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-   -   Grundig A 7400 (CUC220) (https://www.vintage-radio.net/forum/showthread.php?t=178610)

andyw25 6th Apr 2021 5:38 pm

Grundig A 7400 (CUC220)
 
5 Attachment(s)
Evening All

I posted several years ago regarding one of these sets, used to belong to my grandparents but at the time I wasn't very savvy with electronics and let the set go.

Over the years I've taken great interest in vintage electronics repairing all manner of things, having also repaired two Philips 14" portables recently (14CT2006)

Browsing online I found this Identical Grundig set to my grandparents, the only difference I can spot is that this one is badged as having Teletext :)

It does power on but I intend to give it a good clean up as it appears to have came from a smoker.

Also ordered some replacement capacitors to replace a couple of Wima branded ones before the magic smoke escapes from them :-D

I never did remove the back from my Grandparent's set so I'm curious, did these all come with the Hitachi tube?

Also the Varta back-up battery has leaked and caused small corrosion to the board, I've managed to clean this up, what would everyone recommend as a good replacement ?

I can get the same type battery, but I've seen elsewhere someone use an adaptor to allow the use of a coin cell type, admittedly this was on a computer motherboard so I'm not sure wether it would be suitable here, I'll attach some pictures for reference. Although I've noticed there is also provision to fit a two legged battery instead of the 3 legged?



Best Wishes, Andy

andyw25 6th Apr 2021 6:30 pm

Re: Grundig A 7400 (CUC220).
 
10 Attachment(s)
Some more pictures, and the coin cell adapter pictured :)

Here are the other Photos

1955APREN 7th Apr 2021 10:44 am

Re: Grundig A 7400 (CUC220)
 
Hi Andy
I Loved Cuc220 one of the best set's ever. The circuit diagram is
on Pauls list top right of start page it can be downloaded for 1;99.
There are different versions of the panel.s when working on a panel
cheek the No on the panel with the right circuit digram
common faults

1 T634 Bu208a S/c Cause R646 gone high
Might also damaged I/C TDA4600 if so make certain that
C626 is fully discharged b4 fitting new I/C
2 Frame faults
none linar C2762 1000uf, C2764 220uf,C2774 100uf,
C2768 100uf ,
3 Tuner/ If Causing drift flashing video
Remove tuner/If unit ( 2 screws on pc side)
Pull tuner away from pins ( carefully not to bend pins)
remove sides of tuner , resolder all earthing bars to pcb
and replace all small electro/ caps
4. Trippler unit failure
These are the faults I remember hope they may be of help to
I cannot see Battery that you mention possible not on my version
of circuit diagram . Could you give ref No
Kind regards
Derrick

Maarten 7th Apr 2021 11:14 am

Re: Grundig A 7400 (CUC220)
 
You should not use coin cells as they will explode when charged. Rechargeable coin cells will be overcharged so no good either. Or is there a diode in the replacement module? In that case, your only problem will be periodical battery replacement.

I think there's only paper capacitors in the mains filter. Those blue ones should indeed be replaced before they blow, even though they're slightly more reliable than their Rifa cousins.

andyw25 7th Apr 2021 6:54 pm

Re: Grundig A 7400 (CUC220)
 
1 Attachment(s)
Many thanks for the comments so far, I have found and bought/downloaded the service manual ;D

Also checked the photos again and the battery adapter does appear to have a diode on the bottom ?

However I've found some replacement 1.2v NiCd ones, these should last a good few years should they not? :)

ben 7th Apr 2021 11:54 pm

Re: Grundig A 7400 (CUC220)
 
Excellent sets. I have the A8400E and A6400 (both r/c versions) and again in non-remote variants! I think they had a factory here in Spain.

I used 2x AA or AAA NiCads in a caddy in one of them.

The tripler is a weak point too. Apart from that they seem to just go on and on!
You can also use the rear AV socket as a CVBS input.

Richard_FM 8th Apr 2021 9:50 am

Re: Grundig A 7400 (CUC220)
 
I remember one school I went to had a Grundig similar to this one, the landscape remote control was a nice touch from Grundig & one was used in Dr Who as a handheld computer!

Welsh Anorak 8th Apr 2021 10:56 am

Re: Grundig A 7400 (CUC220)
 
I was just about to mention the Doctor Who connection!
Most of these had the Hitachi CRT which just goes on and on giving a crisp picture. The odd capacitor failure, tuner dry joints, the power supply failing due to the resistor mentioned and the tripler are really all I can remember and I serviced loads of these. ISTR you needed the exact tripler or else the A1s were wrong.
I think this was the first Grundig to change from the thyristor line stage following the GSC100 and marked a significant improvement in reliability. The budget CUC95 (small vertical chassis) was a good performer too.
The later G1000 wasn't great, but it wasn't really a Grundig at all.

AndiiT 8th Apr 2021 11:41 am

Re: Grundig A 7400 (CUC220)
 
Great sets, I owned one many years ago. As Ben has already mentioned you can use the 8 pin A/V socket to feed composite video and audio signals to the set - from memory you need to apply around 9 to 12 volts to one of the pins on the A/V socket to allow channel position 8 (it may be 0) to be used as the external input position, when you do so an additional dot will appear on the channel number display to indicate the set is in AV mode.

You can apply the voltage either from pin 8 of the source equipment SCART socket or link two of the pins on the A/V socket (1 and 7 I think, best to check though) as there is a 12 volt supply available on the socket.

Andrew

ortek_service 8th Apr 2021 1:10 pm

Re: Grundig A 7400 (CUC220)
 
Quote:

Originally Posted by andyw25 (Post 1361644)
Many thanks for the comments so far, I have found and bought/downloaded the service manual ;D

Also checked the photos again and the battery adapter does appear to have a diode on the bottom ?

However I've found some replacement 1.2v NiCd ones, these should last a good few years should they not? :)

NiCd's have generally been phased out now.
And PCB-mount 2.4V / 3.6V etc. backup ones, were replaced by NiMH ones many years ago that seem less-prone to leakage (maybe as not as old), so may be preferred.

Although standard NiMH self-discharge may not be as good as other ones -particularly Low-Self Discharge NiMH cells (but haven't seen these in types other than standard AA, AA etc. types)

andyw25 8th Apr 2021 8:34 pm

Re: Grundig A 7400 (CUC220)
 
Thanks again for all the messages and advice :)

I've removed the Backup Battery from the Tuning Module, sadly it has caused a lot of damage when it leaked :( However I've managed to clean it all up and repair the damaged traces. They might not look pretty but they all check for continuity :) Perhaps at some point a spare Tuning Module Board would be handy if anyone happens to have spares for one of these sets?

I do have a complete spare chassis coming that I purchased online, however I've noticed the tuning module on that chassis appears different, rather than the backup battery it has a chip instead, perhaps a non pal chassis?
My Tuning Module is 29504-003.02 but the service manual also lists a 29504-003.01

With regards to spare parts, does anyone know the part number for the Tripler, If I could get my hands on a spare that would be very handy indeed?

Wiring a din for use of the AV socket with a dvd player would be great, I'll have to look up the pin out's

I've also got a Grundig V2000 VCR aswell that I'm sure has a 4 pin din cable to the tv for controlling the recorder with the same remote?

Best Wishes, Andy

Maarten 9th Apr 2021 7:52 am

Re: Grundig A 7400 (CUC220)
 
From the top of my head it would be some variant of the BG1897. It should be on the schematic, possibly dependant on the picture tube used. I haven't seen defective triplers that often. Grundig became well known for them,though, when they switched to the BG2077/BG2087. Pure garbage. Only HSE managed to make reliable generic replacements. At some very late point Grundig used BG2032 or BG2034 replacements, I think.

gallowfields 9th Apr 2021 6:43 pm

Re: Grundig A 7400 (CUC220)
 
the triplers usually have the part number wrote on them ,also the focus pots attached do give trouble


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