Want to remove the LOW Battery Alarm Feature from a Sony Sports FM/AM Radio

[MAVA]

Gentlemen,

This is my first, I searched and found nothing...

I have been repairing/designing electronic things, but lately into the repair/modification of the Latest Mercedes Electronic Transmissions. I'm a Moderator on Benzworld.org under the same screen name if you have Mercedes Benz questions PM me there, and I will point you the direction you need to go...

I'm looking for schematics to a Sony Sports Walkman FM/AM radio Model SRF-M78.

https://www.manualslib.com/manual/16...n-Srf-M78.html

I want to tweak the voltage input comparator to turn-OFF this low battery alarm feature that shuts the walkman as the battery gets low. I RATHER LET IT DIE as the batteries die...

I know this is petty thing, but it was too stupid to at this to the circuit. I bet if I modify this circuit I could get double the run time off the AAA's, but right now it is like 10hrs...

The only Schematic place I found was this place:

https://www.manualslib.com/manual/16...n-Srf-M78.html

Maybe someone has it, or point me to another place that may have it, yet maybe I can get close with another model..

Thank you,

Martin

[goontron]

Re: Want to remove the LOW Battery Alarm Feature from a Sony Sports FM/AM Radio

If you post pictures of th inside we may be able to point you in the right direction.

EDIT: well, looking at the posts below, the B+ monitoring is built into the main chip, so not removable. And PLL is hit and miss on lower voltage. I was hoping it was old enough to be tuned oscillator based, but nope.

[budm]

Re: Want to remove the LOW Battery Alarm Feature from a Sony Sports FM/AM Radio

Try here: https://elektrotanya.com/showresult?...oria=&kat2=all

[eccerr0r]

Re: Want to remove the LOW Battery Alarm Feature from a Sony Sports FM/AM Radio

The voltage limit might be there for a reason, one thing is that PLL tuning requires voltages to be accurate and if the voltage isn't high enough or the divider can't divide fast enough due to low voltage, it won't tune properly, can't lock onto a station anymore, and all you'll get is static/noise.

This is nothing like analog receivers...

[MAVA]

Re: Want to remove the LOW Battery Alarm Feature from a Sony Sports FM/AM Radio

Thank you all for your replies. Budm, the second file contained the schematic. Thank you..

My guess is with pins 14 Vdo and Pin 11 CE on IC 51 (uPD17015) are responsible

IC 52 (S-80720AL) the 2.6v Voltage Detector probably goes low right around 2.6v.

I need to disassemble my unit and power it with the variable bench power supply to watch the states of the Vdo and CE

Here are the schematics, and the two data sheets(IC51 and IC52)

Martin

[budm]

Re: Want to remove the LOW Battery Alarm Feature from a Sony Sports FM/AM Radio

It looks like all you have to do is to disconnect pin 1 of the Vdetect IC then either GND or pull the empty pad HI, I do not know which IC is actually being used, the one with ACTIVE HIGH, or ACTIVE LOW.

[eccerr0r]

Re: Want to remove the LOW Battery Alarm Feature from a Sony Sports FM/AM Radio

Yeah looks like IC52 (voltage detector) probably will drop towards 0V if the voltage input drops below 2V based on the debug information and data sheet. Removing this IC and just connecting vin to vout (2 to 3) should disable the feature.

[kc8adu]

Re: Want to remove the LOW Battery Alarm Feature from a Sony Sports FM/AM Radio

2v for a pair of cells is dead anyway.
if you use nicd/nimh it will protect your batts from over discharge/reversal.
i see no point in removing a useful feature.

[Curious.George]

Re: Want to remove the LOW Battery Alarm Feature from a Sony Sports FM/AM Radio

I want to tweak the voltage input comparator to turn-OFF this low battery alarm feature that shuts the walkman as the battery gets low. I RATHER LET IT DIE as the batteries die...

I know this is petty thing, but it was too stupid to at this to the circuit. I bet if I modify this circuit I could get double the run time off the AAA's, but right now it is like 10hrs...

Why do you think the designers went to the trouble to design that feature into the product and add the necessary components to implement it? Do you think they are out to force you to buy extra batteries?

(Hint: you don't add design effort and recurring cost to a product without a valid reason -- even if that reason is "to sell extra batteries".)

You may discover you end up losing all of your station presets because the NVRAM interface doesn't operate reliably with fallling battery voltage. Or, you may discover that some active is forced to operate in its linear region (instead of as a switch) possibly INSIDE one of those chips.

Buy better batteries or carry a spare set with you if you want/need more than 10 hours of service life.