[alf]

Hi All,

i am working on a BG4002 with speed fluctuations at 33 & 45 rpm !

Martin pointed the finger straight to the DC platter motor and its worn bearings.

fair point !!

After comparing my spare motor with the sick motor I could instantly

feel the difference by finger-spinning its axle .

so far so good – I swapped over the two motors but now I can not sufficiently slowing

down the spare motor ?

new 25-turn trimmer pots – 33 & 45 – were fitted and the speed-change relay replaced by a modern  version.

I asked if by any chance the speed controlling IC 1003C may be faulty but was ruled

out as a likely cause ?

i have to mention that all inputs at the speed controlling IC 1003C show 1 V higher than specified in the circuit diagram !!

as no other suspicious component was found would the spare motor also be in need of new bearings I wonder ??

if indeed its bearings are also worn would that case not rather having a “breaking effect” in the motor with higher friction to be expected and running slower and with speed fluctuations ?

anyone care to share some advice ???

thank you

ALF

• This topic was modified 1 year, 6 months ago by alf. Reason: Forgot to mention

Topic

[Mark-sf]

A relay’s contacts can corrode over the decades especially when not hermetically sealed. This introduces a variable resistance which causes the speed variation. One can affect a temporary fix by carefully cleaning the contacts since the cover is removable; however, this is only a temporary fix and its very easy to bend the thin contact supports making it worse.

• This reply was modified 1 year, 6 months ago by Mark-sf.

[matador]

That’s a fast reply! Thanks.

Ok, I will look a this.

Just for my own knowledge: how is that?
I mean a relay is contact or no contact, haw can he create variations in speed?
Components like capacitors, resistors etc may have their characteristics evolving with heat, time… but a relay, it sticks or it don’t, right? How could he make the speed unstable?

Thanks again.

[Mark-sf]

You most likely need to replace the speed switch relay. There are modern replacement kits available on eBay or Beolover’s site.

[matador]

Hi alls,

Now the OP problem is solved I’d like to add my case.

I’ have two BG4002, one (A) is spinning fine the other (B) not so much. The second (B) was wowing mostly in 45 rpm but now it wows also in 33 rpm. Note that it may be that wowing is more noticeable in 45 than 33 and was ever there.

I know I need to reinfuse the bearings as a starting point but frankly, I’m afraid of this step. So I tried another way.

I swapped parts between A and B: belt, motor, keyboard. B is still wowing.

I did’nt swap the main board because the BG are different types and on the B, there is one of those round flat orange capacitor that is not present on the A board. So there comes my questions:

• Can those old trimmers be responsible for fluctuations? I beleive they can cause imprecise adjustment but once they’re set, they’re set, right?
• what can, as th OP asked, cause fluctuations when the usual suspects (belt and motor) have been ruled out.

Thank you for your advices.

[alf]

I guess I don’t  have to answer Q3 &Q4 ………

not something I suspected, but the shop sold me two 2 KOhm trimmers instead of

5 kOhm trimmers ????????

too much trust is not often rewarded – now both speeds can be set and are in fact

set now.
The W/F is very minimal and will improve further after the DC motor has new bearings.

ALF

[Mark-sf]

Yup need to do some measurements instead of using your ear to answer my questions. Download a turntable App for your phone such as RPM and come back with answers to 3 and 4.

[alf]

My thoughts exactly, the motor should not run faster with a worn bearing !

running faster is not so much the problem because there are trimmer pots to adjust.

the issue is that I can not regulate sufficiently down the 33rpm speed – I can do that with the 45rpm speed though.

i only have one 45 single and can adjust that by ear as I know Bonos voice. To my ears

the speed sounds correct and steady.

the same applies to the 33rpm setting apart from the regulating down issue, which I seem unable to do…it is just a tick too fast, which I can see on a strobo disc and hear – I know McCartneys voice.

both trimmer pots are 5kOhm 25-turn Bourne trimmers.

Both 2R2 and 1R15 are on the edge of their range but it is still too fast spinning.

not sure if that is helping a diagnose ?

ALF

[Mark-sf]

Worn bearings would not cause a motor to run fast. I would approach diagnosing this in this way.

1. Determine if the speed is fast for both 33 and 45.
2. Determine if the speed is faster for 45 to the same extent as it is for 33.
3. Determine what specific speed range for 33 and 45 you can adjust over.
4. Determine whether the speed is steady even though fast.

From the answers to the above, one can pin down the area of the system causing the problem. Feel free to post these and I’ll give you my diagnosis.

[Author]

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