Another DCC-130 problem

Recorders, Players, etc.
1

So, I got a DCC-130 to get rid of the problem of having to desolder/resolder when having to change the belt (which somehow fails quite easily if they are left unused for some time). And I got another headache:-)

Sides A + B seem to play analog quite ok (I haven’t tried much and I am afraid I will have to).

Side A plays DCC perfectly.

Side B starts playing ok (with all0s when looking at errors)

After a while (sometimes 5 minutes, sometimes after 1) suddenly starts to have errors on half of the heads and eventually playback stops. My suspicion is that this period (5 minutes to much less) becomes sorter if the player has played for some time = not totally cold.

I tried a new belt as well, problem remains. Caps have been changed previously. I also had to repair one ground connection to the headphones socket (trace had no continuity).

Is there any known problem or guide I should follow to find the fault? I will obviously have to somehow check the tape path (I guess by removing the top lid). By the way I tried with a second pinch roller from a DCC-170 I had (which was playing side B but …not A because of a torn head flex), same result.

Any help will be greatly appreciated….

Andreas

2

Hi,

Might be temp related on components?

Have you tried using hot/cold technique on various components.

Never ran into this issue btw.

3

So… After a long time I found some hours to spend on this one.

First check with freezing spray showed that when the problem appears, if you spray the PCB it starts working correctly until it gets hot again. I checked spraying different areas of the PCB, a bit far from each other, and the result was the same which means that what is “fixing” the problem is shrinking of the PCB due to cold. So I must be hunting some corrosion/microcrack/via problem.

I also noticed that someone previously had changed capacitors using short profile through hole electrolytics. Although short profile, they were still big, pressing the lower PCB. Moving the upper PCB out of the unit, seemed to cure the problem (same effect as cold spray), again pointing to microcrack somewhere.

Those “new” electrolytics looked quite unhealthy, so I decided to replace with tantalums. I found one 100uF that measured 20nF (!) and another one with very high ESR. I replaced all and after that the problem still gets back from time to time, but much less frequently.

While checking I also noticed another issue: when the unit gets hot, severe distortion (with pops) starts to appear on both channels (especially when phone level is > 4), and when it gets even hotter, one channel is almost muted and you can only hear pops. These distortions are absent from line out.

All these symptoms disappear when the area near/around the phones output is sprayed cold, but so far I didn’t manage to locate a single faulty place. This tells me that I have 1) at least one more faulty capacitor (at high output levels, even when cold, there is distortion which I find more than normal) and 2) a second problem of microcrack from corrosion.

I will start from the most obvious, the severe distortion, by measuring the components on the amplifier section and by using the scope to locate where the distortion begins, and I will keep you posted.

4

Update 2

After measuring voltages, I realized that B4 was around +2.7V instead of +4.6V in service manual. A thermal camera also indicated great heat there, and also on the dc input - so much that it had started to melt the plastic cap under the board around the dc input. Funny fact: using another dc power supply of capable of 600mA instead of the 3A of my bench supply, caused it to even turn off at rewind/ffwd because of the voltage drop!

Inspecting the board my eye fell one tantalum installed with wrong polarity (by observing the +/- designation on the PCB). I am pretty sure the same happened with the capacitor I replaced, as I usually follow the polarity of the cap I remove.

After reinstalling a new capacitor correctly, the voltage of B4 was to +4.7 and overheating stopped (and also all symptoms of pops etc). So either the problem with audio failing was thermal protection kicking in, or if there is some microcrack problem which now is not present as there is no excessive heat to bend the PCB. In any way used the machine all Saturday night and Sunday morning and it worked pretty ok. (I also guess the wrongly installed cap was the one measuring 20nF having been cooked for good!).

(BTW for most of time I was using a 6V ac adaptor instead of 5.5V. With that great power dissipation that ended up in “melting the plastic” but not killing the zener diode at the input, means great engineering and part selection on the power supply circuit. It also means that the dcc-130 can safely tolerate using a commonly found 6V ac adaptor supply instead of a 5.5V one).

The only problem now (minor but annoying) is that sometimes (on side A only) after rewinding/skipping to previous track, I (immediately) start having errors on heads 1 / 2 (usually from 0 to 1 on either head - after the overheatind stopped I never ended up to the point of dropouts, but that can be random).

When switching A< - >B< - >A seems to return to normal for the rest of A side playback. Could a problematic pinch roller cause this? (pinch looks fine in the eye, but that is no proof)?

5

The pinch roller could be the reason for sure. Seen that lots of times.

Good progress btw.

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6

Update 3

While waiting for the new pinch rollers to arrive (thanks Ralf for the immediate dispatch!), the “deaf” left channel reappeared after the unit was getting hotter.

I noticed that I had made a mistake and the problem was also present in line out. When the board was out or slightly touched, it returned to normal, and “provoking” it by bending the PCB would cause it to mute again.

With service manual in hands, I checked the part of the board when the problem was present. Shorting left and right channel caps C346 and C345 made no difference while sorting after signal return to that side, at C347 and C348 the sound “returned”). So, the problem was between vias 133 and 138. Since I already had bridged via 138 with opposite side (as it looked suspicious and was right under a leaky capacitor), I reflowed (with new solder + flux) the 5-6 components for left channel around ic406 and the problem is gone for good. I used it many hours during the weekend and yesterday, problem never appeared no matter how hot, and bending the PCB did not “provoke” it anymore.

So… pinch rollers and that’s it (ok, perhaps I will add a new battery pack (using 18650) from the dcc museum).

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