Technics RS-1500 FF and REW do not stop

[Not that old]

So now after doing this do you get voltages at TR608? (Post #10)

Negative.Power lost for good now. Troubleshooting. I get power on the two blue and two white wires leading to diodes D601 and 604 but nothing on F2 and F3. Difficult to reach the diodes for measuring.

 

[Not that old]

Negative.Power lost for good now. Troubleshooting. I get power on the two blue and two white wires leading to diodes D601 and 604 but nothing on F2 and F3. Difficult to reach the diodes for measuring.

Power supply now rectified and in order. I now get 5V out from TR608 to D-connection pin 2. After that I don't know what to do.
My "expertice" limits stop around here. Badly need help.
FF and REW still cannot be stopped.

 

[dankik]

Now that you fixed the 5V problem, we can start to follow the transport button signals through the logic control to see if we have a bad chip.

1. Find connector B on the board. (It is shown on the board layout towards the top of the board)
2. This is the input from the Key Switch board.
3. Pin 4 (green highlight) goes to the FF logic.
4. DMM set to measure VDC, black lead clipped to chassis ground
5. Red lead on Connector B, pin 4 (FF)
6. Measure the voltage when the button is not pressed, then again as you press and hold the button down
7. You should probably get something like =5V (not pressed) and 0V (pressed and held down)
8. Next, we will try the REW button
9. Connector B, Pin 6 is the REW button
10. Do the same test with button not pressed down, then again as you hold the button down
11. Measure the two voltages on Pin 6
12. This will test to make sure that the buttons are working OK and the signal is getting to the control board.
13. If all of that looks good, we can jump to the output connector "D" and check the signals.
14. Connector D, pin 4 (I think) should be 5v when you pressed the FF button, then go back to 0v when you press the STOP button.
15. Same with Connector D, pin 3. It should do the same for the REW button.
16. Let me know what you find out.

*As a side note, when you see the cross connected "NAND" gates like IC1, that is configured as a logic "latch"
Its purpose is to maintain the last logic state of the input signals. In the case of IC1, when you press the FF button, a 0v signal is input to the latch which "sets" it. When you press STOP, the 0v input on the other input "clears" the latch. All IC1 is doing is holding your input button press until the next button press comes along.

 

[dhnash]

Same with Connector D, pin 4. It should do the same for the REW button.

I believe this should be pin 3.

 

[dankik]

Thanks. I had a couple of errors... too early in the AM. I think I fixed them all.

 

[Not that old]

Now that you fixed the 5V problem, we can start to follow the transport button signals through the logic control to see if we have a bad chip.

1. Find connector B on the board. (It is shown on the board layout towards the top of the board)
2. This is the input from the Key Switch board.
3. Pin 4 (green highlight) goes to the FF logic.
4. DMM set to measure VDC, black lead clipped to chassis ground
5. Red lead on Connector B, pin 4 (FF)
6. Measure the voltage when the button is not pressed, then again as you press and hold the button down
7. You should probably get something like =5V (not pressed) and 0V (pressed and held down)
8. Next, we will try the REW button
9. Connector B, Pin 6 is the REW button
10. Do the same test with button not pressed down, then again as you hold the button down
11. Measure the two voltages on Pin 6
12. This will test to make sure that the buttons are working OK and the signal is getting to the control board.
13. If all of that looks good, we can jump to the output connector "D" and check the signals.
14. Connector D, pin 4 (I think) should be 5v when you pressed the FF button, then go back to 0v when you press the STOP button.
15. Same with Connector D, pin 3. It should do the same for the REW button.
16. Let me know what you find out.

*As a side note, when you see the cross connected "NAND" gates like IC1, that is configured as a logic "latch"
Its purpose is to maintain the last logic state of the input signals. In the case of IC1, when you press the FF button, a 0v signal is input to the latch which "sets" it. When you press STOP, the 0v input on the other input "clears" the latch. All IC1 is doing is holding your input button press until the next button press comes along.

View attachment 3833350
View attachment 3833315

Thank you the great help. Unfortunately I am out of action for a few days (hospital) with no access to the 1500. Hope to start troubleshooting in a few days.

 

[dankik]

Get well soon.

 

[Not that old]

Get well soon.

Thank you

 

[Not that old]

Get well soon.

While I am out of action, I would like you to clarify this.I have taken for granted that I should take mesurements to chassis. I asked ChatGpt about that and was told that is wrong. The yellow rail Gpt mentions, is the yellow wire from the transformer to the pin on the power supply. Quote "A quick question. I thought that pin2 (5V) on connection D should be measured from pin to chassis. In reallity it measures from pin2 to YEW rail. Why is that? " Unquote

 

[dankik]

I asked ChatGpt about that and was told that is wrong. The yellow rail Gpt mentions, is the yellow wire from the transformer to the pin on the power supply.

Looking at the schematic, it looks like they are tied together, but it is not explicit.
If you want to be sure of where to attach the test lead, look at the board schematic and find the connector pin that is connected to the dark black ground line.

Here is what AI says:

"A quick question. I thought that pin2 (5V) on connection D should be measured from pin to chassis. In reallity it measures from pin2 to YEW rail. Why is that? "

I don't have wire colors on my schematic (do you) so I don't know what "YEW rail" means. If you are referring to the transformer secondary center-tap, then there are two as shown in the schematic and both are connected together presumably tied to the common, or ground trace on the boards.



At some point on one of the boards, this signal is tied to chassis ground.

You can easily verify if chassis ground is connected to ground with power off (unplugged) and checking continuity between the chassis and one of the ground pins on a chip or connector on the board.

Does this look like your Power Supply Board or is it different. In doesn't match the board layout in the SM for the transformer connector?
This has 10 wires, but the layout in the SM has only 8 wires?

 

[Not that old]

Looking at the schematic, it looks like they are tied together, but it is not explicit.
If you want to be sure of where to attach the test lead, look at the board schematic and find the connector pin that is connected to the dark black ground line.

Here is what AI says:
View attachment 3835374

I don't have wire colors on my schematic (do you) so I don't know what "YEW rail" means. If you are referring to the transformer secondary center-tap, then there are two as shown in the schematic and both are connected together presumably tied to the common, or ground trace on the boards.

View attachment 3835472
View attachment 3835474
At some point on one of the boards, this signal is tied to chassis ground.
View attachment 3835475
You can easily verify if chassis ground is connected to ground with power off (unplugged) and checking continuity between the chassis and one of the ground pins on a chip or connector on the board.

Does this look like your Power Supply Board or is it different. In doesn't match the board layout in the SM for the transformer connector?
This has 10 wires, but the layout in the SM has only 8 wires?

View attachment 3835480
View attachment 3835488

Seems we have some differences in the inputs from the transformer. I have no color codes on my WD either. The YEW wire is acc. to Gpt be my ground wire.
When I use chassis as ground, I get no meaningful values. Maybe the black one beside YEW is part of the Y-prong shown on the WD. My WD shows no figures/values around
the transformer area.Sitting on a hospital bed and hunting down text and pictures right frome Onedrive, so I hope what I write makes some sense anyway.
I will hopfully sit behind the 1500 soon.

 

[dankik]

It sounds like your transformer to PS board is wired like this. I'm not sure how your two meter lamps are connected?

• BLU = 11.7V
• WHT = 34V
• ORG = 28.5V
• BLK/YEL = Common/GND

The BLK/YEL wire is the transformer secondary CT and is connected to the common (GND) on the PS board.
To connect ground to the chassis, there might be a black wire or board trace that gets connected to the chassis on one board. You might need to have the board mounted to the chassis to connect to the chassis for ground to the other boards.