Revox B225 extremely Hot SAA7010 - diyAudio
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Old 27th August 2013, 07:08 PM   #1
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Default Revox B225 extremely Hot SAA7010

Anyone have any incite as to what could be causing the SAA7010 to get very hot. This is what happened thus far.
1. Opened to lube the tray and clean it as it was squeaking.
2. Pulled boards out and blew dust off. Measured all caps.
3. Found cap 100uf/25v ( C26 on schematic) to be low on power supply board.
4. Found 2 100uf/25v caps on same board as SAA7010 to be very low, so replaced them as well.
5. Also found cap 100uf/10v on same board low, and replaced that as well.
6. All caps were replaced with Panasonic 100uf/50v.
7.After finishing and plugging everything in, hit power and everything lit up. But I noticed that i put the (C26) cap in backwards. So that was corrected.
8. Now disc spins briefly, SAA7010 gets very warm, and NO TOC. If I remove the SAA7010 disc will actually spin much longer, but no TOC.
9. Also, swing arm of CDM-0 stays towards the inner, closer to spindle, it refuses to travel to center or away from spindle.
10. Finally, within it seconds of it being powered on, SAA7010 gets extremely hot.

Any help or suggestions?
Thanks
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Old 27th August 2013, 09:26 PM   #2
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IC13 may have been damaged as without it there is no data address lines and therefore no signal.
The laser will not move from the TOC position until it has read the TOC.
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Old 27th August 2013, 09:41 PM   #3
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I tried a 2nd one, but nothing changed.
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Old 28th August 2013, 05:54 PM   #4
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After further testing, the SAA7010 is definitely bad. Swapped it into another player and it gets awfully hot and won't read TOC. Have inserted a new SAA7010 into the Revox, but it just spins for a few seconds and stops. Must be a short somewhere or a bad resistor/diode? Without an oscilloscope I'm not sure I can find.
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Old 28th August 2013, 07:12 PM   #5
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Default Update..

So I have tested all the diodes on the power supply. Diodes D5,D6,D7,D8,D9 all test as if they have an open circuit. I get a reading in both directions? Is that possible? Can they all could be bad? D11-D14 test fine. I believe they are the 1N4001 diode (50v 1amp).
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Old 29th August 2013, 01:08 AM   #6
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Have you confirmed +5V supply and ground are now good at the C26 disaster site? Hopefully you didn't refit the same cap?

When you say you have measured diodes, what were you measuring, and what with? In or out of circuit?
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Old 29th August 2013, 01:26 AM   #7
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Quote:
Originally Posted by PlasticIsGood View Post
Have you confirmed +5V supply and ground are now good at the C26 disaster site? Hopefully you didn't refit the same cap?

When you say you have measured diodes, what were you measuring, and what with? In or out of circuit?
The C26 cap did not blow as it was on for no more than 5 seconds. I inserted a new capacitor. The disaster cap once it was pulled still measured 75uf.

The diodes were tested in circuit so reading is not accurate. I'm in the process of devising something that will allow me to test it in circuit. Have not tested voltage yet on account board. IC 13 is new so that is fine. Will test diodes in the next day or 2.
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Old 29th August 2013, 08:57 AM   #8
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Quote:
Originally Posted by isitrisky View Post
The C26 cap did not blow as it was on for no more than 5 seconds. I inserted a new capacitor. The disaster cap once it was pulled still measured 75uf.
But it was 100uF
I guess the current was limited somehow, either by the regulator or a fusible resistor.

It's unlikely to be a coincidence that the SAA7010 failed when it did. Also unlikely that lots of diodes blew IMO. I would check for correct DC voltages at regulator outputs. If voltages are OK, then so are the diodes. Also check the voltage and ground at each chip that uses the +5V supply.
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Old 29th August 2013, 08:58 PM   #9
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Tested the power supply rail regulators IC4-IC9, they measure according.
Tested all the 5v points and they measure fine.
And Q6 and Q7 measure according as well.
Now I, at a loss?

Last edited by isitrisky; 29th August 2013 at 09:17 PM.
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Old 30th August 2013, 02:14 PM   #10
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If the 7010 still works in the good machine, and gets much less hot there, and the supply voltages and ground at the chip are good in both machines, then something's wrong on at least one of its other pins.

Perhaps if you take the 7010 out of both machines, and measure the voltages on all the pins, you will find a difference? Measure DC and AC, since you have no scope. Measure with the machine in stop mode first, and then in play mode, until you find a difference.

We should be concerned not to wreck the good 7010, but if the above turns up no clue, then consider repeating with the chip in place.
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