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New 465 issue I posted a video
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On Mon, Jan 3, 2022 at 12:43 PM, KB2LMN wrote:
This is consistent with what you are seeing on the screen: ramp went down (and past) its final voltage. The dot(s) you are seeing are with horizontal sweep at all the way to right. In normal operation it should trigger reset and Q1036 collector should fly back to ~ 12-13V. Q1002B Emitter 13.46 Base 12.71From measurements first set is A, second set is B. Base of B side is connected to Q1036. Base of A side is connected to a fixed voltage ~ 12.7V. If this measurement is correct Q1002B has a base-emitter open or poor connection to PCB. Its base is ~ 13.5V below its emitter. For the correct operation its emitter should not be more than 0.7V below emitter. With emitter of Q1002A/B not following Q1036, Q1012/Q1014 doesn't see ramp has reached its final point. or B, looking at the board it is on the bottom right, looking at theThis is also off. With Q1002A/B emitter at ~13V, cathode of CR1011 should be ~ 14V or so. CR1011 should be off and R1011 should pull base of Q1012 to ~5V. However, you are measuring 2.58V. Q1014 Base -0.545 Emitter 0.131 Collector -2.633Base of Q1014 is connected to a voltage divider R1016/R1017. One end is at +5V the other end is at 0.192V (collector of Q1012). However, the measurement of base is at -0.5V. This should not be possible without a fault. If these three transistors are on sockets I recommend testing Q1002/Q1012/Q1014 off the circuit. There could be multiple faults. With transistors off you can also measure R1013. Ozan |
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Correcting typo for Q1002B:
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"For the correct operation its base should not be more than ~0.7V below emitter. " Ozan On Mon, Jan 3, 2022 at 01:14 PM, Ozan wrote:
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OZAN,
(I referred Andrew to you. Thanks again for your help! I hope to restart my further troubleshooting on the sick Sweep of my own TEK475, next week. In view of Holiday Time, I did not have time to further investigate, but your help is invaluable). One question on the TEK465 of Andrew for the benefit of the forum: Can anybody post a picture the "blocks" (5V TTL) which are supposed to be visible at the A+ Gate Out (and the B+ Gate out) BNC connectors at the back of the scope?. ( NB This is IMO not Off Topic, but can provide additional info to Andrew (provided he has a second scope). As you know, I do NOT get nice blocks (even after terminating the output (s) with a 50 OHm terminator T-BNC, as suggested by yourselves). Hence, I do no know whether the "blocks"(rather needles) are supposed to look like the ones I see. I will also post a picture, and will now use a higher level analog scope (4 x 100 MHz), a PHILIPS PM3264. (This should avoid measuring artifacts). I think montoring A+ Gate Out (and B+ Gate out) might provide more info. Anyhow, a BIG thanks for your help to the Forum Members. I follow this topic with great interest! |
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On Tue, Jan 4, 2022 at 12:36 AM, Redguuz wrote:
Can anybody post a picture the "blocks" (5V TTL) which are supposed to beI don't have a 465 or a 475 but on a 485 they look like the picture in the following link with 50-ohm termination: /g/TekScopes/photo/262059/3193915?p=Name%2C%2C%2C20%2C1%2C0%2C0 You can try looking at the Gate outputs with terminating to 50-ohm at the scope or using a 10x probe (in case they can't drive 50-ohm without distortion) at the BNC connector directly. For Andrew's 465 most likely A-Gate will be stuck high since sweep is not ending Ozan |
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On Wed, Jan 5, 2022 at 03:05 PM, KB2LMN wrote:
Hi Andrew, You already identified the problem with the sweep circuit with your measurements and I added my comments to /g/TekScopes/message/189380 Gate outputs are at the back of 465, Gate-A signal goes high (note says 5.5V) during the sweep. You can pick a slow sweep speed like 10us/div so that termination of the cable is not that critical and observe Gate-A BNC on a second scope. On a working scope you should see pulses that match the sweep time, on your 465 with the fault most likely you will see it stuck at high. Since your measurements on transistors already show problems Gate output won't add much new information. Picture of the 465 boards show transistors are in sockets, sometimes connections become poor and reseating them may help. Removing transistors to test is easy, at least you should see the B-E and B-C diodes if you don't have a transistor checker. R1013 should also be checked in case it went open or its value increased. Ozan |
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KB2LMN
Ok I¡¯ve been sick with Covid so haven¡¯t had any energy to look at anything. I did pull the transistors check with a Chinese MK-328 tester and they show fine. I also cleaned the pins and sockets with99.9% isopropyl. I checked R1013 (2.32k 1%) as suggested and it tests 2.3177k on my Fluke 8824A 4 wire.
Now I¡¯m beet and heading back to bed. Thanks for all your help. |
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