BG 4002: no Volts to arm motor

9 replies
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Offline
Folke (archived)
Bronze
Posted December 21, 2008 at 02:07 GMT
#1677205

New problems surfacing in my Beogram 4002... First the pickup arm motor, now this.🙁

All of a sudden, the pickup arm motor isn't fed any voltage whatsoever. When I press START, STOP or hold down < or > and measure the pins on the edge of PCB1 leading to the motor, zero Volts (actually 0.3V after pressing STOP). It used to be 5,5 and 12 Volts.

Everything else works - platter motor, all lights, pickup arm down/up. I haven't replaced any components, but I have removed, cleaned, oiled and re-installed the arm motor. No short-circuit in the soldering job for the motor wires.

I can see that PCB1 has heat discolouration around TR20, where the board gets warm.

Maybe I need one of Martins upgrade kits...🤔

Again, any help greatly appreciated! I hope it's a "normal" problem...

W(
Offline
wongss (archived)
Bronze
Posted December 25, 2008 at 23:33 GMT
#1677206

u manage to solve the problem?

All the e-cap in your TT still the old original cap? If yes then suggest you to chnage all the e-cap and tantalum cap.

F(
Offline
Folke (archived)
Bronze
Posted December 26, 2008 at 04:46 GMT
#1677207

Hi, Wongss!

Haven't replaced any components, I'd better leave that to someone who actually knows what he is doing! 😳

DI
Offline
Dillen
BronzeModeratorFounder
Posted December 26, 2008 at 08:46 GMT
#1677208

What type number is your deck ?

(53xx or 55xx)

Make sure you have all connectors on correctly, they will easily mount 1 pin off. Check also the soldering of the edge connectors, they are often found cracked.

Martin

F(
Offline
Folke (archived)
Bronze
Posted December 26, 2008 at 13:34 GMT
#1677209

Hi, Martin!

First my apologies for starting two threads on my BG4002! I saw it as two different problems...should have stuck to one thread for one machine, I guess.😳

It's a BG4002 Type 5511. Here's what happened... Before I did anything, I made sketches and took pictures, just to be sure! I just got this unit, and the pickup arm motor was very noisy. I de-soldered the motor wires from the board and cleaned the motor. I also removed all connectors from the main board and cleaned all the pins, removed the board, visually inspected the components and attached everything again. All connectors were in place, just like in my reference pictures. All pins correctly inserted in the sockets, nothing sticking out on the sides. I was very thorough and checked that the colour-coded wires corresponded with my pictures.

When I installed the motor again, it ran backwards! When I pressed STOP the arm would move towards the platter centre spindle, and vice versa. And I hadn't mixed up the black and red motor wires. I re-checked my pictures several times: black-left, red-right. I noticed that the motor wasn't getting 12V any more, but 8-9V. So I resoldered the motor wires to the board, but reversed this time, and the arm moved correctly for a couple of minutes - and then the board stopped outputting any voltage at all to the tone arm motor. Everything else seems to be getting correct voltage, platter motor etc.

I have removed the motor again. No change, minimal voltage from the main board when I use the controls (typically 0.5-1.5V). The motor will run on a 9V battery, but is very noisy.

If I would venture to guess, I'd say that:

1. I did something to the motor that made it run backwards (but all I did was remove the rear plastic cap, clean the tiny contacts and re-assemble, making sure that the contacts were positioned on each side of the motor spindle).

2. I did something to the board that I just can't figure out.

3. One or several components on the main board failed in the process, causing the problem.

4. ...or something I can't think of!

I have removed the main board again and inspected it under a loupe for loose/cracked solder joints. I found three suspicious looking ones at the control panel connector, and resoldered them. But no change.

I'm sure you can tell that I'm just an adventurous amateur, and that I'm feeling my way forward here...😮

Again, any help greatly appreciated!

DI
Offline
Dillen
BronzeModeratorFounder
Posted December 26, 2008 at 16:35 GMT
#1677210

I noticed you wrote that when you put the motor back together... "the contacts were positioned on each side of the motor spindle"

Obviously, these need to go to their correct sides respectively of the commutator or the motor will rotate backwards and/or short the driver circuit, depending on the motor windings timing and start position for each motor activation. Check this.

Then check the transistors in the motor driver H-bridge. I don't have the manual at hand but I seem to remember that they are the ones in the group near the power resistor and speed changing relay in the above photo. There are 8 in total, 4 smaller (plastic house) and 4 larger (metal house).

Martin

F(
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Folke (archived)
Bronze
Posted December 26, 2008 at 17:11 GMT
#1677211

Thanks, Martin!

It's very possible that I didn't reassemble the motor as it should be, I'll see what I can do. The transistors is this lot, I presume? I guess I've got to call in professional help here...😳

F(
Offline
Folke (archived)
Bronze
Posted December 27, 2008 at 09:55 GMT
#1677212
Martin, you have a PM.
F(
Offline
Folke (archived)
Bronze
Posted December 28, 2008 at 01:05 GMT
#1677213
Picture for Martin. Main capacitor.
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