L5973D IC info for Magnavox 32MD231D

[tom66]

Re: L5973D IC info for Magnavox 32MD231D

This'll probably work
http://www.ebay.co.uk/itm/LM2596-DC-...item4ab9d00c8d

I'd recommend replacing the capacitors on it for longevity but otherwise it should be fine.

[m8r-v8qmwe@mailinator.com]

Re: L5973D IC info for Magnavox 32MD231D

johnboy1313, I admire your industrious replacement.
The lead lengths do matter. I suggest a modified approach. Solder pins 1-4 to the PCB like they are supposed to be soldered. Then pull the IC back away from the PCB 90 degrees, bending the soldered leads. When bending the IC, twist the IC up pushing the pins down. You want to avoid a peeling action that might rip the pads off the PCB. Bending in such a way that you are pushing the pins into the PCB should prevent this. Pins 1-4 will be soldered and pins 5-8 sticking up in the air. Use a short ribbon cable to connect the leads that sticking. Basically, what you already did, but with a shorter cable. It may also help to bend pins 5-8 down, for the sake of clearance. If possible, shorten the 12 gauge lead from the exposed pad. Mount the heatsink as you have done. Cut a chunk from the large heatsink for all chips to accommodate the unusual chip mounting with new heatsink. I am not sure if there is enough clearance for this method. Probably is my best guess. The part of the TV where the PS/Scaler board combo mounts is slightly recessed so this should give a bit of additional clearance.
This method, if it fits, would yield shorter leads than the outright replacement of the DC-DC converter.

[electricboyo]

Re: L5973D IC info for Magnavox 32MD231D

Bumping this thread because I'm attempting repair of a Magnavox 32MF231D.

Initially my TV would not power up. It had several bulged/high ESR capacitors on the main power supply board. In fact caps 2079 and 2080 (1200uF 35V) were completely open circuit when tested with my ESR meter. Capacitor 2074 (2200uF 25V) tested with ESR of 1.1 ohms. In comparison, the ESR of a a new 2200uF 25V capacitor is less than 0.05 ohms.

Next, I replaced ALL electrolytic caps on the power supply board. Testing the power supply board by itself confirmed that it worked as it should.

But when I attempted to operate the TV set, the screen lit up for less than a minute, followed by SMOKE coming from behind the scaler PC board. After that the TV would not power up.

Inspection showed that part # 7003 (L5973D 12 volt regulator) had a burned spot. I removed the faulty L5973D IC. Next I rigged up an external DC bench power supply to provide the 12 volt rail current. The power supply has meters and a current limit, so this permitted me to check for short-circuits on the 12 volt rail. Everything then worked correctly. I was able to get a picture on the set. I measured the current drain on the 12 volt rail: It was less than 1 amp. I concluded that it would be safe to put in a replacement L5973D. I did this and the TV worked perfectly.

But the replacement L5973D only lasted about 24 hours. I successfully ran the TV set for several hours. While testing I powered it off and on several times without any problems. I powered it off when I went to bed, but left it connected to the AC outlet.

The next morning, when I switched on the set, I heard a "pop" sound and then the TV switched off before a picture was visible on the screen. Inspection again showed a destroyed L5973D. Each L5973D that failed for me has a small hole near pin 7 (ground). When I searched badcaps forums, I found several photos of L5973D chips with precisely the SAME DAMAGE located in the SAME place (next to pin 7).

This leads me to think there is some other part that fails along with the large power supply caps. I began checking the ESR of the SMT caps on the scaler board. Part # 2002 (100uF 25V SMT cap) tested with ESR of 5.8 ohms. This is much too high! I suspect the high ESR of this capacitor is causing the L5973D to fail during power-up. This capacitor is directly at the 16 volt input to the L5973D chip (pin 8). Although the L5973D supposedly has internal short-circuit protection, perhaps the L5973D is unstable when the input capacitor has high ESR?

I'm afraid that I'll only be able to mount one more L5973D before the foils on the PC board get excessively damaged. So I'm trying to come up with a way to test everything before I do that. I may construct a stand-alone 16 volt to 12 volt regulator circuit with the same components as the actual circuit, and then test it thoroughly first.

I'll post my results here

-Greg

[johnboy1313]

Re: L5973D IC info for Magnavox 32MD231D

Excellent info, thanks for sharing.

[electricboyo]

Re: L5973D IC info for Magnavox 32MD231D

I purchased a 32MF231D scaler board on eBay. It was advertised as "needs repair." Because of that it cost me only $22.

It's L5973D IC is burned, same as my TV.

In fact, the eBay scaler board has a 1 inch long black smoke trail which starts at the L5973D! This board shows no sign of previous repair, which is good.

Hopefully I will be able to remove the bad L5973D without damaging the PC board. My plan is to unsolder the 8 IC pins first. Then I will use my Dremel tool to grind down the plastic case of the bad IC so that I can directly heat the metal back of the bad IC chip. I think this will be the best way to melt the solder underneath the bad L5973D so it can be removed without damaging the PC Board.

[electricboyo]

Re: L5973D IC info for Magnavox 32MD231D

UPDATE:

The non-working main PC board (p/n 313815866881) I bought on ebay is now working.

I replaced the L5973D (item 7003 on PC board). I also replaced capacitors 2002 (100uF 25V) and 2007 (47uF 35V). Both of these capacitors had very high ESR ( > 9 ohms), even though they weren't leaking or bulging. Cap 2002 is directly at the 24V input pin of the L5973D. Although there are several other filter caps on the 24v power rail, none of them are physically close to the L5973D.

Important note: The ONLY way the ESR of capacitor 2002 can be tested is by first removing it from the PC board!

I have a theory for WHY the L5973D fails:

1) When the large caps on the power supply PC board fail, this places a very high level of ripple current on caps 2002 and 2007, causing them to develop high ESR.

2) When the TV is first turned on (after recapping the power supply PC board), the L5973D fails during its initial turn-on as a result of capacitor 2002 having ESR that's too high. Perhaps a high ESR capacitor on the input of the L5973D causes it to enter an unstable state during power up?


Next I'm going to repair several other main boards that have a failed L5973D by replacing both the L5973D and capacitors 2002 and 2007. If this succeeds, I'll post the complete repair procedure, along with photos.