Grundig TK144 - no sound

[Bobblybob]

Morning all.
Ok, so to answer the test recommendations.
1. Resistance to ground either side of R38 is 23.3kOhms
2. Capacitor casing looks ok from what I can tell. No leakage or swelling. (Photo)
3. Took a closer photo of the PCB
4. Voltage across R38 is as follows. AC 1.40V. DC 104V
5. Voltage to ground either side of R38 is (END 1 to ground 17mV AC or 81V DC) and (END 2 to ground is 1.5V AC or 104V DC). I gave all readings in case that helps

Think that’s answered all tests?
Thanks
Alan

[DMcMahon]

1. Sounds somewhat lower than I would have expected, suggest to disconnect the wiring at C15 & C21 and repeat measurements to see if the 23.3k is elsewhere or due to capacitor (s). There is a 35k path to ground via R35 & R36.

3. PCB to me looks typical with messy varnish /solder flux etc. Difficult to be sure but it looks like there may be a few suspect looking soldered dry joints, probably not causing a problem, but recommend resoldering any that look suspect.

With the photo rotated so that lettering is correct way up, above and to the right of "R31" possibly looks like there is a solder splash across 2 tracks (lower track being a Y shape and upper track like a large/wide M. Worth checking to see if there is a solder splash shorting these artwork tracks, suspected solder splash starting at left hand arm of the Y going across to the middle arm of the M.

5. DC voltages are far too low. Recommend rechecking input of R38 (C21) with output of R38 lifted (C15), this will be the main HT voltage at the reservoir C21 with reduced load so woud expect it to be at least the schematic value around 240 volts if not higher.

[Welsh Anorak]

I see what you mean about the solder splash, though it's probably just flux.
Going on the voltages I agree they are far too low. With this in mind, coupled with the overheating resistor, I'd change the bridge rectifier and the dual capacitor together with the resistor. Leakage in the capacitor can cause the bridge to fail.

[DMcMahon]

[QUOTE=Bobblybob;1347196]Found that the 80mA fuse had blown. Replaced with one slightly higher as it was all I had.[ /QUOTE]

Hope you did not go too high with the fuse rating. The original 80mA blowing may tie up with the apparent loading fault making R38 smoke which as already been suggested could be related to bad dual capacitor and/or bridge rectifier.

David

[Bobblybob]

What a forum!
Ok, in no particular order from Dmc post numbering
1. When you say disconnect the wiring at C15 & C21, do you mean desolder and remove?, then check the resistance. (Sorry to be thick, 30 years did since I did anything like this..
3. The apparent s/c near R31 was just a bit of fluff. Removed.
5. Also I take it to mean desolder C15 leg of R38?

I think you probably do mean desolder but just wanted to check.

Re the fuse, all I had was a 1A

My next question will be obviously when I have done all these checks and found that I do have to replace these components, which is fine, where will be the best place to obtain these from?

Loving this....

[DMcMahon]

1. These dual can capacitors often have wires connecting to their terminals but in this case the capacitor connects into the PCB for its connections, so my reference to disconnecting wires was erroneous, so you were not being thick I was

In this case to isolate the dual can you would have to actually unsolder and remove it. Probably on reflection not now worth doing.

3. Good.

5. Yes lift up (unsolder first) the end of R38 that connects through to C15 (so it is no longer connected in circuit). Depending upon result this test will probably negate 1 being done.

1A fuse is far too large, it is quite possible that a lower value replacement fuse nearer the required 80mA may well have blown before R38 started smoking.

Lots of places to get components such as eBay, RS, Farnell, Cricklewood and many others.

David

[DMcMahon]

Visually check out C22 a 0.22uF capacitor across the mains transformer secondary winding (output side of the 80mA fuse).

If it is a Rifa capacitor then these have a habit of going up in smoke/melting and taking out the fuse.

It is possibly physically fitted at the transformer.

David

[Bobblybob]

Morning Dave

5. DC voltage at C21 with R 38 unsoldered at C15 is 214V (rising). DC voltage at C21 is 0.6

The red capacitor looks ok (photo)

C15 with R38 removed down to ground is around 2.9MOhms

[DMcMahon]

214V is a lot better but still somewhat low.

Red capacitor looks OK (as far as I can see) and does not look like one of the problematic Rifa caps so probably is OK, are you happy that it is C22 ?

2.9MOhms is good but it does not exonerate for example C15 which might at its working voltage be electrically leaky.

In terms of faut finding without replacing components it now gets more difficult.

If your meter measures capacitance (needs to measure ideally > 50uF) you could measure C15 and C21, may have to disconnect it completely to get sensible reading, but unless the capacitance reading is abnormally low or high it may not prove much.

Measuring capacitor leakage requires know how and other test equipment so not practical here I would say.

As others have stated it would be worthwhile replacing the dual capacitor can C15/C21.

With the can removed (also may have to disconnect/isolate other components that connect to it) would be good to check the bridge rectifier 4 diode sections for correct diode/resistance readings.

Definately replace the 1A fuse with correct value and get some spares. R38 though it may measure resonably OK, if it has been smoking its resistance may drop when it warms up, so would be good to replace it for future relaibility.

David

[DMcMahon]

Probably nothing to worry about, but in the PCB photo in Post 21 there is a blue tinge near the top right corner of the PCB, check there is nothing leaking on the other side of the PCB.

[Bobblybob]

Hi David

Today’s update. Firstly the blue tinge is nothing to worry about, just reflection.

I unsoldered the can capacitor and tested. (Using Fluke 85). Probably doing something wrong but could not get any readings.

Going to change them anyway, however looking at the component markings on the board, they don’t line up with the capacitor connections. I have taken a couple of photos to show. This then makes it awkward when installing the new ones, to make sure I connect it correctly. Assuming the pcb markings are incorrect as the player had been working for years.
Also the resistor looks well burnt, even though it’s still reading the same value.
Onwards and upwards.
Alan

[Welsh Anorak]

Hi
I think the board markings are correct. What it doesn't make clear is that, going clockwise round the can, pins 1,3 and 5 are connected together and to earth. The positives are to pins 2 and 4, So in replacing them with discrete radial parts you'd put them in as dictated by the markings, then link pins 3 and 5.
However I'd welcome a second opinion on this.

[ms660]

Yes, looks the same to me, two grounding points (3 & 5) connected by the can case (echoes of Dansette there)

Lawrence.

[Bobblybob]

Hi all.
Just had a look at Cricklewood electronics and they do a double 50uf capacitor. Connection is going to be awkward though.

[DMcMahon]

Somewhat unusual to have the separate earthing pins for the 2 capacitors, often the earth (-ve) is a common pin for both.

Maybe just easier physically to use 2 separate 50uF radials or 2 axials, i.e. not a can capacitor.

David

[DMcMahon]

Originally Posted by Bobblybob

I unsoldered the can capacitor and tested. (Using Fluke 85). Probably doing something wrong but could not get any readings.

One specc for the 85 I found shows that maximum capacitance range is 5uF
which seems surpringly low, there maybe different versions of the 85 with different specs.

David

[Bobblybob]

Originally Posted by DMcMahon

Somewhat unusual to have the separate earthing pins for the 2 capacitors, often the earth (-ve) is a common pin for both.

Maybe just easier physically to use 2 separate 50uF radials or 2 axials, i.e. not a can capacitor.

David

I agree. Trying to find one of the same or higher voltage though.... can find 47uf, not 50 separate ones at that voltage. Would 47 do?

[ms660]

Originally Posted by DMcMahon

Somewhat unusual to have the separate earthing pins for the 2 capacitors, often the earth (-ve) is a common pin for both

Can (gehause) is common -ve but two of the three common -ve tags connect two of ground tracks together so far as I can make out.

- pol am gehäuse = - pole on the housing using Google translate.

Lawrence.

[Bobblybob]

Originally Posted by DMcMahon

One specc for the 85 I found shows that maximum capacitance range is 5uF
which seems surpringly low, there maybe different versions of the 85 with different specs.

David

You are correct. 5uf range max. However there is a way to check >5uf it says by setting it to ohms, and multiplying the time it takes to go from 0.00 to OL by a factor dependant on the range set. Did this. On one side it takes around 5 seconds. On the other side of remained at OL. Changed the scale, and whilst one side starts off at 0.8 and climbs slowly, the other side starts at 3 and climbs quicker. Could this be the sign of a faulty capacitor then do you think?

[DMcMahon]

Originally Posted by Bobblybob

I agree. Trying to find one of the same or higher voltage though.... can find 47uf, not 50 separate ones at that voltage. Would 47 do?

Yes 47uF is fine, most new capacitors would be the preferred value of 47uF.

David