Sanyo G-2601KCA - one channel audio - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

michalism · 29th Nov 2018, 1:50 pm

ok, good to know!

michalism · 7th Dec 2018, 6:10 pm

Hi again...
back after a long break...

Eventually, I swapped out all old transistors from the right channel, and replaced them with brand new C1815.
Nothing changed...and all old transistors seem to be fine by all multimeter checks. I do not have a component tester to be absolutely sure.

Anyhow, I did some voltage measurements on every transistor and put them side by side in the attached file.
Measurements with a single letter are with respect to ground, and with two letters are the voltage between the respective pins (BC, BE and CE).

Since all measurements are completely off, I am confused what to check for. Initially, I was suspecting that the biasing of Q4 might be the problem, but I did not find a shorted or open component around that area.

I do not want to randomly start checking every single component to find the fault. I am trying to understand the logic and method around this problem...
so any kind of help is more than welcome!!!

Thank you!

buggies · 7th Dec 2018, 10:04 pm

Any chance you could post picture of the circuit around the four transistors you are measuring. I have just assumed you are talking about the bottom right of the previous circuit picture marked CST-100 but it is too blurry to deduce much. Preferably mark it up with your Q numbers too.

If it is the CST-100 section then I would suggest checking the voltage on the (several) supply decoupling capacitors since if one of those were leaking it would reduce the voltage to the collectors of the transistors.

EDIT: Not sure if the original circuit is as bad as it looks - would posting part of it as a pdf rather than jpg help?

michalism · 8th Dec 2018, 9:31 am

Hi, I have posted a picture of the board on post #13, but I can post more pics if you want. I'll do it later today. And yes, it is the CST-100 section I refer to.

Unfortunately, I do not have a better picture of the schematic, and this is also one of my problems. The jpg I have uploaded is taken from another thread in this forum and it's almost unusable for me as a beginner.

Regarding the capacitors, I have replaced all the ones that were leaky, but I'm leaning towards replacing all electrolytics; maybe I measured something wrong...

buggies · 8th Dec 2018, 12:41 pm

No - sorry, even zooming in on the circuit I can't really get any clues and I can't make any sense of your voltages without understanding the circuit!
Ok - Q2 is a bit out which will upset Q1 but Q3 and Q4 figures look really weird to me. I don't blame your measurements but it would need a bit of reverse engineering of the board to draw a circuit with component values to get a good overview.
All just my opinion - wait for an expert for real information...

PDF of your xlx attached for those of us who cannoit see xlsx files easily.

michalism · 8th Dec 2018, 5:42 pm

Thank you! I do appreciate your efforts

Indeed the schematic is almost useless, it just helps to give a rough idea about some topology, but I can't even figure out how the transistors are connected.
I'm too inexperienced to even try reverse engineering this circuit

I would not be offended if you think my measurements are wrong, I am doing them in a hurry because I do not have much time these days...
Anyway, I will check the rest of the caps tonight and come back with pictures as well...

buggies · 8th Dec 2018, 7:20 pm

Found a better scan of the CST-100 section in another post in the previous thread - some of the component references/values are legible!
At the top of the section it labels the transistors TR401, 402, 403 and 404.
Could you confirm you are numbering in the same left-to-right order?

https://www.vintage-radio.net/forum/...1&postcount=20
Attached below.

Forget my suggestion about the decoupling caps since I can now see the supply rail is shared between the two channels.

michalism · 9th Dec 2018, 9:57 am

Hello George!
thank you for the schematic. Not sure how/ why I missed that one.
My numbering is in line with the schematic.

michalism · 9th Dec 2018, 12:26 pm

Hi again.

Please disregard my previous message. I have misread your post, this is not the right board.

The board I am working on in the AMP-100, not the CST-100.

CST-100 is responsible for the tape player only, and I'm done with that. It had some minor issues I already fixed.

I apologise for the confusion!

Michalis

buggies · 9th Dec 2018, 2:03 pm

Ah - that is a shame - back to the bad circuit which only shows three transistors.
Only suggestion left (from me) is to try and contact the poster in the previous thread <Jimmyhaflinger> who said in post #25 that he had a large sheet of circuit and see if he would scan just the A-100 section.
Otherwise I would disconnect the low value coupling capacitors to see if they affect the DC conditions.
Best of luck.

michalism · 10th Dec 2018, 2:18 pm

Thanks, I was thinking to do the same. He already answered a previous pm about dismandling the unit...
The three transistors of the amplifier are Q2, Q3 and Q4, the last one is the entry point of the audio source. At least this is what I have figured out.
It is really frustrating, as all components seem to measure fine. I have checked almost all resistors by now and none seem to be out of limits.
I want ot feed a pure sinusoidal signal to the source and trace it. This may give me a better understanding.
Let's see....

michalism · 23rd Dec 2018, 10:29 pm

Hi again, and very warm season greetings!!

I have been measuring the resistor values on the amplifier board, and I am noticing a strange behaviour from a particular resistor.
There's a 100k resistor that measures correctly out of circuit, but in circuit it's resistance rises quickly.

What may be causing this behaviour?

The corresponding resistance on the properly working channel measures 10k in circuit.

I am trying to work-out a draft schematic, but in the mean time, I would appreciate some help!

Thank you!

michalism · 3rd Jan 2019, 6:46 pm

Hello and Happy New Year to all!

After some more investigation and the help of a partial reverse engineered schematic that was kindly offered to me in another forum, I was able to find the issue. It was a broken track on the leg of an electrolytic capacitor. This interrupted the power to the left channel.
I fixed it, and now both channels work properly!!

Thanks to everyone here for the support!
Michalis

29th Nov 2018, 1:50 pm	#21
michalism Tetrode Join Date: Apr 2018 Location: Athens, Greece Posts: 50	Re: Sanyo G-2601KCA - one channel audio ok, good to know!

7th Dec 2018, 10:04 pm	#23
buggies Heptode Join Date: Jan 2009 Location: West Lothian, UK. Posts: 761	Re: Sanyo G-2601KCA - one channel audio Any chance you could post picture of the circuit around the four transistors you are measuring. I have just assumed you are talking about the bottom right of the previous circuit picture marked CST-100 but it is too blurry to deduce much. Preferably mark it up with your Q numbers too. If it is the CST-100 section then I would suggest checking the voltage on the (several) supply decoupling capacitors since if one of those were leaking it would reduce the voltage to the collectors of the transistors. EDIT: Not sure if the original circuit is as bad as it looks - would posting part of it as a pdf rather than jpg help? __________________ George Last edited by buggies; 7th Dec 2018 at 10:11 pm.

8th Dec 2018, 9:31 am	#24
michalism Tetrode Join Date: Apr 2018 Location: Athens, Greece Posts: 50	Re: Sanyo G-2601KCA - one channel audio Hi, I have posted a picture of the board on post #13, but I can post more pics if you want. I'll do it later today. And yes, it is the CST-100 section I refer to. Unfortunately, I do not have a better picture of the schematic, and this is also one of my problems. The jpg I have uploaded is taken from another thread in this forum and it's almost unusable for me as a beginner. Regarding the capacitors, I have replaced all the ones that were leaky, but I'm leaning towards replacing all electrolytics; maybe I measured something wrong...

8th Dec 2018, 5:42 pm	#26
michalism Tetrode Join Date: Apr 2018 Location: Athens, Greece Posts: 50	Re: Sanyo G-2601KCA - one channel audio Thank you! I do appreciate your efforts Indeed the schematic is almost useless, it just helps to give a rough idea about some topology, but I can't even figure out how the transistors are connected. I'm too inexperienced to even try reverse engineering this circuit I would not be offended if you think my measurements are wrong, I am doing them in a hurry because I do not have much time these days... Anyway, I will check the rest of the caps tonight and come back with pictures as well...

8th Dec 2018, 7:20 pm	#27
buggies Heptode Join Date: Jan 2009 Location: West Lothian, UK. Posts: 761	Re: Sanyo G-2601KCA - one channel audio Found a better scan of the CST-100 section in another post in the previous thread - some of the component references/values are legible! At the top of the section it labels the transistors TR401, 402, 403 and 404. Could you confirm you are numbering in the same left-to-right order? https://www.vintage-radio.net/forum/...1&postcount=20 Attached below. Forget my suggestion about the decoupling caps since I can now see the supply rail is shared between the two channels. Attached Thumbnails __________________ George

9th Dec 2018, 9:57 am	#28
michalism Tetrode Join Date: Apr 2018 Location: Athens, Greece Posts: 50	Re: Sanyo G-2601KCA - one channel audio Hello George! thank you for the schematic. Not sure how/ why I missed that one. My numbering is in line with the schematic.

9th Dec 2018, 12:26 pm	#29
michalism Tetrode Join Date: Apr 2018 Location: Athens, Greece Posts: 50	Re: Sanyo G-2601KCA - one channel audio Hi again. Please disregard my previous message. I have misread your post, this is not the right board. The board I am working on in the AMP-100, not the CST-100. CST-100 is responsible for the tape player only, and I'm done with that. It had some minor issues I already fixed. I apologise for the confusion! Michalis

9th Dec 2018, 2:03 pm	#30
buggies Heptode Join Date: Jan 2009 Location: West Lothian, UK. Posts: 761	Re: Sanyo G-2601KCA - one channel audio Ah - that is a shame - back to the bad circuit which only shows three transistors. Only suggestion left (from me) is to try and contact the poster in the previous thread <Jimmyhaflinger> who said in post #25 that he had a large sheet of circuit and see if he would scan just the A-100 section. Otherwise I would disconnect the low value coupling capacitors to see if they affect the DC conditions. Best of luck. __________________ George

10th Dec 2018, 2:18 pm	#31
michalism Tetrode Join Date: Apr 2018 Location: Athens, Greece Posts: 50	Re: Sanyo G-2601KCA - one channel audio Thanks, I was thinking to do the same. He already answered a previous pm about dismandling the unit... The three transistors of the amplifier are Q2, Q3 and Q4, the last one is the entry point of the audio source. At least this is what I have figured out. It is really frustrating, as all components seem to measure fine. I have checked almost all resistors by now and none seem to be out of limits. I want ot feed a pure sinusoidal signal to the source and trace it. This may give me a better understanding. Let's see....

23rd Dec 2018, 10:29 pm	#32
michalism Tetrode Join Date: Apr 2018 Location: Athens, Greece Posts: 50	Re: Sanyo G-2601KCA - one channel audio Hi again, and very warm season greetings!! I have been measuring the resistor values on the amplifier board, and I am noticing a strange behaviour from a particular resistor. There's a 100k resistor that measures correctly out of circuit, but in circuit it's resistance rises quickly. What may be causing this behaviour? The corresponding resistance on the properly working channel measures 10k in circuit. I am trying to work-out a draft schematic, but in the mean time, I would appreciate some help! Thank you!

3rd Jan 2019, 6:46 pm	#33
michalism Tetrode Join Date: Apr 2018 Location: Athens, Greece Posts: 50	Re: Sanyo G-2601KCA - one channel audio Hello and Happy New Year to all! After some more investigation and the help of a partial reverse engineered schematic that was kindly offered to me in another forum, I was able to find the issue. It was a broken track on the leg of an electrolytic capacitor. This interrupted the power to the left channel. I fixed it, and now both channels work properly!! Thanks to everyone here for the support! Michalis