Question About Beogram 8002 Recapping

[marcham]

The proper fuses (T300 mA/250V) arrived today; unfortunately, they blow when the power supply is connected to the board. The fuse is okay if I plug in the power supply without connecting it to the board, so I assume there is a short or something somewhere.

This is where my already limited knowledge hits a wall, so I’m hoping for any recommendations. My only thought would be to pull the caps for testing and then start testing the transistors and diodes. Any suggestions on where to start testing or specific components would be appreciated— any way to hunt this down without removing and testing so many components?

Thanks, all.

• This reply was modified 6 days, 1 hour ago by marcham.

[Mark-sf]

I would start by leaving the supply disconnected and measuring resistance on the board side between each pair of windings pins looking for a short. Ex: P7 pins 2 and 4. Then you can desolder to find the shorted part.

[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,

[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!

[spassmaker]

Hi

I’ll try to help a little bit.

P7 – 12 and P 7 – 6 go to ground because

P 7 – 6  is Ground

P 7 – 12 has a conection to ground via the motor coils ( 0 L 1)  related Plug ( P 4 -2; P4 – 5) . Have not measured the coils so far but could be in around 200 or less Ohms.

So desolder one leg of D42 and check for a short.

 

A common issue, what I had already twice for what reason ever, is D 20.

This is a Z Diode  6,3 V and a protective diode for the 5V of Processor and so on.

In case of a overvoltage of the 5 V line this diode is shorted and the fuse could trip to protect the connected uPC and others.

So check D 20

 

Kind regards

Christian

[Mark-sf]

marcham wrote:

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!

Yes, P7 is the only connector you should have removed. I would check for losing the short by selectively removing the gnd sides of D20, 0C1, 0C2 and 0IC1 to find the defect.

[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.

[Mark-sf]

Putting C24 in backwards would definitely take out the F1 transformer fuse but could have damaged part of the diode bridge or transformer secondary. Are you getting AC voltages across each transformer secondary? If so when you connect P7 back only, what voltage are you seeing across C24?

[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]

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.

[Mark-sf]

This is where it gets tough as you may be hitting your original problem. I would check how much current you are drawing on P6-1 as you may have a bad regulator. Normally F1 (800ma) would blow if there was a large draw due to a shorted transistor such as the Lift driver TR9. Also is it at .5v just plugged in?

[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.

[Mark-sf]

The 7805 regulator can source more than 1A of current if working properly which is more than enough to blow the fuse before its short-circuit protection kicks in. I would confirm by measuring the output current when you plug the TT in and see if it exceeds 1A before dropping. If it doesn’t I would replace the regulator. If it does you are not going to have to start disconnecting 5v loads on the board and testing for 5v.

[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!

[Mark-sf]

You measure current by putting your meter in series with the circuit. This means disconnecting the regulator output, soldering a jumper and using your probes in series. If you have alligator clip ends even better.

[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.

[Mark-sf]

I’m afraid that reading does not make sense assuming you are measuring mAs. What you are looking for is not the steady-state reading but a current jump as you plug it in. I would use a second meter or Oscope to catch the drop in voltage at the time. At this point given your limits and these imperfect medium, I would replace the regulator just to rule it out as it’s very cheap.

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