14-07-2013, 07:24 PM
(14-07-2013, 07:14 PM)Mark Hennessy Wrote: I've been a bit pre-occupied with a ex-broadcast sound desk that I've been restoring. It's only 20 years old, but needed all electrolytics replacing. I had to source some obsolete analogue switch ICs from eBay. Also, it had a series of bizarre logic faults that were caused by 4000-series CMOS chips failing. Of course, they weren't fitted in sockets! And to make it worse, they were fitted to double-sided PCBs that didn't have plated-through holes, so getting the old chips out without ripping the component-side tracks off the board was "fun", to say the least. In order to solder these top-side pads to the IC sockets, other components had to be removed, which added to the time taken. And best of all, there are no schematics or any kind of information about this - I've had to reverse-engineer working schematics. I've definitely earned my fee with this one!
As I'm waiting for parts for the desk, I have a Hacker Sovereign 2 RP25B on the bench now. Sadly not one of mine, as it's a nice one... No FM. Normally, FM faults fill me with dread - mostly because accessing the rear of the FM front end PCB involves a lot of dismantling. They're not too bad in most Hackers, happily. It didn't take long to prove that the fault was with the front end, and that there was no oscillator. Then it burst into life. Bugger! From DC measurements taken during this, I was able to prove that the oscillator transistor had no collector current when in fault mode. Checking all components that could cause this, I was rewarded with a dry joint that was invisible to the naked eye. I spent a while touching up a lot of the soldering, and checking things very carefully before the long re-assemble, and so-far, so good. All is back together now, and I just need to do an RF lineup. The audio amplifier has bad noise, but this isn't the usual fault with these, so not the Lockfit for a change. It's white noise rather than the usual 1/f noise, and a distant memory tells me that this might be the AC128 VAS/driver T4. We'll see...
As for this glorious weather, I'm fair-skinned, so not very good in the sun. I did spend most of yesterday afternoon in the park with the kids, but decided to give it a miss this afternoon. My "temporary" workshop is in the cellar, where the temperature is nice and cool - it's 20C at the moment. But, at this time of the year, humidity has been the problem - it's typically a very uncomfortable 90% RH or so. That's because the outside air is brought in via the ventilation, and as it's cooled, the RH shoots up. It's actually quite dry down here during the winter, perhaps surprisingly... Anyway, I recently bought a dehumidifier, and it's proving to be really effective. The RH is now in the mid-60s, and it feels very comfortable now. Of course, the waste heat goes towards heating the space as well, so it's a very economical unit to run (about 170 watts when running, which it does less than 30% of the time at the moment as it's on a humidistat). I've reduced the amount of ventilation to stop it trying to dehumidify the world, though when it gets cooler outside I'll open that up again. And of course, the dehumidifier can be used in the house during the winter if needed.
All the best,
Mark
Good luck with the sound desk Mark, sounds a hands full job, double sided print can be a pain the old Sony Language Lab cassettes had double sided print with the most horrendous hard to find dry joints and lot's off them.
Lawrence.
