Philips CP90 and others: memory battery.
 

I am restoring a few Philips CP- series sets for a project. The common denominator, which also affects the CTX remote sets, is the leaky 2.4v 100mAh memory battery. These damn things have caused damage to the PCB, in one case writing off a set. The original yellow ones seem to leak less, but the white and blue replacements sold in the last couple of decades really were nasty.

A very similar scenario happens in some Thomson sets, which use a disc-shaped Varta type.

So far I have replaced them with what I had to hand, namely battery caddies from old transistor radios with 2x AAA 1,5v, mounted inside the cabinet off the main PCB. However, I'm looking at more elegant less time consuming options. I have a few lithium cells from wireless earphones (like this one, 45mah, 3,7 V). Voltage is a bit higher, but I don't expect it to matter too much. Has anyone tried using one?
The charge circuit is derived from the 6v line via a diode with a series resistor 3901 presumably to limit the current.

Re: Philips CP90 and others: memory bettery
 

I am not familiar with the problem on this set but back up batteries are a real pain in that you don't know they have failed until it is often too late as you describe. These little Lithium packs I have seen used in cheap drones and the capacity and discharge capability are amazing. It might need the R3901 value tweaking a bit but I would measure the charge / discharge currents and see.

Re: Philips CP90 and others: memory bettery
 

Hello,

I've had quite a few problems with those 2.4V NiCad batteries in Philips sets and agree about the leakage. It seems to corrode the copper print foil under the solder mask. One CP110 chassis was badly affected and should really have been a write-off but I managed to carefully repair the print with TCW wire links. It was quite a difficult repair as the corrosion was awkward to deal with. At one time you could obtain NiMH replacements which seemed to be OK.

Some remote control Thorn sets using the TX10 chassis used those Varta stacked cells and they could also corrode the print foil.

I'm not sure I'd be brave enough to try lithium cells. I would want to be sure the cells could never become stressed. Maybe a couple of small NiMH cells with solder tags connected in series and a suitable mounting/plate with jumper wires to where the existing battery is fitted. There's not much room on the CP90/110 chassis to make things easy though.

Regards,
Symon

Re: Philips CP90 and others: memory bettery
 

NiMH cells self-discharge quite quickly and eventually fail altgether. For very low drain memory retention, lithium primary cells can easily outlast the probable entire life of a NiMH that got recharged!

David

Re: Philips CP90 and others: memory bettery
 

Be aware that in the Thomson ICC5 IMC manual it warns that versions of this chassis used either Nicad or Lithium cells and they are not directly interchangeable, it warns you would need to disable the charging circuit if a Lithium cell is used to replace a Nicad, and to add the charging circuit if using a Nicad on the lithium version.

Edit: this was in the Ferguson manual for that chassis

Re: Philips CP90 and others: memory battery.
 

@Ben: Lithium cells cannot be charged safely from a current source that is fed with a higher voltage. They will charge up beyond 4,2V and fail. They can theoretically be used to replace series strings of 3 NiCd cells when a 3,9V zener diode is wired in parallel. They will never be fully charged but they won't fail. Maybe even last longer lacking a full charge.

@redtoblack: that would have been primary (non rechargeable) lithium cells.

Re: Philips CP90 and others: memory battery.
 

Thanks as always for the information, very useful. I have been trying to find the recommended maximum and minimum voltage settings for the memory side of the tmp47c432ap IC, so as to forestall possible unwanted effects of using a battery of more than 2.4v but drawn a blank so far. Will update when more parts arrive for the latest set I'm on.

Re: Philips CP90 and others: memory battery.
 

I fitted a lithium coil cell nearly a couple of decades ago to Philips 16" FST portable. Snipped the resistor that was used to charge the nicad pack. Its still going strong after all these years.

These nicad issues were a problem even when the sets were quite new. Absolutely terrible design imo.

Re: Philips CP90 and others: memory battery.
 

I was considering something similar. I think adding a 3v lithium non rechargeable cell and lifting diode D6901 (see cct in post 1) would do it.

Re: Philips CP90 and others: memory battery.
 

I'm not so sure that would work Ben. I think I would simply replace that 270 ohm by a diode, the anode to the cell.

The chip runs of the main rail normally via D6901 with that diode blocking current from the battery feeding back into the rest of the set when power is off.

Re: Philips CP90 and others: memory battery.
 

I see what you mean. Will give that a go. I had thought that, but then I saw pin 34 has 6v on it too and thought the IC was powered from there.

Re: Philips CP90 and others: memory battery.
 

I ended up mounting a 3v lithium battery type CR123A on a home made caddy off the pcb and replacing R3901 with a 1n4148.

On one set, also model 17CE1231, the front buttons were inoperative. A new TMP47C432AP-8189 was needed.

On another, there was video tearing on all signal sources, improving slightly when warm. Changing all the capacitors on the IF can solved that one.

Another, a 21CE1251, suddenly went off with a whine from the PSU. The BUT12A was s/c. Replaced that and an 1n5 capacitor and tidied up the soldering in the line stage.

Re: Philips CP90 and others: memory battery.
 

The lithium cell should be good for many decades...

I remember on my Philips (which is actually 15" and not 16" as I mentioned earlier) that it pulled and ragged on some VCR's back in the day. Myself and a colleague at work had a think and we modified the flywheel sync but I can't remember exactly what we did now. Probably a cap value change. It was perfect afterwards.

This was the set, now another 12 years older and still going strong with its same lithium cell.

https://www.vintage-radio.net/forum/...53&postcount=5