You can also do it by playing music through it and make a probe that goes into the tape monitor on an integrated amp or receiver. That's what I've always done. I can hear differences in music much better than sine waves.
FET replacement
- Thread starter Vintagecasey
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Vintagecasey
Well-Known Member
I don't have a signal tracer or a scope someone told me that you can do it with a multimeter but I don't know that for a fact.
i am finally making a proper one after using a ghettoad setup i made years ago.
still waiting on the pcb but i got the box and mounted my speaker.
PCB Item 3
Printed Circuit Board # 3 AWA Signal Sniffer, an AF & RF Signal Tracer (Bare PCB Only) Price: $16 including shipping to USA addresses. To order this product, click on the button to the right. The AWA Signal Sniffer PCB circuit … Read More
www.antiquewireless.org
tony made a video about it last year:
you still need a way to inject a 1khz VERY small signal into the phono stage. i mean small. less than 5mV.
phono stages handle delicate signals and they are not that easy to trace the signal thru it because the level is so low until it gets to the output.
if the problem is IN the phono stage, i don't think that a dmm is the way to go.
i am finally making a proper one after using a ghettoad setup i made years ago.
still waiting on the pcb but i got the box and mounted my speaker.
PCB Item 3
Printed Circuit Board # 3 AWA Signal Sniffer, an AF & RF Signal Tracer (Bare PCB Only) Price: $16 including shipping to USA addresses. To order this product, click on the button to the right. The AWA Signal Sniffer PCB circuit … Read Morewww.antiquewireless.org
tony made a video about it last year:
View attachment 3820321
That is vastly more complicated than it needs to be.
I have a nifty little reverse RIAA adaptor that allows me to hook a CD player (or other line level source) to the phono stage, and I just listen through an amp and speaker. I was gonna do a write up about it when I built a new probe to replace my old one, but, I didn't.
anytime i have ever brought up signal tracing on this forum, someone has to piss on my procedure or gear that i use yet they didn't have a damn thing to offer beforehand.That is vastly more complicated than it needs to be.
I have a nifty little reverse RIAA adaptor that allows me to hook a CD player (or other line level source) to the phono stage, and I just listen through an amp and speaker. I was gonna do a write up about it when I built a new probe to replace my old one, but, I didn't.
messaged received.
i will never bring up signal tracing again.
I'm sorry buddy, I didn't mean it like that. I wasn't tryin' to bust yer balls.
Vintagecasey
Well-Known Member
So, can it be done with a DMM set to vac or is that a possibility? Can I assume the problem is in the phono 1 circuit?
No, not really.
I explain the issue with using a DMM in post #25. Do you know your DMM specifications?
What is your source, level frequency ?
Use your DMM to measure your source as a start, you know the gain of each stage, so determine if it matches.
I am pretty sure I can test your circuits with my HP 3478A, it's more than capable.
What is your source, level frequency ?
Use your DMM to measure your source as a start, you know the gain of each stage, so determine if it matches.
I am pretty sure I can test your circuits with my HP 3478A, it's more than capable.
Vintagecasey
Well-Known Member
First, I'm not trying to cause any trouble with the members. My knowledge is limited so sometimes when you say signal Trace that's over my head. These are the tools at my disposal.
I didn't see a reply to the question and suggestions above. @rcs16 is making excellent suggestions by the way!
Recording DC voltages is critical for troubleshooting, and I'd recommend against the shotgun approach. Replacing parts one after another usually ends up costing you a lot of time and money on parts, risking damage, and frustration.
It is possible to use a DMM in ACV mode to measure output levels throughout the circuit to the output, but be careful about loading the circuit with the probes/leads/meter, especially with FETs. You should use a low-level sine wave so your meter can read a steady frequency. You can download a signal generator phone app but it is very likely to damage the MC circuit if you can't attenuate the signal to about .4mV. The MM circuit should handle 2mV with no problem. Even my very expensive Keysight and Agilent signal generators as well as my Siglent can't go down low enough to be safe for MC inputs, so I made a stereo attenuator - input a specific level and it provides the required level for either MC or MM.
Don't forget to verify proper operation of the electromechanical items - switches, pots, relays.
Vintagecasey
Well-Known Member
I took some additional readings hopefully that are what you're asking. As I mentioned everything works normal except for phono 1 left channel. Unfortunately this board is so tight (so tight that they stuck the resistors facing vertical rather than the normal horizontal) that I have to take most of the readings from the back side. I have also swapped Q1 and Q5 to the right channel and Q2 and Q 6 to the left channel no change. I have checked the wires running from the phone 01 RCA jacks in the back to this board they have 00.0 resistance (continuity). I have swapped the RCA cables from the turntable and it stays in that channel. Any assistance is greatly appreciated.
Can you please post pics of the actual PCB?
Can you please upload higher-resolution photos? Some of your annotations are illegible.
Are those DC voltages you have written on the schematic?
What are the comparisons to the good channel?
Have you replaced the electrolytic caps or done any other work on this unit?
If not, have you tested the electrolytic caps?
Have you checked the values of components in the NFB circuit?
Can you please upload higher-resolution photos? Some of your annotations are illegible.
Are those DC voltages you have written on the schematic?
What are the comparisons to the good channel?
Have you replaced the electrolytic caps or done any other work on this unit?
If not, have you tested the electrolytic caps?
Have you checked the values of components in the NFB circuit?
Vintagecasey
Well-Known Member
This problem existed before I did any modifications to this board don't know if I mentioned that before. Replacing components were my attempt to fix the problem. I have replaced Qd9, 13, 14, 10, 18, 17, 19 21, 22 Qd 20. Also replaced are cd23, cd24 ,CD4, CD3 cd33 and 34. All measurements are DC with my ground on a good chassis ground spot. If any of these procedures are wrong please let me know. Not sure how to test the negative feedback circuit?
From what I can see those DC voltages look okay, very close to what is written by Kenwood
Time to do AC testing, apply a 10mV sine signal to inputs and test outputs, using an accurate AC volt meter &/or a scope. vary frequency, use 1kHz as your reference, refer to my post #25. Compare channels.
Time to do AC testing, apply a 10mV sine signal to inputs and test outputs, using an accurate AC volt meter &/or a scope. vary frequency, use 1kHz as your reference, refer to my post #25. Compare channels.
Vintagecasey
Well-Known Member
How exactly do I apply a 10 mV sign signal to the inputs? Can I use my phone in the app for frequency generator to apply the 1000Hz?
I have never used a phone app, no idea if its capable, if you can get the level low enough. Is it calibrated? Do you know what the AC voltage level is? Like I said earlier, verify the AC specification of your DMM. What make, model is it!
connect your phone app signal generator to your DMM, vary the level, vary the frequency characterize the output source across the frequency band from 50Hz to 15kHz, see what you get, then if it's usable, then connect it to the phono input and test for gain and frequency response, compare channels.
connect your phone app signal generator to your DMM, vary the level, vary the frequency characterize the output source across the frequency band from 50Hz to 15kHz, see what you get, then if it's usable, then connect it to the phono input and test for gain and frequency response, compare channels.
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