Repairing the power supply of a stereo system SONY HCD-H5 - Page 1
Forum section: electronics / repair

author: uski
author_rank: Frequent Contributor
timestamp: January 13, 2024, 02:49:52 pm
content: Hi,I am trying to repair a SONY HCD-H5 vintage (1990s) stereo system.I have two different power-supply related issues:- One was fixed by replacing a dried capacitor (C735, if someone else has the same issue... if your 5V Vdd becomes 3V, check it!)- And the other one, I am still stuckHere is the schematics:The section of interest is the top one, using IC901 M5230L as a controller to generate +12V and -7V using two pass transistors, Q905 and Q904.I have checked everything and replaced all the caps just in case, and I think IC901 is dead.I tested the board independently of the rest of the system (I applied 0V through a 270o resistor to the SW to turn the power supply ON, and also connected the different grounds which are normally connected together elsewhere) and I just can't get 12V and -7V.The problem is that the M5230L is long obsolete. I cannot find any replacement. Does anyone have any idea as to how I could replace it?I do not want to get a pull from eBay, especially since this part already failed.I was considering changing the circuit to use LM317/LM337 with external pass transistors, but it would require quite a bit of changes to make work properly. Would there be any other possible replacement for that M5230L, maybe with a different pinout, that is designed to do the same functionality?The particularity is that it uses a NPN pass transistor for the positive rail and a PNP for the negative, which is unusual and the opposite configuration that you can normally find with pass transistors.Any idea? I am looking for something available at Farnell or Radiospares in EuropeThanks

author: uski
author_rank: Frequent Contributor
timestamp: January 13, 2024, 02:52:47 pm
content: PS: I just realize an added complexity is the need for a shutdown circuitry. I can't just use a LM317 and LM337, I need something that can be turned off.

author: coromonadalix
author_rank: Super Contributor
timestamp: January 13, 2024, 03:08:01 pm
content: you can or could order it therehttps://octopart.com/en/m5230l-mitsubishi-2174921some have MOQ of 1 unitnever had problems ordering from themthis sony psu as a reset and yes controlled voltages, you would need to build something like the 5vdc line, you see how the transistor is controlled by another on the sw linebut in the end would mean all your power lines would be aways on, the negative and the 2 positivesbut i never saw this ic getting defective, mostly the lythics on the transistor bases and thoses in the psu, and thoses around the zenners ...

author: uski
author_rank: Frequent Contributor
timestamp: January 13, 2024, 03:14:22 pm
content: Interesting link and attractive unit price!But unfortunately they all seem to want $40-50 for shipping, which puts the price of the order above the price of another stereo on the used market...

author: coromonadalix
author_rank: Super Contributor
timestamp: January 13, 2024, 03:20:50 pm
content: yeah unless your try on Ebay ... many possibilities ?? or fakes ? wich i would doubt on this one,normally its not an intersting part to clonehttps://www.ebay.com/itm/400361578044?AND this one is an american seller wich i would thrust more lollor hack some constant supplies and have a mechanical power on off switch ... not funthe ones i repaired had most of the time bad lythics, never had to change this ic .... you would need to tweak many things in this psuadding regulators and adjust them to the needed specsthe power control .......the reset signal is just when you power the thing / plug - connect it to the ac voltageyou need all the other section, filament drive etc .... in the end any tweaking or mods will cost you more in time and part than trying to buy a new one ?

author: tooki
author_rank: Super Contributor
timestamp: January 13, 2024, 05:35:11 pm
content: Surely it'd be trivial to just use two separate regulators (models with a SHUTDOWN pin) to generate the two voltages?!?

author: uski
author_rank: Frequent Contributor
timestamp: January 13, 2024, 07:15:39 pm
content: As a temporary fix:- I removed IC901, Q904, Q905- For the 12V rail, I generated it from a DC/DC module. GND pin 1 of IC901, +24V from pin 7 of IC901, and output of the DC/DC to E of Q905- For the 7V rail, I used a AC/DC HLK-PM03 module, it is a floating power supply. I modified it by changing its feedback resistor to get 7V output, changed the output cap which was rated at 6.3V only, and connected it "backwards" which essentially generates me a -7V from the GND of the stereo system.And it works fine (the lack shutdown probably just uses more power than necessary during standby).It gives me plenty of time now to either order a M5230L from somewhere, or find something elseStill interested if someone knows about a more modern/available equivalentI posted the details in the hope it helps someone someday who may work on similar equipment :-)Thanks everyone for the suggestions, appreciate it

author: tooki
author_rank: Super Contributor
timestamp: January 14, 2024, 01:48:58 pm
content: Quote from: uski on January 13, 2024, 07:15:39 pmI’d be leery of putting it in standby: having the -7V rail powered while the other rails are not could put strain on some chips.What you can do now is measure the current draw on the +15 and -7V rails, which will enable selection of a substitute part. (I doubt there’s a drop-in replacement for the original chip.)

author: coromonadalix
author_rank: Super Contributor
timestamp: January 14, 2024, 07:47:28 pm
content: i would say no substSony loved to use some "specialities ic's" lollIm not the op but i would have tried some usa parts on Ebay before venturing in many modifications ... or but an power switch on the ac line ... no more consumption ... not the fun way but it works ??

author: tooki
author_rank: Super Contributor
timestamp: January 14, 2024, 07:50:19 pm
content: Quote from: coromonadalix on January 14, 2024, 07:47:28 pmIt’s just a dual (positive/negative) regulator with enable pin. Nothing exotic about that, and easily substituted by whatever regulator or pair of regulators can produce the needed voltages at adequate current.

author: uski
author_rank: Frequent Contributor
timestamp: January 14, 2024, 07:53:29 pm
content: Quote from: tooki on January 14, 2024, 01:48:58 pmAbout putting to sleep - I wouldn't worry - as it is now, all rails are active 24/7.I also told my relative who owns this radio to unplug it when not in use, just in case.The current doesn't worry me too much because there are external pass transistors on a big heatsink for both rails. So those transistors will dissipate most power.Also, the design is horrible in terms of efficiency - they generate the -7V from -25V and the 12V from 25V, so it is not possible that significant currents are in use. The heatsink is internal and not that great based on other designs I have seen.But still good idea on measuring the current. I should do that next time I open it once I decide what to do nextQuote from: coromonadalix on January 14, 2024, 07:47:28 pm3 motivations for not using an eBay pull so far:1) I am at a relative's place for a few days, no way I will receive it on time before leaving. Needed a quick fix, which I achieved :-)2) From experience, pulls works most of the time. But if they don't it's a pain3) That stereo system is not in a great shape - belts are loose, CD drive doesn't eject (unclear why, probably another electrical issue), so I am reluctant at throwing money at it when I can get a used similar stereo for $20-30 locallyI might still order one, for fun, later. But I needed a quick fix :-)

author: tooki
author_rank: Super Contributor
timestamp: January 17, 2024, 01:47:52 pm
content: Quote from: uski on January 14, 2024, 07:53:29 pmI asked because I wouldn’t even bother with keeping the pass transistors if possible, I’d try to use regulators that can handle the load current unaided. (The original chip is only capable of something like 30mA; it’s essentially designed to be a pass transistor controller.)