Bad transistors in a TCD310 - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

KeithsTV · 18th Nov 2015, 10:09 pm

There's one BC156 in the solenoid driver and 2 BC157s in the mic/line input amp. There's also a couple of MPS6518s on each of the Dolby boards. I would assume that the 156 is the lockfit equivalent of the 556.

I've also noticed that the Amplifier 2 board, which has the reel motor sense amplifier and control circuit is different to the circuit in my copy of the service manual. My manual has a date of 9-74 whereas the deck I've been repairing dates from late 76/early 76 and my own deck dates from late 76 (bought early 77) so this board has been changed during the production run.

Keith

paulsherwin · 18th Nov 2015, 11:16 pm

Interesting, I've never come across it, or even seen any other reference to it. Presumably there really are some high voltages floating around that part of the circuit or a BC156 wouldn't have been used.

KeithsTV · 18th Nov 2015, 11:38 pm

The solenoid driver is powered by the +23V supply and the emitter of the BC156, which drives the BD175 solenoid driver, is connected to a capacitor which could potentially raise the emitter to close to twice that voltage. All the other BC transistors are powered by the 13.5V supply.

Keith

fetteler · 19th Nov 2015, 12:19 am

Hi Keith,

Thanks for your offer, I have a copy of the manual which I found online, I guess it is the correct one for me but as I haven't had the machine to bits yet I will have to wait to find out! If I get stuck would it be OK to give you a surprise PM at some unspecified future date??

Also, I agree with your changing the electrolytics and I had already planned to do just that with all of them everywhere just in case.

Steve.

PS 2SC1815 - maximum 10dB noise figure: 2N5089 - maximum 2 dB noise figure. Obviously noise is not critical in solenoid or motor circuitry.

KeithsTV · 19th Nov 2015, 1:16 am

No problem with a PM after all that's what this forum is all about. I've had my TCD310 for nearly 39 years but was recently given another to fix along with a TCD300 which is very similar. Having fixed the 310 I think it may be worth going over my 310 as I found one of the faulty transistors on one of the Dolby boards reduced the output level. I suspect I'll shortly be putting in an order for a large bag of transistors!!

One other fault I had on mine was the head carriage grease solidifying preventing the heads moving into position on play or record. It's a fairly simple matter to remove the carriage, clean off the old grease, regrease it and put it all back together.

Keith

paulsherwin · 19th Nov 2015, 1:49 am

Quote:

Originally Posted by fetteler

PS 2SC1815 - maximum 10dB noise figure: 2N5089 - maximum 2 dB noise figure. Obviously noise is not critical in solenoid or motor circuitry.

You're right Steve, though the typical noise figure is much lower. It's all academic, as the 2N5089 is much cheaper and more easily available, so there's no reason not to use it.

Radio Wrangler · 19th Nov 2015, 3:01 pm

Watch out for noise figure specs, by the way, they depend an awful lot on bias conditions and the presented source impedance. You really do have to be very close to the test circuit conditions to get the advertised figures.

It would have to be awesomely noisy to make a solenoid chatter!

David

18th Nov 2015, 10:09 pm	#21
KeithsTV Nonode Join Date: Aug 2007 Location: South Bradford, West Yorkshire, UK. Posts: 2,574	Re: Bad transistors in a TCD310 There's one BC156 in the solenoid driver and 2 BC157s in the mic/line input amp. There's also a couple of MPS6518s on each of the Dolby boards. I would assume that the 156 is the lockfit equivalent of the 556. I've also noticed that the Amplifier 2 board, which has the reel motor sense amplifier and control circuit is different to the circuit in my copy of the service manual. My manual has a date of 9-74 whereas the deck I've been repairing dates from late 76/early 76 and my own deck dates from late 76 (bought early 77) so this board has been changed during the production run. Keith

18th Nov 2015, 11:16 pm	#22
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,970	Re: Bad transistors in a TCD310 Interesting, I've never come across it, or even seen any other reference to it. Presumably there really are some high voltages floating around that part of the circuit or a BC156 wouldn't have been used.

18th Nov 2015, 11:38 pm	#23
KeithsTV Nonode Join Date: Aug 2007 Location: South Bradford, West Yorkshire, UK. Posts: 2,574	Re: Bad transistors in a TCD310 The solenoid driver is powered by the +23V supply and the emitter of the BC156, which drives the BD175 solenoid driver, is connected to a capacitor which could potentially raise the emitter to close to twice that voltage. All the other BC transistors are powered by the 13.5V supply. Keith

19th Nov 2015, 12:19 am	#24
fetteler Octode Join Date: Jul 2011 Location: Staffordshire Moorlands, UK. Posts: 1,479	Re: Bad transistors in a TCD310 Hi Keith, Thanks for your offer, I have a copy of the manual which I found online, I guess it is the correct one for me but as I haven't had the machine to bits yet I will have to wait to find out! If I get stuck would it be OK to give you a surprise PM at some unspecified future date?? Also, I agree with your changing the electrolytics and I had already planned to do just that with all of them everywhere just in case. Steve. PS 2SC1815 - maximum 10dB noise figure: 2N5089 - maximum 2 dB noise figure. Obviously noise is not critical in solenoid or motor circuitry. __________________ Those who lack imagination cannot imagine what is lacking... Last edited by fetteler; 19th Nov 2015 at 12:36 am. Reason: PS

19th Nov 2015, 1:16 am	#25
KeithsTV Nonode Join Date: Aug 2007 Location: South Bradford, West Yorkshire, UK. Posts: 2,574	Re: Bad transistors in a TCD310 No problem with a PM after all that's what this forum is all about. I've had my TCD310 for nearly 39 years but was recently given another to fix along with a TCD300 which is very similar. Having fixed the 310 I think it may be worth going over my 310 as I found one of the faulty transistors on one of the Dolby boards reduced the output level. I suspect I'll shortly be putting in an order for a large bag of transistors!! One other fault I had on mine was the head carriage grease solidifying preventing the heads moving into position on play or record. It's a fairly simple matter to remove the carriage, clean off the old grease, regrease it and put it all back together. Keith

19th Nov 2015, 3:01 pm	#27
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,902	Re: Bad transistors in a TCD310 Watch out for noise figure specs, by the way, they depend an awful lot on bias conditions and the presented source impedance. You really do have to be very close to the test circuit conditions to get the advertised figures. It would have to be awesomely noisy to make a solenoid chatter! David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done