
HELP! Low voltage reading
#1
Posted 25 November 2017 - 06:10 PM
#2
Posted 25 November 2017 - 06:51 PM
#3
Posted 25 November 2017 - 07:09 PM
#4
Posted 25 November 2017 - 08:18 PM
I had this happen one time with a different model stereo. Ended up being a bad electrical connection at the transformer. Can't remember if it was a dirty voltage selector switch or if it was dirty contacts on the DC (barrel plug) input on the back. Either one could cause a low voltage issue.
Another place I would look is at that switch. You may want to remove power from the radio and ohm out the switch to see if it is restricting power. Powering the bulb through that switch could've arched a contact within it and now the switch is not sending full power from the transformer to the stereo circuitry.
I'm not nearly as experienced as you guys but I would check voltage going in and coming out of the transformer first. Then look at that switch second.
#5
Posted 25 November 2017 - 09:17 PM
I had this happen one time with a different model stereo. Ended up being a bad electrical connection at the transformer. Can't remember if it was a dirty voltage selector switch or if it was dirty contacts on the DC (barrel plug) input on the back. Either one could cause a low voltage issue.
Another place I would look is at that switch. You may want to remove power from the radio and ohm out the switch to see if it is restricting power. Powering the bulb through that switch could've arched a contact within it and now the switch is not sending full power from the transformer to the stereo circuitry.
I'm not nearly as experienced as you guys but I would check voltage going in and coming out of the transformer first. Then look at that switch second.
Thank you for the input. I really appreciate it. I actually have checked everything you mentioned and tried batteries as well. I believe it’s somewhere on the power rail or actually on power board but can’t really find it in the scheme.
#6
Posted 26 November 2017 - 07:48 AM
701b 16.11
701e 18.2
701c 2.80
702b 17.23
702e 18.1
702c 17.97
Notice collector side is supposed to have high 16.7v reading according to scheme but only has 2.80v reading. There is a resistor between base side 702 and Collector side 701. I tried changing resistor with used resistor I found with no change. So I’m Hoping someone can help. Here is the scheme for area.

Also readings on Q706 are as follows
B 2.67v
C 2.79v
E 2.12v
#8
Posted 26 November 2017 - 09:15 AM
Oh and if possible, check PS board with output connectors disconnected if possible to see if the issue is with the PS, or if you have a short after the output that is dragging down voltage.
#9
Posted 26 November 2017 - 09:27 AM
#10
Posted 26 November 2017 - 09:51 AM
Mmm....If PS board is power supply board then that’s what I’m working on.
Ok I understand
OK I disconnected the power board and checked and yeah I’m getting the correct readings now I’m getting correct readings on Q701
So now I’m stumped.
#11
Posted 26 November 2017 - 10:28 AM


#12
Posted 26 November 2017 - 11:22 AM
#13
Posted 26 November 2017 - 11:50 AM
are not as good as it used to be. I did check 902 and looks to be like low-voltage 2.38 or so volts going into leg 4 which I guess should be 10.2v
while the deadbulb was hooked up I held the two leads to the joints to test it and that’s when everything went dim
#14
Posted 27 November 2017 - 11:44 PM
Bill, I really hate to say this and please don't take this the wrong way, but this isn't the first time you've tested something live and something goes kaput. So I suspect that your test probes are too thick, not sharp so they slip on the joints, shaky hands, whatever. The point is that it's easy to fry something when boards are live. I recommend that you get yourself a good set of micro spring hook probes. They have small hook shaped ends that hook on and don't let go. I use them all the time in locations where I don't feel 100% comfortable that something might slip and maybe cause a small puff of smoke. I'm serious. They aren't expensive and will end up saving you tons of headaches the more you use them. Plus the good thing is that once the hooks are clipped on, it leaves you hands free.
Now as to your VZ2000, something is dragging down the voltage. You mentioned you checked IC902 and the voltage is low, but we already know that. The question is whether A the supply at the pin is low or B the IC itself is internally shorted dragging down the supply. Why you focused on IC902 I don't know, but I am guessing that anything connected to that supply rail right now is going to be showing low voltage. You need to find the source of the short or drain. There are a couple ways to do this. The simplest for you right now is to start disconnecting to isolate the problem and narrow down possibilities.
Based on your original measurements, C:Q701is showing low voltage condition with PS hooked up but normal voltage disconnected. Looking at the circuit diagram, that rail also powers 2 connectors: CNS403 to tape deck, and CNS501 to microcomputer. Disconnect one or the other and see if the voltage returns to normal. If voltage is normal with one of those connectors hooked up (and not the other), at least you've narrowed it down.
Follow this same technique to further isolate. Once you've narrowed it down to the problem board, then you are getting somewhere.
#15
Posted 28 November 2017 - 06:13 PM
#16
Posted 04 December 2017 - 02:30 PM
#17
Posted 05 December 2017 - 07:30 AM

#18
Posted 05 December 2017 - 09:32 AM
#19
Posted 05 December 2017 - 11:37 AM
Think I’ve narrowed it down to IC amp chip.
Wow. Who would've thought. Do you think it was just a coincidence that this happened while checking the bulb?
#20
Posted 05 December 2017 - 11:50 AM
#21
Posted 05 December 2017 - 07:08 PM
#22
Posted 05 December 2017 - 09:19 PM
Bill I have some amp chips in my scrapper vz 2000 e , I'm not sure if they are the same as the USA vz 2000. I haven't removed them yet but if you need them let me know .
Not 100% sure just yet Floyd but I’ll let you know. Thank You
Wow. Who would've thought. Do you think it was just a coincidence that this happened while checking the bulb?
Think I’ve narrowed it down to IC amp chip.
Not sure yet still checking
Doubtful, amps don’t fry unless the outputs are shorted, which can cause damage quickly.
Haven’t had much time but one chip seemed shorted. Hopefully I’ll have more time this weekend.
#23
Posted 30 October 2018 - 05:42 PM
#24
Posted 31 October 2018 - 11:03 AM
#25
Posted 19 November 2019 - 04:18 PM
Hi, I have the same problem with a vz-2000. Do you remember the changed transistor?