Philips FCD565 midi system ~1987 - Transformer buzz

[quattro alex]

Model: Philips FCD565 midi system (1987 ish)

Faults: Transformer buzzing occurs with no load after 10 minutes or so. Also tuner display does not light up

Observations:
1. Diode wires 6527 & 6528 are broken these have a 4 8 T designation
2. One of the bulbs for the crystal display appears burnt out

Testing so far:

1a. All caps on the top circuit board tested with esr meter - 7 found to be out of tolerance:

Position on board
2594 - 25v 100uf (74.10uf & 0.46 esr)
2698 - 10v 100uf (30.98uf & 1.29 esr)
2521 - 10v 220uf (141uf & 0.49 esr)
2522 - 10v 100uf (33.86uf & 1.11 esr)
2655 - 63v 10uf (6.62uf & 3.0 esr)
2523 - 63v 2.2uf (open / low cap)
2525 - 10v 47uf ('leaky' & 11.6 esr)

2a. - Diodes - these tested fine

3a. - Resistors - values matched almost perfectly - except 2 which I will ask about in a moment.

Questions:

A) Are the orange components film capacitors or resistors? ( some have 0.27k and one has 0.1k on the top)

B) The resistor at 2534 measures at 100k but the one underneath shows no continuity and shows as open when testing resistance - is this because of the component in between the two of them?

C) I make the resistor at location 2600 a 100ohm resistor (brown/black/brown/silver) but it is testing at 2ohms - have I interpreted the original value correctly?

D) Is the original soldering of the transistors acceptable, or should I redo these? (marked in red)

Any other suggestions or observations greatly welcomed!

[retiredcaps]

Re: Philips FCD565 midi system ~1987 - Transformer buzz

A) Are the orange components film capacitors or resistors? ( some have 0.27k and one has 0.1k on the top)

They look like capacitors.

B) The resistor at 2534 measures at 100k but the one underneath shows no continuity and shows as open when testing resistance - is this because of the component in between the two of them?

C) I make the resistor at location 2600 a 100ohm resistor (brown/black/brown/silver) but it is testing at 2ohms - have I interpreted the original value correctly?

If you get suspicious readings, remove them and retest out of circuit.

In circuit readings are not 100% reliable as they could be affected by other components.

[999999999]

Re: Philips FCD565 midi system ~1987 - Transformer buzz

Yes the orange components are film caps, 0.1uF and 0.27uF

I'm not so sure those 2534 and the one below it (2612?) are resistors. They look more like fuses or inductors to me, or even capacitors more than resistors.

[quattro alex]

Re: Philips FCD565 midi system ~1987 - Transformer buzz

Do film caps degrade in the same way as normal caps do, or do they have a longer / more stable lifespan? Also if I use my peak esr70 meter will the esr reading be worthwhile or are these film caps too small in capacitance terms?

As per retiredcaps - I will test the others out of circuit.

[999999999]

Re: Philips FCD565 midi system ~1987 - Transformer buzz

Film caps do not degrade like electrolytic caps, they're generally good for decades except those on AC mains circuits which are subject to voltage spikes. There's very little chance those caps are the problem unless you see some physical evidence looking at them. I doubt any of the capacitors are the source of the problem since the 10 minute period makes a difference, though certainly it'd be good to replace any electrolytics that are out of spec or for longer future use - but I'd wait till the primary problem is found and fixed.

If I had to make a random guess, you have a transistor that's getting leaky when it warms up. I'd measure voltages on their pins before and after it starts buzzing. You could try reflowing the solder points you circled but they look no worse to me than others in the picture. If you're going to be ordering parts you might consider ordering some equivalent transistors too since they're probably only a few cents each.

[quattro alex]

Re: Philips FCD565 midi system ~1987 - Transformer buzz

With regard to measuring voltages is this a live test (dc volts?) and which pins should I test?

The original transistors have the following identification:

F199
F245B
BB112

I've checked farnell, rs and mouser and it appears these are no longer available or well over 2-3 months wait. Can these be substituted with another version?

[selldoor]

Re: Philips FCD565 midi system ~1987 - Transformer buzz

Hi - Yes Voltage measurements have to be done live - otherwise there would be no voltage? or very little once the caps had discharged

If you have a data sheet for the Transistors you will be able to see what
voltages are expected and set up the meter accordingly. If Auto ranging then you are ok.
If you havent got the data sheet to be safe start at 600dc and work down.

[vinceroger69]

Re: Philips FCD565 midi system ~1987 - Transformer buzz

answer to c yes 100 ohms maybe unsolder one leg and retest and double check on the colour bands

[Longbow]

Re: Philips FCD565 midi system ~1987 - Transformer buzz

Good photos. Are you referring to 60 cycle mechanical buzzing in the transformer? Mechanical buzzing happens because the core plates are physically vibrating in step with the magnetic field. There is little you can do short of finding another transformer. Sometimes mounting the transformer on rubber feet, etc will cut the noise down a bit.

[selldoor]

Re: Philips FCD565 midi system ~1987 - Transformer buzz

Good photos. Are you referring to 60 cycle mechanical buzzing in the transformer? Mechanical buzzing happens because the core plates are physically vibrating in step with the magnetic field. There is little you can do short of finding another transformer. Sometimes mounting the transformer on rubber feet, etc will cut the noise down a bit.

If it was that would injecting it with superglue help?

[999999999]

Re: Philips FCD565 midi system ~1987 - Transformer buzz

If it was that would injecting it with superglue help?

IMO, that's not a very common fault but you could desolder the transformer, submerge in hot lacquer, cure and resolder it.

[999999999]

Re: Philips FCD565 midi system ~1987 - Transformer buzz

With regard to measuring voltages is this a live test (dc volts?) and which pins should I test?

The original transistors have the following identification:

F199
F245B
BB112

I've checked farnell, rs and mouser and it appears these are no longer available or well over 2-3 months wait. Can these be substituted with another version?

Yes live, DC volts, they'll probably be under 36VDC and likely much less. Measure all pins and record the values measured then compare to values after the noise starts.

Yes there's bound to be substitute transistors, after the originals are identified and spec sheets found, or something the critical parameter can depend on the circuit around it and you have to trace that circuit to see how it's used.

F245B appears to be BF45B n-channel FET, 30V, 15mA to 25mA max drain current, 10 mA gate current. I didn't find the other two and am not really following the circuit.

Upon searching for Philips FCD565, I get hits for a bookshelf stereo system. Is it a bookshelf stereo system or is it an electronic music synthesizer? I take back my guess about transistors - it could be a leaky transistor but I did not realize this is a junky integrated stereo system not a MIDI synthesizer, you're only showing a little bit of the entire integrated stereo system including an NJM4558 opamp, TA2030 power amp IC, and other parts we don't see.

You'll need to probe around other places too and measure signal levels before and after the opamp, power amp IC, and elsewhere as well as considering other components we can't see pictured. Personally, I'd just throw this unit away as you might be able to find a working one at a garage sale for a very low price and once you heard it, wouldn't want to use it for anything.

[quattro alex]

Re: Philips FCD565 midi system ~1987 - Transformer buzz

Good photos. Are you referring to 60 cycle mechanical buzzing in the transformer? Mechanical buzzing happens because the core plates are physically vibrating in step with the magnetic field. There is little you can do short of finding another transformer. Sometimes mounting the transformer on rubber feet, etc will cut the noise down a bit.

It is a mechanical buzzing that starts as soon as I turn on the unit. It gets progressively louder over about 25 mins and then stays at that level.

Questions:

1. I have desoldered the transformer, now should I remove the outer strip of metal and copper section to reveal the core?

2. If I do need to apply lacquer does it have to be of a certain spec?

3. If I am looking for replacement transformers what are the key specs to check?

[budm]

Re: Philips FCD565 midi system ~1987 - Transformer buzz

Do you get hum if you just have the primary side hook up to power only?

[quattro alex]

Re: Philips FCD565 midi system ~1987 - Transformer buzz

Do you get hum if you just have the primary side hook up to power only?

Budm would you mind pointing out which connections I should disconnect to carry out this test?

[budm]

Re: Philips FCD565 midi system ~1987 - Transformer buzz

I need good picture of the bottom side of the the board as shown on post #13 picture #3, and the other side of the transformer of th pic #1 in post 13 (the picture #1 seems to be showing the secondary winding of the transformer).

[999999999]

Re: Philips FCD565 midi system ~1987 - Transformer buzz

It is a mechanical buzzing that starts as soon as I turn on the unit. It gets progressively louder over about 25 mins and then stays at that level.

Questions:

1. I have desoldered the transformer, now should I remove the outer strip of metal and copper section to reveal the core?

2. If I do need to apply lacquer does it have to be of a certain spec?

3. If I am looking for replacement transformers what are the key specs to check?

If there is a sufficient gap somewhere so you can use a spray varnish with sprayer nozzle that has a straw, you may not need to remove anything. Otherwise, you may... dipping the entire thing upside down is the typical approach but that may or may not be enough.

Electrical lacquer or varnish can be found at electronics supply house, here are a few from a UK supplier as an example:
http://uk.farnell.com/jsp/search/bro...atchallpartial

Since this transformer has a plastic frame on it, you should probably avoid any varnishes that need to be baked rather than air dried.

The hardest part in finding a replacement would be that it's the same form factor given it is mounted on the PCB. Otherwise you could remotely mount the transformer and connect it with wire to the PCB. Key specs are the same voltage and the same or higher current rating, or at least close (depends on how loud you want this to be capable of).

Measure the voltage to determine if you are dealing with +/- rails of the same value and ground (for example +18V/0V/-18V) or dealing with a single higher voltage rail like +18V and a second lower voltage rail that powers various lower voltage components on the board(s) rather than the audio output stage. Based on its physical size I doubt it is rated for more than a couple amps current on the highest voltage rail(s), if even that.

To hook up the primary side alone to see if it buzzes then, it appears all you need to do is connect an AC electrical cord to the primary winding pins, the two on the side of the transformer closer to the AC outlet. By that I mean a leftover/salvaged power cord from something that you cut the product end of the plug off of and striped back insulation and modestly soldered to the transformer pins, if you don't have a more secure way of using aligator clip ended jumper wires or similar. Either way be careful working with HV AC, and confirm which pins are the AC primaries by looking at the back of the PCB to confirm those solder pads trace to the AC power socket.

[quattro alex]

Re: Philips FCD565 midi system ~1987 - Transformer buzz

I need good picture of the bottom side of the the board as shown on post #13 picture #3, and the other side of the transformer of th pic #1 in post 13 (the picture #1 seems to be showing the secondary winding of the transformer).

Hopefully these are ok, unfortunately too late for daylight shots so I've bumped the ISO up a bit.

[budm]

Re: Philips FCD565 midi system ~1987 - Transformer buzz

This transformer has mutiple windings on the primary side, There is a black recetacle and then there is also a balck cord (with Blue and Brown wires) iwth female IEC at the end of it. Can you tell me where that black power cord goes to and the black receptacle is for?

[quattro alex]

Re: Philips FCD565 midi system ~1987 - Transformer buzz

There is a black recetacle and then there is also a balck cord (with Blue and Brown wires) with female IEC at the end of it. Can you tell me where that black power cord goes to and the black receptacle is for?

The black recepticle is the mains AC input for the unit. The black cord I think is for the CD player section or turntable which my colleague hasn't given me.