Sony TC-458 not changing speed . - UK Vintage Radio Repair and Restoration Discussion Forum

NorfolkDaveUK · 10th Jan 2019, 2:00 pm

As per the title . I`m finding this one difficult to track down if anyone has any idea ?

I`ve had the switch out and cleaned it , the transistor Q901 is supposed to have 80v at the collector , but it only has 20v but i cant figure out why , as always any help you can give will be greatly appreciated..

ms660 · 10th Jan 2019, 2:34 pm

Presumably that's 20 volts WRT the servo ground and not the main signal ground ?

Lawrence.

NorfolkDaveUK · 10th Jan 2019, 2:53 pm

I`m not sure what you mean Lawrence , sorry for the ignorance . I followed the schematic , read the voltages to reference to ground .

NorfolkDaveUK · 10th Jan 2019, 2:55 pm

In forward play mode . Pins one through seven on the IC have the correct voltages , but eight through fourteen dont .

ms660 · 10th Jan 2019, 3:08 pm

Quote:

Originally Posted by NorfolkDaveUK

I`m not sure what you mean Lawrence , sorry for the ignorance . I followed the schematic , read the voltages to reference to ground .

No problem, I was just pointing out that the servo ground ref. is separate from the main signal ground ref.

Lawrence.

NorfolkDaveUK · 10th Jan 2019, 3:12 pm

The motor seems to be working fine . Someone had put the flippin voltage selector in wrong (because the sticker had fallen off) so it was doing all kinds of weird stuff then I got it . I sorted that out , removed the switch and cleaned it , but still there is no 3.75 speed , its just stuck on 7.5. Its a bit weird this machine as it has little power supplied all over the place . Where is the servo ground ref then please ?

ms660 · 10th Jan 2019, 3:21 pm

Quote:

Where is the servo ground ref then please ?

It's shown on the schematic I'm looking at..."Servo Control Ground Line" Eg: Pin 12 of the servo IC.

Maybe report the voltages you can measure WRT the above ground line for all the IC pins and all Q901 connections?

Lawrence.

NorfolkDaveUK · 10th Jan 2019, 3:44 pm

OK measurements taken in FWD play mode :

1 - 4.56
2 - 0v
3 - 0.5v
4 - 1.9v
5 - 7.86v
6 - 8.57v
7 - 14.5v
8 - 14.7v
9 - 0.6v
10 - 0v......(fault)
11 - 0v .....(fault)
12 - gnd ref
13 - 0.14v
14 - 0.14v

C : 20.25v
B : 0.23v
E : 0.69v

Chip is borked isnt it . 10 and 11 are output pins .

I was using pin 2 when I did the measurements before by the way so the results are the same . I dont use the chassis . unless i need too .

ms660 · 10th Jan 2019, 3:50 pm

What speed is it actually playing back at?

Lawrence.

NorfolkDaveUK · 10th Jan 2019, 3:55 pm

Its going wild at the minute Lawrence because the tension is all over the place .

NorfolkDaveUK · 10th Jan 2019, 4:01 pm

pins 10 and 11 of the IC are the output from the inverter so its going to be messing with everything isnt it . Bit of a nuisance but there is one board on Ebay , its in the states but hey ho . The chip is a Sony special so I guess it`s going to have to do .

NorfolkDaveUK · 10th Jan 2019, 4:23 pm

Sorry 11 is the output from the inverter , not too sure what 10 is , it looks like its driving the transistor no ?

ms660 · 10th Jan 2019, 4:28 pm

It might be worth checking the transistor and the diode bridge as well.

Lawrence.

NorfolkDaveUK · 10th Jan 2019, 4:33 pm

The transistor is coming up good , about to pull the the bridge .

NorfolkDaveUK · 10th Jan 2019, 4:41 pm

Bridge is good . re-capped the board . still nothing so that only leaves resistors and the IC

NorfolkDaveUK · 10th Jan 2019, 4:48 pm

Well at least I got to the bottom of it so thats a win by all accounts mate (thanks as always for your assistance its always treasured thank you) I will order the new board and wait . Thanks .

ms660 · 10th Jan 2019, 6:56 pm

Good luck with it, by the way I don't know if the manual you have has a circuit description for the servo motor control, the copy of the manual I have doesn't but there's a very good circuit explanation given in the Sony TC-440 manual that's available from the vintageshifi site if you have not got the circuit description and need to do any final eliminations.

That servo IC and circuit arrangement was used in quite a few models.

Lawrence.

NorfolkDaveUK · 10th Jan 2019, 9:39 pm

Thanks Lawrence , I`ve ordered a new board and moved on now bud I`m pretty sure it can`t be anything else but the IC . I`ve checked every componant on the board and the only discrepancy are those 2 pins , but I will down load the manual you suggest , the one for the 458 is pretty poor to be fair.

Thanks mate.

8 Tracker · 11th Jan 2019, 4:53 pm

Before you give up and wait for the new board to arrive, check the motor. I had one of these models drive me round the bend with a speed control fault. I changed the IC and it made no difference at all. The motor has a separate disc on it which provides feedback to the control board via a sensor next to the disc. This disc was loose on the motor shaft, so the speed control was all over the place. You need to take out the motor to check it, but it may be worth a try.

Mark.

NorfolkDaveUK · 15th Jan 2019, 2:36 pm

Many thanks for that . I wont give up , thats for sure and I`ll try your suggestion . I just replaced the IC and as you say its made diddly squat difference so thats £30 wasted ..haha . I did only pay £40 for the machine though so we arent done yet .

I dont have a speed "all over the place " issue though , i just have no speed change at all . I will check the motor and have a look and see if that sensor is the problem . The q901 transistor with very low voltage is whats making me think its more likely to be a power issue though .

Many thanks .

If anyone else has any suggestions I`m more than happy to listen and try them out . Would be great to get this one back from the brink !

10th Jan 2019, 2:00 pm	#1
NorfolkDaveUK Banned Join Date: May 2018 Location: Norwich, Norfolk, UK. Posts: 605	Sony TC-458 not changing speed . As per the title . I`m finding this one difficult to track down if anyone has any idea ? I`ve had the switch out and cleaned it , the transistor Q901 is supposed to have 80v at the collector , but it only has 20v but i cant figure out why , as always any help you can give will be greatly appreciated..

10th Jan 2019, 2:34 pm	#2
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Sony TC-458 not changing speed . Presumably that's 20 volts WRT the servo ground and not the main signal ground ? Lawrence.

10th Jan 2019, 2:53 pm	#3
NorfolkDaveUK Banned Join Date: May 2018 Location: Norwich, Norfolk, UK. Posts: 605	Re: Sony TC-458 not changing speed . I`m not sure what you mean Lawrence , sorry for the ignorance . I followed the schematic , read the voltages to reference to ground . Attached Thumbnails

10th Jan 2019, 2:55 pm	#4
NorfolkDaveUK Banned Join Date: May 2018 Location: Norwich, Norfolk, UK. Posts: 605	Re: Sony TC-458 not changing speed . In forward play mode . Pins one through seven on the IC have the correct voltages , but eight through fourteen dont .

10th Jan 2019, 3:12 pm	#6
NorfolkDaveUK Banned Join Date: May 2018 Location: Norwich, Norfolk, UK. Posts: 605	Re: Sony TC-458 not changing speed . The motor seems to be working fine . Someone had put the flippin voltage selector in wrong (because the sticker had fallen off) so it was doing all kinds of weird stuff then I got it . I sorted that out , removed the switch and cleaned it , but still there is no 3.75 speed , its just stuck on 7.5. Its a bit weird this machine as it has little power supplied all over the place . Where is the servo ground ref then please ?

10th Jan 2019, 3:44 pm	#8
NorfolkDaveUK Banned Join Date: May 2018 Location: Norwich, Norfolk, UK. Posts: 605	Re: Sony TC-458 not changing speed . OK measurements taken in FWD play mode : 1 - 4.56 2 - 0v 3 - 0.5v 4 - 1.9v 5 - 7.86v 6 - 8.57v 7 - 14.5v 8 - 14.7v 9 - 0.6v 10 - 0v......(fault) 11 - 0v .....(fault) 12 - gnd ref 13 - 0.14v 14 - 0.14v C : 20.25v B : 0.23v E : 0.69v Chip is borked isnt it . 10 and 11 are output pins . I was using pin 2 when I did the measurements before by the way so the results are the same . I dont use the chassis . unless i need too . Last edited by NorfolkDaveUK; 10th Jan 2019 at 3:51 pm.

10th Jan 2019, 3:50 pm	#9
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Sony TC-458 not changing speed . What speed is it actually playing back at? Lawrence.

10th Jan 2019, 3:55 pm	#10
NorfolkDaveUK Banned Join Date: May 2018 Location: Norwich, Norfolk, UK. Posts: 605	Re: Sony TC-458 not changing speed . Its going wild at the minute Lawrence because the tension is all over the place .

10th Jan 2019, 4:01 pm	#11
NorfolkDaveUK Banned Join Date: May 2018 Location: Norwich, Norfolk, UK. Posts: 605	Re: Sony TC-458 not changing speed . pins 10 and 11 of the IC are the output from the inverter so its going to be messing with everything isnt it . Bit of a nuisance but there is one board on Ebay , its in the states but hey ho . The chip is a Sony special so I guess it`s going to have to do .

10th Jan 2019, 4:23 pm	#12
NorfolkDaveUK Banned Join Date: May 2018 Location: Norwich, Norfolk, UK. Posts: 605	Re: Sony TC-458 not changing speed . Sorry 11 is the output from the inverter , not too sure what 10 is , it looks like its driving the transistor no ?

10th Jan 2019, 4:28 pm	#13
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Sony TC-458 not changing speed . It might be worth checking the transistor and the diode bridge as well. Lawrence.

10th Jan 2019, 4:33 pm	#14
NorfolkDaveUK Banned Join Date: May 2018 Location: Norwich, Norfolk, UK. Posts: 605	Re: Sony TC-458 not changing speed . The transistor is coming up good , about to pull the the bridge .

10th Jan 2019, 4:41 pm	#15
NorfolkDaveUK Banned Join Date: May 2018 Location: Norwich, Norfolk, UK. Posts: 605	Re: Sony TC-458 not changing speed . Bridge is good . re-capped the board . still nothing so that only leaves resistors and the IC

10th Jan 2019, 4:48 pm	#16
NorfolkDaveUK Banned Join Date: May 2018 Location: Norwich, Norfolk, UK. Posts: 605	Re: Sony TC-458 not changing speed . Well at least I got to the bottom of it so thats a win by all accounts mate (thanks as always for your assistance its always treasured thank you) I will order the new board and wait . Thanks .

10th Jan 2019, 6:56 pm	#17
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Sony TC-458 not changing speed . Good luck with it, by the way I don't know if the manual you have has a circuit description for the servo motor control, the copy of the manual I have doesn't but there's a very good circuit explanation given in the Sony TC-440 manual that's available from the vintageshifi site if you have not got the circuit description and need to do any final eliminations. That servo IC and circuit arrangement was used in quite a few models. Lawrence.

10th Jan 2019, 9:39 pm	#18
NorfolkDaveUK Banned Join Date: May 2018 Location: Norwich, Norfolk, UK. Posts: 605	Re: Sony TC-458 not changing speed . Thanks Lawrence , I`ve ordered a new board and moved on now bud I`m pretty sure it can`t be anything else but the IC . I`ve checked every componant on the board and the only discrepancy are those 2 pins , but I will down load the manual you suggest , the one for the 458 is pretty poor to be fair. Thanks mate.

11th Jan 2019, 4:53 pm	#19
8 Tracker Hexode Join Date: Jul 2009 Location: Mablethorpe, Lincolnshire, UK. Posts: 286	Re: Sony TC-458 not changing speed . Before you give up and wait for the new board to arrive, check the motor. I had one of these models drive me round the bend with a speed control fault. I changed the IC and it made no difference at all. The motor has a separate disc on it which provides feedback to the control board via a sensor next to the disc. This disc was loose on the motor shaft, so the speed control was all over the place. You need to take out the motor to check it, but it may be worth a try. Mark.

15th Jan 2019, 2:36 pm	#20
NorfolkDaveUK Banned Join Date: May 2018 Location: Norwich, Norfolk, UK. Posts: 605	Re: Sony TC-458 not changing speed . Many thanks for that . I wont give up , thats for sure and I`ll try your suggestion . I just replaced the IC and as you say its made diddly squat difference so thats £30 wasted ..haha . I did only pay £40 for the machine though so we arent done yet . I dont have a speed "all over the place " issue though , i just have no speed change at all . I will check the motor and have a look and see if that sensor is the problem . The q901 transistor with very low voltage is whats making me think its more likely to be a power issue though . Many thanks . If anyone else has any suggestions I`m more than happy to listen and try them out . Would be great to get this one back from the brink !