OA2 Tubes not lighting up

Each new day starts with a new surprise. I chose 12 songs on my Seeburg DS100 (not the one that had the sound problem) and started doing other things. I noticed only about six selections had played when the mech parked. I made another selection of one of the songs I had not heard and I got the dreaded 2 scans and park routine. I made several other selections with the same results.

I performed the "D" battery test and no selections are picked up, only the two scans and park.

The OA2 tubes do not light up. I have changed the OA2 tubes with known good OA2 tubes and I have done likewise with the 6X4 tube. OA2 tubes still refuse to light up.

I would suspect a bad socket, but, what are the odds of both sockets going bad at the same time?

Any advice where to go from here would be appreciated?

Best
Darrell

Darrell, this is straightforward. At the lower left hand side of the selection receiver (rear) are two 15mfd 450 vdc caps.

Look for around 400 vdc on one and slightly lower on the other.

Check against the voltages here:
http://www.fileconvoy.com/dfl.php?id=gd ... ca703bb016

A likely culprit is the 2.7k-ohm resistor opening up.

A "bad socket" is of course possible, but simple examination for missing contacts will reveal that. Has this unit been rebuilt?

Rob/NYC

Rob

Thank you I will do as you suggest. I do not reecall seeing your schematic in my printed documentation for this unit.

Yes, it was rebuilt along with the stepper approximately one year ago by a pro from this board.

Best
Darrell

Rob

Is it possible that fused resistor part No. R518 (3,300 OHM - but now has a 3,500 OHM) has failed as we did not get anywhere near 400 volts while the 2.7 OHM resistor appears to have continuity in circuit?

The two mfd 450 vdc caps were actually two 20 mfd caps that the pro put in.

Thank you
Darrell

The 20 mfd's are fine as a value (I often used 22 or more if that is what I had) the question here is simple: Do you have anywhere near 400 vdc at the first filter cap? That voltage is on one side of the 3.3k (3.5k is OK) the roughly 340vdc is on the other side of that resistor.

Since the resistor is wirewound and appears good, in these sorts of situations you first look for excessive loads as indicated by much larger drop across the resistor. This could be due to shorted cap (yes, new ones can short) or some other circuit abnormality.

I had one case where that first cap went open and the 0A2 were barely lit with input voltage being around 320vdc. There was some filtering due to the following cap and surprisingly, the machine had still worked normally.

If the drop appears to be in the normal ratio and the voltage going into the resistor appears low, check the AC volts into the 6X4. this will be pin 7 to chassis ground.

The schematic shows about 325 vac. If that is low is is likely that the transformer has gone bad or that the other end of that winding has a poor ground connection to the chassis.

Rob

Rob

I have 475 vdc on one side of the 3.5k resistor and 14 vdc on the other side of the resistor. Since it is not anywhere close to 340 vdc I would suspect this part is defective and needs to be replaced? or are there other tests I should do first?

Thank you
Darrell

I agree. It is unusual for that resistor to open up. What is odd is getting a erroneous ohms reading. My guess is that the resistor burned out and there is a residual of carbon deposit inside the ceramic at the break point that is providing the bridge for the meter test.

i recommend adding an in-line fuse 1/2 amp fast in series with Pin 7 of the 6X4.

Rob

Rob

I have attempted to locate a 3.3k Ohm Fuse Resistor and the tech at mouser said they are not available. Does the in line 1/2 fast acting fuse you suggest installing remedy/replace the missing fuse that is missing from the resistors that are available?

Where do you get 1/2 amp fuses and what voltage should they handle? It looks like pin 7 is handling 325 volts and the 1/2 amp glass fast acting fuses I can find are only rated for 250 volts?

Thank you
Darrrell

Darrell, I've never had to replace the 3.3K but I would just use any old 5 (or more) watt wirewound there. The fuse is needed imo to prevent a shorted 6X4 from destroying the transformer. Two of the selection units I bought had trans ruined that way -so they were cheap

I use any standard glass fuse. I have had two blow properly, one in a TSR-3 when a cap shorted and another in the B+ of an amp. Make sure the fuse is enclosed in an inline holder.

Rob

Parts arrived and put new 3.3k ohm resister in and also put 1/2 amp fast blow fuse in series at pin 7 of the 6x4 tube. OA2 tubes now light up, but still two scans and park routine going on?

Will try D battery test tomorrow. The unit is playing every record, so I guess I need to proceed to "G" Test.

I do not have a Seeburg Test Lamp to perform this test. What are the specifications for making/buying such a test lamp?

While listening to both sides of 50 records and looking for specs on test lamp, I remembered having a similar situation a while back. Ron had me pull both Cinch Jones plugs Deoxit them, work them in and out a few times to remedy the problem.

You guessed it, the unit is now back on line and operating as intended!

Many thanks to all that assisted.

Best
Darrell