|
Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment. |
|
Thread Tools |
31st Jan 2020, 9:59 am | #1 |
Pentode
Join Date: Dec 2011
Location: Camelford, Cornwall, UK.
Posts: 188
|
Frg7700 display issues
I have just decided to have a look at my frg7700 display problem.
One segment seems to be on I think all the time. Same one on each digit. ie the 6 looks like an 8 . I believe it may be a faulty chip , oki msm5524. So any ideas? And does anyone have a spare chip please? Quite rare. |
31st Jan 2020, 10:02 am | #2 |
Nonode
Join Date: Nov 2015
Location: Welwyn Garden City, Hertfordshire, UK.
Posts: 2,015
|
Re: Frg7700 display issues
I have known leaky diodes to cause that sort of thing on a Kenwood.
If there are any used around it, it's well worth checking them before blaming a rare and hard to get driver IC. 2x 1N4148 fixed it for me! |
31st Jan 2020, 12:36 pm | #3 |
Pentode
Join Date: Dec 2011
Location: Camelford, Cornwall, UK.
Posts: 188
|
Re: Frg7700 display issues
Thanks jon I will lookout diagram
|
31st Jan 2020, 1:30 pm | #4 |
Heptode
Join Date: Nov 2009
Location: London, Ontario, Canada
Posts: 675
|
Re: Frg7700 display issues
Here is an interesting thread on that display chip:
https://www.hamradioforum.net/archiv...hp/t-2631.html Also interesting is the Japanese web-page that thread is pointing to, where they started to reverse engineer the counter/display chip. You need to run it through the translator though. Regards, Peter |
31st Jan 2020, 4:23 pm | #5 |
Nonode
Join Date: Nov 2015
Location: Welwyn Garden City, Hertfordshire, UK.
Posts: 2,015
|
Re: Frg7700 display issues
D24, D25 in the attached snippet were to blame for my TS130V doing strange things in the display.
|
3rd Feb 2020, 2:26 pm | #6 |
Heptode
Join Date: Jun 2009
Location: St Helens, Lancashire, UK.
Posts: 641
|
Re: Frg7700 display issues
If it is just one segment on each digit, then it is very likely the chip that is faulty (MSM5524)
Unfortunatly this is virtualy unobtainable, and replacement with an alternative very difficult, as it does all the clock functions also! However do check the board for dry joints/bad connections, and check resistor network RB01. It could be the display, but unlikely, but worth measuring the volts from the driver chip. If I recall correctly the display runs about -100Vdc and the driver chip sinks the volts to turn on the segment. If it was one digit, then it would likely be a driver transistor
__________________
SPECIALIST.....Knows everything about nothing EXPERT..........Knows nothing about everything |
3rd Feb 2020, 4:47 pm | #7 |
Dekatron
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,567
|
Re: Frg7700 display issues
Kernow, how do you feel about ordering from China?
https://www.alibaba.com/product-deta...666429832.html (If you search more carefully on Alibaba there is at least one seller selling them in ones, but it is not clear whether they are the DIP version or the flat-pack SMD version). Last edited by SiriusHardware; 3rd Feb 2020 at 4:54 pm. |
3rd Feb 2020, 7:32 pm | #8 |
Dekatron
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,567
|
Re: Frg7700 display issues
I've noticed that there is a LED output version of this chip, the MSM5523RS. If it is generally pin compatible (I have not checked) you could either:-
Remove the VFD display and build / fit an equivalent LED display directly driven by the '23 IC, or, Fit the '23 IC, isolate the LED drive outputs from the existing display and introduce extra buffer / driver circuitry as required to allow the LED driver chip to drive the original display. This second scheme would have the merit of separating the actual display driving components from the complex, hard to get controller chip so if any of the drivers failed again you would just replace those. It would also keep the radio / display looking original. |