Today's Project - H/K T-403 Recap

Worked on this tuner I got at GW. Writeup at TIC noted the sound quality, but not very sensitive nor selective. Sound was decent for how dirty it was, but it's now nice and clean inside and out. I guess someone had been inside it before as I found some cap substitutions with no-name brands, even switching out film caps for polarized electrolytics! :withstpd:

Anywho, got rid of the tantalums, increased the output caps from 10uF to 22uF (Nichi Fine Golds) and even threw in a Muse after the rectifier. Bypass caps on the main filter caps which I used Nichi UHEs. I had listened earlier and it ws sounding good, but wanted to install sockets to swap out the CFs for narrower ones. The hole spacing was non-standard and I tried to bend the pins on the sockets, but I don't think I got a really good connection as the tuning meter doesn't work now (it had before) and reception is a little spotty, where it was fine before. So, I'll need to open 'er up again tomorrow and redo the joints, perhaps no sockets or trying to make some extensions somehow.

John

John, I don't want to hijack this thread, but I have a really basic question (I'm rather new at all this), and this seemed to be a good time/place to ask: how does one tell if a capacitor needs replacing? And by that I mean, by visual inspection. Does a leaky cap ooze something out of the bottom? Are the sides bulged and cracked? I have a Harman Kardon HK350i open up on my workbench right now for cleaning, and I am thinking that I should look to see if there are any capacitors that really should be replaced. But I realized that I don't really know what I am looking for.

Thanks in advance for your help.

Unfortunately not all dead/dying capacitors are visibly damaged. You'll need a multimeter to test them.

You can use your multimeter as an ohmmeter to test the capacitor.

1) Discharge the capacitor by shortening its leads. That is - use a wire and connect the leads of the capacitor together. This will discharge it.

2) put your multimeter in the high ranges 10K-1M

3)CONNECT MULTIMETER TO CAPACITOR LEADS(OBSERVE THE POLARITY IF ELECTROLYTIC). AT SOON AS THE LEADS MAKE CONTACT, THE METER WILL SWING NEAR ZERO. IT WILL THEN MOVE SLOWLY TOWARD INFINITY. FINALLY THE METER WOULD COME TO BE INFINITE OHMS BECAUSE THE CAPACITOR IS BEING CHARGED BY THE BATTERY OF THE MULTIMETER.

4) IF THE CAPACITOR IS BAD, IT WILL GO TO ZERO OHMS AND REMAIN THERE. THIS IS CALLED A SHORTENED CAPACITOR

5) IN THE CASE OF AN OPEN CAPACITOR THERE WILL BE NO OHMMETER INDICATION.

6)SOME CAPACITORS HAVE A LOW DIELECTRIC LEAKAGE. YOU WILL KNOW THIS IF THE OHMMETER COMES TO REST AT A POINT LOWER THAN INFINITE. TEST A KNOWN GOOD CAPACITOR OF THE SAME TYPE TO BE SURE

Click to expand...

Stolen from another forum because I'm too lazy to type it out myself.

if the unit is 15 or 20 years old, you can figure on changing all the caps if it is an important piece in your collection....

First off, my reception problem has been solved. It wsa the sockets I installed for the ceramic filters. They weren't making good enough contact to pass the signal, so the meter appeared dead. I pulled them out and cut them to individual pins as opposed to the bank of three which can be seen in the last photo. Now I've got 2 150kHz filters in there and selectivity is much improved. Now, to remove the 300ohm balun for better sensitivity or not...that is the question.

But as to how to know whether to recap or not, lots of good advice has been given already, but I'll throw in what MY (very limited) experience has shown. I've recapped my CT-810, KT-815 and now this T-403. None of the capacitors showed any REALLY visible signs of problems and the units were working "fine." There were a couple in which the outer sleeve had shrunk back a little, but the tops weren't bulging. I put "fine" in quotes as neither have had a recent alignment, so I don't have the greatest reference point to start from, just that they played music and had decent sound and reception.

I went on the advice here and elsewhere to figure on replacing the electrolytic capacitors if the units are 25-30 years old or more. I didn't measure all of the caps removed, and I only have a DMM that can read up to 4000uF. No ESR meter. None of the caps I measured were out of tollerance capacitance-wise, though some initially appeared that way until I jiggled the clip a bit for better contact with the cap leads.

So, if it ain't broke, don't fix it right??? Well...I have noticed a difference in the listening. The music seems more defined, more lively, more engaging. I am now really motivated to get my tuners properly aligned so I can see what they'll REALLY do!

I did lots of reading over on the Tuner Info Center, especially the modifications sections. So, I didn't just replace the capacitors with like values and types always. I also didn't do extensive listening tests prior to recapping, or during the process to see what difference was happening as I didn't want to have to keep waiting for caps to discharge, etc. So MY take on recapping is that it's definitely worth it. You're able to put special caps for special purposes and that definitely affects the sound.

I bought all the caps except the main filter caps, some diodes and resistors for the following from Mouser for less than $100 shipped: KT-815, TX-9500II, T-403, SX-780, AH-5971 and some extra caps for my CA-800 and CT-810 which digikey didn't stock when I was recapping those units. For the expense involved, there is a big payout in that the equipment will be good for a lot longer, you can put higher quality parts in key areas that the manufacturers didn't want to go to the expense for in mass production, but on a hobby scale it can be done, and the sound is improved. If I couldn't do the soldering myself and had to have a tech do it, I couldn't justify it, because labor and parts markups would be killer.

John