Pioneer SA-7800 restoration

Some parts are missing, cosmetically damaged, what was spilled inside?

Disclaimer

  All trademarks mentioned and links are presented here for informational purposes only and to confirm statements made by the author. The author of these pages DOES NOT receive any remuneration from the mentioned brands and the listed links.

  In any case if you decide to use the suggestions on this page you do so at your own risk. Repairing electronic equipments, even just opening it, can put your life at risk, so don't do it.

  If you do not accept and/or not understand the statements in this disclaimer, written in blue, exit this page immediately.

  Everything exposed in this web page is only a suggestion, probably you won't obtain the aim from you prefixed following it.

  A true collector is looking for a) original items without any replaced parts, b) or if a Critical Restoration has been done that it is possible to go back to the original version. Lacking the previous 2 statements the object (not only for me) has a value of zero euros.

Pioneer SA-xxx

  Here we could include the history of Pioneer, or at least the history of the SA-xxx series, but that would take away space from the reconstruction of this integrated amplifier.

  If you are interested in the list of models, here are some interesting links:

• On HiFi Wiki a list of "all" Pioneer models of integrated amplifiers,
• At Audiofanzine there is a Pioneer SA user review,
• Audio Database present a list of Pioneer amplifier,

  To be clear, we do not recommend purchasing a vintage Pioneer amplifier, but we cannot advise against it either. The problem is that prices are out of control for all vintage items. Even though they were good devices, the prices being asked for them today are crazy.

  Just as an example, €2,900 for a Pioneer C21+M22 (Feb. 26) or €1,500 for a Yamaha B2 (Dec. 25) or, worse still, €4,000 for an unreliable Sansui 20000 (Nov. 2025), more then €1900 for Accuphase E-202, are high prices for devices that are excellent when new but may need to be completely rebuilt inside (see the section on capacitors here) or, worse still, have been tampered with but are sold as immaculate.

  However, after walking around audio fairs and seeing CD players sold for €28,000, we have some doubts about a market that exploits our weaknesses. Not to mention the $108,000 cable between an amplifier and speakers. Perhaps they new sellers/brands are right: "They have the money, so let's take it from them".

  If you really want to make a crazy purchase of a vintage item, I recommend NOT turning it on. The best thing would be to pick it up at the seller's house and see/hear it working. Nothing can be said about what will happen in a month, but at least "it works now". Fortunately, my friend did NOT turn on the Pioneer!

  If you buy it switched off, take it to an honest technician to have a look inside and switch it on for the first time.

Inside this Pioneer

  We are interested in this Pioneer SA-7800, back to 1979, its history, its visible and hidden defects, its internal components (which we hope are original) and any parts that have already been replaced.

Fig.1, Our SA-7800 seen from the front. From this photo taken from a distance, you cannot see all the scratches and marks on the faceplate and even on the knobs, nor the damaged display frame, but you can see the missing knob

  Let's open it up (the screws are original) and take a look inside, and here are the surprises, first in the photo below.

Fig.2, Inside, we find a plastic bag with some components in it. What are they for? Which ones? Are they broken?

  Here is the list of components in the envelope:

1. Bad e not working, 2SC945, 2SA913, 2SC945, 2SC1384, 2SC945, 2SA733, 1N4148, M130, 2SC3281, and a strange 2x 2SC2240
2. Ok, working, 2SA1301, 2SA1948, 2SC3280

  All the broken ones can also be found on the wiring diagram, apart from the 2SC2240? The working ones are not on the schematic, but the 2SA1301 and 2SC3280 are original, vintage, Toshiba power transistors, why here?

Fig.3, here is a photo of the interior, which is very dirty. But that's not all. You can see the dirt more clearly in the high-resolution photo

  It is not clear from the photo, but at the bottom of the device there is something dried up, like a Cola or Chinotto liquid that may have fallen through the ventilation slots on the lid. Let's take a closer look.

Fig.4, let's take a look at the power supply section. You can see the second transformer on the right, the 4x 8000μF/50V Nichicon capacitors in the centre, and the stabilisation circuit on the left. Some liquid has been spilled and there is a lot of dust

  Unfortunately, this means dismantling the entire front panel, the bottom panel and anything else that can be removed, covering the transformer with plastic bags and adhesive tape, and washing it on the terrace with a garden hose (then flush with distilled water). All this has to be done early in the morning on a nice sunny day.

Fig.5, removing the rusted bolts from the bottom was easy, but the ones securing the front panel from underneath are stuck. Using a flame torch is not an option, so we will cut off the heads. Here is a video of the surgical procedure (.MP4, 7.9MB)

  Once the front panel has been removed, which will then need to be cleaned and restored in some way, we can see the damage caused by the spill.

Fig.6, to remove the panel, we had to use force, so even the frame, after careful cleaning, will need to be straightened. What a disaster! Then we will try to remove the screw, which now has no head, to secure the front with a nice screw from another Pioneer

  Surely removing the remains of that screw without causing further damage is a complex task.

And what about the circuit?

  First, we find the service manual, or rather, we discover that there are 3: one complete manual and 2 additional for the sub-versions.

  As always, in the Download section you will find all the project files, services, diagrams, etc.

Fig.7, the service describes what other documents we need depending on the version. Ours is HG, and the "additional" one is found. Fortunately, we do not need ART-354-0, which is truly impossible to find

  Where do the components in the plastic bag come from? Are they replacement parts? Let's take a look at the PCB.

Fig.8, You can immediately see that some components are missing and that repairs were left half-finished. We note that transistors 2SC5200 and 2SA1943 are fixed to the heat sink and soldered with colored wires, an excellent choice. Fortunately, the amplifier was NOT turned on. Here is the original photo.

  However, the components in the envelope are insufficient to fill all the gaps, some were left on the repairer's table.

  The presence of the broken 2SC2240 confirms that the production series is much larger than stated by the service manual. But which part in the diagram was replaced with 2SC2240?

  Manufacturers secretly replace parts for improvements and economic savings. This is confirmed by the Toshiba 2SA1301 and 2SC3280 power transistors found in the envelope. One has colored wires still attached, these were the original power transistors.

  The famous pundits, geniuses, barkers, and shouters will then explain to us, from the height of their incompetence, that the XUZ version is better than the SWA, obviously without knowing how a lateral FET works or difference with vertical FET.

Fig.9, and here we are already repairing. The ENTIRE device must be inspected with a magnifying glass to look for manufacturing or usage problems. Here, in the centre of the photo, is a badly bent reoforo that we will have to be repaired. Does it touch? Does it not touch? It certainly cannot be left like this (it must be repaired immediately)

  You should only spend half an hour at a time on research (I set an Alarm Clock) because after that your eyes start to strain and you miss some flaws.

Fig.10, this is a typical fault after 30 or more years of use, or in this case almost 50 years: defective solder joints. They are difficult to find. You need a magnifying glass and a torch to change the angle of illumination, as well as time and patience (and these can be repaired immediately, otherwise you'll forget about them)

  We were talking about buying vintage items. It can be done, but expect problems like the one in fig. 10. And don't blame the seller, it worked at his house, but the car journey didn't do it any good.

  Years ago, I repaired a Krell KSA-200B belonging to a friend who was an editor at Stereoplay. It took months of work. There were hundreds of them (see fig. 10). The thermal paste had melted, and the resistors were still working but burnt out.

  But what would you expect to find inside a class A amplifier that gets so hot?

  Krell in the US... wonderful, they sent me all the original components, even the plastic screws (but only service manual cutouts, defective areas only, and calibration).

  I still dream about it once the job is done, but starting over on another similar one is a nightmare.

Fig.11, there is something good about it. It may not be a Noble, Penny & Giles, A&B, or TKD, but it seems to be a good potentiometer, unlike many other brands that use ones that look like shirt buttons

  Potentiometer PCW-113-0 , 117Y100KΩX2 probably an Ohmite.

The Wire Wrap

  Remember that the entire device uses wire wrapping for connections.

  But what exactly is wire wrapping? It is a technique for twisting two wires together that originated in jewelry making as early as 2000 bCE and is still used today.

  The electronics industry adapted it in the 1950s. It was a method of reducing soldering. A machine wraps stripped rigid wire around a square pin.

Fig.12, it could have been worse. If you slowly unravel the wire wrap, you can see a little oxide on them, but only in a few places. It seems that the contact is still good, at least on the ones that have been dismantled. With Mouse Over we can see other wrapping near potentiometer.

  However, after 30 years of use, moisture and oxygen get between the pin and the bare wire. The resulting oxide reduces contact to the point of preventing it.

  Some people solder over it to repair it, but that makes things worse because the tin does not get between the coils and does not stick to the oxide. This requires unwrapping the wire. However, we will discuss that later since all the contacts on the final PCB are made this way.

The damage

  But how do you repair an audio amplifier? You can find a long, explanatory article on Rod Elliott's website, but he forgot to mention the use of the Hameg HZ65-3. To avoid the nightmare of repairing a CD, we'll leave it all until tomorrow (but in the meantime, you can read the 216 pages of Ken Clements' book).

  One of the faults could be the wire wrap itself, but we will only know for sure when everything else is working.

Fig.13, first, we print out a large copy of the PCB design for the amplifier stage and look for the codes of the missing components. Fortunately, we have the design for our GWH-122

  By searching the circuit for the missing components on the PCB and finding the corresponding ones on the circuit, we can narrow down the fault, then discover some resistors that are still present but burnt out.

Fig.14, a circle on all faulty components, even the power transistors were faulty, but here we find them already replaced and installed. In Fig. 8, we see the power transistor soldered to the circuit. Here is the enlarged drawing

  It seems that the left channel has broken, but strangely it has taken the entire protection circuit with all its transistors and diodes with it.

  Since we cannot study the original fault, but only what remains, the repair is really difficult.

  The components chosen for repair are highlighted in yellow. It is preferable to use original parts, thanks to the 2 sellers (fortunately, given the difficulty of finding 2SC1384), or substitutes.

  We will obviously also change the mirror component, for example R53 when we replace R51.

  A word of advice for anyone who wants to try their hand at repairs: NEVER accept an item that has already been tampered with and that they have not been able to finish.

Fig.15, we don't know if the various switches and potentiometers will also need to be repaired, we'll find out when we turn it on for the first time

  And where can we find the original transistors, or at least the replacements mentioned in the service manual? As my friends know, I usually buy from 2 distributors of audio and Hi-Fi parts in Germany and from a well-known international distributor.

Fig.16, they don't pay me, they don't give me discounts, they don't sponsor me: but we need to highlight companies that are struggling to stay in the market, distributing original (not fake) products at reasonable prices. Kudos also for their courtesy in transactions

  On forums, I often see complaints and even insults directed at my 2 famous German suppliers. Those who write are people who are naturally argumentative and hostile. Instead of being grateful for the availability of genuine components, they complain because there is a delay of a few days and because only half of the order has arrived (without mentioning that the other half will arrive later, free of charge).

  And maybe some strange people even protest against these two.

  After carefully reading the reviews, I realised that those reporting negative experiences are not repair experts but hobbyists who think they can solve their problems through a distributor (who is actually there to sell).

The supply capacitors

  In Fig. 4, we see the four 8000μF capacitors, and we immediately notice their proximity to the long cooling heat sink.

  This is a typical problem for designers, who have two alternatives: a) place the capacitors near the final transistors to improve current flow, or b) place them further away to protect them from the heat generated during operation.

  An interesting example of this logic is the Audio Research SP8 family. In the first versions, all the capacitors were on the component side, but by issue 7 almost all the capacitors had been moved to the underside, away from the heat that rises.

  Now we need to dismantle and measure the four capacitors for comparison with the datasheet.

Fig.17, Nichicon 8000μF 50V N8015 85°C, 3 pinout. No datasheet can be found, after 45 years! Note the drops of glue that secured it to the PCB; we will put them back on the new ones

  Even the value today is strange: you can find 8200μF, but not 8000 (like the 160μF of my Marantz 7C, which is almost impossible to find).

  We solder all the negatives together with a 1 mm wire, which we will need later, and then measure the four capacitors one by one.

Fig.18, the LCR meter allows us to measure various parameters of the capacitor at various frequencies. We choose 100Hz

  After carefully self-calibrating the instrument (better than the simple calibration described in the manual), we measure.

  That's not quite right. The best one measures 5000μF instead of the 8000μF on the label. Before replacing them, let's try to regenerate them.

Capacitor regeneration, reforming

  There are thousands of pages on capacitor reforming, some of which are written by audiophiles trying to save old equipment. Many of these pages describe industrial processes where capacitors are essential, and failure can cause serious problems. Let's leave impulse techniques aside and focus only on those involving DC voltage.

  By the way, in the downloads section, you will find a document from Cornell Dubilier (wonderful capacitors) on how a capacitor is made, and on page 7, it talks about reforming.

  If you are working with voltages above 50V, it becomes dangerous. Reforming a 47μF 500V capacitor puts your life at risk due to electric shock and explosion. DO NOT do this.

  We have already connected all the negatives; now let's put a 100 ohm R in series with the positive and build a small half-wave power supply with a very small filter capacitor (10μF) to leave plenty of ripple.

  We will use a Variac to power the 230-24+24 transformer so that we can regulate the voltage on the capacitors.

Fig.19, the 4 capacitors reformning, on the left there is the list of voltages and times. You can perhaps see the single 1N4007 diode to leave a little ripple

  Each time the applied voltage changes, the voltage across the four resistors must be measured immediately, i.e. the leakage current. The same must be done after one hour and the results compared.

Fig.20, we measure the voltage across the 100 ohm resistor. A leakage current of 1 mA produces a voltage of 100 mV, which is easily measurable

  How much should the leakage current be? Preferably 0mA but I suggest never more then 1-3mA in reforming. If we had the capacitor datasheet, we would find the values also as a function of temperature, but the datasheets for the Mallory capacitors used by the McIntosh MC30 cannot be found, like those for the capacitors from 50 years ago.

  After 24 hours, do not switch off the variac immediately, but first quickly unsolder the four resistors and leave the capacitor disconnected.

Fig.21, measurement of residual voltage after 2 hours, damn bleeders that kill capacitors every time I turn off a device. But let's look at the green resistor we'll need to discharge them before measuring

  During reforming, I strongly recommend measuring the temperature of the case, perhaps with an inexpensive IR thermometer. The temperature must not rise.

  As soon as you disconnect the power supply, touch the case. It should be cold, otherwise throw away the capacitor without further checks.

  About bleeder ... if you send all the political rejects, runaways, and friends of friends to Europe, what kind of rules and laws do you think will come back? The bleeder resistor, invented by idiots for idiot technicians. If you don't know that the capacitors in an amplifier with a pair of Amperex 845s can still hold 1000 V even after being turned off for a day, then quit this job and go work as a pizza maker and watch how the oven burns.

  Looking at the values, and Fig.19, the capacitors seem fine, leaking less than 1 mA even at nominal voltage, no self-discharge even after hours, but ....

  The capacitance value has not been restored with reforming, the best we have achieved is +3% on C42.

  The list is getting longer, we have to change these capacitors, but this time we will use 105°C ones, and also all those in the supply section that have been flooded by some colored drink.

Fig.22, instead of using boutique capacitors, we choose 105°C long life, low ESR, for high ripple design, used in switching power supply

  Since they are snap-in type, you will need a few tricks to fix them in place of the originals.

  It seemed that the fault was confined to the amplifier stage, or rather to the final power section, but over the years the power supply had also been affected.

  And we have many doubts about the famous fluorescent display, fingers crossed.

Fixing the power supply section

  nces.

Fixing the amplifier section

  nces.

Download

1. the original service manual of SA-7800 (type KU), ART-344
2. SA-7800, l'additional manual ART-345-0 (type HG)
3. SA-7800, l'additional manual ART-354-0 (type KC, S, S/G), when I find it
4. the power PCB of SA-7800, type HG, in one file
5. schematic of power section of SA-7800, type HG, in one file
6. datasheet of MZ-130 or WZ-130 diode
7. datasheet of 2SC1914A
8. Cornell Dubilier Electronics, Aluminum Electrolytic Capacitor Application Guide v2. Everything you need to know about capacitors
9. old Cornell Dubilier Electronics, Aluminum Electrolytic Capacitor Application Guide v1. Previous version, more information
10. the well-known manufacturer of capacitors for industry explains the Capacitor Electrical Characteristics

           
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