Discussion in 'Turntables' started by Grotus, Jan 12, 2017.
Yeah, feel like I may have touched something I shouldn't have and fried it.
Ok, that report raises confidence that you're getting the proper readings now. In that case, you've got no voltage off of the core power supply. You'll need to work backwards then.
1) Set your volt meter to measure AC volts. If needed, adjust the 2 probe wires to different jacks if that's required to measure AC volts. Most don't.
2) Now, go back to the board layout above and find the 2 wires on the transformer that are labeled WHT and ORG - white and orange. See where they are attached to the board? Put your meter probes there and measure the AC voltage. Report what you read there. You can use either probe on either connection - this is AC so there's no polarity.
All of this is being done with the Power Switch in the ON position and with the TT plugged in, right?
Okay, will do. Just for the sake of full detail, here are the photos I promised from the last step, measuring the central posts. Yes, all tests being done with the power on and plugged in.
Voltmeter set to DC Volts: http://imgur.com/G8u0tj2
Central Row of posts to be tested: http://imgur.com/ZwN27X8
Test in progress: http://imgur.com/CTgdxn5
Couldn't get a photo of the reading during the test unfortunately.
Yes, you are doing it correctly - thanks for the pics!
I'm concerned now that there's AC either not getting to or not coming from the transformer. That's the next area you're checking.
Okay, that was easy. Set the DVM to the VAC - 200 setting in the picture above, and it read 120.8
So there's power to the board. Something went pop, huh?
Ok, that's what we want to know: That you have a full AC input to the power transformer.
Next, we're going to check the output of the transformer. Keep your meter on AC volts. This time, however, we're going back to that same set of wire wrapped points in the middle of the board.
In the snip below, I've highlighted the 2 red and 1 black wire that comes from the transformer and are wire wrapped to the board. I've circled the 3 wires that we're interested in.
What you're going to do is to take your black lead and connect it to the black wire wrapped terminal. Then, you'll take the red lead and measure each of the red wire wrapped terminals individually. There better be an AC voltage there and it should be roughly the same for both of the red wires.
Unfortunately, I'll out of town the rest of the week and will not be available until the middle of next week. Perhaps one of the other 'arm chair bench techs' around here can pick it up.
To that crowd:
- The OP reports he's got no power to anything on the TT but it did at one time.
- I've had him check the DC output of the regulating transistor and he's confirmed there no voltage there. That would be the red wire-wrapped terminal in the middle of the PS board.
- He has confirmed that there's 120 volts getting to the power transformer.
- Now we need to confirm there's AC getting out of it (suspect so).
Measured per your instructions. Both red posts measured 17.2 on the AC-200 scale.
Hope your trip goes well! Look forward to your return!!
While Dave is out, you have time to get some grabber clips for you meter. The reason I broke that resistor is because a meter lead slipped and boy what that quick, dead turntable.
These allow you to grab only the item you want to connect to, one meter lead at a time.
Did you test the resistance of that one I was able to fry?
Thanks, Shadow, I just ordered a set of clips from Amazon on your recommendation. I feel pretty sure that I accidentally popped something while testing. Total noob doing more harm than good.
As for testing the one you mentioned, I'm not even sure how to do that, honestly. Do I set it to Ohms and put a lead to either pin of it? What shoud it read?
yes, ohms, and it doesn't matter the reading as it is still in the circuit and other items may be in that particular test. If you get something other then the same thing as then the meter leads are not touching on the Ohms setting you are fine. With your meter, not auto-ranging, always start at the highest setting for what you are measuring and step down a notch when the reading is not the number you want. Do all ohm reading with the unit unplugged and turned off until you learn otherwise. for example, can't test an on-off switch with it always off.
De-soldered R100 from the board and tested it like you recommended. There was no reading at all on the meter. I assume that means its blown?
Tested a few other resistors on the board to make sure the meter was reading right, and most of them read where they were supposed to. A couple read low, and may need to be replaced as well, but I'll wait on those until I figure out everything else upstream.
Yes, no reading is Blowed UP! If the other resistors were not spot on but read something, they are probably fine. The reading is being affected by the other parts of the circuit since you are not lifting a leg.
Replace the bad resistor with proper unit and let us know. The part of the board shown above is for the Non-US models. The US model shows a 3.9Ω resistor for the US and no resistor for the Canadian models. I don't know why. Maybe someone could explain and see if that resistor is absolutely necessary or if the jumper used north of the border would work for a test. But someone needs to post a link to the manual or part of the diagram with those details on it. VE has the SM for the PS-X6 and X7 if anyone wants to jump in. Otherwise, there will be a resistor purchased sooner rather than later.
My table came back to life with the replacement of the resistor. Hopefully yours will too and David can finish up getting it all sorted with you.
Thanks, went out and got the resistors and replaced that one. Sadly, it didn't revive the TT. I guess I'm stuck until David gets back and saves me. Thanks for all your help!
OK, back for a few moments. Next step:
- Set your volt meter to DC volts.
- Connect the black lead to one of the black wire-wrapped terminals in the center of the power supply board.
- Connect the red lead to the red wire-wrapped terminal that is closest to the adjustable pot. That's the red wire on the opposite end of that row of terminals where you measured last.
- What is that voltage measurement?
Next, while the black meter lead is still connected to the black wire wrapped terminal, move the red lead over to R100. Measure both sides of it. What voltages do you read?
Good to hear from you again! Okay, the readings are as follows:
Red Post: 2.10
R100: 23.6 and 3.25
* I have pictures I can post tomorrow showing where I put the leads for these measurements.
One thing I did notice is that the Start/Stop light is lit, and I cannot get it to turn off. It was a little sticky when the table worked, but now its activated all the time the power is on. Don't know if that is relevant or not.
Hmmmm, you should be getting ~14 volts where you're reading 2.1 volts. This means that the positive voltage regulator isn't regulating. The fact that you have 23.6 volts on one side of R100 tells me that the main rectifiers are working and the filter cap, C102 is working ok.
Q101, however, isn't turning on. Have you turned the pot, RV101 at all? This could account for that if its dirty. Turn off the 'table, note the position it is in and then gently turn it to one end and then the other 4-5 times - don't force it. Then, put it back in the position you found it. Then, test that same red wire-wrapped terminal again and see if you get some voltage.
Out again until Wednesday....
Back again, after much family and work travel. Okay, so I rotated that pot, even put a spritz of DeOxit on there in case it was crusty. Put it back in place and repeated the measurements from the last step. They have not changed at all.
I, too, have been away for a bit and only now getting settled to pay attention here at AK. On the Start/Stop light, if it doesn't shut off, the auto arm return mechanism is being told it is still engage (think that's right). But all that is bogus until the power supply has been proven to be operating by producing the required voltages. Your testing thus far hasn't met that criteria.
On your measurements, the voltages across the resistor tell me there's very little current flowing through it, which means that Q101 is not conducting as it should. Further, the voltage adjustment, which you cleaned and turned, hasn't made any difference.
This pretty much confirms that Q101 and/or Q102/103 and D5 are suspect at this point. Rather than try to diagnose this thing at the run rate we're going, I'd suggest you consider taking it to a local outfit that specializes in vintage audio gear. Got anyone close like that? Where are you located?
If you hand them this thread, they'll quickly get it diagnosed, I'm sure.
I can understand that you want to learn how to repair electronics - and analog gear in this case. What you do not yet have is an understanding of electronics theory to be able to do the analysis. That's what you rely on the AK armchair bench techs (ACBT's) for. You are, essentially, the eyes, ears and measurement taker. The more accurate those functions are, the better the ACBT's can help you.
On Q101, no need to replace it right now. That's called 'shotgunning' and it usually back fires on you in that you introduce more problems rather than solve the one you have now.
The key to understanding what's happening is the analysis of the voltages throughout the power supply. As you can see from the schematic and the board layout, there are specific expected voltages.
Since you're still in diagnostic mode - you don't know what the root cause is yet - then finding what voltages are in spec and what ones are not is the top priority. As the measuring dude, your job is to record them accurately and present them back to the ACBT's who can figure out from them what's working and what isn't.
Rather than to do the 'check this, check that', perhaps it is better that you go through the entire power supply circuit, take the measurements it calls for and record them on a copy of the schematic. Take a pic of that marked up schematic and post it back here. That will speed up the process.
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