general-el: 'Locomotive'; 10T1 - restoration tips

These GE Locomotives are popular TVs for collectors, and restoration threads come up often.  I just finished a 10T1 (similar to the 805 and other Locomotives), and thought I'd pass along some of the fixes, since these seem to have a pattern to them, with most of these sets needing some of the same things.  In addition to the usual replacement of paper and electrolytic capacitors, replacement of bad tubes, and cleaning of tuner and potentiometer contacts, the following problems were corrected in this set:

1.  Open filament choke.  Just one bad one in this set, but sometimes you'll see multiple failures, due to corrosion with age.  The inductors in question are L371-L375 in Rider, or L51-L55 in Sams.  Replace with any low resistance (less than 3 ohms) ferrite inductor (the ones that look like a 1 watt resistor with a single layer coil around them of about #24 wire).  These are easily scavanged from junker sets.

2.  Burned up filament string series dropping resistors, along with their terminal strips inside the HV cage.  Replaced with modern 10 watt 75 ohm power resistors and some new terminal strips.  The resistors are R373 and R374 in Rider, R116 and R117 in Sams.

3.  Open 1700 ohm power resistor in focus circuit.  This is located on the little vertical circuit board on the top center of the chassis under the picture tube neck.  It's R377 in Rider, R111 in Sams.  Replace with modern 1700 ohm 5 watt resistor.  Alternatively, a 2000 ohm 5 watt resistor with a 12K ohm 1 watt resistor in parallel.

4.  Replace the selenium rectifiers with 1N4007 diodes.  To bring the B+ back to the correct value, remove the 4.6 ohm power resistor (R115 in Sams, R372 in Rider) and replace it with a 20 ohm 10 watt power resistor (or two 10 ohm 5 watt power resistors in series, as I did this time).

5.  Replace the "large" micas in the horizontal AFC to improve sync stability.  I replaced them with 630 V polystyrene caps, but 500 V micas will also work.  These are the following:

3900 pF:  C96 and C102 in Sams, C398 and C404 in Rider
1800 pF:  C99 in Sams, C402 in Rider
1000 pF:  C101 in Sams, C403 in Rider

If the sync is still behaving badly, check all resistor values in the sync separator and horizontal AFC stages, and also replace remaining small value micas in these circuits.

6.  Speaker replaced.  It's kind of funny, but for some reason, the location of the speaker on these GE chassis is right where the serviceman is tempted to grab the chassis.  I've damaged a few speakers myself on a few of these chassis, and I also notice that the speakers already tend to be damaged by previous servicemen in the past.  This set had a totally destroyed speaker when it came to me.

7.  This set has the "faint white line" problem when using with certain signal sources (such as the Digital Stream DTV converter box).  This was discussed in great depth in this Philco Predicta thread on ARF.  The net is that increasing the value of a capacitor in the filter network right after the video detector can improve this a lot.  In the GE 10T1, the capacitor is a 5 pF capacitor inside the video detector can (L36 in Sams, L247/248 in Rider, with the capacitor itself labeled C266 in Rider).  To fix the problem, you add an additional 47 pF in parallel with this capacitor.  Fortunately you can do this on one of the external terminals of the video detector can; you don't need to go inside it.  Look for the terminal with L37 (Sams) or L249 (Rider) connected to it, and add a 47 pF cap to chassis ground (right next to the can; don't use the negative common bus).  Choosing the value is a matter of taste.  With about 30 pF, the sharpness of the picture is hardly affected at all, but the faint white line still shows up a bit.  At 60 pF, the faint white line is completely gone, but picture sharpness is noticeably affected.  47 pF looked like a good compromise on this set, although sometimes I choose lower, since I like a very sharp picture.

8.  Although I often replace the old germanium diodes (this GE has one as the video detector, and another one in the DC restoration circuit), the ones in this set seem to be holding up nicely.  Will keep an eye on it for a while.  Not a bad idea to replace them if you have video image quality problems, or want to prevent a future failure.

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