What does a Vintage Stereo restoration consist of?
There are several stages of steps we go through when we get a unit in for restoration, either one of our own, or a customer’s unit. We try to do all the units the same, following the same procedure so that the process gets standardized. This helps to minimize any mistakes we might make, or the possibility of forgetting to do something that requires removal of the front panel, and realizing it when the whole thing is back together and in final checkout. disassembling the front panel is a big deal on these QRX’s.
1) Initial checkout The first thing is to do a complete check of all functions. I do this on my workbench, taking note of what works and what doesn’t, light bulbs, scratchy pots, channel dropouts, all that. All four outputs are measured for voltage offset, FM and quad performance, etc. All of this gets written down on a piece of notebook paper and taped to the transformer so it will not get lost. The unit will not be powered up again, until the end. If the cabinet is to be refinished, we send it out to Gabe’s shop.
2) Recapping starts The removable boards get pulled out of the unit. On the 9001 there are 7 of them, and the recapping gets under way, in no particular order. The removable boards are the easiest, and currently my son Jonathan is doing these. Justin will do all the recapping of boards behind the front panel and the others mounted to the chassis and soldered in. All these are rather difficult, even with the front panel taken apart.
3) Pass through repair With the front panel completely disassembled, the 4 ch board, the one with the push buttons mounted on it, gets all its pass through joints pinned and soldered. The trace on each side of the board going to the pass through joint is scraped clean with a small screwdriver, and the pin is soldered to the trace on each side. This is the most tedious and time consuming part, and takes 6 hours or more.
4) Output boards Practically all units get the Diff Mod, so the two output driver have all their capacitors, fusible resistors, and a bunch of transistors, changed, plus new parts added. Some of this is done by one of my sons, but the final parts are put in by me later after the first power up.
5) Additional mods The unit is partially reassembled and goes to my workbench, where all the test gear is. I will add the 25v regulator for the quad boards, do whatever has been requested for the panel lighting, add some more diff mod components to the driver boards, and just in general, check everything done so far.
6) First power up Time for power up. No matter how many of these we have done, this is always a stressful and anxiety ridden moment. Sometimes I take a break first, LOL. In a few years of doing this, I have only had one unit that came up badly, but it’s still anxiety time. I power up and quickly check a few voltages, then the voltage offsets on the outputs. If all is good, I calm down and proceed. whew!
7) Checkout I then proceed to check out various functions, and there are a lot of them in the 9001. I do an initial dial in of offset and bias. And listen for good audio quality. 90% of the time, all the problems noted in the initial checkout are fixed.
8) Diff Mod I finish the Diff Mod, which requires installing a couple custom circuits that we make up, and two small 10 turn pots on the output boards, and then adjust some very small voltages while the unit is running. Then I set the offset and bias again, and then redo, again, the same adjustments. I then pull the pots, measure their value, and replace them with resistors that I make up with two or three resistors, to an accuracy of 1 ohm. This achieves balance in the input circuitry, which is very important. I have racks and racks of 1% resistors so that I can do this.
9) Quad alignment I hook up the HP generator and align the quad boards, to the standard called Holy Grail. Very often there are bad IC’s on the quad boards, which require trouble shooting to figure out which ones, and then replacement.
10) FM alignment I spend some time touching up the FM alignment, Usually, this is pretty close, but not always. The most time consuming is when the frequency calibration is way off.
11) Dolby alignment I align the dolby circuitry in the unit. This is always way off and always a pain. Especially, cause I don’t think anyone ever uses it, and the very complicated dolby switch is the most troublesome switch in the unit.
12) Final test Then we play it through the shop system, a pair of B&W 802 S2 in the front and EV monitors in the rear. I check for output levels and distortion, check the 2X power out, the CD4 decoder, and so on.
13) Final assembly If all is good, the front panel gets a total cleaning. If there are scratches on any of the three layers of plastic dials, we will polish them out with rubbing compound. The knobs get soaked in detergent solution and polished. Then we play it for as much as a week. We also have a second testing station, in the shipping area where we do all the foam cutting and packing.
14) Additional repairs Sometimes an additional problem will show up in the testing phase. I consider it a small victory when that happens. That’s a problem the customer didn’t get to have at home. It’s the units that have been sitting around, unused for years, that usually have the additional problems.