ITT CRC4000 radio alarm/calculator

[Crackle]

I have been fixing a couple of these little ITT Radio/calculator/alarm clocks from around 1982.
I bought a second one because the first one only worked on AM and the calculator side was dead.

I now have one completely working on AM & FM and the calculator and LCD screen are also working.
But the radio on FM has a hiss even when tuned in to a strong station.
   
Can anybody help with identifying the coloured and numbered coils in the attached photo, is there a standard colour code for these small RF & IF transformers to denote their function.
   
I have identified some of the trimmers with numbers, and marked the ones I think I know;
1
2
3
4
5
6
7
8 FM oscillator L
9 FM aerial L (I think)
10 FM aerial C
11 FM Oscillator C
12 AM aerial C
13 AM Oscillator L

thanks
Mike

[Murphyv310]

Hi Mike.
Im sure there were standard colours Red and White could have been for AM. Thing is it wasn't yesterday and the specific colours used is gone. Does the hiss change with the calculator being on or off? Is it distorted when tuned correctly and is FM sensitive or quite deaf?

[pwdrive]

Some Toko stuff including colour codes, there might be similarities?:

http://joefreeman.weebly.com/uploads/1/3...l_data.pdf

Lawrence.

[Terry]

I'm in broad agreement with Trevor here and it didn't matter who manufactured the radio, the colours were always the same, I think, pointing towards some kind of standard. However, we didn't see the range of colours on those early sets that we see here!

First off - 13 should be AM Oscillator C (not L) which points to 7 -with its traditional Red core being AM oscillator L.

1, 3, 4 & 5 have two dots in the core whereas the others don't so perhaps it is reasonable to suggest that this differentiates the FM inductors from the AM ones?

In which case, I would go for 6 being the 1st AM IFT, although that conflicts with the Toko list provided by Lawrence which shows a Yellow core as being 2nd AM IFT - but then, we don't have the orange core of the Toko 1st IFT!

Could 4 & 5 be a bandpass coupled pair for FM IF? Certainly both colours appear against 10.7MHz coils in the Toko list, although there is no mention of bandpass anywhere.

2 has no dots so, assuming that it is for AM it would be the 2nd AM IFT/det, although there isn't a match for it in the Toko list and I can't see the detector diode anywhere.

Two diodes next to 1 point to it being the ratio detector in conjunction with 3 but it seems a little odd to stick the AM detector between them and the colours conflict with the Toko list which shows a choice for pink cores - one being for an FM quadrature detector which might fit with that IC hiding under a paper label.

Is it possible to identify the IC, Mike?

That's the best I can do for now - I will be interested to see what others come up with!

[Crackle]

The IC is a ULN2240 here is some information that I extracted from a large Sprague document.

  ULN_2240A.pdf (Size: 1.23 MB / Downloads: 8)

Mike

[Crackle]

Note the part number of the IC in the radio is ULN2240 and the one in the Sprague document above is ULN2240A. By the look of the circuit there may be a difference.

But I have been able to make a small improvement to FM by opening the spacing slightly of coil 9.
I can definitely say that 7 is the AM oscillator coil, and yes Terry I made a typo 13 should be AM oscillator C.

What is leading to my confusion is some coils appear to effect both AM and FM.

Mike

[Murphyv310]

Hi Mike.
If AM coils effect FM and vice versa then I'd be inclined to leave them until you've checked the decouplers around the area that you get the effect.
It's just possible there is an open circuit cap that is causing the interaction, or even a bit of O/C print.

[Terry]

The IC is a ULN2240 here is some information that I extracted from a large Sprague document.

I think I've found the same document, albeit with a slightly better quality. There is also an application note covering different receiver designs using these chips which might be of interest.

I found it here: http://bitsavers.trailing-edge.com/compo...rcuits.pdf

The data sheet that you posted starts at page 402 of the pdf and the application note, if you haven't already seen it, starts at page 468.

Interestingly there is a reference at the end to a design published in Practical Wireless using the similar ULN2290 but that covers MW, LW, 3 SW bands and FM so might be a bit of overkill for working on your little set.

At least, with the information you now have, you can identify which coil is which by seeing which pin of the IC they are connected too.

Oh, and it appears I was wrong about the ratio detector diodes! I wonder what they are for?

[Crackle]

Sorry guys, the number on the IC is ULN2204 not 2240, I dont know why I wrote it down wrong.
I noticed when I counted the number of pins.
http://www.alldatasheet.com/datasheet-pd...2204A.html
Mike

[Crackle]

Looking at the "typical" circuit in the ULN2204 data sheet I can now see a something which is similar to the circuit of the ITT radio.
I can go through comparing the schematic to the circuit and try and identify the inductors. It is not identical as I can only count 1 diode in the schematic. I wonder if there are any significant differences between the ULN2204 22 (in my radio) and the ULN2204A.

   

On the second radio I have AM working very well, but FM only has hiss, no stations what so ever.

Mike

edit, just discovered the IC is equivalent to the TDA1083 so I may be able to find out a little more on that.