List of parts needed for the Fender Princeton Chorus overhaul

Thinking about purchasing the zeners from ELFA. The jacks and pots would be from UralTone, except 50K15A and 1M5C would be from Music Parts Guru or some other store. Total without postage would be about 58€.

Description	Schematic pos.	Schematic/part info	Fender pno	Store part no	number	price á
9-pin stereo 1/4” jack, Fender	J1, J2, J6-J8		0031570000 0025931000	428-H507-A	5	3.55€
4-pin mono 1/4” jack, Fender	J3-J5		0037036000 0025929000	428-H506-A	3	3.30€
pot	R10 (pos. 1 VOLUME)	50K B / B50K 8839	0027941000	636-R-VSN-50KL-DS	3	2.50€
pot	R40 (pos. 2 TREBLE)	50K 15A / 15A50K 8840	0027940000	FPHD-50KA-DS, FEN-002-7950-000	2	$4
pot	R42 (pos. 3 MID)	2K 15A / 15A2K 8846	0027937000	FPHD-2KA-DS / 636-R-VSN-2KA-DS	1	2.50€
pot	R41 (pos. 4 BASS)	50K 15A / 15A50K 8840	0027940000	FPHD-50KA-DS	see above
pot	R55 (pos. 5 REVERB)	50K B / B50K 8839	0027941000	636-R-VSN-50KL-DS	see above
pot	R20 (pos. 6 GAIN)	100K 30C / 30C100K 8830	0027947000	636-R-VSN-100KC-DS	1	2.50€
pot	R23 (pos. 7 LIMITER)	1M 5C / O5C1M 8835	0027950000	FEN-002-7950-000	1	$3
pot	R31 (pos. 8 PRES.)	50K 2B / 2B50? ????	0027942000	636-R-VSN-50KLD-DS	1	2.50€
pot	R34 (pos. 9 VOLUME)	50K B / B50K 8839	0027941000	636-R-VSN-50KL-DS	see above
pot	R131 (pos. 10 RATE)	100K B / B100K 882?	0027945000	636-R-VSN-100KL-DS	2	2.50€
pot	R139 (pos. 11 DEPTH)	100K B / B100K 8840	0027945000	636-R-VSN-100KL-DS	see above
zener diode	CR19, CR20	1N5353	?	1N5353BG	2 (+spare)	0.76€

Fender Princeton Chorus disassembly and inspection Part 1

I disassembled my Fender Princeton Chorus. This meant undoing four screws on top of the amp and then one on each side. After I had slid out the panel which holds the circuit board, I took photos for reference, detached all leads, removed the nuts around the pots and jacks and finally undid six screws holding the circuit board to the panel.

Immediately as I glanced upon the backside of the circuit board, I noticed a dark spot surrounding two components placed next to each other. The two components had the schematic numbers CR19 and CR20, which I quickly found in my paper schematic. Next to the markings CR19 and CR20 read the text '1N5353', which I assumed to be some sort of a part number. Using google, I found out the two components were 16V zener diodes (http://www.datasheetcatalog.com/datasheets_pdf/1/N/5/3/1N5353.shtml).

After a second round of googling, I had found a store selling such diodes in my home town. The price for three was 2.79€. Not too bad. Will get them on Monday.

Coming up: Fender Princeton Chorus maintenance?

The circuit board of a 1988 Fender Princeton Chorus solid-state amp

Let's see what happens...

A Smiths tachometer adventure

Left to right: Smiths RVC 1410/00AF, Smiths RVC 1414-01F

Bought a Smiths RVC 1410/00AF tachometer with the purpose of installing it to my '66 Volvo Amazon. The car I own didn't originally have one, but many people installed Smiths tachs to Amazons in the 60s and 70s, so it sort of is OK to put one in. Also, I gather the sportier models apparently had 80mm Smiths tachs installed as standard.

The tach that didn't work (RVC 1410/00AF, 4-cylinder negative earth,
no calibration pot, 80mm fitting size, possibly inteded for an MG MGB?)

The tachs I have don't read 'Volvo', as they are from British cars of the era. Why are there two? After buying the older one (RVC 1410),  I noticed that it doesn't work. One wire was loose, but the tach didn't work properly even after re-soldering it - the indication was something like 5500rpm at idle, although the needle did respond to changes in rpm. I noticed that disconnecting the +12V lead had no effect on the read-out. I suspect some component on the (very simple) circuit board has gone bad, possibly a resistor. Notably, Rick Astley posits in MGB Electrical Systems that the 1410/00AF "has been shown to be quite unreliable" and that it is unserviceable as the integrated circuit is unavailable nowadays (2006: 152).

The tach that worked (RVC 1414-01F, 4-cylinder negative earth tach,
no calibration pot, 80mm fitting size, probably intended for an MG Midget)

So I bought another one off eBay, an RVC 1414-01F that was supposed to work. And it did work. Opened both up and found them very similar. The 1414 had a better casing, because it had a green bulb cover relevant to my interests, and, of course, it had the better mechanism/circuit board. However, the 1410/00AF was prettier: it had a nice chrome bezel, a prettier needle and a prettier, more "old-skool" face.

Identical circuit boards, nearly identical construction otherwise, RVC1410 on the left and 1414 on the right

So I combined the two into a single unit, pretty and functional. From the RVC1410 I took the face, protective glass, bezel, needle and light bulb, and from the RVC1414 I took all the rest (the mechanism, internal structural components, circuit board, wiring and the case). The face is attached to the internal structure with two screws, and the bezel is even easier to separate from the case, so no problems there. Needle removal was the potentially tricky part, but I used two tea spoons and a piece of thick paper to pry it off. No problem. End result? A prettier RVC1414-01F, basically. Shame it still doesn't have a calibration pot, though...
 

Tools for needle removal