Need help on Marconi TF2002B repair. - UK Vintage Radio Repair and Restoration Discussion Forum

Navigator · 13th Aug 2021, 7:01 am

Dear Marconi-Specialists,
I need your help to repair the Marconi TF2002B Signalgenerator
Type: 52002-035T, SN: 116613/21
Problem:
- Incremental Frequency control (A0 R30) is not working
- FM Modulation is not working, even if it is correctly indicated on the Mod.- Level Meter (RF output checked with ICOM IC-7300)

what I have checked so far:
- checked all voltages of the power supply and the are correct
- RF-output and level is correct on all selected frequencies
- AM-modulation works correctly
- Crystal Calibrator is working
- Attenuators are working

I have replaced the following parts with no positive effect:
- A4 IC3
- A3 IC1

My manual is No. EB 2002B / 1973, 139 pages, PDF with ca. 12 Mb
Is there a more detailed description anywhere available, regarding the troubleshooting procedure?

turretslug · 13th Aug 2021, 10:43 am

Hi Armin,

These signal generators have a notorious weak spot in that the fine-wire filter chokes used in the decoupling networks for the power, modulation and control lines going between the main chassis and the central screened RF box have a tendency to go open circuit. They're under the long, thin aluminium panel at the back of the RF box and are relatively easy to check with an ohm-meter but unfortunately something of a pain to repair. The incremental frequency/FM modulation will be connected through one of these networks. I believe that the sleeving used over the wire ends emerging from the pot cores causes the problem by sulfurous emission with age, and humidity probably makes it worse.

Good luck with your investigations, these are a very good instrument, if a little odd in their tuning scheme!

Colin

Navigator · 13th Aug 2021, 11:36 am

Thanks Colin for your hint.
I will investigate it accordingly and let you know the result.

Navigator · 14th Aug 2021, 9:30 am

Hi Colin,
The problem was exactly what you have suspected:
Filter L10 on Board A8 was faulty.
You are right, those parts are really a pain to repair.
Finally the 2002B is working again.
For accurate measurements I am using my HP 8640B, which is a phantastic Signalgenerator,
but I wanted my 2002B working even if I will use it very seldom.

Thank you again and have a nice weekend

13th Aug 2021, 7:01 am	#1
Navigator Triode Join Date: Jul 2021 Location: Near Munich, Germany. Posts: 18	Need help on Marconi TF2002B repair. Dear Marconi-Specialists, I need your help to repair the Marconi TF2002B Signalgenerator Type: 52002-035T, SN: 116613/21 Problem: - Incremental Frequency control (A0 R30) is not working - FM Modulation is not working, even if it is correctly indicated on the Mod.- Level Meter (RF output checked with ICOM IC-7300) what I have checked so far: - checked all voltages of the power supply and the are correct - RF-output and level is correct on all selected frequencies - AM-modulation works correctly - Crystal Calibrator is working - Attenuators are working I have replaced the following parts with no positive effect: - A4 IC3 - A3 IC1 My manual is No. EB 2002B / 1973, 139 pages, PDF with ca. 12 Mb Is there a more detailed description anywhere available, regarding the troubleshooting procedure? __________________ Regards, Armin

13th Aug 2021, 10:43 am	#2
turretslug Dekatron Join Date: Nov 2011 Location: Surrey, UK. Posts: 4,395	Re: Need help on Marconi TF2002B repair. Hi Armin, These signal generators have a notorious weak spot in that the fine-wire filter chokes used in the decoupling networks for the power, modulation and control lines going between the main chassis and the central screened RF box have a tendency to go open circuit. They're under the long, thin aluminium panel at the back of the RF box and are relatively easy to check with an ohm-meter but unfortunately something of a pain to repair. The incremental frequency/FM modulation will be connected through one of these networks. I believe that the sleeving used over the wire ends emerging from the pot cores causes the problem by sulfurous emission with age, and humidity probably makes it worse. Good luck with your investigations, these are a very good instrument, if a little odd in their tuning scheme! Colin

13th Aug 2021, 11:36 am	#3
Navigator Triode Join Date: Jul 2021 Location: Near Munich, Germany. Posts: 18	Re: Need help on Marconi TF2002B repair. Thanks Colin for your hint. I will investigate it accordingly and let you know the result. __________________ Regards, Armin

14th Aug 2021, 9:30 am	#4
Navigator Triode Join Date: Jul 2021 Location: Near Munich, Germany. Posts: 18	Re: Need help on Marconi TF2002B repair. Hi Colin, The problem was exactly what you have suspected: Filter L10 on Board A8 was faulty. You are right, those parts are really a pain to repair. Finally the 2002B is working again. For accurate measurements I am using my HP 8640B, which is a phantastic Signalgenerator, but I wanted my 2002B working even if I will use it very seldom. Thank you again and have a nice weekend __________________ Regards, Armin