TS427 collector -143mV and with SK15 Wind pressed -94mV

 

So TS427 is in a conducting state. Is TS429 conducting ?

Les.

 

Well, you didn't say emitting so I assumed you meant collecting?

 

No I said conducting. When it is conducting there is current passing between the emitter and collector. The amount of this current depends on the current through the base emitter junction and the gain (hfe) of the transistor. In a switching circuit such as this bistable it will switch between almost no current between emitter and collector and the current being limited by the value of the resistor between the collector and the power supply rail. (In this case about -12 volts as it is a PNP transistor.) In this circuit when it is conducting the emiter collector voltage will be less than 1.0 volts. You will need to read up on how transistors behave to be able to work out what is wrong. It is not practical to get you to do one test at a time and wait for a responce. Do you have any friends with a knowledge of electronics that can help you ?

Les.

 

Sorry I don't have anyone at all to look to for guidance, I am willing to learn, maybe a YouTube video would be a way forward?
Once I knew how to undertake this kind of test you would then need to give me a list of the ones to test.

 

It would take more than a youtube to teach you to understand how you recorder works. let's see if we can get a few tests done at a time. Power on the recorder but don't press any of the buttons. measure the base and collector voltages of TS427 and TS429 with respect to ground and make a note of them.(This is relating to the slide solenoid not working.) Measure the voltages on pins 2 and 3 of IC455 with respect to ground and make a note of them. (This is relating to the reel motor not working.) Press and release the wind button. Repeat the above measurments.
I have not realy thought what the function of the slide solenoid is up till now. I think it may be to lock the buttons in the down position untill the stop button is pressed. When it was working did the buttons stay down when they were pressed but now do they spring back up again ?

Les.

 

Power on the recorder but don't press any of the buttons. measure the base and collector voltages of TS427 and TS429 with respect to ground and make a note of them.(This is relating to the slide solenoid not working.)

TS427 base -0.75v and with SK15 Wind pressed -0.69v
collector -143mV and with SK15 Wind pressed -94mV

TS429 base -145mV and with SK15 Wind pressed -96mV
collector -11.59v and with SK15 Wind pressed -11.6v

Measure the voltages on pins 2 and 3 of IC455 with respect to ground and make a note of them. (This is relating to the reel motor not working.) Press and release the wind button. Repeat the above measurements.

IC455 Pin 1. (centre) -11.20v
Pin 2. -1.6v and with SK15 Wind pressed -3.4v
Pin 3. -2.9v and with SK15 Wind pressed -4.7v

I have not really thought what the function of the slide solenoid is up till now. I think it may be to lock the buttons in the down position until the stop button is pressed. When it was working did the buttons stay down when they were pressed but now do they spring back up again ?
Les.

The solenoid relay RE476 (circled G65, G66, voltages, grey +96mV, Red 120mV and rising); if you look at the photos, you can see it would push the connecting cam and bring in to motion some of the surrounding gears, this is for play, for fast forward I think the cam moves and brings in other gears in to motion and also the notched black wheel you can see in the other photo which tells the inferred (detecting) unit that there is motion, and allow the buttons to stay active/set. When it was working; the buttons stayed set and when the cassette came to an end it would switch from play to stop.


It seems that these buttons (SK15 Wind) use the negative side for switching; I wonder if any other switching is negative, then you would expect to see positive voltages on certain components, like coils or motors?

I took the RE476 voltages so you can see; maybe something might come to light, I was going to take the motor 2 voltages (circled H63, 64), I am sure they terminate on connection block 12. in section H, page 9, I cannot find H63, H64 on the connection block?

You can see the gears and the black notched wheel in play mode on my OneDrive
https://1drv.ms/f/s!AuQDAPiShOjc9RoD2G3xlbzfvUuQ

 

Hi Michael,
As you say that the buttons remained in the pressed position when the unit was working what mechanism held them in the pressed position ? I suspected it would be the slide solenoid. Can you manualy operate the slide solenoid ? This is to check if it is sticking. When you caused the fault what were you doing ? What was it that was wrong before you caused this fault ? This may give a clue to what may be wrong.
Can you monitor the voltage on the collector of TS427 with respect to ground and connect it's base to ground via a resistor of about 1K . The voltage should change from about zero volts to about -11 volts.
Can you check the voltages on the collectors of TS451 and TS452 with respect to ground both without the wind button pressed and with it held in the pressed position ?
Don't worry about RE475 as it will only need to actuated in play and record modes.

Les.

 

As you say that the buttons remained in the pressed position when the unit was working what mechanism held them in the pressed position ?

I am guessing that the inferred (detecting) unit detects that there is motion and allows the buttons to function, because there is movement. If I remember correctly; once you insert a cassette this top slide solenoid is activated straightaway, this is part of the problem.

I suspected it would be the slide solenoid.
Can you manually operate the slide solenoid ? This is to check if it is sticking.

Yes I did manually move the slide solenoid across and press play; tape just came out of the cassette, I suspect the capstan motor just pulled it through. It isn’t fast.

When you caused the fault what were you doing ? What was it that was wrong before you caused this fault ? This may give a clue to what may be wrong.

I had fitted new transistors to boards U301 and U302; after refitting and testing these; motor 2 that turns the gears does not work.

I realised after studying the diagram that transistors TS450, 452, 451, 453 were fitted wrong, these are fitted completely different, my mistake.

After removing and testing with my hFE meter these were still giving good readings; I have checked all the transistors on both of these two boards using the diode test, all appear to be good, I have replaced IC455, IC435, IC447 as I could not test these, I have done many other resistor testing.

I have 25 volts on connection 25 and whilst checking this I caused a short on the leg on one of the components on the board (I can be more precise about this) this blew one of the 2 amp fuses; after replacing the fuse, both the solenoid valves don’t power up now. I have 25 volts leaving U402.
At this stage I started my post on here.

Can you monitor the voltage on the collector of TS427 with respect to ground and connect it's base to ground via a resistor of about 1K . The voltage should change from about zero volts to about -11 volts.
Can you check the voltages on the collectors of TS451 and TS452 with respect to ground both without the wind button pressed and with it held in the pressed position ?

TS427 collector to ground -143mV then I used a Through Hole Trimming Potentiometer set at 1k and made an additional connection between base and ground via this resistor, this now alters the reading to -9.2v

TS451 collector -300 to 400mV (alternating) and with SK15 Wind pressed -300mV and decreasing.

TS452 collector -0.4v and with SK15 Wind pressed -250mV to -0.3v

 

Why did you replace the transistors and which ones did you replace ?

Les.

 

I had No sound on the left side outputs; both VU meters are responding very well whilst playing a tape. The advice given was; that the problem is likely to be a Japanese made transistor, not the BC/BD ones.

I decided to replace all of them whilst I was replacing the non BC/BD transistors. I replaced the ones on U410 Mixer/Headphone Amplifier, U405 Main board, it was whilst replacing these I came across two solder joints that had popped and this was the problem, it was likely that whilst refitting the PC board above it, had caused this to happen.


After completing the main board, I reassembled all the boards and tried it, it was working again, I decided to continue because I had spent much time finding out about each type of transistor, finding suitable ones to replace and buying them.

I replaced the ones on U301 Logic Control and U302 Motor Control boards and it was here that I realised my mistake of fitting TS450, 452, 451, 453 which were to be fitted differently than the standard fitting sequence, c b e, these were to be fitted e c b from left to right of the flat side.

 

All of the transistors on U301 except TS471 only drive the LED indicators. As the output on pin 6 of U301 seems to be working correctly then TS471 is probably working correctly. As all the transistors that you replaced on U302 form part of the H bridge for the wind motor it is likely the fault is in the area of this H bridge. Can yo create a table of the emitter, base, and collector voltages (With respect to ground.) of the 6 transitors (TS450, TS451,TS452, TS453, TS454 & TS449 ) in the H bridge first without the wind button pressed and then with it pressed. (You will probably need to hold it pressed.)

Les.

 

Further observations; the unit is powered up, insert a cassette and the bottom solenoid is then activated, press SK15 Wind button and this solenoid deactivates.

I very much appreciated your time and knowledge with helping me, thank you.

 

I think transistor TS452 has an open circuit base emitter junction. If you still have the original transistor you could try refitting it. (My understanding is that you replaced them even though there was nothing wrong with them,)
When you say the bottom solenoid do you mean the Slide or the pressure roller one ?

Les.

 

I think transistor TS452 has an open circuit base emitter junction. If you still have the original transistor you could try refitting it. (My understanding is that you replaced them even though there was nothing wrong with them,)

You were quite right and not only TS452, also TS450, I bought 5 of these and they are all open circuit between base and collector maybe the damage could of been worse if they had been good?

This explains why I had to fit the transistor in my meter adaptor the other way (ebc/cbe) to get an hFE reading, I thought something was different, this was before fitting and afterwards whilst testing, I read that if you get a hFE reading you don’t need to make other tests on the transistor, I believe this is still true.

I have just raised this issue with Farnell and awaiting an answer; I want to continue fitting new, because I don’t want problems arising again in the future, with this unit, I am getting old, and sorting these issues takes some doing.

When you say the bottom solenoid do you mean the Slide or the pressure roller one ?

Correct.

 

You have not answered the question "When you say the bottom solenoid do you mean the Slide or the pressure roller one ?" Is it the slide solenoid ? Or is it the pressure roller solenoid ?
If you bought the transistors from Farnell I think it is very unlikely that they are faulty. I have checked data sheets for the BC636 from several manufacturers and they all show the same pinout as the Fairchild datesheet downloaded from Farnell. I had a look at the layout diagram for the motor control board (Fig 24) and the pinout labeling for the BC636s is wrong. NOTE the view in Fig 24 is from the copper side of the board. If the connections on the BC636s that you have match the data sheet then you should not have to cross over any connections. NOTE the base is NOT the middle pin. It is pin 3.

Les.

 

You have not answered the question "When you say the bottom solenoid do you mean the Slide or the pressure roller one ?" Is it the slide solenoid ? Or is it the pressure roller solenoid ?

The solenoid that is working is the Electromagnet Pressure Roller RE475

If you bought the transistors from Farnell I think it is very unlikely that they are faulty. I have checked data sheets for the BC636 from several manufacturers and they all show the same pinout as the Fairchild datesheet downloaded from Farnell. I had a look at the layout diagram for the motor control board (Fig 24) and the pinout labeling for the BC636s is wrong. NOTE the view in Fig 24 is from the copper side of the board. If the connections on the BC636s that you have match the data sheet then you should not have to cross over any connections. NOTE the base is NOT the middle pin. It is pin 3.

This is the information I came up with for TS450 and TS452, they are both the same type a BC636, I came across a very useful website that has identified all the transistors for this unit, I am sure you know it very well.
https://alltransistors.com/transistor.php?transistor=23484

This is the suitable replacement that I found
https://uk.farnell.com/on-semiconductor/bc638ta/transistor-pnp-60v-1a-to-92-3/dp/2825082?CMP=i-bf9f-00001000

Fig 23 is the one that I rely on to use; because I can relate to it, the other side is much harder to relate to, I place a piece of making tape near the connections and take measurements from the front.

Yes I found that out too late; that the base was pin 3 or the middle pin is the collector, when they are fitted they don’t look as the drawing shows, the package is TO92.

I am going to have ago refitting the old ones tomorrow; to confirm that is the problem.

 

The transistor pinouts on Fig 23 (From component side.) are correct. The flat side should be the same way as shown in Fig. 23.

Les.

 

When I had a look at the package in more detail that you kindly provided I could see straightaway that it isn’t just a TO-92 it has a 3L after it; so I had originally fitted it correctly, I removed TS450 and 452 and diode tested this time on the correct pins, the readings were equal on both, I refitted them and now have fast, forward winding and rewinding.

With play; motor 2 works, the top electromagnetic slide RE476 does not work, this should slide across, connecting with the play gears, to give play.

I am thinking have I got TS451 and 453 right; they are BC635 they are NPN, the following link gives the specifications, but not all the information required for the package, although Fig 23 should keep me right?
https://alltransistors.com/transistor.php?transistor=23480

This is the suitable replacement that I found; the data sheet on here gives the pinout references, at the beginning, this is how I have fitted them, I had to turn them a bit to fit and move the centre base pin to the outside this allowed the collector to be centre pin.
https://cpc.farnell.com/diodes-inc/ztx450/transistor-npn-e-line/dp/SC10969

 

Forget about TS451 and TS453. They must be working for the reel motor to run in forward and reverse. We now need to look at the drive circuit for the slide solenoid in the top left corner of the U302 schematic. I am a believer in the saying "If it's not broke don't fix it." I will look at that problem to find a way to find out what is wrong with that. I just wanted to stop you from creating another fault now you have fixed the reel motor H bridge.

Les.