va3ext wrote:I just picked up a used A-7550 for parts, lid & soft case for my 1200S.
It starts up & goes past the boot screen to the spectrum screen, then after a few seconds freezes up. Can't do anything.
If I hit the Menu button just after the boot screen, it brings up menu, but then freezes.
Any ideas where to start looking?
Does it mysteriously work pretty much all ok (except a tad off freq) with AUTOCAL disabled? (jumper installed ON JB1 on interface board) ? But normal A-7550 operation is AUTOCAL enabled (jumper JB1 off)...jumper JB1 installed should only be used during calibration procedure...
I had picked one up for cheap. Unit did just that. Recapped supply even with low ESR on all caps...lithium 3v cell was 0.4 or something...so desoldered it...but didnt replace it right away...service manual doesnt say its critical...just it saves memory...
i troubleshooted this for hours..read sm inside out...so odd unit was working pretty much ok with AUTOCAL disabled...with AUTOCAL disabled navigating menus (running out ideas) I noticed accessing STORE function I would lock up unit...more and more was looking like a cpu-memory issue...could that lithium 3V play an important role and needs to be there and good?...does the firmware keep important AUTOCAL or other values in the backed up ram...?
It does!...i installed a plastic lithium cell holder (tight fit with a resistor network close) and a new 3v cell...a couple of ON OFFs and unit is working fine now...with AUTOCAL disabled...100Mhz ref now right down center
Not a unit for serious work anymore but fine for occasional ham & hobby use!