This guy is restoring VINTAGE audio gear. It is definitely younger than the Boatanchors we usually work on, but it is a lot older than more recent gear that is made with largely pick-and-place machines and surface mount components. There are mostly through hole components here.
There are some challenges I've never thought about: glue that over time starts to mess up the circuitry. Fusible resistors? Who knew? And then there are relay contacts that go really bad. We use a lot of these kinds of relays.
All in all, there are a lot of good ideas in this video. His other videos are probably worth watching too. I think it will be especially useful for my friend Bob, KD4EBM who does a lot of work in this area.
Please let me know what you think. Comment below.
In the mid 90's I was repairing a 2 part VCR system (one with a main VCR tape transport section and a wired remote camera - the predecessor to the portable camcorder) where the main VCR part's tape control buttons (Play, Record, FF, Rewind) would work fine, but the remote camera's controls were intermittent some times and wouldn't work at all other times. The remote control functionality between the two units was implemented using a pair of custom ASIC integrated circuit chips. Troubleshooting suggested that the problem was most likely in these two chips, which I replaced at considerable expense ($190), but the trouble remained after replacing these chips. At that point I was at a loss as to what the problem could be so I began to really dig deep into the circuit and eventually discovered that problem to be a rubber pad between the circuit board and the metal chassis. This pad was glued on the PCB and covered several traces of which were corroded and the glue created a conductive path between the traces causing a short between the traces. I removed the glue and problem solved. Lesson learned the hard (expensive) way. 73 - Rick - N3FJZ
ReplyDeleteThat problem with silicone adhesive absorbing water over time is, I think, #2 on the "closet rot" hit parade, right after the 80's capacitor plague. Besides becoming conductive, it also can get corrosive, damaging parts and traces.
DeleteNice video! I think I might leave the DeOxit Red on the relay contacts, but fully agree with the larger point that replacement is best practice.
Rick: Glue! Who knew? Thanks and 73. Bill
ReplyDeleteNever heard of these problems. Nice to know. I don't think I have ever heard of fusable resistors or component glue in ham radio gear. Has anyone? I do a lot of restoring but mostly gear built before 1970.
DeleteGrayson, KJ7UM
I have not seen either fusible resistors or component glue in amateur gear, possibly because some manufacturers had both military and amateur manufacturing "under one roof". Hallicrafters, Collins etc and it certainly wasn't the norm there. I have never used in my defense work, weather radar or cellular base station equipment.
DeleteThe "component glue" does have a purpose after manufacturing consumer electronics. It also provides support during shipping. Large radial electrolytics with only two wire leads needed the support during transport otherwise the massive component could wobble, flex and break the radial leads or solder joints to the PCB. Military and some industrial used metal braces and hardware for vibration support, just as they had for vacuum tubes (thermatrons!). The HP8970 NF Meter had several huge electrolytics on the power assembly. These had such support and did break. Easy fix!
I viewed his other videos. Good material.
Oooops- Meant to say the HP8970 has NO such support.....my bad.
DeleteThat's a cool tool to bend the leads!
ReplyDeleteRogier: I had the same thought. Also, the plastic bag of scraping tools to get rid of the glue -- that was pretty cool too. 73 Bill N2CQR
DeleteGo to the Bezos store and look for "Spudger" these things are very handy to open, remove and scrape things without damaging them.
DeleteI learned about fusible resistors when my Hitachi HA-7700 just died on one channel. I assumed that one of the power mosfets had decided to die, so it languished in the loft for about 5 years. I took it down last year, and had a real look into the problem. All four mosfets tested fine, but the volts on one channel were plain bizarre. The circuit was all DC coupled, so that made it more tricky. Eventually, I concluded an open circuit resistor must be the problem. It turned out THREE fusible resistors had opened! So the whole lot came out, and then the amp started working. Whilst it was in bits, I recapped it and cleaned the contacts and the tracks. It's now like new. Fusible resistors - replace on sight. Definitely.
ReplyDelete