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-   -   Stella ST459 motorboating (https://www.vintage-radio.net/forum/showthread.php?t=197438)

Welsh Anorak 13th Jan 2023 4:54 pm

Stella ST459 motorboating
 
I can't recall the Philips eqivalent of this - it's a 4-speed, 4-track machine. Unusually for 1964 it's transistorised with OC series transistors.

There's a quiet motorboating (no hum) in the background, varying with the volume in stop. In play it's very much louder, but the playback sound behind the noise is fine. Oddly, in record mode the motorboating is almost silent.

The HT is stable at around -16v and doesn't vary. I've done the usual cleaning of switches but no good. The caopacitors are silver Philips which I haven't had much trouble with in the past, so not my first port of call.

Any ideas?

DMcMahon 13th Jan 2023 6:07 pm

Re: Stella ST459 motorboating
 
The Stella ST459A/15 and Cossor CR1605A/15 are clones of the Philips EL3549A/15.

David

peter_sol 13th Jan 2023 7:32 pm

Re: Stella ST459 motorboating
 
Have you cleaned the record / playback switch?

dazzlevision 13th Jan 2023 8:02 pm

Re: Stella ST459 motorboating
 
Quote:

Originally Posted by Welsh Anorak (Post 1528383)
I've done the usual cleaning of switches but no good.

Already been done?

PYE 405 13th Jan 2023 8:11 pm

Re: Stella ST459 motorboating
 
A total guess here.... too much negative feedback via a high ESR electrolytic?

Restoration73 13th Jan 2023 8:38 pm

Re: Stella ST459 motorboating
 
Might even be a soldered joint. I have a mint ST459 here, all working except rewind and
play take-up as a thin belt has turned to goo. It is the only machine I have with 15/16ips.

DMcMahon 13th Jan 2023 10:16 pm

Re: Stella ST459 motorboating
 
The fact that the motor boating varies with the volume control suggests that the instability/oscillation that is generating the motor boating is occurring in the stages prior to the volume control. So suggest that the other 3 HT supplies, i.e. the -1, -2 & -3 supply rails be checked for stable voltage and also oscilloscope checked (if available) for any abnormalities.

Is it normal with this model that you get sound in the Stop mode ? i.e. many models mute the playback amplifier in Stop mode.

David

Welsh Anorak 14th Jan 2023 4:02 pm

Re: Stella ST459 motorboating
 
Agreed - the fact that the noise is virtually absent in record monitor mode would tend to confirm this. I'll have a close look at the manual then scope the supply rails as you suggest. Last time I used the machine it worked fine - just happened when someone wanted to borrow it, of course...
It's an odd one!
Unusual to have 15/16 ips - the only others I have are, of course, the Uher Reports.

Restoration73 18th Jan 2023 11:18 am

Re: Stella ST459 motorboating
 
Your thread has prompted me to service mine. The rewind belt goo was removed and
although in this early (Sept 1963) /00 version the belt was square, as it is crossover I
decided to use a round belt instead. I also had to remake one of the leaf switches where
the plastic disintegrated. Although the deck was similar to the earlier hybrid machines,
(I moved on my ST454 as it had no 7.5ips) it is an excellent diecast build with a massive
flywheel that you need for 15/16. Works well, low noise. I hope you found your fault.

Welsh Anorak 18th Jan 2023 1:53 pm

Re: Stella ST459 motorboating
 
Well, sort of!
Swinging the PCB out (thanks Philips - nice to have servicing in mind) the sound could be made to come and go, but not a dry joint. Looks like perhaps I'm not the first person here as a couple of wires had been freed from the paper tape loom running around the board. Earthing doesn't help, and it comes back loud and clear when the board is swung home - the earthing screws have no effect.

Moving the wires does help and it's almost usable so it's now waiting for inspiration...

However please let me know if your machine shows any sign of this noise.

DMcMahon 19th Jan 2023 9:05 am

Re: Stella ST459 motorboating
 
Could it be a screen off a screened cable that has broken away/come disconnected ?

David

Welsh Anorak 19th Jan 2023 3:11 pm

Re: Stella ST459 motorboating
 
Not that I can see, and it does act like it's picking up the interference from somewhere, but it's too slow to be from the motor or miains hum - maybe 4 clicks a second. Odd!


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