Choosing diodes for Magnavox 37MF337B/37 power supply repair

[Junkrepair]

Hi---

I'm trying to revive a dead Magnavox 37MF337B/37 that was given to me.

I opened it and found (with joy) four popped CapXons (C952, C953, C956, C955) on the PSU board. I also found signs of overheating of a couple diodes. And I've read various posts calling for replacement of other caps and diodes on this board.

I've chosen (with a little help) replacements for all nine CapXons on the PSU board, and I'm fairly confident in those choices.

As for the diodes, do you think I can do better than simply replacing them with the same part numbers? I'm not building a hundred thousand of these, so I don't mind spending a little more per part, if I can beef up the TV set a little, where you think it's advisable.

The PSU schematic is on page 52 of the service manual, found at: https://cdn.badcaps-static.com/pdfs/...1b217abb49.pdf

To be thorough, I note that the board is marked 715T2484-3 and bears a sticker with a number ADPF24220R1P.

I plan to replace the following diodes:

ZD906: This is a P4KE250A-E3. The board shows obvious heat discoloration a half inch on each side of this TVS.
Stock replacement: http://www.digikey.com/scripts/DkSea...97353939127020

ZD908: This is a BZX79-B18. There is obvious discoloration a quarter inch on each side of this part.
Stock replacement: http://www.digikey.com/scripts/DkSea...97353939137020

ZD902, ZD904: These two P6KE120A voltage suppressors are wired in series.
The surrounding area of circuit board is very slightly discolored. I've read elsewhere that these often go bad.
Stock replacement: http://www.digikey.com/scripts/DkSea...97353939147020

Please advise as to any good way of improving upon the stock parts, or that I should be happy with the original design.

Also please mention any other diodes or other parts you think I should replace or that I should order to have on hand in case the planned replacements don't do the job.

I plan to summarize the results after the repair is done.

[Junkrepair]

Re: Choosing diodes for Magnavox 37MF337B/37 power supply repair

Below is a close-up of ZD908 showing the heat discoloration mentioned in the OP.

The discoloration from ZD906 is even worse, but the picture doesn't show it very well. There was a blob of white glue on top of ZD906 and its neighbor D924. I'm hoping for some enlightenment regarding the purpose of that glue. And I wonder whether D924 may have suffered damage by being next to ZD906 when it was hot. I'm also worried about damage to the blue disk capacitor next to ZD906.

[sam_sam_sam]

Re: Choosing diodes for Magnavox 37MF337B/37 power supply repair

Have you checked the diode with a meter if so
What is the reading you are getting

Disk cap migh be alright as long as it is not discolor or cracked if you have a cap meter I would check it

What brand of caps did you use for that were pop up

Have tried to run the TV after replacing the four caps

[stj]

Re: Choosing diodes for Magnavox 37MF337B/37 power supply repair

some bad small caps there - the light green colour is an indication of heat.

[Junkrepair]

Re: Choosing diodes for Magnavox 37MF337B/37 power supply repair

The two pictures show the same single light-green cap (C958). But C934 is elsewhere on the board and is the same as C958. They are 5mm x 12mm Lelon RGA 105 degC 25V 47uF without vents---just plain flat tops. I assumed that they are their original color, but IDK. They are the only electrolytics on the board other than the nine CapXons. I guess I might as well replace the Lelons too, or at least order some backups for them.

I've removed the four popped caps but haven't ordered replacements yet. I'll be using Panasonic FM for those, same voltages as the originals. I'm trying overall to use high quality replacements (Panasonic, Nichicon, Chemi-con, etc.) with the best specs.

I'll test the diodes as well as I can after I remove them. I have digital and analog multimeters. I also have an old Heathkit transistor tester that I don't know how to use. I'm inclined to replace the most-likely-bad components summarily, without much testing.

[Junkrepair]

Re: Choosing diodes for Magnavox 37MF337B/37 power supply repair

Sorry, my links above seem to be broken. Trying again:

ZD906: This is a P4KE250A-E3. The board shows obvious heat discoloration a half inch on each side of this TVS.
Stock replacement: https://www.digikey.com/product-deta...ICT-ND/3306414

ZD908: This is a BZX79-B18. There is obvious discoloration a quarter inch on each side of this part.
Stock replacement: https://www.digikey.com/product-deta...5-1-ND/2762620

ZD902, ZD904: These two P6KE120A voltage suppressors are wired in series.
The surrounding area of circuit board is very slightly discolored. I've read elsewhere that these often go bad.
Stock replacement: https://www.digikey.com/product-deta...STR-ND/1050354

[Junkrepair]

Repairing a Magnavox/Philips Model 37MF337B/37 LCD TV. It was making a chirping sound and not booting up.

The manufacture date of the back panel of the plastic case is Oct 7, 2007.
S/N BZ3A0742110835. Power Supply board is version 715T2484-3.

Opened it and found four bad CapXon caps on the power supply board. PS board
has a sticker with bar code reading: ADPF24220R1P and P5PA74151155. There is
at least 34 mm clearance in case I need to use tall capacitors.

This refers to the Service Manual TPM1.OU LA H_16643_001.eps 040507 Part 2
covering numerous models including 37MF337B/37. The part number of the set
seems to be (according to the Service Manual) 9965 000 44331.

I replaced all 11 CapXon and Liton aluminum caps on the PS board, except the
biggest one. And based on reading other posts, I replaced 5 diodes.

Take care when desoldering components (especially the diodes) that you don't damage the conductive traces on the circuit board.

The set seems to be working great, for a couple weeks now.

Components replaced:
-----------------------------
C952, C953, C956:
Markings: CapXon 1000 uF, 35V, GF 105F, P738, VENT
13.2 mm diam x 25.5 mm tall
Observations: bulged
Remark: These three caps are in parallel.
Schematic and spare parts list: 1000 uF, 35V
CapXon spec: 1000uF, 35V, 20%, 105 degC, lead spacing: 5mm, ripple: 2780 mA @105degC and 150 MHz, impedance@20degC: 0.019, 5000 hrs.
Replacement: Panasonic EEU-FM1V102 Description CAP ALUM 1000UF 20% 35V RADIAL 1000uF 35V Aluminum Capacitors Radial, Can 7000 Hrs @ 105°C, 12.5 x 25 mm, ripple:3190, impedance: 0.015, lead spacing: 5mm.
-----------------------------
C955:
Markings: CapXon 2200 uF, 16V, GF 105F, P733, VENT
13.2 mm diam x 26.5 mm tall
Observations: bulged
Schematic: 1000 uF, 16V
Spare parts list: not mentioned.
CapXon spec: 2200uF, 16V, 20%, 105degC, lead spacing: 5mm, ripple: 2750, impedance@20degC: 0.022, 5000 hrs.
Replacement: Panasonic EEU-FM1C222, CAP ALUM 2200UF 20% 16V RADIAL 2200uF 16V Aluminum Capacitors Radial, Can 7000 Hrs @ 105°C, ripple:3190, impedance: 0.015
-----------------------------
C921:
Markings: CapXon, 25V, 100uF, KM105F, Vent, P725
Observations: normal, 6.5 x 11.
CapXon spec: Ripple@105degC@120Hz: 145. No impedance spec mentioned.
Replacement:Panasonic EEU-FR1E101B, 5000 Hrs @ 105°C, 318.5mA @ 120Hz, 130 mOhm, 6.3 x 12.7, 5mm spacing
-----------------------------
C947:
Markings: CapXon, 50V, 10uF, KM105F, Vent, P706?
Observations: normal, 5x11
CapXon spec: Ripple@120Hz@105degC: 48 mA, 2000hrs@105degC
Replacement: Kemet ESH106M050AC3AA or Wurth 860240672002
-----------------------------
C954:
Markings: CapXon 47 uF, 35V, KM 105F, P727, VENT
Observations: normal, 6.5x11
CapXon spec: not found, assume ripple@105degC@120Hz: 110mA or 140mA.
Replacement: United Chemi-con ELE-350ELL470MF11D
-----------------------------
C957:
Markings: CapXon, 25V, 10uF, GS85F, Vent, P724
Observations: normal, 5x11
Remark: stabilizes the Vcc to IC907
CapXon spec: ripple@120Hz@85degC: 50mA, lead spacing: 5mm.
Replacement: Panasonic ECA-1EM100B
-----------------------------
C946:
Markings: CapXon, 50V, 2.2uF, NK105F, Vent, P726, [no negative stripe]
Observations: normal, 5x11. The printing on the circuit board indicates a polar capacitor.
CapXon spec: ripple@120Hz@105degC: 17mA, bipolar.
Replacement: Nichicon UEP1H2R2MDD or Panasonic ECE-A1HN2R2U
-----------------------------
C958, C934: 5mm x 11mm Liton RGA 105 degC 25V 47uF without vents---just plain flat tops.
Observations:
Liton spec: ripple @105degC @120Hz: 97 mA. endurance: 2000 hrs@105degC.
Replacement: Panasonic EEU-FR1E470B
-----------------------------
ZD906:
Observations: It was covered with a blob of white opaque glue. After pulling the blob away with long-nose pliers, there remains something like a more translucent white stringy glue or grease between the cap and the board. The surrounding area of the circuit board is noticeably discolored (about a half-inch each side).
Remark: I'm concerned about the possibly of heat damage to nearby C945, a blue disk capacitor.
Remark: The board layout diagram in the service manual reverses the positions
of ZD906 and D924 relative to my board.
Schematic: P4KE250A-E3.
Spare parts list: absent.
Replacement: Vishay Semiconductor Diodes Division, P4KE250A-E3/54, TVS DIODE 214VWM 344VC AXIAL
-----------------------------
ZD908:
Observations: The surrounding area of the circuit board is noticeably
discolored (about a quarter-inch each side).
Schematic:BZX79-B18.
Spare Parts List: absent, but BZX79-B18 A is used for a different model.
Replacement: Nexperia USA Inc., Manufacturer Part Number:BZX79-B18,133, DIODE ZENER 18V 400MW ±2% Through Hole ALF2
-----------------------------
ZD902, ZD904:
Remark: These voltage suppressors are wired in series.
Observations: surrounding area of circuit board very slightly discolored
Schematic: P6KE120A
Spare Parts List: absent, but P6KE120A DO-15 is used in other models.
Replacement: Fairchild P6KE120A
-----------------------------
D924:
Remark: This is next to ZD906, so it may have gotten pretty hot.
Schematic: UF1007
Replacement: Diodes Inc. UF1007-T
=================================

[Junkrepair]

I also replaced D908 with a Fairchild RGP10D.