FAQ
TL;DR: How do I fix a dead Stanmore SMPS? "You must identify the individual elements" using the typical diagram; RI on SG6841SZ = 33 kΩ. [Elektroda, aaanteka, post #17044585]
Why it matters: It lets DIYers and repair techs correctly ID U1, R18, and R104 to restore power safely.
Quick Facts
- U1 confirmed as OB2268CP in a successful Stanmore repair. [Elektroda, DJ Davi, #19305738]
- Some units show U1 marked OB2269CP; verify your board revision. [Elektroda, Lolo81700, post #17053877]
- R18 and R104 marked “R100” on certain boards (low-ohm shunts). [Elektroda, Lolo81700, post #17053877]
- Other repairs reported 10 Ω for both R18 and R104; double-check before ordering. [Elektroda, DJ Davi, #19305738]
- Common weak point noted: 220 µF / 35 V electrolytic capacitor failed, causing issues. [Elektroda, Darekg, post #17445259]
What is U1 on the Marshall Stanmore power supply?
U1 was identified as OB2268CP in a confirmed repair. "The damaged U1 chip is OB2268CP." Check your PCB revision and markings before ordering the controller. [Elektroda, DJ Davi, #19305738]
Could U1 be OB2269CP on some Stanmore boards?
Yes. One owner reported U1 marking as OB2269CP. "I read on mine ob2269cp." Always verify the exact printed code and package on your board. [Elektroda, Lolo81700, post #17053877]
What is the value or marking for R18?
On working units documented, R18 is marked "R100." That denotes a low-ohm current-sense shunt near the SMPS section. Inspect location and compare against high-resolution board photos. [Elektroda, Darekg, post #17445259]
What is the value or marking for R104?
R104 is also marked "R100" on boards matching that layout. The same user confirmed both R18 and R104 with the R100 mark. [Elektroda, Lolo81700, post #17053877]
Are there boards where R18 and R104 are 10 instead of R100?
Yes. A successful repair reported both resistors as 10 . Confirm your PCB revision and surrounding circuit before sourcing replacements. [Elektroda, DJ Davi, #19305738]
I replaced U1 and key resistors, but it still wont power. What next?
Check the AC power terminal and its solder integrity. One repair only succeeded after replacing a faulty power terminal in addition to U1. [Elektroda, DJ Davi, #19305738]
What is U15 (the power amplifier), and what should I verify around it?
The thread references TIs TAS5342A. "One must measure these voltages present in the system and verify with catalog data." Confirm amplifier supply rails and control pins before blaming the transformer. [Elektroda, aaanteka, post #17301796]
How do I safely troubleshoot the Stanmore SMPS?
- Recreate the PSU around U1 using the typical diagram and SG6841SZ application note.
- Replace burnt parts, then power via a current limiter or variac.
- Measure controller and output rails, and compare against the reference design.
[Elektroda, aaanteka, post #17044585]
What is Tristar 13030122 and how do I find its pins?
Its the main flyback transformer. Pinout isnt published. Trace windings with continuity, then map primary, auxiliary, and secondaries using the typical application diagram as a guide. [Elektroda, aaanteka, post #17044585]
Do burnt R18/R104 always indicate the same root cause?
No. A moderator noted such cases are only similar by symptom. Treat each board independently and verify surrounding parts and rails. [Elektroda, aaanteka, post #17274697]
Could 1cU1 1d be a MOSFET like FQPF10N60C on some revisions?
Yes. One report listed U1 as FQPF10N60C. Designators can shift between revisions, so confirm whether U1 is the PWM IC or the switch. [Elektroda, harnol, post #17299481]
Which electrolytic capacitor commonly fails in this PSU?
Check the 220 8F / 35 V electrolytic on the SMPS side. A failed cap there was documented and replacement restored function. [Elektroda, Darekg, post #17445259]
Which nearby small parts often fail together with R18/R104?
Inspect R10, R19, and DZ3 on the primary side. One user found all three broken alongside the low-ohm shunts. [Elektroda, Lolo81700, post #17053877]
If I substitute SG6841SZ for OB226x, what should RI (pin 4) be?
Use 33 kA for RI on SG6841SZ as guided. That value differs from some OB226x implementations, so adjust only when using SG6841SZ. [Elektroda, aaanteka, post #17044585]
