fault that would cause the display to always show four red dots and the table to constantly spin at a slow speed, even when off.

[marcham]

Hey, Glitch (and others),

It has been a while since I popped into this thread, as I’ve had some of my projects on hold. I was waiting on parts for the Beogram and then had to solve an issue with the ribbon cable connecting PCB2. Luckily, all that has been handled, and I’m down to troubleshooting what is hopefully the last issue, and I need a bit of assistance.

Long story short, there is an issue with my -15V rail; I’m getting 5V and 15V fine, but the -15V is nonexistent. I’ve uploaded a photo of the schematic for additional detail. Red spots are where I have tested for voltage and only received around .75 V. The blue spot is an example of a place I tested and received +15V. The components highlighted in green appear to be working when tested.

Any thoughts? I figured if there were an issue with the 15V rail, I would find it in one of these highlighted components. Any advice?

Thanks, all,

[marcham]

I appreciate the feedback, Dillen. Luckily, I got everything sorted out!

I am posting the solution here in case anyone else has the same issue. I solved the problem by better isolating the tweeter diaphragms’ speaker wires. When replacing the diaphragms, the wires must run down a metal channel on the front of the tweeter plate. I was isolating the wires in this channel with heat shrink tubing, but I also needed to ensure the thin wires weren’t coming into contact with the edges of the round center cutout.

You can prevent contact with very thin heat shrink tubing or electrical tape.

[marcham]

Posting in the crossover schematic. While I redid the caps, everything else is original. As I mentioned, I redid the tweeters with new diaphragms, but I would assume a signal is getting to them that shouldn’t, making it the crossovers.

[marcham]

​Thanks, Glitch; I appreciate the feedback and help along the way!

While I’ve made mistakes throughout the process, and the board has certainly seen better days visually, I’ve taken the time to improve my soldering skills and learn how to better care for my equipment. Funny enough, I have quite a bit of repair gear sitting around now (even if I don’t know how to use it all 100%): a soldering station, variable power supply, multimeter, component tester, tone generator, and oscilloscope. Each project I tackle has allowed me to move forward with more knowledge and learn to use more of my gear. In the meantime, I’ve brought a Beocord 9000 and a pair of Beovox S75 speakers back to life, so that’s been a nice win!

The partial good news: After investigating the board, reflowing joints, and replacing a shot resistor (that component tester is fantastic), the machine shows the standby light when fed power and doesn’t blow a fuse when powered on! The 8002 is now back to the state I received it in, but with new, fresh caps that don’t cause the tonearm to move inward 1 inch and then return when pressing Play. However, it is not all finished, as two other issues have appeared.

​New issue #1 popping up: Pressing turn will spin the turntable without issue, and pressing stop will bring it to an end. However, the Beogram will not play. When pressing Play, the tonearm moves inward and does not stop even when it reaches the spindle. The motor continues to spin, the belt slipping on the spindle as it tries to continue moving it inward. I searched the Beoparts website (now: Danish Sound Parts) and found they sell an IR LED for the Beogram. They note that when this component fails, “the Beogram will not stop the carriages’ travel at the beginning of the record, but instead keep traveling leftwards until it can’t go any further, so I think this could be my fix.

​New issue #2 popping up: A second issue (which might be causing the first) has popped up, too. When P4 is plugged in, and the board is prodded in the same area (as P4), one of two things happens: the platter will change its movement (stopping or starting), or the Beogram will blow its fuse. The latter occurs most often. Do you know what could be causing the issue in this area? I don’t see any obvious solder cracks or visually failed components.

Thanks again!

[marcham]

Thanks, Glitch.

I appreciate you taking the time to share your experience. I’m looking forward to the upgraded multimeter and component tester arriving tomorrow. I also have some new soldering iron tips coming, as the old ones were past their prime and causing heating issues. Luckily, I have a USB microscope, so I’ll take that out and use it to examine the board and double-check any future fixes.

When you say to avoid the urge to debug by part swapping, how would I test components properly then? In this case, I was going to try to trace the failure point from the power supply pins, where I can now detect continuity between two pin pairs, unplugging components as I test them. Is there a better option?

I’ll be sure to ask questions as I go. I’m busy this week, so all the fun might have to wait until next, but I’m looking forward to it. Frustrated since an electronic failure hasn’t happened to me like this in the past. I have a few B&O things to work on, and this was supposed to be the easy cap swap out, but oh well! Thanks again!

[marcham]

I discovered that the odd reading had something to do with the black connector on the board for PCB2. With a bit of pressure applied, it did indeed show the amps increase to a healthy sub-100 mA level. I decided to re-solder the connector, but unfortunately, an ultra-small solder bridge caused two pins to connect and a short to occur. So, now I’m tracing down another short. To make it worse, I’m not sure which two pins connected.

Rather than bother everyone here about it, I’ve decided to upgrade my equipment to a proper multimeter with capacitance testing, grab a small component tester, and an ESR meter. Hopefully, this will help me track down the problem with greater ease, following the schematic.

And before the suggestion comes through, yes, I would very much prefer to send this board to a trained repair specialist. But my budget does not really account for that. I’m assuming it would be hundreds of dollars to have this board looked at and repaired. If anyone knows that that’s not the case, please feel free to let me know.

If I can get this new issue fix, I may pop back in for help with the original problem. Thanks again.

[marcham]

Thanks, Marc.

Without PCB2 plugged in I get 8.53. When I plug PCB2 into the main board, it drops to 7.57. I’m measuring between the 5v regulator output leg and the board.

[marcham]

Mark, do you measure the regulator’s current the same way you measure voltage?

When connecting my negative probe to ground and the red probe to the regulator output, I can measure 5V, but when I switch it over to the Amp setting on my multimeter, I get nothing, 0 Amps. This is the same with PCB2 plugged in or unplugged.

Is this not the proper way to test it? Thanks!

[marcham]

I’m wondering if it’s the original problem, because the original problem at least had the standby light come on. That’s why I’m going to double check that the capacitor swap out didn’t mess something up, but didn’t see anything my first look.

But yes, if PCB2 is disconnected then at P6-1 I get 5 volts. As soon as I plug in PCB2 via the ribbon connector, it drops to .5 volts.

[marcham]

Had a bit more time to test around with the circuit. I can tell that the 5 volt regulator is outputting correctly and it makes its way to the main board via P2. I can then test the connector that goes to the PCB2 (via P6) and this is where things get odd.

The first pin (P6-1) should send out 5 volts to PCB 2, but it only does this when PCB2 is unplugged. If I test with PCB2 plugged in, the voltage on that pin drops to only .5 volts.

I visually examined PCB2 and I don’t see anything that seems to be improper. I also already replaced the capacitor on that board, which was a pain, but it seems to have been installed correctly. Before anyone asks, yes, I did get the solder on the top side of the negative leg of the cap.

Any thoughts what could be happening here? Thanks.

[marcham]

It lives! Happy to say that I have found signs of life.

I was poking around the board and found some odd signs of continuity around the C27 cap, so I decided to do some investigating. I swapped out C27 for the original cap, and now I have power to the board. This tells me that my method of testing capacitors is obviously faulty.

My meter doesn’t have a proper capacitance mode, so I was simply seeing if the cap would recharge and then discharge. This means I’ll be treating myself to a new meter with a capacitance setting and maybe even a little component tester to prevent this in the future.

Anyway, not everything is working, but things are looking better. I still don’t get a standby LED, but a small light turns on near the tonearm and I can feel the motor warm up if I touch it. I’ve begun by testing all the caps to see the power flowing across them:

• C27: 22v
• C29: 23v
• C24: 12v
• 5v Regulator: 5v

The one cap that doesn’t have proper power flow is the cap on PCB2. When measuring, the cap has 0V across it with the machine off and 0.5V across it with the machine on. I’m assuming this means it isn’t a ribbon connection problem. I also followed Beolover’s advice of snipping the ribbon to make it fit into the connectors better, and it does sit very firmly now.

I’ll see if I can work backwards, discovering why that cap on PCB2 isn’t getting the proper power, but if anyone has any advice in the meantime, feel free to let me know. Thanks, all!

[marcham]

Thanks for the assistance, Spassmaker and Mark,

I checked D20 and D42, and both appear to operate as they should, with continuity in only one direction.

To double-check, is it normal or not to have continuity between P7-12 and P7-6? It sounds like I’m being told it’s normal due to the motor. This would make sense since the continuity between those two pins P7 pins only occurs when the P4 connector is plugged in.

Regarding checking 0c1, 0c2, and olc1, I’ve removed and checked these parts, which seems to operate fine. Although I don’t know if anything on this board would have an affect since the short occurs even with all connectors detached.

Shocked this simple capacitor swap out went down hill, but I can’t complain as I’m learning. Just want to find this short already.

[marcham]

Update: I retested the pins you suggested but left the other connectors plugged in. With this setup, pins P7-12 and P7-6 do have continuity.

The schematic screenshot below shows where P7-12 leads; P7-6 goes to ground. The bottom-most path is from P-712, leading to D42 and a relay. Would you suggest following both paths and testing each component as I go, or is there a more efficient way to test?

Thanks!

[marcham]

Thanks. I checked for continuity between the following P7 pins, and everything seemed fine: 4-2, 1-3, 10-7, 8-9, 5-11, and 12-6. No buzzes or resistance was shown; it was completely open.

Out of curiosity, I unplugged everything from the board so only the power supply and the main board were connected; it tripped. So, it is something on the main board.

I did my best to test the diodes in the two bridge rectifiers, but everything seemed to flow only in one direction, which looked good.

I think something happened when C27 or C24 was installed incorrectly or backward. I looked over the board for any signs of damage, but everything looks good, so I’m still lost.

Thanks again,

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