NAD Tuner Preset Memory Issue

[dbxdx5]

I'm working on an NAD 7225PE. I can program stations into the memory presets, but it doesn't retain them after powering off the unit. From what I can discern of the main tuner IC (TC-9147P), the memory function works through pins 41 and 42. Now in the NAD 7140, which uses the same IC, a super capacitor (C213) is employed, which makes sense. My experience is that either a super cap or a battery is typically used for something like this. However, in the 7225PE, it appears that a regular cap is used, albeit a relatively high capacitance one (C914). This seemed odd to me, but ok, it's how it came from the factory. . . .

I did go ahead and replace the original 4700uF 6.3V cap at C914 with a Nichicon UKL of the same value, since the parts list in the service manual specs "low leakage." This didn't solve the problem. Checking the voltages against the SM, I have the expected 4.9V at pins 41 and 42. I've also replaced the other electrolytic in this part of the circuit, C913, just in case it was causing the issue, but again, no change.

So I'm scratching head here. Should there actually be a super cap here?

First schematic snippet is from the 7140, and the second is from the 7225PE (what I'm working on).

 

[Blumop]

There is a member on here @Ylli who has helped me in past with Tuner sections of NAD receivers. You could try him?

 

[Blumop]

I found datasheet for TC9147AP in English. Seems similar to TC9147P ( only one I could see was in Japanese). It seems memories are stored in RAM, not capacitor. Pinouts shown in data sheet. Maybe this could assist ?. Assume you have 7225PE SM & Owners Manual - both available from here to double check memory store procedure...
https://www.hifiengine.com/manual_library/nad/7225pe.shtml
Memory button contact failure could be another point to trouble shoot perhaps?. Cheers

 

[dbxdx5]

Thanks. I had come across that datasheet, too. The RAM needs 2V minimum at pin 42 (VDD) in order to function properly, which is stored in cap C914 after powering down. (The datasheet says this can also be supplied by a battery.) I checked to make sure pin 40, for the Inhibit function, is getting the necessary 4.8V to stop all IC operations (aside from RAM) at power down. I did replace Q909 and C918 for good measure, and now the presets are being retained in the memory. If this acts up again, I'm leaning toward a problem with the IC itself.

 

[bongos]

I picked up an NAD 7125 - perfect rig for the garage. It sounds great and I love the size and simplicity. But I too had the issue of the presets not holding in memory after turning power off, even though it remained plugged in.

Based on this discussion I located the two caps with high uF ratings close to the tuner IC. They were C76 and C77 - rated at 2200uF 6.3V. I found the exact Nichicon Gold replacements on Amazon. Popped 'em in and voila, preset memory holds like a charm when powered off!