CA-800, no output from amp

OK, just a few basic points to verify:

I set my DMM on the 200 Ohm range?

I can see the three solder points for each transistor on their boards. Do I test them in place or do they need to be removed? The latter operation would be way more than I would consider doing.

How do I tell the emitter, collector and base terminals apart?

Finally, do these questions make you want to shout "BACK AWAY FRON THE YAMAHA"?

To accurately verify a leaky or shorted condition at least 2 of the three transistor leads need to be isolated from the circuit. Short answer .yes.they need to be removed.Otherwise you will get misleading resistance values from the surrounding components within the immediate area of the circuit.
 
To accurately verify a leaky or shorted condition at least 2 of the three transistor leads need to be isolated from the circuit. Short answer .yes.they need to be removed.Otherwise you will get misleading resistance values from the surrounding components within the immediate area of the circuit.

According to the referenced book, Homer states that you can accurately check a transistor IN-circuit using the diode test function of the DMM. The OP stated he set his DMM to check ohms.

Question: Though both measurements are displayed in ohms, is there a difference in the way the DMM takes the ohm readings vs diode test which would require out-of-circuit testing for accuracy? Or, was Homer just stating the you'll get a "good enough" reading to determine basic functionality?

He does state in other tests to remove such things as diodes (at least one leg) from the circuit for accurate readings. Obviously from a business perspective, the less time spent troubleshooting, the quicker turnaround and more profit a tech can make. So not removing unless necessary would make sense.

The way I was understanding his approach was to do everything as possible in circuit until you find some suspect numbers, and then remove from circuit to verify.

John
 
Fortunately, in the CA-800 the situation is very simple. If you remove the fuses F601 and F602, the power transistors are almost isolated from the rest of the circuit and you can test them without desoldering a single lead. The power transistors are in the TO-3 metal can case style, thus the collector is common to the case.

The most important junction to test is the C-E. Connect one lead of your tester to the case of the power transistor (his collector) and the other test lead to the bias test point corresponding to the transistor under test. For example, to test TR610, use the TP4 test point. This is the emitter of TR610.

Unless the driver transistors are shorted between C and E, you should measure a very large resistance between C and E of the power transistors, in both direction. I mean, measure the resistance with the + test lead of your tester on the collector, and repeat the measurement with the - test lead on the collector.

If you follow the traces on the board it should be easy to identify the base, and test the other junctions B-C and B-E
 
Fortunately, in the CA-800 the situation is very simple. If you remove the fuses F601 and F602, the power transistors are almost isolated from the rest of the circuit and you can test them without desoldering a single lead. The power transistors are in the TO-3 metal can case style, thus the collector is common to the case.

The most important junction to test is the C-E. Connect one lead of your tester to the case of the power transistor (his collector) and the other test lead to the bias test point corresponding to the transistor under test. For example, to test TR610, use the TP4 test point. This is the emitter of TR610.

Unless the driver transistors are shorted between C and E, you should measure a very large resistance between C and E of the power transistors, in both direction. I mean, measure the resistance with the + test lead of your tester on the collector, and repeat the measurement with the - test lead on the collector.

If you follow the traces on the board it should be easy to identify the base, and test the other junctions B-C and B-E

Thanks, this seems to make it simple. I noticed that each output transistor had a corresponding test point.

My cheap DMM has a diode test. Here is the info on the new version, mine is identical except it was made before Fluke convinced the courts it had actually patented the colour yellow:

http://www.vellemanusa.com/us/enu/product/view/?id=350297

I will pull the fuses, put my DMM on diode test and get back later with my findings.
 
I pulled the fuses from the output board and the board underneath to test them while I was at it. I wondered why one of the 400ms 250v fuses underneath looked weird. I found out when I pulled them. They are like slinkeys and the end caps are loose so they have gotten pulled out and stretched over the years as they are pulled and tested. I think I will replace them with something fresh. What exact type should I ask for to avoid problems?

I tested the outputs on one side using the test points. On diode test my DMM started off indicating 1. On each output, one direction had no effect, the display stayed at one. In the other direction the reading jumped around, settling higher than 1 but less than 2. I checked the outputs using the pins soldered to the board for the heck of it. the two leads across the top yielded .333 in both directions on both outputs. The other pairs would give 1 in one direction and a reading of between .7 and 1.5 on the other.

I might as well find out if this is at all meaningful before doing the other side.
 
It's not clear to me what your DMM displays. Can you test a simple diode, both directions, to see what your DMM displays? Most DMM, in diode test mode, display the voltage drop in mV. For example, if you test a diode you will get something like 600 in one direction, and OL (for Overload) in the other direction.

Consult the manual for your meter, or try a simple diode to familiarize yourself with this testing function on your meter.
 
This meter displays forward voltage drop in one direction and displays 1 if the connection is reversed.

On all the ouputs I get 1 between the case and test point in one direction and in the other direction the reading cycles between 1 and values such as 1.853, 1.548, 1.397 and repeats.
 
At this point I will wait until my tech looks at it.

Any suggestions on what type of fuse to ask for to replace those ones in the PS that came apart?
 
Got the CA-800 back from our very own AKer Chap. The problem was a few caps in the protection circuit that bad and keping the relay from coming on. Seems the amp is very healthy, very low DC offset, re-biased and even has a new power light. I just hooked it up to confirm that it does inded work in both A and A/B modes (powered off before switching).

Looking forward to giving it a good listen. I really love my CA-1010 so I expect this should be a nice one also.
 

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And Rob was right, this one is vinyl wrap also. I could have sworn it was wood since it was craking and lifting just a bit all across the top of the case. Must be the plywood underneath that was dried out and cracked a bit.
 
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