Question About Beogram 8002 Recapping

[Glitch]

marcham wrote:

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?

Apologies in advance it you already know this… What I consider “debugging by part swapping” would be something like blindly replacing any component because it might be the one causing the problem. For example, if you aren’t getting a good 5v signal, you could replace D16 to D19 with new parts. It is unlikely that this would fix the problem. Instead, I think that it is better to understand how the power supply works, then devise and run tests to verify it it is working or not. The 5v supply is very similar to that described here. Using your meter, check to see if the voltages and waveforms are what they should be. If not, the problem could be in the circuit or external to it. Isolating the power circuit would be the next step. I would start by removing connector P2 and verifying the output of the rectifier and transformer. If that checks out, remove P2-2 (pin2 2 of connector 2) and reinstall the connector. This isolates most of the 5v power supply from the external circuit (it also provides a convenient place to measure 5v current draw later). Retest the 5v power signals. Still no joy? The problem must be in either the power supply circuit or reset circuit. Lifting a leg of R75 further isolates the power supply from anything else. If the power supply still doesn’t work, there are only a couple of parts that could be the problem and it should be pretty obvious which one(s) based on the meter readings. Now is the time to start removing, testing, and possibly replacing individual components (based on data instead of hunches). I purposefully went into painful detail here to illustrate an approach that is based on 1) understanding how the circuit works, 2) measuring to verify proper operation and 3) isolating the circuit for ease of debugging. Also, note that there was a minimal amount of soldering involved. Much of what I described above is implicit in the advice that you got from others. Hopefully my explanation provides insights into why things are being suggested.

Based on your posts it sounds like you are getting more serious about this hobby. Check out the Digilent Analog Discovery. It might be useful to you. In general, anything that it does can be done better with dedicated bench equipment. However, everything that it does, it does well and is often all that is needed.

Glitch

[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!

• This reply was modified 4 weeks ago by Dillen.

[Glitch]

marcham wrote:

I’ve taken the time to improve my soldering skills and learn how to better care for my equipment.

That should help with making the rest of the debugging more effective. At the very least, it should make working on things more enjoyable.

marcham wrote:

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.

That is good to know. It is helpful to people trying to give advice to understand what resources (both skill level & equipment) are available.

marcham wrote:

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!

It sounds like you are taking the right approach. Even if a repair doesn’t turn out to be successful, if you learned something in the process, it is a win.

marcham wrote:

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.

That’s great news. I’m sure it is a big relief to you.

marcham wrote:

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.

This could be example where you could resist “parts swapping”. One could just order the part from Beoparts (now: Danish Sound Parts) and swap parts. There is a decent chance that this will fix the issue. Alternatively, you could run tests to check if the circuit is operating as expected. Use the camera of your cell phone to check if the IR (transmitter) LED is lighting up. If the LED isn’t lit, it is getting power or is the component bad?  If the LED is lit, then hook up your oscilloscope to see if the IR receiver is reacting to changes in the light received. These circuits usually work by blocking or passing light between the two parts. You can use B&O’s “light blockers” or do it manually by inserting something like a piece of cardboard. The general idea is to think of and run tests that enable making better (data driven) decisions on how to proceed. If you do end up replacing the part and the machine starts to work, run the same tests again on the now working machine to gain the experience of what the signals should look like. BTW, a second, properly working, machine is an invaluable luxury for debugging purposes (if you are looking for an excuse to buy more B&O stuff 😉 ).

marcham wrote:

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.

The problem could be a number of things. One guess would be a related to the motor control circuit not always getting a clean feedback signal. It could be a cracked trace that is hard to see. Below is an example of one that took me a while to find.

The open trace was under the solder flux residue and not apparent until I cleaned the board. I wouldn’t have known to look in this spot unless I ran tests that indicated that there was an opening “somewhere” along the circuit that was causing the signal not to get through. I’ve found other really unusual things causing open/intermittent circuits like broken pins inside of a connector and a failure of plating of an edge connector pin. Hook up your oscilloscope to the tachodisc receiver and observe the signal when the motor is turning properly. Prod the board to recreate the failure and observe the signal. Don’t be afraid to change the place where you are making the measurement (i.e. on either side of the connector along the signal path) as this can often provide clues. Another debugging method possibility is to hook up your scope to monitor voltages and see if they change while prodding the board.

It is worthwhile to pay attention to the information included on the schematic. If B&O went through the trouble of indicating a voltage value or including a plot of what a signal should look like, it is a good idea to make the measurement for yourself. This is one of those things that seems like it would be obvious, but people often miss. Also, the passing along the results of those tests (both good and bad) is helpful to those trying to provide debugging advice.

Glitch

 

• This reply was modified 4 weeks ago by Dillen.

[Author]

Posts