[EdHolland]

I mentioned this one in the "What did you fix" thread, but since it is a radio (albeit with ICs and transistors) a thread here might be of interest. 

The radio is a neat hand-held (7" x 3.5" x 2.5") that covers everything from lonkg wave (150 kHz) to the top of the FM band (108 MHz). No gaps, and various receive modes. Vintage is late 80's to early 90's. Golden age of solid state? 

The set was not operable when handed to me by a friend for "a look with no expectations". The speaker clicked when the power switch was operated, but that was all. I have a service manual, and a replacement capacitor kit, and steadily have been working my way through the surface mount boards to change electrolytics, clean up leakage and diagnose problems.

Testing as parts were replaced brought the audio amp back to life, but little else. 

The computer and display boards occasionally showed feint signs but were basically unresponsive. This was traced to a feed from the 6 V battery pack via a diode pair package, which had become open circuit or very high series resistance. Making a substitution with 1N4148 devices brought the display and keypad back to life, but no reception achieved.

Last night I spent more time cleaning the board, checking for soldering errors (tiny traces and components) and restored the operation of a DC to DC converter that feeds the oscillator section. Still no reception, but the RF board still needs lots of attention to e-caps. Each one is about the size of a pencil top eraser (or smaller) and the very devil to hold in place and solder with a point-tipped iron, but we are getting there.

Good fun, as always!

[Arran]

Ed;
  If those a surface mount electrolytics I have heard of people replacing them with through hole ones by bending the leads accordingly to line up with the pads, and also with judicious use of soldering paste, but surface mount boards are honestly not my bag. Hopefully your Sony doesn't have something like a proprietary IC that has gone bad, Sony was starting to go down that dark road by the 90s after Mr. Morita retired.
Regards
Arran

[BrendaAnnD]

Good results can be obtained by using SMT chip caps as well.

[EdHolland]

Good advice folks, thanks Arran and BrendaAnn

On another project with SMT electrolytics, (Squeeze-box Hifi component) I replaced them as Arran suggested, and it was easy.

On this board, with nothing to lose except $12 for a cap kit, I thought I'd have a go with SMT. It sure isn't tag strips and tube sockets though!

I found a few on-line pointers with this set and its cousins.. What I'm finding does not seem to be unusual, and there is a fair chance of recovery. Now the "Brains" are working, I can start to figure out the radio elements like oscillators and IF. More familiar territory, even if it is tiny and doesn't glow in the dark..

[EdHolland]

I'm still tinkering with this radio. More work this weekend, an hour or so, but no progress. There's nothing getting through the IF, although the audio stage is good. Caps on the RF/IF board still need to be replaced. Voltages here look uncertain compared to the service sheet so I'll recheck when the caps are done and go from there.

[OZ4]

Ed  does the IF have crystal filters or transformers? This old Sony has crystal filters.

[EdHolland]

It has some of each. I still think the FM/IF amp chip is not operating properly, and this could well be down to failure of any/all the 7 or so electrolytics associated with it.

You bring up an interesting point, though, as I have recently encountered faulty crystal filters in 3 radios. One of these was so degraded that the peak in the remaining passband was around 9 kHz off the expected 455 kHz centre.

[EdHolland]

Caps replaced on the RF/IF board - no improvements. I'll have to start probing around to see if the oscillator section is working, and the signal swtiching controls lines for AM, FM, SSB etc.

One thing it is doing now is keeping the audio muted (indicator light tells the state of the mute operation). Previously this could be defeated by turning the squelch to minimum. I suppose that tells me something...

More tomorrow.

Ed

[EdHolland]

More testing, but I found one of the unobtanium flex connectors is damaged. Sony, in their wisdom, used one of these to attach two of the boards permanently. I shall have to devise a repair work-around with fine hookup wires.

[EdHolland]

More fiddling this past weekend, and it looks as if there is a fault in the flex connection between the CPU and PLL/power board. This part is soldered in place, so the only option (if it can't be rescued) is to replace with fine hookup wire.

Bound and determined to fix this thing, but it is challenging me to a duel!