Grundig 3028 & similar models - UK Vintage Radio Repair and Restoration Discussion Forum

agardiner · 6th Oct 2022, 5:11 pm

Mods - sorry if this is in the wrong place, please move as needed.
=========================================

So, I hope this may be of help to someone. I restore a lot of the large German receivers such as the 3028, although there are many models including radiograms that have the same chassis. Lovely performers as anyone who owns one will know.

I have recently had several of these chassis with VHF failure; usually just quiet but on one set it occasionally gave a very distorted, low level output. The front end is fairly common and built around an ECC85 mounted in a separate can. I attach a part schematic. Every time I have come across the fault, it has been C17, a 15pf feedback capacitor from pin 6 of the valve. Voltage tests on the valve won't help, as they broadly remain correct. What I have found is that the IF output shifts to around 15 - 17MHz, way off the expected 10.7MHz.

If you remove and test C17, it will appear fine, but test it at 100V and it turns into a 300K resistor. Replace with a good quality silver mica cap with adequate voltage rating and normal service will be restored.

Regards,
Adrian.

PJC58-Hythe · 6th Oct 2022, 5:23 pm

Thanks Adrian that's very useful information, fortunately all the ones I have worked on didn't exhibit this symptom. Just out of curiosity what type of capacitor is C17?

Freya · 6th Oct 2022, 6:13 pm

Thanks for that, must have taken some time to find that fault.

vinrads · 6th Oct 2022, 6:17 pm

Another thanks Adrian ,that's one for my little black book Mick.

agardiner · 6th Oct 2022, 8:00 pm

Peter - in the sets I have repaired, C17 was a low tolerance, tubular ceramic capacitor. I like to replace with a silver mica, as I have not then had to perform any realignment of the front end.

Stephen - first one took a little while to find, but actually not too long. My tool of choice is a frequency counter rather than a scope, and this instantly showed me the problem was in the front end, while also confirming that the oscillator was running but at the wrong frequency. After checking the voltages on the ECC85, C17 became prime suspect.

Freya · 6th Oct 2022, 9:21 pm

The Grundig sets were a favourite of mine for a few years and have to say that several sets had faulty tubular ceramic capacitors dotted around in various roles. Only have the 5050w/3D and the 97A, which was great fun making a new clutch for the tuning.

agardiner · 7th Oct 2022, 9:01 am

Yes, the tuning system is very clever, but when the clutch goes it is a pain! I keep in stock replacement clutch pads for them.

Tim · 7th Oct 2022, 12:27 pm

I’ve done a couple of these and they are fine performers once those horrible blue or brown capacitors have been replaced. ISTR I had a faulty polystyrene capacitor in one of these, but can’t remember which cap.

skodajag · 7th Oct 2022, 2:49 pm

Quote:

Originally Posted by Freya

The Grundig sets were a favourite of mine for a few years and have to say that several sets had faulty tubular ceramic capacitors dotted around in various roles. Only have the 5050w/3D and the 97A, which was great fun making a new clutch for the tuning.

What are the symptom/s if the clutch goes?

agardiner · 7th Oct 2022, 2:52 pm

The tuning dial slips when turning on either VHF or AM or both. Usually VHF is the first to go. It is because the rubber has perished.

murphy512 · 10th Oct 2022, 9:33 pm

I had a similar problem with a Grundig 2147 and it has taken me about 10 years of thinking to work it out.
After several attempts to fix it, I eventually changed C14 and C41 (I think it would be C10 on the 3028) and VHF came back to life and working almost as well as it did originally.

murphy512 · 10th Oct 2022, 9:55 pm

[QUOTE=skodajag;1504369]

Quote:

Originally Posted by Freya

The Grundig sets were a favourite of mine for a few years and have to say that several sets had faulty tubular ceramic capacitors dotted around in various roles. Only have the 5050w/3D and the 97A, which was great fun making a new clutch for the tuning.

I also had this clutch problem with the 2147 and managed to slip in two cut out discs of sandpaper glued back to back and has been working fine for some years now.

stevehertz · 11th Oct 2022, 7:45 am

Great find thanks!

LyntonP · 11th Oct 2022, 10:50 am

I restored a 3028 late last year. I found someone had previously inserted a rubber tap washer into the tuning mechanism! After removal and some careful adjustment the tuning worked fine.
Recently the set has developed a fault of varying volume levels when on FM, but if it is left switched on it will eventually correct itself and work fine. Not had chance to put it back on the bench due to a resurgence of my interest in amateur radio.
Lynton

6th Oct 2022, 5:11 pm	#1
agardiner Octode Join Date: Sep 2020 Location: Thetford, Norfolk, UK. Posts: 1,741	Grundig 3028 & similar models Mods - sorry if this is in the wrong place, please move as needed. ========================================= So, I hope this may be of help to someone. I restore a lot of the large German receivers such as the 3028, although there are many models including radiograms that have the same chassis. Lovely performers as anyone who owns one will know. I have recently had several of these chassis with VHF failure; usually just quiet but on one set it occasionally gave a very distorted, low level output. The front end is fairly common and built around an ECC85 mounted in a separate can. I attach a part schematic. Every time I have come across the fault, it has been C17, a 15pf feedback capacitor from pin 6 of the valve. Voltage tests on the valve won't help, as they broadly remain correct. What I have found is that the IF output shifts to around 15 - 17MHz, way off the expected 10.7MHz. If you remove and test C17, it will appear fine, but test it at 100V and it turns into a 300K resistor. Replace with a good quality silver mica cap with adequate voltage rating and normal service will be restored. Regards, Adrian. Attached Thumbnails

6th Oct 2022, 5:23 pm	#2
PJC58-Hythe Heptode Join Date: Sep 2010 Location: Hythe, Hampshire, UK. Posts: 630	Re: Grundig 3028 & similar models Thanks Adrian that's very useful information, fortunately all the ones I have worked on didn't exhibit this symptom. Just out of curiosity what type of capacitor is C17? __________________ Peter - M0HYT - BVWS Member - GQRP Club http://www.retroworkshop.co.uk

6th Oct 2022, 6:13 pm	#3
Freya Octode Join Date: Jan 2009 Location: Falmouth, Cornwall, UK. Posts: 1,990	Re: Grundig 3028 & similar models Thanks for that, must have taken some time to find that fault. __________________ Stephen _________"It`s only an old telly" ___

6th Oct 2022, 6:17 pm	#4
vinrads Dekatron Join Date: Feb 2009 Location: Chesterfield, Derbyshire, UK. Posts: 3,762	Re: Grundig 3028 & similar models Another thanks Adrian ,that's one for my little black book Mick.

6th Oct 2022, 8:00 pm	#5
agardiner Octode Join Date: Sep 2020 Location: Thetford, Norfolk, UK. Posts: 1,741	Re: Grundig 3028 & similar models Peter - in the sets I have repaired, C17 was a low tolerance, tubular ceramic capacitor. I like to replace with a silver mica, as I have not then had to perform any realignment of the front end. Stephen - first one took a little while to find, but actually not too long. My tool of choice is a frequency counter rather than a scope, and this instantly showed me the problem was in the front end, while also confirming that the oscillator was running but at the wrong frequency. After checking the voltages on the ECC85, C17 became prime suspect.

6th Oct 2022, 9:21 pm	#6
Freya Octode Join Date: Jan 2009 Location: Falmouth, Cornwall, UK. Posts: 1,990	Re: Grundig 3028 & similar models The Grundig sets were a favourite of mine for a few years and have to say that several sets had faulty tubular ceramic capacitors dotted around in various roles. Only have the 5050w/3D and the 97A, which was great fun making a new clutch for the tuning. __________________ Stephen _________"It`s only an old telly" ___

7th Oct 2022, 9:01 am	#7
agardiner Octode Join Date: Sep 2020 Location: Thetford, Norfolk, UK. Posts: 1,741	Re: Grundig 3028 & similar models Yes, the tuning system is very clever, but when the clutch goes it is a pain! I keep in stock replacement clutch pads for them.

7th Oct 2022, 12:27 pm	#8
Tim Dekatron Join Date: Jan 2003 Location: Bradford on Avon, Wiltshire, UK. Posts: 3,310	Re: Grundig 3028 & similar models I’ve done a couple of these and they are fine performers once those horrible blue or brown capacitors have been replaced. ISTR I had a faulty polystyrene capacitor in one of these, but can’t remember which cap. __________________ "Nothing is as dangerous as being too modern;one is apt to grow old fashioned quite suddenly."

7th Oct 2022, 2:52 pm	#10
agardiner Octode Join Date: Sep 2020 Location: Thetford, Norfolk, UK. Posts: 1,741	Re: Grundig 3028 & similar models The tuning dial slips when turning on either VHF or AM or both. Usually VHF is the first to go. It is because the rubber has perished.

10th Oct 2022, 9:33 pm	#11
murphy512 Pentode Join Date: Mar 2008 Location: London, UK. Posts: 122	Re: Grundig 3028 & similar models I had a similar problem with a Grundig 2147 and it has taken me about 10 years of thinking to work it out. After several attempts to fix it, I eventually changed C14 and C41 (I think it would be C10 on the 3028) and VHF came back to life and working almost as well as it did originally.

11th Oct 2022, 7:45 am	#13
stevehertz Dekatron Join Date: Sep 2011 Location: Rugeley, Staffordshire, UK. Posts: 8,831	Re: Grundig 3028 & similar models Great find thanks! __________________ A digital radio is the latest thing, but a vintage wireless is forever..

11th Oct 2022, 10:50 am	#14
LyntonP Hexode Join Date: Nov 2018 Location: Greater Manchester Posts: 305	Re: Grundig 3028 & similar models I restored a 3028 late last year. I found someone had previously inserted a rubber tap washer into the tuning mechanism! After removal and some careful adjustment the tuning worked fine. Recently the set has developed a fault of varying volume levels when on FM, but if it is left switched on it will eventually correct itself and work fine. Not had chance to put it back on the bench due to a resurgence of my interest in amateur radio. Lynton __________________ Never buy a mermaid a pair of socks!