Evidence of Past Repairs

It’s always interesting to see what’s happened with equipment that’s been worked on previously. It’s often a mixed bag with some great repair jobs, some that have a lot of room for improvement, and some that really just don’t measure up. I like to think I’m in that first category, but I let my work stand for itself backed up with a set of photos.

Sometimes I’ll get lucky and find a good quality repair or even an upgrade, as was the case in this Bose 901 Series I equalizer which had upgraded first filter capacitors.

There are quite a few that probably worked well at the time, but the repair has exceeded its working life, or something else has gone bad.

I believe these to be 1960s or 1970s film drop capacitors. They’ve been bad in every piece of equipment I’ve found them in, and are often even slightly physically discolored in the center. Not to mention, this one had the speaker wired incorrectly, so it’s unlikely it actually worked after whatever service was done to it that included this capacitor replacement. (Farnsworth K-262P)

That type of bad capacitor turns up in the Bose equalizers, too. In this case, the one with the upgraded filters, had original defective film capacitors. (#31131)

As did this one.  (#35793)

This unknown 1940s Gilfillian radio had been serviced a few times. The original paper capacitors are intact, then later sealed paper capacitors, and finally the same ’70s era film capacitors were installed.

Sometimes it’s a little less pretty. Like when a previous technician destroys a solder pad, and manages to leave a pretty poor solder joint after scraping a new pad on the trace. I suspect those two things may have been connected. This work was performed locally in Seattle, although I don’t specifically know which shop.

It was pretty common back in the day to add additional capacitors to a circuit, without removing the old ones. This sort-of worked, but was very poor practice. This poor http://blog.kf7lze.net/2012/03/10/1936-grunow-566-repair-finished-part-2/ had this treatment: the on-chassis replacement failed and was replaced with the 8/16…and then three more 10s across different places in the circuit, including one connected in parallel with the field coil for some reason.

That same radio, though, did have the electrodynamic speaker replaced with a (very beefy) permanent magnet speaker and substitute resistor in what is actually pretty good, and likely a modification from the 1940s, so fairly period.

There’s also this, where “they should know better”. A shop nowhere near-by serviced this one fairly recently, and it failed shortly thereafter. There are several eras of components installed, but most notably, the newest set was installed after it was a well-understood best practice to replace all those sorts of components preemptively, as if they aren’t bad now, they will be soon.

I like seeing the history of previous repairs and doing some detective work to find out why that might have happened, but sometimes it can be frustrating to have to go in and fix mistakes which might have been the reason these devices fell out of service in the first place.

Do you have any stories about surprises left in your work by someone who’d been there before? Please share!

Advertisements
This entry was posted in Collections, Commentary, DIY, Electronics and tagged , , , , , , , , , , . Bookmark the permalink.

One Response to Evidence of Past Repairs

  1. Audio Tweak says:

    Really nice blog, thank you for your link.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s